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Showing 1 - 200 of 3044 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 22, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 21, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 84, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 23, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 29, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 343, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 1)
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 215, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 10, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 23, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
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Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 3)
Acute Pain     Full-text available via subscription   (Followers: 13)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 5)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 21)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 134, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 25, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
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Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 25, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 26, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Dermatology     Full-text available via subscription   (Followers: 12)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 5)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 41, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 40, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 48, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 21, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.497, h-index: 31)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 35, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.764, h-index: 15)
Advances in Lipobiology     Full-text available via subscription   (Followers: 2)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 15, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 22)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 24, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 13)
Advances in Pharmacology     Full-text available via subscription   (Followers: 15, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 7, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 19, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 61)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 2, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 348, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
Advances in Surgery     Full-text available via subscription   (Followers: 7, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 16)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 43, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 318, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 5, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 8, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 408, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 39, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 54, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 5, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 9, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 8)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access  
Algal Research     Partially Free   (Followers: 8, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 4, SJR: 0.776, h-index: 35)
Alpha Omegan     Full-text available via subscription   (SJR: 0.121, h-index: 9)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 8, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 47, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 48, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 45, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 39, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 16, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 31, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 24, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 32, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 46, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 193, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 56, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 4)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 24, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 26, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 21, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 34, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 55, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 9)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 37, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 166, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 8, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 1)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 22, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 157, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (Followers: 1, SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
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Journal Cover Additive Manufacturing
  [SJR: 1.039]   [H-I: 5]   [7 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 2214-8604
   Published by Elsevier Homepage  [3044 journals]
  • Effects of thermal cycles on the microstructure evolution of Inconel 718
           during selective laser melting process
    • Authors: Xiaoqing Wang; Kevin Chou
      Pages: 1 - 14
      Abstract: Publication date: December 2017
      Source:Additive Manufacturing, Volume 18
      Author(s): Xiaoqing Wang, Kevin Chou
      A staircase Inconel 718 block was fabricated to investigate the effects of the thermal cycles on the microstructure evolution in the selective laser melting (SLM) part using optical scope (OM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The laser beam scanning strategy was clearly shown in the part under OM, including laser scanning pattern and hatch spacing. The Y-plane (side surface) was characterized by elongated colonies of cellular dendrites with an average cell spacing of 0.511∼0.845μm. In addition, Laves phase was observed in the inter-layers and inter-cellular regions. Under the continuing effects of the thermal cycles, the fraction of the Laves-phase showed a significant drop with their morphology changing from coarse and interconnected particles to discrete Laves phase. This is attributed to the reheating process as Laves phase can be dissolved at a proper heat treatment. In terms of the width of the cellular dendrites, the longer the thermal cycle period is, the coarser the elongated grains are. Due to the preferred orientation of the crystal, the Y-plane and Z-plane had a strong texture of < 1 0 1> and < 0 0 1>, respectively. With the repeating thermal cycle period elongating, the maximum intensity of the texture, together with the fraction of larger grains and the high misorientation angles, increased. At the same height, there was no significant changes with the grains size, but the fraction of the high misorientation angles (>15°) increased with the subsequent building of the part. Moreover, the area fraction of the porosity was below 0.2%, with no remarkable effects found from the thermal cycles and the build height.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.08.016
      Issue No: Vol. 18 (2017)
  • Polymer recycling in an open-source additive manufacturing context:
           Mechanical issues
    • Authors: Fabio A. Cruz Sanchez; Hakim Boudaoud; Sandrine Hoppe; Mauricio Camargo
      Pages: 87 - 105
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Fabio A. Cruz Sanchez, Hakim Boudaoud, Sandrine Hoppe, Mauricio Camargo
      Nowadays, the low recycling rate of polymers is still a challenge to humankind due to energy, economic and logistical issues. In the context of additive manufacturing, there is an exponential use of thermoplastic materials in the industrial and public open-source additive manufacturing sector, leading to an increase in global polymer consumption and waste generation. However, the coupling of the open-source 3D printers with polymer processing could potentially offer the basis for a new paradigm of distributed recycling process. It could be a complementary alternative to the traditional paradigm of centralized recycling of polymers, which is often uneconomical and energy intensive due to transportation embodied energy. In order to achieve this goal, a first step is to prove the technical feasibility to recycle thermoplastic material intended for open-source 3D printing feedstock. The contribution of the present study is twofold: first, a general methodology to evaluate the recyclability of thermoplastics used as feedstock in open-source 3D printing machines is proposed. Then, the proposed methodology is applied to the recycling study of polylactic acid (PLA) material addressed to the fused filament fabrication (FFF) technique, which is currently the most widely used. The main results of this application contribute to the understanding of the influence of the material's physico-chemical degradation on its mechanical properties as well as its potential distributed recyclability.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.05.013
      Issue No: Vol. 17 (2017)
  • The origins for tensile properties of selective laser melted aluminium
           alloy A357
    • Authors: Jeremy H. Rao; Yong Zhang; Xiya Fang; Yu Chen; Xinhua Wu; Chris H.J. Davies
      Pages: 113 - 122
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Jeremy H. Rao, Yong Zhang, Xiya Fang, Yu Chen, Xinhua Wu, Chris H.J. Davies
      In this work the tensile behaviour of selective laser melted (SLMed) aluminium alloy A357 in the as-fabricated and heat-treated states is explained using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission electron backscatter diffraction (t-EBSD). The as-built sample has an ultrafine microstructure, with high residual stresses and non-equilibrium solid solute concentration of Si in the supersaturated Al matrix. Consequently, the tensile properties of the SLMed Al alloy A357 are comparable or better than traditional cast counterparts. The Al grains in the SLMed alloy consist of sub-micron sized Al cells, and both high angle and low angle boundaries are initially occupied by eutectic nano-sized Si particles, which are beneficial for strength but detrimental for ductility. With subsequent solution heat treatment, the Si particles on the low angle cell boundaries (LACBs) dissolve while those at the high angle grain boundaries (HAGBs) coarsen. Simultaneously internal stresses decrease, as does solute content in the matrix. The evolution of these microstructural features explains the improved tensile ductility (at its maximum >23%) and reduced tensile strength for the heat treated SLMed aluminium alloy A357 samples.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.007
      Issue No: Vol. 17 (2017)
  • Residual stress measurements on AISI 316L samples manufactured by
           selective laser melting
    • Authors: Thomas Simson; Andreas Emmel; Anja Dwars; Juliane Böhm
      Pages: 183 - 189
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Thomas Simson, Andreas Emmel, Anja Dwars, Juliane Böhm
      This paper aims to understand the formation and the effect of residual stress on selective laser melting (SLM) parts. SLM is a powder bed based additive manufacturing (AM) process and can be compared to a laser welding process. Due to the high temperature gradients and the densification ratio, which are characteristic of this process, residual stresses occur. The investigation of residual stress is performed using X-ray diffraction (XRD) for samples made of austenitic stainless steel AISI 316L (EN 1.4404). This research examines residual stress at different depths and at two outer surfaces. For the measurement of stresses at different depths, the samples’ surface layers were removed by electropolishing. At sufficiently large distances from the top surface, the stresses in the area of the edge layer initially increase strongly and then decline again. The value and orientation of the resulting main stress components are dependent on the examined layer. At the top surface, the residual stresses are higher in scan direction than in perpendicular direction. In contrast, at the lateral surface the maximum main stress is perpendicular to the scan and parallel to the building direction. These two cases can be described very well by the two mechanisms in SLM, namely the temperature gradient mechanism (TGM) and the cool-down phase. It is also shown that at samples with a relative structural density of >99%, the residual stress values are independent of the applied energy density.

      PubDate: 2017-09-16T12:00:18Z
      DOI: 10.1016/j.addma.2017.07.007
      Issue No: Vol. 17 (2017)
  • Three-dimensional finite element thermomechanical modeling of additive
           manufacturing by selective laser melting for ceramic materials
    • Authors: Qiang Chen; Gildas Guillemot; Charles-André Gandin; Michel Bellet
      Pages: 124 - 137
      Abstract: Publication date: August 2017
      Source:Additive Manufacturing, Volume 16
      Author(s): Qiang Chen, Gildas Guillemot, Charles-André Gandin, Michel Bellet
      A model for additive manufacturing by selective laser melting of a powder bed with application to alumina ceramic is presented. Based on Beer–Lambert law, a volume heat source model taking into account the material absorption is derived. The level set method is used to track the shape of deposed bead. An energy solver is coupled with thermodynamic database to calculate the melting-solidification path. Shrinkage during consolidation from powder to liquid and compact medium is modeled by a compressible Newtonian constitutive law. A semi-implicit formulation of surface tension is used, which permits a stable resolution to capture the liquid/gas interface. The influence of different process parameters on temperature distribution, melt pool profiles and bead shapes is discussed. The effects of liquid viscosity and surface tension on melt pool dynamics are investigated. Three dimensional simulations of several passes are also presented to study the influence of the scanning strategy.

      PubDate: 2017-06-12T15:19:52Z
      DOI: 10.1016/j.addma.2017.02.005
      Issue No: Vol. 16 (2017)
  • Mechanical strength of welding zones produced by polymer extrusion
           additive manufacturing
    • Authors: Chelsea S. Davis; Kaitlyn E. Hillgartner; Seung Hoon Han; Jonathan E. Seppala
      Pages: 162 - 166
      Abstract: Publication date: August 2017
      Source:Additive Manufacturing, Volume 16
      Author(s): Chelsea S. Davis, Kaitlyn E. Hillgartner, Seung Hoon Han, Jonathan E. Seppala
      As more manufacturing processes and research institutions adopt customized manufacturing as a key element in their design strategies and finished products, the resulting mechanical properties of parts produced through additive manufacturing (AM) must be characterized and understood. In polymer extrusion (PE), the most recently extruded polymer filament must bond to the previously extruded filament via polymer diffusion to form a “weld”. The strength of the weld limits the performance of the manufactured part and is controlled through processing conditions. Understanding the role of processing conditions, specifically extruder velocity and extruder temperature, on the overall strength of the weld will allow optimization of PE-AM parts. Here, the fracture toughness of a single weld is determined through a facile “trouser tear” Mode III fracture experiment. The actual weld thickness is observed directly by optical microscopy (OM) characterization of cross sections of PE-AM samples. Representative data of weld strength as a function of printing parameters on a commercial 3D printer demonstrates the robustness of the method.
      Graphical abstract image

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.06.006
      Issue No: Vol. 16 (2017)
  • Topology optimization for additivemanufacturing: accounting for overhang
           limitations using a virtual skeleton
    • Authors: Yoram Mass; Oded Amir
      Abstract: Publication date: Available online 14 September 2017
      Source:Additive Manufacturing
      Author(s): Yoram Mass, Oded Amir
      This article proposes a new method for reducing the amount of support material required for 3-D printing of complex designs generated by topology optimization. This procedure relies on solving sequentially two structural optimization problems – the first on a discrete truss-based model and the second on a continuum-based model. In the optimization of the discrete model, the maximum overhang limitation is imposed based on geometrical parameters. The optimized discrete pattern is then projected on to the continuum so that it influences the material distribution in the continuum optimization. The method is explained and investigated on a set of test cases in 2-D and subsequently demonstrated on examples in 3-D. Numerical results indicate that the designs obtained by this approach exhibit improved printability as they have fewer overhanging features. In some cases, practically no supporting material will be required for printing the optimized design.

      PubDate: 2017-09-16T12:00:18Z
      DOI: 10.1016/j.addma.2017.08.001
  • Ultrafast 3D High Precision Print of Micro Structures for Optical
           Instrument Calibration Procedures
    • Authors: Felix Ströer; Julian Hering; Matthias Eifler; Indek Raid; Georg von Freymann; Jörg Seewig
      Abstract: Publication date: Available online 9 September 2017
      Source:Additive Manufacturing
      Author(s): Felix Ströer, Julian Hering, Matthias Eifler, Indek Raid, Georg von Freymann, Jörg Seewig
      Multi-photon polymerization, like the so-called direct laser writing (DLW) technique allows for flexible additive manufacturing of three-dimensional ultra-precise structures on the micro- and nanoscale. A possible application for DLW is the manufacturing of measurement standards for calibration procedures of optical measurement instruments. This requires flexible and high precision manufacturing of individualized geometries with high quality surfaces. However, many of the process parameters in DLW have to be selected based on experience and previous knowledge. In this article, the influence of DLW process parameters on the micro-geometry and surface roughness produced are systematically studied, and optimized in terms of printing speed and manufacturing accuracy. Resulting microstructures are being evaluated with different measurement techniques, i. e., a stylus instrument, SEM and AFM. Based on optimized process parameters, a new measurement standard for the novel interferometric measurement instrument Ellipso-Height-Topometer is manufactured and examined as a case study. As a result, it can be shown, that DLW is able to manufacture ultra-precise micro geometries in a very flexible and very fast way and satisfies the tolerances for manufacturing of the designed measurement standard.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.09.001
  • On the effect of throughout layer thickness variation on properties of
           additively manufactured cellular titanium structures
    • Authors: Esmat Sheydaeian; Zachary Fishman; Mihaela Vlasea; Ehsan Toyserkani
      Abstract: Publication date: Available online 8 September 2017
      Source:Additive Manufacturing
      Author(s): Esmat Sheydaeian, Zachary Fishman, Mihaela Vlasea, Ehsan Toyserkani
      Over the past two decades, additive manufacturing has opened a new window of opportunities in fabricating complex porous matrix structures such as cellular solids. Several factors including design, material and process parameters can selectively be varied to tailor the porous properties of products based on the intended application. This article addresses the effect of variable throughout layer thickness configuration in the binder-jet additive manufacturing of titanium structures for orthopedic applications. Two layer thicknesses of 80 and 150μm are selectively controlled inside of each titanium sample with four different configurations. Several studies were performed, including shrinkage analysis, porosity measurements, and mechanical compression tests to quantify the effect of layer thickness on part quality and mechanical properties. The results of the porosity measurement revealed that there is about 5% variation among the samples with different layer thickness configuration. Bulk porosity values obtained from micro computed tomography (μCT) scan data placed the bulk porosity of the samples combining more than one layer thickness, in between of the results for control specimens, which were manufactured by applying a single layer thickness throughout the samples. Mechanical properties did not show any significant variation, which is attributed to the low range of the porosity deviation (less than 5%). The highest Young’s modulus of 3.50±0.4GPa and yield stress of 175±25MPa were obtained from analysis of the data achieved from the compression test.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.08.017
  • Digital light processing 3D printing of conductive complex structures
    • Authors: Quanyi Mu; Lei Wang; Conner K. Dunn; Xiao Kuang; Feng Duan; Zhong Zhang; H. Jerry Qi; Tiejun Wang
      Abstract: Publication date: Available online 6 September 2017
      Source:Additive Manufacturing
      Author(s): Quanyi Mu, Lei Wang, Conner K. Dunn, Xiao Kuang, Feng Duan, Zhong Zhang, H. Jerry Qi, Tiejun Wang
      3D printing has gained significant research interest recently for directly manufacturing 3D components and structures for use in a variety of applications. In this paper, a digital light processing (DLP®) based 3D printing technique was explored to manufacture electrically conductive objects of polymer nanocomposites. Here, the ink was made of a mixture of photocurable resin with multi-walled carbon nanotubes (MWCNTs). The concentrations of MWCNT as well as the printing parameters were investigated to yield optimal conductivity and printing quality. We found that 0.3wt% loading of MWCNT in the resin matrix can provide the maximum electrical conductivity of 0.027S/m under the resin viscosity limit that allows high printing quality. With electric conductivity, the printed MWCNT nanocomposites can be used as smart materials and structures with strain sensitivity and shape memory effect. We demonstrate that the printed conductive complex structures as hollow capacitive sensor, electrically activated shape memory composites, stretchable circuits, showing the versatility of DLP® 3D printing for conductive complex structures. In addition, mechanical tests showed that the addition of MWCNT could slightly increase the modulus and ultimate tensile stress while decreasing slightly the ultimate stretch, indicating that the new functionality is not obtained at the price of sacrificing mechanical properties.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.08.011
  • Continuous lattice fabrication of ultra-lightweight composite structures
    • Authors: Martin Eichenhofer; Joanna C.H. Wong; Paolo Ermanni
      Abstract: Publication date: Available online 1 September 2017
      Source:Additive Manufacturing
      Author(s): Martin Eichenhofer, Joanna C.H. Wong, Paolo Ermanni
      This paper introduces continuous lattice fabrication (CLF) – a novel additive manufacturing (AM) technique invented for fiber-reinforced thermoplastic composites – and demonstrates its ability to exploit anisotropic material properties in digitally fabricated structures. In contrast to the layer-by-layer approaches employed in most AM processes, CLF enables the directed orientation of the fibers in all spatial coordinates, that is in the x-, y-, and z-directions. Based on a serial pultrusion and extrusion approach, CLF consolidates commingled yarns in situ and allows for the continuous deposition of high fiber volume fraction (>50%) materials along a programmable trajectory without the use of molds or sacrificial layers by exploiting the high viscosities of fiber-filled polymer melts. The capacity of CLF to produce high-performance structural components is demonstrated in the fabrication of an ultra-lightweight load-bearing lattice structure with outstanding stiffness-to-density and strength-to-density performance (compression modulus of 13.2MPa and compressive strength of 0.20MPa at a core density of 9mg/cm3). This digital fabrication method enables new approaches in load-tailored design, including the possibility to build freeform structures, which have previously been overlooked due to difficulties and limitations in modern fiber composite manufacturing capabilities.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.013
  • Additive Manufacturing of Multifunctional Reactive Materials
    • Authors: Trevor J. Fleck; Allison K. Murray; I. Emre Gunduz; Steven F. Son; George T.-C Chiu; Jeffrey F. Rhoads
      Abstract: Publication date: Available online 1 September 2017
      Source:Additive Manufacturing
      Author(s): Trevor J. Fleck, Allison K. Murray, I. Emre Gunduz, Steven F. Son, George T.-C Chiu, Jeffrey F. Rhoads
      This paper demonstrates the ability to 3D print a fluoropolymer based energetic material which could be used as part of a multifunctional reactive structure. The work presented lays the technical foundation for the 3D printing of reactive materials using fusion based material extrusion. A reactive filament comprising of a polyvinylidene fluoride (PVDF) binder with 20% mass loading of aluminum (Al) was prepared using a commercial filament extruder and printed using a Makerbot Replicator 2X. Printing performance of the energetic samples was compared with standard 3D printing materials, with metrics including the bead-to-bead adhesion and surface quality of the printed samples. The reactivity and burning rates of the filaments and the printed samples were comparable. Differential scanning calorimetry and thermal gravimetric analysis showed that the onset temperature for the reactions was above 350°C, which is well above the operation temperature of both the filament extruder and the fused deposition printer.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.008
  • A systematic study on numerical simulation of electrified jet printing
    • Authors: A. Rahmat; B. Koc; M. Yildiz
      Abstract: Publication date: Available online 31 August 2017
      Source:Additive Manufacturing
      Author(s): A. Rahmat, B. Koc, M. Yildiz
      In this paper, a numerical model based on a systematic study of electrified jet printing is presented. The Volume of Fluid (VOF) method which suits for modeling multiphase flows with a continuous interface is used. The surface tension force is calculated with the Continuum Surface Force (CSF) method and the electric forces are added to the momentum equation by taking the divergence of the Maxwell stress tensor. A systematic study is carried out by introducing three dimensionless numbers, namely Reynolds, Electro-Weber and Weber numbers. Employing these dimensionless numbers, the number of effective parameters is reduced, and a relative comparison of the importance of competing forces on the process becomes possible. It is observed that the electric forces contribute to the formation of the jet by acting on its tip, and by pulling the jet towards the deposition surface. The results show that an increase in Reynolds and Electro-Weber numbers both lead to form a thinner jet. It is also observed that further increase in Electro-Weber and Reynolds numbers leads to the formation of an unstable jet.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.004
  • Partitioning of Laser Energy during Directed Energy Deposition
    • Authors: Frederick Lia; Joshua Park; Jay Tressler; Richard Martukanitz
      Abstract: Publication date: Available online 30 August 2017
      Source:Additive Manufacturing
      Author(s): Frederick Lia, Joshua Park, Jay Tressler, Richard Martukanitz
      An energy balance that describes the transfer of energy is proposed for the laser-based directed energy deposition process. The partitioning of laser energy was experimentally measured and accurately validated using a special process calorimeter for Ti-6Al-4V and Inconel 625™ alloys. The total energy provided by the laser was partitioned as: the energy directly absorbed by the substrate, the energy absorbed by the powder stream and deposited onto the substrate, the energy reflected from the substrate surface, and the energy reflected or absorbed and lost from the powder stream. Titanium alloy Ti-6Al-4V showed higher overall or bulk absorption than the Inconel 625™ alloy. Processing with powder resulted in lower laser energy absorption within the substrate than without powder, due to the “shadowing” effect of the powder stream within the beam and loss of energy representing unfused powder. During processing at a laser power of approximately 1kW the total energy absorbed during the deposition process was found to be 42% for the Ti-6Al-4V alloy and 37% for the Inconel 625™ alloy. Under these conditions 14% of the total energy was lost by the Ti-6Al-4V unfused powder; whereas only 11% was lost by the Inconel 625™ powder.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.012
  • On characterization of separation force for resin replenishment
           enhancement in 3D printing
    • Authors: D. Gritsenko; A.A. Yazdi; Y. Lin; V. Hovorka; Y. Pan; J. Xu
      Abstract: Publication date: Available online 30 August 2017
      Source:Additive Manufacturing
      Author(s): D. Gritsenko, A.A. Yazdi, Y. Lin, V. Hovorka, Y. Pan, J. Xu
      Additive Manufacturing (AM), which is also referred to as 3D Printing, is a class of manufacturing techniques that fabricate three dimensional (3D) objects by accumulating materials. Constrained Surface based Stereolithography is one of the most widely used AM techniques. In the process, a thin layer of liquid photosensitive resin is constrained between a constrained surface and the platform or part. The light penetrates the transparent constrained surface and cures that layer of liquid polymer. Then the platform is moved up to separate the newly cured layer to let new liquid resin fill into the gap and get cured. The separation of newly cured layer from the constrained surface is a grand challenge that limits the printable size and printing speed in this manufacturing technique. Numerous experimental work has been performed to understand how to reduce the separation force in the process. In this paper we study a new design of constrained surface with radial groove texture that significantly influences the effectiveness of reduction of the separation force and hence the manufacturing capability via theoretical modeling. In particular, we investigate an influence of grooves shape, grooves depth and the number of grooves on the separation force. The proposed model is validated with numerical simulations demonstrating an excellent agreement. We demonstrate the possibility of drastic reduction of the separation force (up to 112%) via surface texturing of the permeable window for continuous 3D printing.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.010
  • Study of Moineau-based pumps for the volumetric extrusion of pellets
    • Authors: Enrique Canessa; Marco Baruzzo; Carlo Fonda
      Abstract: Publication date: Available online 30 August 2017
      Source:Additive Manufacturing
      Author(s): Enrique Canessa, Marco Baruzzo, Carlo Fonda
      A volumetric, mini extruder for pellets or granules of recycled plastic that can be used in a RepRap FDM 3D printer for rapid prototyping is discussed. It combines a rotor of a Moineau progressing cavity pump coupled with an Auger screw, both contained inside a stator at high temperatures. The steer Auger portion is added to increase the pressure inside a helix stator container of n-lobes as a helical rotor is turned. A novel, alternative multi-layer Moineau-based pump −easier to build, implement and clean– is also introduced to extrude a quantity of viscous material in vertical direction.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.015
  • Electron beam melted scaffolds for orthopedic applications
    • Authors: Ibrahim Eldesouky; Ola Harrysson; Harvey West; Hassan Elhofy
      Abstract: Publication date: Available online 26 August 2017
      Source:Additive Manufacturing
      Author(s): Ibrahim Eldesouky, Ola Harrysson, Harvey West, Hassan Elhofy
      Ti6Al4 V porous scaffolds of two unit cell geometries (reentrant and cubic) were investigated as candidates for load-bearing biomedical applications. Samples were fabricated using an Arcam A2 electron beam melting (EBM) machine and evaluated for geometric deviation from the original CAD design using a digital optical microscope. The mass and bounding volume of each sample were also measured to calculate the resulting relative density. The scaffolds were loaded in compression in the build direction to determine the relative modulus of elasticity and ultimate compressive load. Experimental results were used to calculate the Gibson and Ashby relation parameters for the studied unit cell geometries. The results suggest that samples with the cubic unit cell geometries, with struts oriented at an angle of 45° to the loading direction, exhibited higher stiffness than samples with the reentrant unit cell geometry at equivalent relative densities. A cubic scaffold is verified to withstand high compressive loads (more than 71kN) while having an approximate pore size in the range of 0.6mm. These characteristics demonstrate its suitability for load bearing biomedical implants.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.005
  • Anisotropic Mechanical Properties of Oriented Carbon Fiber Filled Polymer
           Composites Produced with Fused Filament Fabrication
    • Authors: Delin Jiang; Douglas E. Smith
      Abstract: Publication date: Available online 26 August 2017
      Source:Additive Manufacturing
      Author(s): Delin Jiang, Douglas E. Smith
      Fused Filament Fabrication (FFF) is a widely used Additive Manufacturing (AM) technique. Recently, mechanical properties of plastic FFF parts have been enhanced by adding short carbon fibers to the thermoplastic polymer filament to form a carbon fiber filled (CFF) polymer composite. Unfortunately, improvements to the material properties of commercially available CFF filament are not well understood. This paper presents a study of CFF FFF parts produced on desktop 3D printers using commercially available filament. Tensile test samples fabricated with CFF polymer composite and unfilled polymer were printed and then tested following ASTM D3039M. Test bars were printed with FFF bead orientations aligned with the direction of the applied load at 0degree, and also at 45 degrees, ±45 degrees, and normal to the loading axis at 90 degrees. The filament considered here was purchased from filament suppliers and included both CFF and unfilled PLA, ABS, PETG and Amphora. Results for tensile strength and tensile modulus show that CFF coupons in general yield higher tensile modulus at all print orientations and higher tensile strength at 0degree print orientation. The addition of carbon fiber was shown to decrease tensile strength for some materials when printed with beads not aligned with the loading direction. Additionally, CFF samples are evaluated for fiber length distribution (FLD) and fiber weight fraction, where it was found that the filament extrusion process contributes very little to fiber breakage. Finally, fracture surfaces evaluated under SEM show that voids between the beads are reduced with CFF coupons, and poor interfacial bonding between fibers and polymer become a prominent failure mechanism.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.006
  • Geometric Characterization of Additively Manufactured Polymer Derived
    • Authors: Jacob M. Hundley; Zak C. Eckel; Emily Schueller; Kenneth Cante; Scott M. Biesboer; Brennan D. Yahata; Tobias A. Schaedler
      Abstract: Publication date: Available online 26 August 2017
      Source:Additive Manufacturing
      Author(s): Jacob M. Hundley, Zak C. Eckel, Emily Schueller, Kenneth Cante, Scott M. Biesboer, Brennan D. Yahata, Tobias A. Schaedler
      The high hardness, melting temperature and environmental resistance of most ceramic materials makes them well-suited for propulsion, tribilogical and protective applications. However, these same attributes pose difficulties for manufacturing and machining of ceramics and ultimately limit the achievable design space of these materials. Recently, a new class of preceramic photopolymers has been developed that enables additive manufacturing of ceramics using commercially available stereolithography systems. By consolidating preceramic monomers via layer-wise exposure to ultraviolet light and subsequently pyrolyzing under an inert atmosphere to form a ceramic, this method allows for complex geometry parts that cannot be produced with traditional sintering, pressing or vapor infiltration processes. In order to retain geometric fidelity and generate flaw-free microstructures, volumetric and gravimetric changes during the polymer-to-ceramic conversion must be quantified. To this end, we present x-ray micro-computed tomography (micro-CT) measurements of the dimensional stability and uniformity of additively manufactured silicon-based ceramics as a function of geometry and processing conditions.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.009
  • Effect of powder oxidation on the impact toughness of electron beam
           melting Ti-6Al-4V
    • Authors: W.A. Grell; E. Solis-Ramos; E. Clark; E. Lucon; E.J. Garboczi; P.K. Predecki; Z. Loftus; M. Kumosa
      Abstract: Publication date: Available online 25 August 2017
      Source:Additive Manufacturing
      Author(s): W.A. Grell, E. Solis-Ramos, E. Clark, E. Lucon, E.J. Garboczi, P.K. Predecki, Z. Loftus, M. Kumosa
      Powder quality in additive manufacturing (AM) electron beam melting (EBM) of Ti-6Al-4V components is crucial in determining the critical material properties of the end item. In this study, we report on the effect of powder oxidation on the Charpy impact energy of Ti-6Al-4V parts manufactured using EBM. In addition to oxidation, the effects on impact energy due to hot isostatic pressing (HIP), specimen orientation, and EBM process defects were also investigated. This research has shown that excessive powder oxidation (oxygen mass fraction above 0.25% and up to 0.46%) dramatically decreases the impact energy. It was determined that the room temperature impact energy of the parts after excessive oxidation was reduced by about seven times. We also report that HIP post-processing significantly increases the impact toughness, especially for specimens with lower or normal oxygen content. The specimen orientation effect was found to be more significant for low oxidation levels.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.002
  • In situ real time defect detection of 3D printed parts
    • Authors: Oliver Hammond; Xiaodong Li
      Abstract: Publication date: Available online 25 August 2017
      Source:Additive Manufacturing
      Author(s): Oliver Hammond, Xiaodong Li
      Additive manufacturing (AM) allows for the production of custom parts with previously impractical internal features, but comes with the additional possibility of internal defects due to print error, residual stress buildup, or cyber-attack by a malicious actor. Conventional post process analysis techniques have difficulty detecting these defects, often requiring destructive tests that compromise the integrity (and thus the purpose) of the part. Here, we present a “certify-as-you-build” quality assurance system with the capability to monitor a part during the print process, capture the geometry using three-dimensional digital image correlation (3D-DIC), and compare the printed geometry with the computer model to detect print errors in situ. A test case using a fused filament fabrication (FFF) 3D printer was implemented, demonstrating in situ error detection of localized and global defects.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.003
  • Thermal analysis of additive manufacturing of large-scale thermoplastic
           polymer composites
    • Authors: Brett G. Compton; Brian K. Post; Chad E. Duty; Lonnie Love; Vlastimil Kunc
      Abstract: Publication date: Available online 30 July 2017
      Source:Additive Manufacturing
      Author(s): Brett G. Compton, Brian K. Post, Chad E. Duty, Lonnie Love, Vlastimil Kunc
      The incremental deposition process utilized by most additive manufacturing (AM) technologies presents significant challenges related to residual stresses and warping which arise from repeated deposition of hot material onto cooler material. These issues are magnified at larger scale, where even a small thermal strain can correspond to several millimeters of deformation. In this work we investigate the thermal evolution in thin walls of carbon fiber/acrylonitrile butadiene styrene (CF/ABS) composite materials fabricated via Big Area Additive Manufacturing (BAAM). We measure the thermal evolution of composite parts during the build process using infrared imaging, and develop a simple 1D transient thermal model to describe the build process. The model predictions are in excellent agreement with the observed temperature profiles and from the results we develop criteria to guide deposition parameter selection to minimize the likelihood of cracking during printing.

      PubDate: 2017-08-04T12:05:36Z
      DOI: 10.1016/j.addma.2017.07.006
  • Functionally graded Ti6Al4V-Mo alloy manufactured with DED-CLAD®
    • Authors: Catherine Schneider-Maunoury; Laurent Weiss; Philippe Acquier; Didier Boisselier; Pascal Laheurte
      Abstract: Publication date: Available online 29 July 2017
      Source:Additive Manufacturing
      Author(s): Catherine Schneider-Maunoury, Laurent Weiss, Philippe Acquier, Didier Boisselier, Pascal Laheurte
      This paper presents the results of functionally graded Ti6Al4V-Mo alloy manufactured with directed energy deposition called CLAD® (Construction Laser Additive Direct) process. Single track width sample with five gradients of composition, from 0 to 100wt.%Mo, was manufactured using a coaxial nozzle. Both Ti6Al4V and Mo ratios were modified with a 25wt.% increase or decrease in the chemical composition of each gradient. A two-powder feeder was used to input the correct ratio of each powder, so as to obtain the desired chemical composition. XRD analysis allowed to define the phases present in each deposition, as well as the lattice parameter. SEM observations showed microstructural evolution from 25wt%Mo on, namely where the β-phase becomes dominant. Moreover, dendrites appear from 50wt.%Mo on. Microhardness analysis revealed variation along the deposition depending on the chemical composition. The homogeneity of the powder mixture under laser beam was highlighted thanks to tomography on the manufactured samples, which validates the processability of functionally graded material (FGM) by CLAD® process.

      PubDate: 2017-08-04T12:05:36Z
      DOI: 10.1016/j.addma.2017.07.008
  • On the Development of Antenna Feed Array for Space Applications by
           Additive Manufacturing Technique
    • Authors: S.S. Gill; Hemant Arora; Jidesh; Viren Sheth
      Abstract: Publication date: Available online 24 July 2017
      Source:Additive Manufacturing
      Author(s): S.S. Gill, Hemant Arora, Jidesh, Viren Sheth
      Space agencies are looking for advanced technologies to build light weight and stiff payload components to bear space environment and launch loads. Additive manufacturing (AM) techniques like Direct Metal Laser Sintering (DMLS) is one of the suitable option which can be explored for space applications. This paper highlights the development process of Antenna Feed Array (AFA) using DMLS as an Additive Manufacturing (AM) technique. A high efficiency horn element is used in the array. Such horns are preferred for this development as they are the prime choice for feed elements in High Throughput satellites (HTS) that employ Multibeam Antennas. A brief description of Multibeam antennas along with the RF design process for the high efficiency horn is presented. In the development process, certain design rules of AM are adopted based on consideration to produce self-sustaining structures. AFA realized by DMLS is evaluated by functional testing, vibration testing for space qualification test levels. Test results shows its structural intactness which proves its space worthiness. Procedures are very well established for further development of space payload components.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.06.010
  • Distortion Prediction and Compensation in Selective Laser Melting
    • Authors: Shukri Afazov; Willem A.D. Denmark; Borja Lazaro Toralles; Adam Holloway; Anas Yaghi
      Abstract: Publication date: Available online 23 July 2017
      Source:Additive Manufacturing
      Author(s): Shukri Afazov, Willem A.D. Denmark, Borja Lazaro Toralles, Adam Holloway, Anas Yaghi
      This paper presents a new approach for modelling additive layer manufacturing at component scale. The approach is applied to powder-bed selective laser melting (SLM) and validated, where the mechanical behaviour of macro-scale industrial components has been predicted and compared with experimental results. The novelty of the approach is based on using a calibrated analytical thermal model to derive functions that are implemented in a structural finite element analysis (FEA). The computational time for a complete analysis has been reduced from many days to less than three hours for a 3D blade component with a height of 80mm. The induced distortion in SLM has been compensated for by modifying the initial geometry using FE predicted distortion. A newly developed distortion compensation method, based on optical 3D scan measurements, has also been implemented. The two distortion compensation methods have been experimentally validated. In summary, the research presented in this paper shows that the mitigation of distortion in SLM is now possible on industrial macro-scale components.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.07.005
  • Hierarchical structures of stainless steel 316L manufactured by Electron
           Beam Melting
    • Authors: Lars-Erik Rännar; Andrey Koptyug; Jon Olsén; Kamran Saeidi; Zhijian Shen
      Abstract: Publication date: Available online 22 July 2017
      Source:Additive Manufacturing
      Author(s): Lars-Erik Rännar, Andrey Koptyug, Jon Olsén, Kamran Saeidi, Zhijian Shen
      One of the serious obstacles preventing wide industrial use of additive manufacturing (AM) in metals and alloys is a lack of materials available for this technology. It is particularly true for the Electron Beam Melting (EBM®) process, where only a few materials are commercially available, which significantly limits the use of the method. One of the dominant trends in AM today is developing processes for technological materials already widely used by other methods and developed for other industrial applications, gaining further advantages through the unique value added by additive manufacturing. Developing new materials specifically for additive manufacturing that can utilize the properties and specifics of the method in full is still a research and development subject, and such materials are yet far from full scale industrial usage. Stainless steels are widely used in industry due to good mechanical properties, corrosion resistance and low cost of material. Hence, there is potentially a market for this material and one possible business driver compared with casting for example is that lead times could be cut drastically by utilizing an additive approach for one-off or small series production. This paper presents results from the additive manufacturing of components from the known alloy 316L using EBM®. Previously the samples of 316L were made by laser-based AM technology. This work was performed as a part of the large project with the long term aim to use additively manufactured components in a nuclear fusion reactor. Components and test samples successfully made from 316L stainless steel using EBM® process show promising mechanical properties, density and hardness compared to its counterpart made by powder metallurgy (hot isostatic pressing, HIP). As with the other materials made by EBM® process, 316L samples show rather low porosity. Present paper also reports on the hierarchical microstructure features of the 316L material processed by EBM® characterized by optical and electron microscopy.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.07.003
  • Algorithm-driven design of fracture resistant composite materials realized
           through additive manufacturing
    • Authors: Grace X. Gu; Susan Wettermark; Markus J. Buehler
      Abstract: Publication date: Available online 20 July 2017
      Source:Additive Manufacturing
      Author(s): Grace X. Gu, Susan Wettermark, Markus J. Buehler
      Fracture, the breakdown of materials as cracks advance, is one of the most intriguing materials phenomena; it can happen even to very tough biological tissues including tendons, skin, bone and teeth, materials whose critical physiological functions can be compromised by structural irregularities. It has been suggested that creating composites by mixing heterogeneous constituents of contrasting material properties can yield designs that can better adapt to stress concentration, leading to synthetic materials with higher toughness than their constituents. Here, an optimization algorithm is used to assess material fracture resistance in the presence of a crack. The analysis is further extended through experiments that involve the use of additive manufacturing. Optimal solutions are composed solely of soft and stiff material elements, and are compared to various benchmarks. Multi-material three-dimensional-printing (3D-printing) is used to create material samples. Experimental results and mechanical testing show that an algorithmic design coupled with 3D-printing technology can generate morphologies of composites more than 20 times tougher than the stiffest base material, and more than twice as strong as the strongest base material. Direct comparison of strain fields around cracks shows excellent agreement between simulation and experiment. The results suggest that the systematic use of microstructure optimization to generate enhanced fracture resistance constitutes a new materials design paradigm.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.07.002
  • The Extrusion-based Additive Manufacturing of Moisture-Cured Silicone
           Elastomer with Minimal Void for Pneumatic Actuators
    • Authors: Jeffrey Plott; Albert Shih
      Abstract: Publication date: Available online 15 July 2017
      Source:Additive Manufacturing
      Author(s): Jeffrey Plott, Albert Shih
      The extrusion-based additive manufacturing (AM) of moisture-cured silicone elastomer with minimal voids and high strength, elongation, and fatigue life is presented. Due to the soft nature and extended cure time of moisture-cured silicone, AM is technically challenging. When each layer is deposited, it can compress and deform previous layers. This compression is exploited to prevent void formation in silicone AM. This research aims to explore process parameters for voidless silicone AM of solid and thin-wall structures for pneumatic actuators. Experiments were performed to study effects of flowrate, layer height, and distance between adjacent silicone lines on the solid and thin-wall vertical layer deformation and void generation. The results were then applied in AM of two thin-walled hollow silicone pneumatic parts: the sphere-like balloons and finger pneumatic actuators. The sphere-like balloons exhibited diametric expansion between 152 and 207% with burst stress between 1.46 and 2.55MPa (which is comparable to the base material properties) while the pneumatic finger actuators were able to fully articulate over 30,000 cycles before failure.

      PubDate: 2017-07-19T03:20:04Z
      DOI: 10.1016/j.addma.2017.06.009
  • Investigation of pore structure in cobalt chrome additively manufactured
           parts using X-ray computed tomography and three-dimensional image analysis
    • Authors: F.H. Kim; S.P. Moylan; E.J. Garboczi; J.A. Slotwinski
      Abstract: Publication date: Available online 15 July 2017
      Source:Additive Manufacturing
      Author(s): F.H. Kim, S.P. Moylan, E.J. Garboczi, J.A. Slotwinski
      Pore structures of additively manufactured metal parts were investigated with X-ray Computed Tomography (XCT). Disks made of a cobalt-chrome alloy were produced using laser-based powder bed fusion (PBF) processes. The additive manufacturing processing parameters (scan speed and hatch spacing) were varied in order to have porosities varying from 0.1% to 70% so as to see the effects of processing parameters on the formation of pores and cracks. The XCT images directly show three-dimensional (3D) pore structure, along with cracks. Qualitative visualization is useful; however, quantitative results depend on accurately segmenting the XCT images. Methods of segmentation and image analysis were carefully developed based, as much as possible, on aspects of the images themselves. These enabled quantitative measures of porosity, including how porosity varies in and across the build direction, pore size distribution, how pore structure varies between parts with similar porosity levels but different processing parameters, pore shape, and particle size distribution of un-melted powder trapped in pores. These methods could possibly serve as the basis for standard segmentation and image analysis methods for metallic additively manufactured parts, enabling accurate and reliable defect detection and quantitative measures of pore structure, which are critical aspects of qualification and certification.

      PubDate: 2017-07-19T03:20:04Z
      DOI: 10.1016/j.addma.2017.06.011
  • An open-architecture metal powder bed fusion system for in-situ process
    • Authors: P. Bidare; R.R.J. Maier; R.J. Beck; J.D. Shephard; A.J. Moore
      Abstract: Publication date: Available online 17 June 2017
      Source:Additive Manufacturing
      Author(s): P. Bidare, R.R.J. Maier, R.J. Beck, J.D. Shephard, A.J. Moore
      We report the design of a metal powder bed fusion system for in-situ monitoring of the build process during additive manufacture. Its open-architecture design was originally determined to enable access for x-rays to the melt pool, but it also provides access to the build area for a range of other in-situ measurement techniques. The system is sufficiently automated to enable single tracks and high-density, multiple layer components to be built. It is easily transportable to enable measurements at different measurement facilities and its modular design enables straightforward modification for the specific measurements being made. We demonstrate that the system produces components with >99% density. Hence the build conditions are representative to observe process fundamentals and to develop process control strategies.

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.06.007
  • Anisotropy of Thermal Conductivity in 3D Printed Polymer Matrix Composites
           for Space Based Cube Satellites
    • Authors: Corey Shemelya; Angel De La Rosa; Angel R. Torrado; Kevin Yu; Jennifer Domanowski; Peter J. Bonacuse; Richard E. Martin; Michael Juhasz; Frances Hurwitz; Ryan B. Wicker; Brett Conner; Eric MacDonald; David A. Roberson
      Abstract: Publication date: Available online 17 June 2017
      Source:Additive Manufacturing
      Author(s): Corey Shemelya, Angel De La Rosa, Angel R. Torrado, Kevin Yu, Jennifer Domanowski, Peter J. Bonacuse, Richard E. Martin, Michael Juhasz, Frances Hurwitz, Ryan B. Wicker, Brett Conner, Eric MacDonald, David A. Roberson
      Polymer extrusion three dimensional (3D) printing, such as fused deposition modeling (FDM), has recently garnered attention due to its inherent process flexibility and rapid prototyping capability. Specifically, the addition of electrical components and interconnects into a 3D printing build sequence has received heavy interest for space applications. However, the addition of these components, along with the thermal load associated with space-based applications, may prove problematic for typical thermally insulating 3D printed polymer structures. The work presented here addresses thermally conductive polymer matrix composites (specifically, graphite, carbon fiber, and silver in an acrylonitrile butadiene styrene polymer matrix) to identify the effect of composite geometry and print direction on thermal anisotropic properties. The work also examines the effect of these composites on print quality, mechanical tensile properties, fracture plane analysis, micrograph imaging, and cube satellite thermal analysis. The thermal conductivity of 3D printed material systems in this work may enable the production of thermally stable 3D printed structures, supports, and devices. Key results of this work include anisotropic thermal conductivity for 3D printed structures related to print direction and filler morphology meaning that thermal conductivity can be controlled through a combination of print raster direction and material design. When the materials analyzed in this work are incorporated with other active cooling systems, space-based 3D printed applications can then be designed to incorporate increasing thermal loads, opening a new door to producing space-ready 3D printed structures.

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.05.012
  • Bending Behaviors of 3D-printed Bi-material Structure: Experimental Study
           and Finite Element Analysis
    • Authors: Yi-Tang Kao; Ying Zhang; Jyhwen Wang; Bruce L. Tai
      Abstract: Publication date: Available online 16 June 2017
      Source:Additive Manufacturing
      Author(s): Yi-Tang Kao, Ying Zhang, Jyhwen Wang, Bruce L. Tai
      This paper investigates the bending behaviors of a bi-material structure (BMS) using both experimental and numerical methods The BMS is a composite material built by a 3D-printed, open-cellular brittle plaster structure filled with a silicone elastomer. The composition and configuration of the two materials determine the overall mechanical properties. Four-point bending test results show a non-linear elastic property, enhanced strength and toughness of BMS samples compared to either material phase alone. Such behavior is believed to be a result of delayed microcrack propagation in the brittle phase and a hardening effect of elastomer. In the numerical study, finite element analysis (FEA) is employed to verify these hypotheses. The FEA incorporates a brittle cracking material model for the plaster and a hyperelastic model for the silicone. The brittle cracking model enables the estimation of element degradation as a result of crack development and thus eliminates the need for the extremely refined mesh. Simulation result confirms the non-linear elastic transition and crack-induced material degradation and visualizes the silicone strengthening mechanism that can avoid rapid structural rupture.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.005
  • Poly-l-lactic Acid: Pellets to Fiber to Fused Filament Fabricated
           Scaffolds, and Scaffold Weight Loss Study
    • Authors: Prashanth Ravi; Panos S. Shiakolas; Tré R. Welch
      Abstract: Publication date: Available online 15 June 2017
      Source:Additive Manufacturing
      Author(s): Prashanth Ravi, Panos S. Shiakolas, Tré R. Welch
      Poly-l-lactic acid (PLLA) is a bioresorbable polymer used in a variety of biomedical applications. Many 3D printers employ the fused filament fabrication (FFF) approach with the ubiquitous low-cost poly-lactic acid (PLA) fiber. However, use of the FFF approach to fabricate scaffolds with medical grade PLLA polymer remains largely unexplored. In this study, high molecular weight PL-32 pellets were extruded into ∼1.7mm diameter PLLA fiber. Melt rheometric data of the PLLA polymer was analyzed and demonstrated pseudo-plastic behavior with a flow index of n=0.465 (<1). Differential scanning calorimetry (DSC) was conducted using samples from the extruded fiber to obtain thermal properties. DSC of the 3D printed struts was also analyzed to assess changes in thermal properties due to FFF. The DSC and rheometric analysis results were subsequently used to define appropriate FFF process parameters. Constant porosity scaffolds were FFF 3D printed with 4 distinct laydown patterns; 0/90° rectilinear (control), 45/135° rectilinear, Archimedean chords, and honeycomb using the in-house developed custom multi-modality 3D bioprinter (CMMB). The effect of laydown pattern on scaffold bulk erosion (weight loss) was studied by immersion in phosphate-buffered saline (PBS) over a 6-month period and measured monthly. A repeated measures analysis of variance (ANOVA) was performed to identify statistically significant differences between mean percent weight loss of the four laydown patterns at each time point (1-6 months). The resulting data follows distinct temporal trends, but no statistically significant differences between means at individual time points were found. Cross-sectional scanning electron microscope (SEM) images of the 6-month degraded scaffolds showed noticeable structural deterioration. The study demonstrates successful processing of PLLA fiber from PL-32 pellets and FFF-based 3D printing of bioresorbable scaffolds with pre-defined laydown patterns using medical grade PLLA polymer which could prove beneficial in biomedical applications.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.002
  • Fabrication of Continuous Carbon, Glass and Kevlar fibre reinforced
           polymer composites using Additive Manufacturing
    • Authors: Andrew N. Dickson; James N. Barry; Kevin A. McDonnell; Denis P. Dowling
      Abstract: Publication date: Available online 15 June 2017
      Source:Additive Manufacturing
      Author(s): Andrew N. Dickson, James N. Barry, Kevin A. McDonnell, Denis P. Dowling
      This study evaluated the performance of continuous carbon, Kevlar and glass fibre reinforced composites manufactured using the fused deposition modelling (FDM) additive manufacturing technique. These nylon composites were fabricated using a Markforged Mark One 3D printing system. The mechanical performance of the composites was evaluated both in tension and flexure. The influence of fibre orientation, fibre type and volume fraction on mechanical properties were also investigated. The results were compared with that of both non-reinforced nylon control specimens, and known material property values from literature. It was demonstrated that of the fibres investigated, those fabricated using carbon fibre yielded the largest increase in mechanical strength. Its tensile strength values were up to 6.3 times that obtained with the non-reinforced nylon polymer. As the carbon and glass fibre volume fraction increased so too did the level of air inclusion in the composite matrix, which impacted on mechanical performance. As a result, a maximum efficiency in tensile strength was observed in glass specimen as fibre content approached 18%, with higher fibre contents (up to 33%), yielding only minor increases in strength.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.004
  • Investigation of Mechanical Anisotropy of the Fused Filament Fabrication
           Process via Customized Tool Path Generation
    • Authors: Carsten Koch; Luke Van Hulle; Natalie Rudolph
      Abstract: Publication date: Available online 15 June 2017
      Source:Additive Manufacturing
      Author(s): Carsten Koch, Luke Van Hulle, Natalie Rudolph
      To aid in the transition of 3D printed parts from prototypes to functional products it is necessary to investigate the mechanical anisotropy induced by the Fused Filament Fabrication (FFF) process. Since the mechanical properties of an FFF part are most greatly affected by the bead orientation and printed density, or solidity ratio, techniques to precisely control these variables are required. An open source Python program, SciSlice, was developed to create the desired tool paths/layer orientations and convert them into machine commands (e.g. G-Code). SciSlice was then used to develop tool paths which either directly printed tensile specimens or printed sheets from which specimens could be water-jet cut. The effects of proper bed leveling and feed wheel adjustment are noted and a careful analysis of both bead orientation and solidity ratio are presented. Printing artifacts related to turns made at the part edges are discussed having been found to have strong effects on the measure strength in the weakest orientation. Finally, it is shown that with proper bead orientation, low layer heights, and a maximum solidity ratio, tensile strengths within 3% of injection molded parts are achievable.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.003
  • A Tripropylene Glycol Diacrylate-based polymeric support ink for material
    • Authors: Yinfeng He; Fan Zhang; Ehab Saleh; Jayasheelan Vaithilingam; Nesma Aboulkhair; Belen Begines; Chris J. Tuck; Richard J.M. Hague; Ian Ashcroft; Ricky D. Wildman
      Abstract: Publication date: Available online 12 June 2017
      Source:Additive Manufacturing
      Author(s): Yinfeng He, Fan Zhang, Ehab Saleh, Jayasheelan Vaithilingam, Nesma Aboulkhair, Belen Begines, Chris J. Tuck, Richard J.M. Hague, Ian Ashcroft, Ricky D. Wildman
      Support structures and materials are indispensable components in many Additive Manufacturing (AM) systems in order to fabricate complex 3D structures. For inkjet-based AM techniques (known as Material Jetting), there is a paucity of studies on specific inks for fabricating such support structures. This limits the potential of fabricating complex 3D objects containing overhanging structures. In this paper, we investigate the use of Tripropylene Glycol Diacrylated (TPGDA) to prepare a thermally stable ink with reliable printability to produce removable support structures in an experimental Material Jetting system. The addition of TGME to the TPGDA was found to considerably reduce the modulus of the photocured structure from 575MPa down to 27MPa by forming micro-pores in the cured structure. The cured support structure was shown to be easily removed following the fabrication process. During TG-IR tests the T5% temperature of the support structure was above 150°C whilst the majority of decomposition happened around 400°C. Specimens containing overhanging structures (gate-like structure, propeller structure) were successfully manufactured to highlight the viability of the ink as a support material.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.001
  • Prospective study on the integration of additive manufacturing to building
           industry- Case of a French construction company.
    • Authors: Imane Krimi; Zoubeir Lafhaj; Laure Ducoulombier
      Abstract: Publication date: Available online 24 May 2017
      Source:Additive Manufacturing
      Author(s): Imane Krimi, Zoubeir Lafhaj, Laure Ducoulombier
      The objective of this paper is to present a reflection on the use of Additive manufacturing in construction. In this research examples from manufacturing industries are presented. Some Advantages of additive manufacturing in industry were identified. Relevant cases used to promote AM for construction are: building rate improvement and schedules shortening. This study investigated these advantages in three parts. Firstly, a comparison between construction and manufacturing industry was presented. Secondly, Design and Building rate for construction were studied using data from a French construction company. Finally a comparison was made between conventional processes and Additive manufacturing. Conventional processes included prefabrication and casting on site. Results showed that pre-casting may be faster than AM in some cases. Time saving is not necessary the best advantage from applying additive manufacturing to construction.

      PubDate: 2017-05-29T05:18:46Z
      DOI: 10.1016/j.addma.2017.04.002
  • Wire and Arc Additive Manufactured Steel: Tensile and Wear Properties
    • Authors: C.V. Haden; G.S. Zeng; F.M. Carter; C. Ruhl; B.A. Krick; D.G. Harlow
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): C.V. Haden, G.S. Zeng, F.M. Carter, C. Ruhl, B.A. Krick, D.G. Harlow
      The present study systematically investigated the mechanical properties of wire-based (wire and arc additive manufacturing, known as WAAM) deposition of steel metals, both stainless steel 304 and mild steel ER70S. Graded material properties of stainless steel 304 were observed for wear and hardness in the direction of deposition and in Z height, due to variations in local thermal histories of the metal. Wear rates decreased significantly (p=5.6×10−12 by one-way ANOVA) along the length of the deposited material, from μ=2.62×10−5 mm3/N · m and σ=2.32×10−6 mm3/N · m, to μ=0.63mm3/N · m and σ=3.08×10−6 mm3/N · m, whereas microhardness values increased significantly (p∼0 by one-way ANOVA) along the same path from μ=202.3 HV and σ=5.82 HV to 210.9 HV and σ=5.91 HV. The yield and ultimate strength, however, were not found to be statistically significantly different (p=0.55) along the direction of deposition for SS304. During wear testing, a grain refinement was observed directly beneath the wear scar in these materials in a focused ion beam channel observed under scanning electron microscopy. Additionally, no significant difference in yield strength was observed in printed mild steel (ER70S) between vertical and horizontal specimens. The observed graded mechanical properties in stainless steel 304 allow the opportunity for varying the processing conditions to design parts with locally optimized or functionally graded mechanical properties.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.010
  • Design Framework for Multifunctional Additive Manufacturing: Coupled
           Optimization Strategy for Structures with embedded functional Systems
    • Authors: Ajit Panesar; Ian Ashcroft; David Brackett; Ricky Wildman; Richard Hague
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): Ajit Panesar, Ian Ashcroft, David Brackett, Ricky Wildman, Richard Hague
      The driver for this research is the development of multi-material additive manufacturing processes that provide the potential for multi-functional parts to be manufactured in a single operation. In order to exploit the potential benefits of this emergent technology, new design, analysis and optimization methods are needed. This paper presents a method that enables in the optimization of a multifunctional part by coupling both the system and structural design aspects. This is achieved by incorporating the effects of a system, comprised of a number of connected functional components, on the structural response of a part within a structural topology optimization procedure. The potential of the proposed method is demonstrated by performing a coupled optimization on a cantilever plate with integrated components and circuitry. The results demonstrate that the method is capable of designing an optimized multifunctional part in which both the structural and system requirements are considered.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.009
  • 316L stainless steel mechanical and tribological behavior − a comparison
           between selective laser melting, hot pressing and conventional casting
    • Authors: F. Bartolomeu; M. Buciumeanu; E. Pinto; N. Alves; O. Carvalho; F.S. Silva; G. Miranda
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): F. Bartolomeu, M. Buciumeanu, E. Pinto, N. Alves, O. Carvalho, F.S. Silva, G. Miranda
      This work presents a comprehensive study on the influence of three different processing technologies (Selective Laser Melting, Hot Pressing and conventional casting) on the microstructure, mechanical and wear behavior of an austenitic 316L Stainless Steel. A correlation between the processing technologies, the obtained microstructure and the mechanical and wear behavior was achieved. The results showed that the highest mechanical properties and tribological performance were obtained for 316L SS specimens produced by Selective Laser Melting, when compared to Hot Pressing and conventional casting. The high wear and mechanical performance of 316L Stainless Steel fabricated by Selective Laser Melting are mainly due to the finer microstructure, induced by the process. In this sense, Selective Laser Melting seems a promising method to fabricate customized 316L SS implants with improved mechanical and wear performance.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.007
  • Tailoring residual stress profile of Selective Laser Melted parts by Laser
           Shock Peening
    • Authors: Nikola Kalentics; Eric Boillat; Patrice Peyre; Snežana Ćirić-Kostić; Nebojša Bogojević; Roland E. Logé
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): Nikola Kalentics, Eric Boillat, Patrice Peyre, Snežana Ćirić-Kostić, Nebojša Bogojević, Roland E. Logé
      The paper describes a new approach in controlling and tailoring residual stress profile of parts made by Selective Laser Melting (SLM). SLM parts are well known for the high tensile stresses in the as − built state in the surface or subsurface region. These stresses have a detrimental effect on the mechanical properties and especially on the fatigue life. Laser Shock Peening (LSP) as a surface treatment method was applied on SLM parts and residual stress measurements with the hole − drilling method were performed. Two different grades of stainless steel were used: a martensitic 15-5 precipitation hardenable PH1 and an austenitic 316L. Different LSP parameters were used, varying laser energy, shot overlap, laser spot size and treatments with and without an ablative medium. For both materials the as-built (AB) residual stress state was changed to a more beneficial compressive state. The value and the depth of the compressive stress was analyzed and showed a clear dependence on the LSP processing parameters. Application of LSP on SLM parts showed promising results, and a novel method that would combine these two processes is proposed. The use of LSP during the building phase of SLM as a “3D LSP” method would possibly give the advantage of further increasing the depth and volume of compressive residual stresses, and selectively treating key areas of the part, thereby further increasing fatigue life.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.008
  • Effect of minor alloying elements on crack-formation characteristics of
           Hastelloy-X manufactured by selective laser melting
    • Authors: Dacian Tomus; Paul A. Rometsch; Martin Heilmaier; Xinhua Wu
      Abstract: Publication date: Available online 9 May 2017
      Source:Additive Manufacturing
      Author(s): Dacian Tomus, Paul A. Rometsch, Martin Heilmaier, Xinhua Wu
      Two batches of pre-alloyed Hastelloy-X powder with different Si, Mn and C contents were used to produce specimens by Selective Laser Melting (SLM). Cracks with various morphologies were found in some of the parts. Two major reasons that control crack formation and propagation were considered: (i) internal strain accumulation due to the thermal cycling that is characteristic to SLM processing; (ii) crack formation and propagation during solidification. This phenomenon, known as hot tearing, is frequently found in conventional casting and is dependent on chemical composition. Using thermodynamic software simulation, the temperature vs fraction of solid curves was used to determine hot tearing sensitivity as a function of Si, Mn and C content. It was found that low Si and C contents help in avoiding crack formation whereas cracking propensity was relatively independent of Mn concentration. Hence, the cracking mechanism during SLM is believed to be as follows: crack initiation is mainly induced during solidification and is dependent on the content of minor alloying elements such as Si and C, whereas crack propagation predominantly occurs during thermal cycling. If microstructures free of micro-cracks after solidification can be generated with optimised SLM parameters, these manufactured parts can sustain the internal strain level and, thus, crack formation and propagation can be avoided.

      PubDate: 2017-05-13T10:52:10Z
      DOI: 10.1016/j.addma.2017.05.006
  • Quantitative texture prediction of epitaxial columnar grains in additive
           manufacturing using selective laser melting
    • Authors: Jian Liu; Albert C. To
      Abstract: Publication date: Available online 5 May 2017
      Source:Additive Manufacturing
      Author(s): Jian Liu, Albert C. To
      Metal additive manufacturing (AM) such as selective laser melting (SLM) has the powerful capability to produce very different microstructural features, hence different mechanical properties in metals using the same feedstock material but different values of process parameters. However, the relation between processing-microstructure is mostly investigated by experiments, which is expensive and time-consuming since the parameter space is quite large. The lack of a reliable theoretical model of the processing-microstructure relationship of AM material is preventing AM technology from being widely adopted by the manufacturing community. Hence, the goal of this work is to establish the link between the microstructure (texture) and the process parameters (laser power, scanning speed, preheat and scanning strategy) of a metal SLM process. To achieve the above goal, a quantitative semi-empirical method is proposed to predict the texture of the epitaxial columnar grains grown from polycrystal substrates. Combined with the melt pool prediction by the Rosenthal solution, the processing and microstructure were linked together quantitatively. The proposed method is used to estimate the texture evolution with the number of layers for EOS-DMLS-processed AlSi10Mg (unidirectional scanning direction in one layer and no rotation of scanning direction between layers). The texture reaches a steady state after five layers, and the steady state texture has similar pattern and intensity to that obtained from the experiment using the same process parameter values and scanning strategy.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.005
  • Thermomechanical model development and in situ experimental validation of
           the Laser Powder-Bed Fusion Process
    • Authors: Erik R. Denlinger; Michael Gouge; Jeff Irwin; Pan Michaleris
      Abstract: Publication date: Available online 4 May 2017
      Source:Additive Manufacturing
      Author(s): Erik R. Denlinger, Michael Gouge, Jeff Irwin, Pan Michaleris
      A three-dimensional finite element model is developed to allow for the prediction of temperature, residual stress, and distortion in multi-layer Laser Powder-Bed Fusion builds. Undesirable residual stress and distortion caused by thermal gradients are a common source of failure in AM builds. A non-linear thermoelastoplastic model is combined with an element coarsening strategy in order to simulate the thermal and mechanical response of a significant volume of deposited material (38 layers and 91 mm3). It is found that newly deposited layers experience the greatest amount of tensile stress, while layers beneath are forced into compressive stress. The residual stress evolution drives the mechanical response of the workpiece. The model is validated by comparing the predicted in situ and post process distortion to experimental measurements taken on the same geometry. The model accurately predicts the distortion of the workpiece (5 % error).

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.001
  • Sub-wavelength Lithography of Complex 2D and 3D Nanostructures without
           Two-photon Dyes
    • Authors: Raghvendra P Chaudhary; Arun Jaiswal; Govind Ummethala; Suyog R Hawal; Sumit Saxena; Shobha Shukla
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): Raghvendra P Chaudhary, Arun Jaiswal, Govind Ummethala, Suyog R Hawal, Sumit Saxena, Shobha Shukla
      One-photon or two photon absorption by dye molecules in photopolymers enable direct 2D & 3D lithography of micro/nano structures with high spatial resolution and can be used effectively in fabricating artificially structured nanomaterials. However, the major bottleneck in unleashing the potential of this useful technique is the indispensable usage of dyes that are expensive, highly toxic and usually insoluble in commercially available photopolymers. Here we report a simple, inexpensive and one-step technique for direct-writing of micro/nanostructures, with sub-wavelength resolution at high speeds without using any one photon or two photon absorbing dye. We incorporated large amount (20 weight %) of inexpensive photoinitiator, which has not been done to best of our knowledge, into the photopolymer and utilized its two-photon absorbing property for sub-wavelength patterning. Complex 2D patterns and 3D meshes were fabricated with sub-micron resolution, in commercially available liquid photopolymer to show the impact/versatility of this technique.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.003
  • On the use of spatter signature for in-situ Monitoring of Laser Power Bed
    • Authors: Giulia Repossini; Vittorio Laguzza; Marco Grasso; Bianca Maria Colosimo
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): Giulia Repossini, Vittorio Laguzza, Marco Grasso, Bianca Maria Colosimo
      In-situ monitoring of metal additive manufacturing (AM) processes is a key issue to determine the quality and stability of the process during the layer-wise production of the part. The quantities that can be measured via in-situ sensing can be referred to as “process signatures”, and can represent the source of information to detect possible defects. Most of the literature on in-situ monitoring of Laser Power Bed Fusion (LPBF) processes focuses on the melt-pool, laser track and layer image as source of information to detect the onset of possible defects. Up to our knowledge, this paper represents a first attempt to investigate the suitability of including spatter-related information to characterize the LPBF process quality. High-speed image acquisition, coupled with image segmentation and feature extraction, is used to estimate different statistical descriptors of the spattering behaviour along the laser scan path. A logistic regression model is developed to determine the ability of spatter-related descriptors to classify different energy density conditions corresponding to different quality states. The results show that by including spatters as process signature driver, a significant increase of the capability to detect under-melting and over-melting conditions is observed. This is why future research on spatter signature analysis and modelling is highly encouraged to improve the effectiveness of in-situ monitoring tools.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.004
  • Finite Element Simulation and Experimental Validation of Distortion and
           Cracking Failure Phenomena in Direct Metal Laser Sintering Fabricated
    • Authors: Yi Zhang; Jing Zhang
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): Yi Zhang, Jing Zhang
      A new one-way coupled thermal-mechanical finite element based model of direct metal laser sintering (DMLS) is developed to simulate the process, and predict distortion and cracking failure location in the fabricated components. The model takes into account the layer-by-layer additive manufacturing features, solidification and melting phenomena. The model is first validated using experimental data, then model is applied to a DMLS fabricated component. The study shows how the stress distribution at the support-solid interface is critical to contributing to cracking and distortion. During the DMLS process, thermal stress at the support-solid interface reaches its maximum during the printing process, particularly when the first solid layer is built above the support layer. This result suggests that cracking at the interface may occur during the printing process, which is consistent with experimental observation. Using a design parametric study, a thick and low-density porous layer is found to reduce residual stress and distortion in the built component. The developed finite element model can be used to future design and optimize DMLS process.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.002
  • Compressive failure modes and energy absorption in additively manufactured
           double gyroid lattices
    • Authors: I. Maskery; N.T. Aboulkhair; A.O. Aremu; C.J. Tuck; I.A. Ashcroft
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): I. Maskery, N.T. Aboulkhair, A.O. Aremu, C.J. Tuck, I.A. Ashcroft
      Lattice structures are excellent candidates for lightweight, energy absorbing applications such as personal protective equipment. In this paper we explore several important aspects of lattice design and production by metal additive manufacturing, including the choice of cell size and the application of a post-manufacture heat treatment. Key results include the characterisation of several failure modes in double gyroid lattices made of Al-Si10-Mg, the elimination of brittle fracture and low-strain failure by the application of a heat treatment, and the calculation of specific energy absorption under compressive deformation (16×106 J m−3 up to 50% strain). These results demonstrate the suitability of double gyroid lattices for energy absorbing applications, and will enable the design and manufacture of more efficient lightweight parts in the future.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.04.003
  • Microstructured Monofilament via Thermal Drawing of Additively
           Manufactured Preforms
    • Authors: P.M. Toal; L.J. Holmes; R.X. Rodriguez; E.D. Wetzel
      Abstract: Publication date: Available online 29 April 2017
      Source:Additive Manufacturing
      Author(s): P.M. Toal, L.J. Holmes, R.X. Rodriguez, E.D. Wetzel
      A process is presented for the rapid production of microstructured monofilaments via thermal drawing of additively manufactured polymer preforms. Preforms are produced wholly, or in part, via fused filament fabrication of acrylonitrile-butadiene-styrene (ABS) and polycarbonate materials. The preforms are heated and drawn under tension to convert the preforms into lengths of monofilament that closely reproduce the geometric structure of the parent preform. Example monofilaments include “microprinted” monofilaments that contain an arbitrary image embedded in the monofilament cross section; microfluidic monofilaments in which flow channels are formed by combining optically transparent and opaque materials; dual-material monofilaments that combine ABS and polycarbonate into a regular spoked geometry with five-fold symmetry; and a microfluidic preform co-drawn with glass optical fiber, allowing both fluid and light transmission through the monofilament. The primary advantages of this monofilament fabrication technique include short lead times; minimal investment in materials and equipment; a means of directly combining multiple materials into a single monofilament, even if the material components have different thermorheological properties; and the ability to create arbitrary and complex geometries.

      PubDate: 2017-05-03T14:38:20Z
      DOI: 10.1016/j.addma.2017.03.009
  • Rate limits of additive manufacturing by fused filament fabrication and
           guidelines for high-throughput system design
    • Authors: Jamison Go; Scott N. Schiffres; Adam G. Stevens; A. John Hart
      Abstract: Publication date: Available online 16 March 2017
      Source:Additive Manufacturing
      Author(s): Jamison Go, Scott N. Schiffres, Adam G. Stevens, A. John Hart
      While additive manufacturing (AM) advances rapidly towards new materials and applications, it is vital to understand the performance limits of AM process technologies and to overcome these limits via improved machine design and process integration. Extrusion-based AM (i.e., fused filament fabrication, FFF) is compatible with a wide variety of thermoplastic polymer and composite materials, and can be deployed across a wide range of length scales. However, the build rate of both desktop and professional FFF systems is comparable (∼10’s of cm3/hr at ∼0.2mm layer thickness), suggesting that fundamental aspects of the machine design and process physics limit system performance. We determine the rate limits to FFF by analysis of machine modules: the filament extrusion mechanism, the heater and nozzle, and the motion system. We determine, by direct measurements and numerical analysis, that FFF build rate is influenced by the coincident module-level limits to traction force exerted on the filament, conduction heat transfer to the filament core, and gantry velocity for positioning the printhead. Our findings are validated by direct measurements of build rate versus part complexity using desktop FFF systems. Last, we study the scaling of the rate limits using finite element simulations of thermoplastic flow through the extruder. We map the scaling of extrusion force, polymer exit temperature, and average printhead velocity onto a unifying trade-space of build rate versus resolution. This approach validates the build rate performance of current FFF systems, and suggests that significant enhancements in FFF build rate with targeted quality specifications are possible via mutual improvements to the extrusion and heating mechanism along with high-speed motion systems.

      PubDate: 2017-03-17T12:56:18Z
      DOI: 10.1016/j.addma.2017.03.007
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