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Acta Mechanica Solida Sinica
Journal Prestige (SJR): 0.542  Citation Impact (citeScore): 1 Number of Followers: 8  Hybrid journal (It can contain Open Access articles)ISSN (Print) 0894-9166 - ISSN (Online) 1860-2134 Published by Springer-Verlag  [2468 journals]
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- Applying the Infrared Self-heating Method to a Comprehensive Fatigue
Analysis of NiTi Shape Memory Alloys-
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Abstract: Abstract This paper aims to seek expedited fatigue analysis methods using the infrared self-heating technique. The fatigue analysis of NiTi shape memory alloys is obtained through a hybrid approach: fatigue tests to failure yield relatively shorter fatigue lives, while determining the fatigue limit, normally involving extremely high cycles approaching 107 cycles, is directly achieved via self-heating tests. This methodology significantly reduces testing cycles, costing only a fraction of the several-thousand-cycle tests typically required. The validity of this approach is successfully demonstrated through fatigue testing of 18Ni steel: the entire S–N curve is examined using the traditional fatigue test until a life of up to 107 cycles, and the indicated fatigue limit agrees well with the one directly determined through the self-heating method. Subsequently, this developed approach is applied to the fatigue analysis of shape memory alloys under complex loading, enabling the concurrent estimation of the limits of phase transformation-dominated low-cycle fatigue and high-cycle fatigue in the elastic regime on a single specimen. The results obtained align well with other supporting evidence.
PubDate: 2024-08-05
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- Bending and Vibration Analysis of Trigonometric Varying Functionally
Graded Material via a Novel Third-Order Shear Deformation Theory-
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Abstract: Abstract Given the significant potential of multi-directional functionally graded materials (MFGMs) for customizable performance, it is crucial to develop versatile material models to enhance design optimization in engineering applications. This paper introduces a material model for an MFGM plate described by trigonometric functions, equipped with four parameters to control diverse material distributions effectively. The bending and vibration analysis of MFGM rectangular and cutout plates is carried out utilizing isogeometric analysis, which is based on a novel third-order shear deformation theory (TSDT) to account for transverse shear deformation. The present TSDT, founded on rigorous kinematics of displacements, is demonstrated to surpass other preceding theories. It is derived from an elasticity formulation, rather than relying on the hypothesis of displacements. The effectiveness of the proposed method is verified by comparing its numerical results with those of other methods reported in the relevant literature. Numerical results indicate that the structure, boundary conditions, and gradient parameters of the MFGM plate significantly influence its deflection, stress, and vibration frequency. As the periodic parameter exceeds four, the model complexity increases, causing result fluctuations. Additionally, MFGM cutout plates, when clamped on all sides, display almost identical first four vibration frequencies.
PubDate: 2024-08-05
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- A Numerical Model of Heating and Cooling Cycles to Study the Driven
Response for Twisted and Coiled Polymer Actuator-
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Abstract: Abstract Twisted and coiled polymer actuator (TCPA) is a type of artificial muscle that can be driven by heating due to its structure. A key issue with TCPA performance is the low driven frequency due to slow heat transfer in heating and cooling cycles, especially during cooling. We developed a numerical model of coating heating and nitrogen gas cooling that can effectively improve the driven forces and frequencies of the TCPA. Results indicate that natural cooling and electric fan cooling modes used in many experiments cannot restore the TCPA to its initial configuration when driven frequencies are high. Nitrogen gas cooling, at high driven frequencies, can fully restore the TCPA to its initial configuration, which is crucial for maintaining artificial muscle flexibility. In addition, as driven frequency increases, the corresponding driven force decreases. Systematic parametric studies were carried out to provide inspirations for optimizing TCPA design. The integrative computational study presented here provides a fundamental mechanistic understanding of the driven response in TCPA and sheds light on the rational design of TCPA through changing cooling modes.
PubDate: 2024-08-05
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- A Two-Way FSI Model for Pathologic Respiratory Processes with Precisely
Structured and Flexible Upper Airway-
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Abstract: Abstract The human body displays various symptoms of altitude sickness due to hypoxia in environments with low pressure and oxygen levels. While existing studies are primarily focused on the adverse effects of hypoxia and oxygen supplementation strategies at high altitudes, there is a notable gap in understanding the fundamental mechanisms driving altitude hypoxia. In this context, we propose a sophisticated two-way fluid–structure interaction model that simulates respiratory processes with precisely structured and deformable upper airways. This model reveals that, under identical pressure differentials at the airway’s inlet and outlet, the inspiratory air volume remains largely consistent and is minimally affected by specific pressure changes. However, an increase in the pressure differential enhances gas inhalation efficiency. Furthermore, airway morphology emerges as a pivotal factor influencing oxygen intake. Distorted airway shapes create areas of high flow velocity, where low wall pressure hampers effective airway opening, thus diminishing gas inhalation. These results may shed light on the effects of low-pressure conditions and upper airway structure on respiratory dynamics at high altitudes and inform the development of effective oxygen supply strategies.
PubDate: 2024-08-05
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- In-Plane Small-Deformation Equivalent Method for Kinematic Analysis of
Tubular Miura-Ori-
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Abstract: Abstract The tubular Miura-ori (TMO) structure has attracted much attention due to its excellent folding capability and rich application diversity. However, the existing theoretical research on origami structure is overly complex, and kinematic analysis rarely involves bending motion. In the present work, based on geometric kinematics, “equivalent deformation mechanism” is proposed to study the axial and bending motions of TMO under small in-plane deformations. Firstly, the geometric design is studied using the vector expression of creases. To simplify the kinematic analysis of axial motion, TMO deformation is equated to a change in angle. The proposed method is also applicable to bending motion, because both bending and axial motions can be described using similar deformation mechanisms. In addition, the accuracy of the proposed method is validated through numerical analysis, and the error between analytical and numerical solutions is sufficiently small for the folding angle \(\gamma \in \left[ {25^\circ , 65^\circ } \right]\) . Finally, the numerical simulation is validated with mechanical experiments. Results show the effectiveness of the proposed method in describing the kinematic law of TMO structures in a simple way. This research sheds light on the kinematic analysis of other origami structures and establishes a theoretical framework for their applications in aerospace engineering, origami-based metamaterials, and robotics.
PubDate: 2024-07-30
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- Investigation on the Very High Cycle Fatigue Life of Titanium Alloys by
Near-β Forging and Shot Peening-
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Abstract: Abstract In order to enhance the fatigue properties of metallic materials, a feasible rationale is to delay or prevent the interior and surface fatigue crack initiation. Based on this rationale, the study investigates the approach of improving the very high cycle fatigue properties of TC6 titanium alloys through near-β forging coupled with shot peening, conducted at 930 ℃ and ambient temperature, respectively. To unveil the associated mechanisms, microstructure, microhardness, residual stress, and fatigue properties are thoroughly analyzed after each process. Results indicate a considerable refinement in microstructure and significant mitigation of the initially existed strong texture post near-β forging and annealing, efficiently delaying crack initiation and propagation. As a result, the very high cycle fatigue property of TC6 achieves remarkable enhancement after forging. Compared to near-β forging, shot peening might not necessarily improve the very high cycle fatigue performance, particularly beyond 106 cycles.
PubDate: 2024-07-30
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- A Semi-analytical Model of Maxienmal First Principal Stress at Mode I
Crack Tip-
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Abstract: Abstract The first principal stress plays a key role in ductile fracture processes. Investigation of the distribution and evolution of the first principal stress at the crack tip is essential for exploring elastoplastic fracture behaviors. A semi-analytical model was developed in this study to determine the maximal first principal stress at the mode I crack tip with 3D constraints for materials following the Ramberg–Osgood law. The model, based on energy density equivalence and dimensional analysis, was validated through finite element analysis (FEA) of various materials and geometric dimensions of specimens with mode I cracks, under over 100 different types of working conditions. The dimensionless curves of maximal first principal stress versus load, as predicted by the model, agreed well with the FEA results, demonstrating the accuracy and applicability of the model. This research can provide a basis for future theoretical predictions of crack initiation and propagation.
PubDate: 2024-07-30
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- New Insight into the Flexoelectricity in the View of Mechanics of
Materials: Prismatic Beams Subjected to Bending-
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Abstract: Abstract Flexoelectricity is a fascinating electromechanical phenomenon that occurs in non-homogeneously deformed dielectric materials. Unlike piezoelectricity, the flexoelectric effect is highly dependent on both the material scale and the deformation gradient. Although several theoretical models have been proposed to explain the mechanism of flexoelectricity, these models can be rather complicated for those who are interested in studying the topic. This paper aims to simplify the understanding of flexoelectricity by focusing on the bending behavior of a prismatic dielectric beam from a mechanics of material perspective. We avoid using complicated mathematical formulations based on continuum mechanics, including advanced tensor algebra and calculus of variations. Our formulation clearly explains how inhomogeneous deformations and material size affect the electromechanical coupling, changing the effective bending stiffness, deflection, and rotation angles of a bending beam. We hope this paper can help undergraduate students and researchers, who are unfamiliar with the electromechanical coupling in flexoelectricity, to develop an understanding of this phenomenon and encourage further research in this area.
PubDate: 2024-07-11
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- Effect of Tacticity on the Dynamic Response of Chiral Mechanical
Metamaterials-
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Abstract: Abstract In this work, a tacticity strategy is proposed to adjust the mechanical properties of chiral mechanical metamaterials for vibration isolation. By applying the finite element method, the impact of tacticity on tensile deformations, band structures, and vibration transmission spectra of chiral metamaterials is investigated. The axial deformations of isotactic configuration and syndiotactic configuration are similar under tensile loads, but rotational deformation occurs in the isotactic configuration. With the same geometric and material parameters, the first band gap of the syndiotactic configuration is lower than that of the isotactic configuration. The vibration suppression performance of chiral mechanical metamaterials is verified by numerical simulations and experiments. Parametric analysis of the band gap provides valuable insights for the manipulation and expansion of vibration reduction. Gradient design based on parametric analysis achieves an extended range of vibration suppression.
PubDate: 2024-07-01
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- Hysteresis Analysis on Origami Energy Dissipation Braces with Local Miura
Units-
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Abstract: Abstract A local design scheme for origami energy dissipation braces was proposed by combining local Miura units at both ends and a straight segment in the middle. This design was implemented to address the issue of uneven axial stiffness observed in global origami braces. Globally and locally designed origami braces were simulated and compared under cyclic loading to validate the advantages of the proposed design scheme in terms of hysteretic properties. Additionally, an analysis was conducted on the designed braces with varying straight segment lengths, geometric angles, and origami plate thicknesses for comparison. Results indicate that the local design significantly increases the tensile bearing load, enhances the anti-buckling capability, and improves the energy dissipation performance compared to the global design. The positive impact on bearing capacity and energy dissipation performance was observed with increased straight segment length, geometric angles, and origami plate thickness. However, excessively large parameter values result in brace buckling under compression, diminishing energy dissipation capacity.
PubDate: 2024-06-28
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- Enhanced Flexoelectricity in Barium Titanate-Cellulose Composite Thin
Films-
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Abstract: Abstract Biopolymers, the potential flexoelectric materials, are environment-friendly, degradable, lightweight, cost-effective, and possess remarkable processing properties catering to the requirements of advanced devices. However, the flexoelectric coefficient of biopolymers is normally much weaker than that of ceramic materials, limiting their potential applications for designing high-performance green electromechanical coupling devices. To improve the flexoelectric response in biopolymers, we composited barium titanate (BTO) with 2,2,6,6-tetramethylpiperidine-1-oxyl -oxidized cellulose nanofibrils (TOCNF) to enhance the flexoelectric response of TOCNF. Owing to the high permittivity and flexoelectric effect of BTO, the relative dielectric constant and flexoelectric coefficient of 33.3 wt% BTO-TOCNF films reached 30.94 @ 1 kHz and 50.05 ± 1.88 nC/m @ 1 Hz, which were almost 172 times and 27 times higher than those of TOCNF, respectively. The composite thin film contains high dielectric constant and flexoelectric coefficient, as well as excellent flexibility. Our study provided a straightforward and efficient method for improving the flexoelectric effect of biopolymers, and demonstrated its great potential applications in flexoelectric-based devices.
PubDate: 2024-06-26
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- Preface to the “Theory and Applications of Flexoelectricity” Special
Issue of Acta Mechanica Solida Sinica-
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PubDate: 2024-06-19
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- Total Internal Reflection (TIR) Behavior of Heterogeneous Interface Shear
Waves in Layered Soft Structure-
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Abstract: Abstract The total internal reflection (TIR) behavior of interface shear waves is crucial for ensuring the reliability of dielectric elastomer (DE) devices. However, due to the complex force-electric coupling and large deformation of DEs, the TIR behavior of shear waves in heterogeneous force-electric interface models is still unclear. This study modeled an elastic/DE bi-material interface to analyze the trajectory of out-of-plane shear waves. Employing Dorfmann and Ogden’s nonlinear electroelastic framework and the related linear small incremental motion theory, a method has been developed to control the TIR behavior of interface shear waves. It has been found that the TIR behavior is significantly influenced by the strain-stiffening effect induced by biasing fields. Consequently, a biasing field principle involving preset electric displacement and pre-stretch has been proposed for TIR occurrence. By controlling the pre-stretch and preset electric displacement, active regulation of TIR behavior can be achieved. These results suggest a potential method for achieving autonomous energy shielding to improve the reliability of DE devices.
PubDate: 2024-06-18
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- Size and Interface Effects on Tensile Strength of Polymers with Nano/Micro
Particle Inclusions-
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Abstract: Abstract Polymers with particle inclusions have wide applications, and the mechanical properties of polymer composites affect their reliability in service. The strength of these composites is dependent on factors such as particle fraction, size, distribution, and interface interaction between the two phases, in addition to the properties of the polymers and particles. The size effect of particles and interface damage play an important role and thus draw considerable attention. In this paper, the size- and interface-dependent strength of polypropylene (PP) with nano/micro silica (SiO2) particles of different fractions is studied through a combination of tensile experiments on a series of samples and corresponding three-dimensional (3D) finite element modeling. The results indicate that PP with 2% SiO2 nanoparticles of 50 nm exhibits relatively higher tensile strength, shedding light on the microstructure mechanism where smaller particle sizes lead to better interface bonding. Furthermore, the particle size and interface coupling effect is analyzed based on the size-dependent elastic modulus model and the interface-cohesive model. The simulation demonstrates the local interface damage evolution around a particle of the composites in tension. These findings are beneficial for designing polymer composites with nanoparticle inclusions.
PubDate: 2024-06-12
DOI: 10.1007/s10338-024-00498-0
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- Linear and Nonlinear Formulation of Phase Field Model with Generalized
Polynomial Degradation Functions for Brittle Fractures-
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Abstract: Abstract The classical phase field model has wide applications for brittle materials, but nonlinearity and inelasticity are found in its stress–strain curve. The degradation function in the classical phase field model makes it a linear formulation of phase field and computationally attractive, but stiffness reduction happens even at low strain. In this paper, generalized polynomial degradation functions are investigated to solve this problem. The first derivative of degradation function at zero phase is added as an extra constraint, which renders higher-order polynomial degradation function and nonlinear formulation of phase field. Compared with other degradation functions (like algebraic fraction function, exponential function, and trigonometric function), this polynomial degradation function enables phase in [0, 1] (should still avoid the first derivative of degradation function at zero phase to be 0), so there is no \(\Gamma \) convergence problem. The good and meaningful finding is that, under the same fracture strength, the proposed phase field model has a larger length scale, which means larger element size and better computational efficiency. This proposed phase field model is implemented in LS-DYNA user-defined element and user-defined material and solved by the Newton–Raphson method. A tensile test shows that the first derivative of degradation function at zero phase does impact stress–strain curve. Mode I, mode II, and mixed-mode examples show the feasibility of the proposed phase field model in simulating brittle fracture.
PubDate: 2024-06-11
DOI: 10.1007/s10338-024-00501-8
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- Size-Dependent Analysis of Piezoelectric–Elastic Bilayer Microbeams
Based on General Strain Gradient Theory-
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Abstract: Abstract The classical piezoelectric theory fails to capture the size-dependent electromechanical coupling behaviors of piezoelectric microstructures due to the lack of material length-scale parameters. This study presents the constitutive relations of a piezoelectric material in terms of irreducible transversely isotropic tensors that include material length-scale parameters. Using these relations and the general strain gradient theory, a size-dependent bending model is proposed for a bilayer cantilever microbeam consisting of a transversely isotropic piezoelectric layer and an isotropic elastic layer. Analytical solutions are provided for bilayer cantilever microbeams subjected to force load and voltage load. The proposed model can be simplified to the model incorporating only partial strain gradient effects. This study examines the effect of strain gradient by comparing the normalized electric potentials and deflections of different models. Numerical results show that the proposed model effectively captures size effects in piezoelectric microbeams, whereas simplified models underestimate size effects due to ignoring partial strain gradient effects.
PubDate: 2024-06-06
DOI: 10.1007/s10338-024-00492-6
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- Preface to the Special Issue in Celebration of Professor Shouwen
Yu’s 85th Birthday-
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PubDate: 2024-06-01
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- Analytical Solutions for an Isotropic Elastic Half-Plane with Complete
Surface Effects Subjected to a Concentrated/Uniform Surface Load-
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Abstract: Abstract Within the context of Gurtin–Murdoch surface elasticity theory, closed-form analytical solutions are derived for an isotropic elastic half-plane subjected to a concentrated/uniform surface load. Both the effects of residual surface stress and surface elasticity are included. Airy stress function method and Fourier integral transform technique are used. The solutions are provided in a compact manner that can easily reduce to special situations that take into account either one surface effect or none at all. Numerical results indicate that surface effects generally lower the stress levels and smooth the deformation profiles in the half-plane. Surface elasticity plays a dominant role in the in-plane elastic fields for a tangentially loaded half-plane, while the effect of residual surface stress is fundamentally crucial for the out-of-plane stress and displacement when the half-plane is normally loaded. In the remaining situations, combined effects of surface elasticity and residual surface stress should be considered. The results for a concentrated surface force serve essentially as fundamental solutions of the Flamant and the half-plane Cerruti problems with surface effects. The solutions presented in this work may be helpful for understanding the contact behaviors between solids at the nanoscale.
PubDate: 2024-06-01
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- Different Types of Bone Fractures Observed by Terahertz Time-Domain
Spectroscopy-
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Abstract: Abstract Microcracks are common in compact bone, but their continued propagation can lead to macroscopic fractures. These microcracks cannot be visualized radiographically, necessitating alternative noninvasive methods to identify excessive microcracking and prevent fractures. In this study, terahertz time-domain spectroscopy (THz-TDS) was used to examine bone interiors near cracks resulting from loading in bovine tibia samples. Various loading configurations, such as impact, quasi-static loading, and fatigue loading, known to induce different types of micro-scale damage, were applied. The values of refractive index and absorption coefficient of the bone samples were then determined from the THz-TDS spectra acquired before loading and after fracture. The study revealed that different loading configurations led to varying terahertz optical coefficients associated with various types of bone fractures. Specifically, the refractive index notably increased under fatigue loading but remained relatively stable during quasi-static bending. The absorption coefficient of bone decreased only under fatigue loading. Furthermore, samples were subjected to axial and radial impacts without sustaining damage. Results indicated that in the undamaged state, the change in refractive index was smaller compared to after impact failure, while the change in absorption coefficient remained consistent after failure. Under radial impact loading, changes in refractive index and absorption coefficient were significantly more pronounced than under axial loading. Prior to loading, the measured value of refractive index was 2.72 ± 0.11, and the absorption coefficient was 6.33 ± 0.09 mm−1 at 0.5 THz.
PubDate: 2024-04-15
DOI: 10.1007/s10338-024-00482-8
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- Peeling of Magneto-responsive Beams with Large Deformation Mediated by the
Parallel Magnetic Field-
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Abstract: Abstract Elasto-capillarity phenomena are prevalent in various industrial fields such as mechanical engineering, material science, aerospace, soft robotics, and biomedicine. In this study, two typical peeling processes of slender beams driven by the parallel magnetic field are investigated based on experimental and theoretical analysis. The first is the adhesion of two parallel beams, and the second is the self-folding of a long beam. In these two cases, the energy variation method on the elastica is used, and then, the governing equations and transversality boundary conditions are derived. It is shown that the analytical solutions are in excellent agreement with the experimental data. The effects of magnetic induction intensity, distance, and surface tension on the deflection curve and peeling length of the elastica are fully discussed. The results are instrumental in accurately regulating elasto-capillarity in structures and provide insights for the engineering design of programmable microstructures on surfaces, microsensors, and bionic robots.
PubDate: 2024-04-15
DOI: 10.1007/s10338-024-00480-w
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