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Mechanics of Soft Materials
Number of Followers: 0  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2524-5600 - ISSN (Online) 2524-5619
Published by Springer-Verlag Homepage  [2626 journals]
  • A review on recent development of theoretical modeling of hydrogel phase
           behavior subject to mechanics and multiphysics coupled effects
    • Abstract: Abstract Hydrogel is a class of hydrophilic crosslinked polymeric network filled with interstitial fluid. The specified composition and network structure enable the soft material to exhibit different mechanical properties, ranging from elastic solid to viscous liquid, subject to environmental stimuli. In this process, they are able to imbibe a large amount of water or other biological fluid, and thus solid-solid or solid-liquid phase transition may occur due to discontinuous changes of certain properties, where large elongation and nonlinear deformation are coupled with multiphysics changes, such as mass diffusion, heat conduction, and crosslinks forming/breaking. This paper reviews the recent development of theoretical modeling and simulation work for the soft materials, with emphasis on the phase behavior subject to mechanics and multiphysics coupled effects. Discussions cover bulk phase modeling for equilibrium states and critical conditions, two-phase modeling for gel-gel and gel-sol phase transitions, as well as simulation for interface behavior during phase transition with both sharp and diffuse interface models.
      PubDate: 2019-10-15
  • Tailorable elasticity of cantilever using spatio-angular functionally
           graded biomimetic scales
    • Abstract: Abstract Cantilevered beams are of immense importance as structural and sensorial members for a number of applications. Endowing tailorable elasticity can have wide ranging engineering ramification. Such tailorability could be possible using some type of spatial gradation in the beam’s material or cross section. However, these often require extensive additive and subtractive material processing or specialized casts. Herein, we demonstrate an alternative bio-inspired mechanical pathway, which is based on exploiting the nonlinearity that would arise from a functionally graded (FG) distribution of biomimetic scales on the surface using an analytical approach. This functional gradation is geometrically sourced and could arise from either spatial or angular gradation of scales. We analyze such FG cantilever beams under different loading conditions including point loading at the free end, uniform traction, linearly distributed traction, and concentrated moment loading at the free end. In comparison with uniformly distributed scales for all cases of the loading addressed, we find significant differences in bending stiffness for both spatial and angular gradations. Spatial and angular functional gradations share some universality but also sharp contrasts in their effect on the underlying beam. We also quantify the landscape of spatio-angular tailorability on stiffness gains. We compare our models with select experiments for validation. This highlights that a combination of both types of gradation in the structure can be used to alter stiffness and therefore offer a pathway to tailor the elasticity of a cantilever beam relatively easily. These results demonstrate an architected framework for designing and optimizing scale-covered FG beams.
      PubDate: 2019-10-03
  • Stable fitting of noisy stress relaxation data
    • Abstract: Abstract The mechanical behavior of a viscoelastic material can often be described by a spectrum of Maxwell-Wiechert elements. The inverse problem associated with estimating the parameters of this spectrum from the results of viscoelastic relaxation (ramp-and-hold) test is in general ill-posed and unstable, with estimates highly sensitive to initial conditions and noise. Here, we demonstrate stable estimation of a continuous viscoelastic spectrum from stress relaxation experiments using Tikhonov regularization. We assess the effects of noise and sampling frequency on these estimates, and describe regularization parameter selection. We demonstate the algorithm by estimating the viscoelastic relaxation spectra of soft vinyl samples.
      PubDate: 2019-08-06
  • Constitutive model of human artery adventitia enhanced with a failure
    • Abstract: Abstract A constitutive model of a human artery adventitia is presented and calibrated in uniaxial tension tests in longitudinal and circumferential directions. Both the experiment and the model describe the descending branch of the stress-stretch curve and, thus, failure becomes a part of the constitutive law. The theoretical failure description is provided by the introduction of energy limiters and it does not use internal damage variables. The latter feature allows for an easy analysis of material instability and the onset of failure. Particularly, the failure envelope is created in biaxial tension under various stretch ratios. In addition, the loss of ellipticity is analyzed in equibiaxial stretch and pure shear and it is found that the localized failure—crack—is approximately aligned with the directions of collagen fibers in accordance with experimental observations.
      PubDate: 2019-05-03
  • Nonlinear contact mechanics for the indentation of hyperelastic
           cylindrical bodies
    • Abstract: Abstract The mechanical properties of biological materials are commonly found through the application of Hertzian theory to force-displacement data obtained through micro-indentation techniques. Due to their soft nature, biological specimens are often subjected to large indentations, resulting in a nonlinear deformation behavior that can no longer be accurately described by Hertzian contact. Useful models for studying the large deformation response of cylindrical specimens under indentation are not readily available, and the morphologies of biological materials are often closer to cylinders than spheres (e.g., cellular processes, fibrin, collagen fibrils, etc.). In this study, a computational model is used to analyze the large deformation indentation of an incompressible hyperelastic cylinder in order to provide a generalized formulation that can be used to extract mechanical properties from indentation into soft cylindrical bodies. The effects of specimen size and indentation depth are examined in order to quantify the deformation at which the proposed force-displacement relationship remains accurate.
      PubDate: 2019-04-01
  • Analytical and experimental investigation of puncture-cut resistance of
           soft membranes
    • Abstract: Abstract Modeling and evaluating critical puncture-cutting force and total applied energy are among the most important steps in characterizing the resistance of protective materials to sharp-tipped object insertion. This paper explores the relationship between these two mechanical properties, force and energy, corresponding to the insertion of a pointed blade into soft membranes. The paper’s main contribution includes the addition of friction energy to the existing analytical cutting model in order to develop a more comprehensive model. This energy is provided by the normal stress (contact pressure) caused by the created fracture surface. The contact pressure is applied on both lateral sides of the pointed blade. In this work, a model describing the combined puncture and cutting of protective materials is developed using force distribution analysis and basic concepts of fracture mechanics. Results show that the critical puncture-cutting force (FP/C) required for complete insertion of a pointed blade decreases with the increase of the puncture-cut ratio, ζ, given by the shape of the pointed blade. In other words, the puncture cutting of soft membranes is easier when the pointed blade has a high cutting edge angle than when it has a small cutting edge angle. Fracture mechanics theory is then used to determine the relationship between FP/C and the total puncture-cutting energy, GTotal, that includes fracture toughness of material and friction energy. The presented model is verified by comparing the predicted values of FP/C with experimental data obtained from puncture-cutting tests of soft elastomeric materials and soft-coated fabrics by three pointed blades. According to the proposed model, the methods corresponding to force measurement (FP/C) or energy calculation (GTotal) are both able to evaluate accurately the puncture-cut resistance of protective materials by any sharp-tipped objects.
      PubDate: 2019-03-28
  • Electroactive polymer (EAP) actuators—background review
    • Abstract: Abstract Certain polymers can be excited by electric, chemical, pneumatic, optical, or magnetic field to change their shape or size. For convenience and practical actuation, using electrical excitation is the most attractive stimulation method and the related materials are known as electroactive polymers (EAP) and artificial muscles. One of the attractive applications that are considered for EAP materials is biologically inspired capabilities, i.e., biomimetics, and successes have been reported that previously were considered science fiction concepts. Today, there are many known EAP materials. Some of the EAP materials also exhibit the reverse effect of converting mechanical strain to electrical signal allowing using them as sensors and energy harvesters. Efforts are made worldwide to turn EAP materials to actuators-of-choice and they involve developing their scientific and engineering foundations including the understanding of their operation principles. These are also involve developing effective computational chemistry models, comprehensive material science, and electro-mechanics analytical tools. These efforts have been leading to better understanding the parameters that control their capability and durability. Moreover, effective processing techniques are developed for their fabrication, shaping, electroding, and characterization. While progress have been reported in the research and development of all the types of EAP materials, the trend in recent years has been growing towards significant development in using dielectric elastomers.
      PubDate: 2019-03-22
  • The effect of local inertia around the crack-tip in dynamic fracture of
           soft materials
    • Abstract: Abstract Phase-field or gradient-damage approaches offer elegant ways to model cracks. Material stiffness decreases in the cracked region with the evolution of the phase-field or damage variable. This variable and, consequently, the decreased stiffness are spatially diffused, which essentially means the loss of the internal links and the bearing capacity of the material in a finite region. Considering the loss of material stiffness without the loss of inertial mass seems to be an incomplete idea when dynamic fracture is considered. Loss of the inertial mass in the damaged material region may have significant effect on the dynamic failure processes. In the present work, dynamic fracture is analyzed using a theory, which takes into account the local loss of both material stiffness and inertia. Numerical formulation for brittle fracture at large deformations is based on the Cosserat point method, which allows suppressing the hourglass type deformation modes in simulations. Based on the developed algorithms, the effect of the material inertia around a crack tip is studied. Two different problems with single and multiple cracks are considered. Results suggest that in dynamic fracture the localized loss of mass plays an important role at the crack tip. It is found, particularly, that the loss of inertia leads to lower stresses at the crack tip and, because of that, to narrower cracks as compared to the case in which no inertia loss is considered. It is also found that the regularized problem formulation provides global convergence in energy under the mesh refinement. At the same time, the local crack pattern might still depend on the geometry of the unstructured mesh.
      PubDate: 2019-02-01
  • A new approach to modeling the thermomechanical, orthotropic,
           elastic-inelastic response of soft materials
    • Abstract: Abstract This paper generalizes six previously developed nonlinear distortional deformation invariants for general hyperelastic orthotropic materials to model the thermomechanical, orthotropic, elastic-inelastic response of soft materials. These new invariants depend on two independent functions of elastic dilatation and temperature and characterize elastic distortional deformations from Hydrostatic States of Stress (HSS). When the Helmholtz free energy depends on these invariants, elastic dilatation and temperature, the correct response in HSS is automatically satisfied so the determination of the functional form of the Helmholtz free energy is simplified and can focus on modeling the response causing deviatoric stress. In addition, the new invariants are based on an Eulerian formulation of evolution equations for microscructural vectors that describe elastic deformation and directions of anisotropy. In contrast with the standard Lagrangian formulation, the Eulerian formulation is unaffected by arbitrary choices of the reference configuration, an intermediate configuration, a total deformation measure, and an inelastic deformation measure.
      PubDate: 2018-12-19
  • Magic angles in the mechanics of fibrous soft materials
    • Abstract: Abstract We discuss a ubiquitous intriguing issue that arises in the mechanics of fibrous soft materials, namely the occurrence of a “magic angle” associated with the fiber direction which gives rise to special features of the mechanical response. Classically, the magic angle concept arose in connection with hydrostatic skeletons or muscular hydrostats such as the common worm, octopus arm, or elephant trunk. It also arises in the field of soft robotics in connection with artificial muscles as well as in nuclear magnetic resonance. Such angles also occur in analysis of the mechanical behavior of fiber-reinforced incompressible elastic soft solids. In this context, the magic angle concept occurs most commonly in structural elements composed of circular cylindrical tubes or solid cylinders reinforced by helically wound fibers. An everyday example of the former is the common garden hose. The fibers can be inextensible as in reinforced rubber or extensible such as collagen fibers in soft tissue. Fibers orientated at the magic angle result in quasi-isotropic mechanical response and can lead to material instability.
      PubDate: 2018-12-05
  • Editorial
    • PubDate: 2018-11-29
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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