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Resilient mounts are essential for anti-vibration and shock absorption applications, making accurate predictions of their static and dynamic behaviors critical for effective design and mechanical performance. This study investigates static and dynamic characteristics of resilient mounts to predict their effects. Tension, compression, and shear tests were performed under quasi-static loading conditions to obtain stress-strain cycle curves. This study includes a review of the Yeoh hyperelastic model, which consists of three parameters, and discusses the calibration of these parameters to describe the hyperelastic material behavior. The parameters were validated through numerical analysis by comparing them with experimental results from quasi-static tests on the resilient mount. The dynamic behavior was further analyzed using modal analysis and frequency response simulations under various preload conditions. Results show that increasing preload significantly shifts the transmissibility curves and resonance peaks to lower frequencies. This study offers valuable insights into static and dynamic characteristics of resilient mounts, contributing to the design and optimization of vibration isolation systems for naval applications. [ABSTRACT FROM AUTHOR]

This article presents the design and fabrication of a soft gripper made of hyperelastic materials and driven by pneumatics for application in a bento box robot system. The soft fingers are designed based on material properties and morphological studies. The design prototypes are then simulated using the finite element method in Abaqus software to predict the actual behavior of the gripper. Finally, the design prototypes are fabricated using molding and 3D printing methods, going through 5 versions, and are tested to evaluate their ability to grasp various food items without causing spillage or damage, as required by the company. [ABSTRACT FROM AUTHOR]

In this study, the primary resonance of a hyperelastic thin-walled cylindrical shell subjected to external excitation is examined. The incompressible Moony–Rivlin model, nonlinear Donnell's shell theory, and Hamilton principle are employed to extract the fundamental equations in three directions. The Galerkin approach is employed to reduce the governing equation into ordinary differential equations form. Then, by neglecting the membrane inertia, three equations are reduced to one equation to analyze the transverse vibrations of the hyperelastic shells. Natural frequencies of different asymmetric modes are used to define the fundamental mode. Then, the multiple scales method is applied to evaluate the frequency–amplitude curves for various parameters. In addition, the model's accuracy is validated with those presented in the literature for a cylindrical shell and the comparison shows good arrangement results. In the simulation part, the effects of the amplitude of excitation, the ratio of thickness–radius, and the ratio of radius–length on the primary resonances of shells are evaluated. The simulation plots show that for small values of radius-to-length ratios, increasing its value causes to decrease in the stiffness of the thin hyperelastic shell. Also, by increasing the radius–length ratios from 0.3 to 1.18 the hardening of the shell is decreased, and by increasing the radius–length ratios from 1.18 to 2 the hardening behavior is increased. [ABSTRACT FROM AUTHOR]

AbstractIn order to achieve fast and convenient design of fully flexible actuators suitable for special gripping modes, a soft actuator for gripper based on pneumatic metastructure is proposed inspired by the pulvinus of Mimosa pudica. The hyperelastic material is used to fabricate the soft actuators. Finite element models are built to analyze and predict the deformation of both the single unit cell and entire metastructures. Finally, the automatic design method is presented. The actuators designed corresponding to the modes are fabricated and tested. The experimental results show that the gripper achieves a higher grasping stability in special gripping modes. [ABSTRACT FROM AUTHOR]

The material point method (MPM) adopts the dual description of Lagrangian particles and Euler grids, so it can deal with large deformation and contact problems conveniently. The large deformation problem of thin shell structures was analyzed based on the framework of the convected particle domain interpolation material point method (CPDIMPM) . The quadrilateral mesh was used to discretize the shell structure. The basis function was calculated by the double mapping from the material point to the shell element node and then to the background grid node. The momentum equation was solved on the background grid, and the internal force of the material point was updated based on the Belytschko-Tsay (BT) shell element theory. In the numerical example, the comparison of large deformations of the shell structure with reference solutions verifies the accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

This is Part II of a multipart article on a hyperelastic extended Kirchhoff–Love shell model with out-of-plane normal stress. We introduce an isogeometric discretization method for incompressible materials and present test computations. Accounting for the out-of-plane normal stress distribution in the out-of-plane direction affects the accuracy in calculating the deformed-configuration out-of-plane position, and consequently the nonlinear response of the shell. The return is more than what we get from accounting for the out-of-plane deformation mapping. The traction acting on the shell can be specified on the upper and lower surfaces separately. With that, the model is now free from the "midsurface' location in terms of specifying the traction. In dealing with incompressible materials, we start with an augmented formulation that includes the pressure as a Lagrange multiplier and then eliminate it by using the geometrical representation of the incompressibility constraint. The resulting model is an extended one, in the Kirchhoff–Love category in the degree-of-freedom count, and encompassing all other extensions in the isogeometric subcategory. We include ordered details as a recipe for making the implementation practical. The implementation has two components that will not be obvious but might be critical in boundary integration. The first one is related to the edge-surface moment created by the Kirchhoff–Love assumption. The second one is related to the pressure/traction integrations over all the surfaces of the finite-thickness geometry. The test computations are for dome-shaped inflation of a flat circular shell, rolling of a rectangular plate, pinching of a cylindrical shell, and uniform hydrostatic pressurization of the pinched cylindrical shell. We compute with neo-Hookean and Mooney–Rivlin material models. To understand the effect of the terms added in the extended model, we compare with models that exclude some of those terms. [ABSTRACT FROM AUTHOR]

The development of various machines and equipment containing parts or assemblies made of hyperelastic materials (e.g., rubber, silicone) is difficult because of the intricacies involved in the description of their mechanical properties. This is especially seen in calculations using simulation modeling. The behavior of hyperelastic materials is described by utilizing the results of research conducted with specialized equipment. This allows for the most accurate determination of their mechanical properties. Hyperelastic materials are widely used across diverse industries, encompassing mechanical engineering, the chemical and petrochemical sectors, cement production, and beyond. To determine the mechanical characteristics of SKR-788 silicone, batches of test samples were prepared, varying solely in the ratio of the base to the catalyst. Laboratory testing of silicone samples was performed on an Instron 4500 device, and data such as loads, displacements, and deformations were obtained. In order to verify the results of the tests against the results of simulation modeling in Ansys software, a model of the experimental sample was built. The obtained results of uniaxial tensile testing of the experimental sample were taken into account during the description of the material in the Mooney-Rivlin model. The calculation scheme for the test sample during simulation modeling is similar to the one used during its laboratory testing. Applying the load to the test sample during the simulation proceeded incrementally based on time. As a result of the work, the constants of the SKR-788 silicone material for the three-parameter Mooney-Rivlin model were defined (C10 = -0.10335 MPa, C01 = 0.57534 MPa, and C11 = 0.093309 MPa). As a result of simulation modeling of the experimental silicone sample, the values of its displacements and stresses were obtained. Upon comparing the stress values derived from the results of laboratory testing on the Instron 4500 equipment with those obtained from simulation modeling, a discrepancy of up to 7% was identified. For the first time, the characteristics of the SKR-788 silicone material have been established and verified. This will facilitate the design and research of various equipment and machine components made from hyperelastic materials. [ABSTRACT FROM AUTHOR]

In this study, we propose an explicit topology optimization approach for multi-material composite structures that considers both geometric and material nonlinearities. Our method identifies each material using moving morphable components, resulting in explicit geometric descriptions and fewer design variables. In finite-element analysis, redundant degrees of freedom are removed to prevent highly distorted elements and improve computational efficiency. A numerical example demonstrated the methodology’s validity and the importance of accounting for geometric and material nonlinearities when designing a multi-material structure. We also show that, even with the same objective function and structural volume, the optimal usage ratio of the constituent materials varies depending on the problem. Using the proposed method, optimized structures with superior performance that cannot be achieved with a single material can be obtained. [ABSTRACT FROM AUTHOR]

Experimental setups using steel and transparent glass pipes, along with equally spaced steel stamped and transparent plastic tees, were designed for testing. The experimental results provided insights into the influence of flow directions, pig length, material properties, and air consumption on the dynamics and strength of the pigs within the tees. Furthermore, the study identified the causes of temporary halting, jamming, and the mechanisms of damage to cylindrical pigs made of hyperelastic materials within pipeline tees.

Some soft tissues of the human body and biomaterials are considered as multi-layer structures with layer-specific material properties. Identification of the material parameters of these distinct layers is challenging and has attracted considerable attention in recent decades. In this research, an inverse finite element method, which uses the data obtained from simulated suction experiments, is developed. The method employs a limited number of surface-measured data to recover the layer-specific hyperelastic material parameters of a two-layer structure. The Gauss-Newton method is employed to minimize a cost function, which is defined in terms of the difference between measured and calculated displacements of the surface points. The sensitivity analysis during the optimization process is carried out by the finite difference method. The effects of pipette diameter, noise in experimental data, the initial guess and the hyperelastic material model, on the robustness and efficiency of the inverse method are investigated. [ABSTRACT FROM AUTHOR]

In this study, an analytical solution has been developed to examine the mechanical behavior of an incompressible functionally graded hyperelastic cylinder subjected to simultaneous extension and torsion. The recently proposed exp-exp strain energy density is employed to predict the behavior of hyperelastic material, and its related material parameters are assumed to vary along the radial direction in an exponential fashion. Finite element analysis is conducted by preparing a userdefined UHYPER subroutine in ABAQUS to evaluate the proposed analytical solutions. FEM results and those of the analytical solution are in good agreement for various stretches and twists and reveal that the form of stress distributions and the maximum stress depend on the exponential power in the material variation function. In contrast to axial stretch, the effect of twist on the distribution of longitudinal stress is more complicated, and for large twists, two extrema in the stress distribution plot are observed, which move toward the center and outer surface of the cylinder on further twisting. Moreover, the longitudinal stress controls the variation of von-Mises and strain energy density throughout the radial direction. Additionally, considering an axial stretch, a point is identified where the axial force arising from torsion is compressive for stretches below this value, and it brings about the cylinder to elongate under twisting. However, this part of the total axial force varies from a tension state to a compression one for larger stretches, i.e., by increasing the twist, the cylinder first tends to shorten and then elongates on further twisting. [ABSTRACT FROM AUTHOR]

Summary: This work proposes a higher‐order unified shell finite element for the analysis of cylinders made of compressible and nearly incompressible hyperelastic materials. The nonlinear governing equations are derived employing the Carrera unified formulation (CUF), thanks to which it is possible to build shell elements with the capability to capture three‐dimensional (3D) transverse and out‐of‐plane effects. The material and geometric nonlinearities are expressed in an orthogonal curvilinear reference system and the coupled formulation of hyperelastic constitutive law is considered. The principle of virtual work and a total Lagrangian approach is used to derive the nonlinear governing equations, which are solved by a Newton–Raphson scheme. The numerical investigations deal with a curved arch and both thick and thin cylinders subjected to line and point loadings. The obtained results are validated by comparing them with those from the literature. They demonstrate the reliability of the proposed method to analyze compressible and incompressible hyperelastic shell structures. [ABSTRACT FROM AUTHOR]

In this paper we propose a new optical-based technique to identify the constitutive relation coefficients of the hyperelastic material using a hybrid optimisation approach. This technique can be used in place of traditional mechanical testing of elastomers for applications that involve inhomogeneous deformation. The purpose of the proposed method is to identify the incompressible hyperelastic material constitutive relation coefficients using a single experiment under different loading cases. The method comprises sample surface 3D reconstruction and uses finite element simulations to replicate the experiments, and uses a hybrid optimisation technique to minimise the error between actual 3D deformations and FE simulation results. The proposed hybrid technique predicts the hyperelastic constitutive relation coefficients more accurately than other optimisation methods. This study introduces a novel approach by employing a subpixel image registration algorithm for 3D reconstruction. The method requires a single experiment with diverse loading cases to accurately determine the coefficients of hyperelastic constitutive relations. The setup is portable and can be accommodated in a small suitcase. For this purpose, an apparatus was constructed comprising a stereoscopic system with eight cameras and a six-degree-of-freedom force-torque sensor to measure the induced forces and torques during the experiments. We identified the constitutive relation coefficients of Ogden N1, Ogden N3, Yeoh, and Arruda-Boyce relations which are commonly used models for silicone materials, using a traditional uniaxial test, optical uniaxial test (experiments performed using a constructed optical system), and inhomogeneous deformations tests. The study demonstrated that the coefficients obtained from inhomogeneous deformation tests provided the most accurate FE predictions. It was also shown that hyperelastic constitutive relation coefficients obtained from traditional uniaxial tests are insufficient to describe the material behaviour when the material undergoes inhomogeneous deformations. [ABSTRACT FROM AUTHOR]

The FE-based structural design of components made of rubber materials requires an experimental characterization to calibrate a proper hyperelastic material model. A strain energy density (SED) parameter is typically adopted to describe the hyperelastic behavior of isotropic rubbers. This can be written as a function of the strain tensors, the strain invariants or the stretch ratios and proper material parameters. The latter must be calibrated on experimental data generated by testing rubber materials under different loading conditions, typically two among uniaxial tension, pure shear and biaxial tension. In this context, the mechanical behavior of Ethylene–Propylene–Diene Monomer (EPDM) rubbers, both in the dense and expanded configurations, which are typically employed to manufacture automotive seals, has been investigated. First, uniaxial tension tests have been performed. Afterwards, a new fixture has been developed to perform equi-biaxial tension tests using a uniaxial testing machine. The fixture has been adopted to test EPDM cruciform specimens under equi-biaxial tension loading. Finally, both uniaxial and equi-biaxial data have been employed to fit a Mooney–Rivlin material model for each tested EPDM rubber, which has been validated by comparing the results of FE simulations with the experimental ones. [ABSTRACT FROM AUTHOR]

Pipelines have been increasingly used as an efficient and economic means for the transportation of large quantities of resources such as water, fuel and gases. While there are various modes of transporting resources, pipeline systems happen to be among the safest. In the present study, the integrity of different components of the distribution network is checked for the sustainability of its designated pressure. The rubber gasket used as a sealing element in the distribution system is made from ethylene-propylene diene monomer (EPDM) and is tested to determine its stress-strain behavior, which is further analyzed in finite element analysis. From the study, it is concluded that the Mooney-Rivlin nine-parameter model is best suited for EPDM, and full analysis of the joint shows that it can sustain the designated pressure without failure. In this way, a new class of pipe can be designed without an experimental setup, which is very costly and requires considerable space. This will revolutionize the distribution field and save the surrounding environment affected by leakage and failure. [ABSTRACT FROM AUTHOR]

IntroductionIn an effort of gaining a better understanding of the lens mechanics, ex vivo lenses samples are often used. Yet, ex vivo tissue might undergo important postmortem changes depending on the unavoidable preservation method employed. The purpose of this study was to assess how various storage conditions and the removal of the lens capsule affect the mechanical properties of ex vivo porcine lens samples.MethodsA total of 81 freshly enucleated porcine eyes were obtained and divided into six groups and preserved differently. In the first three groups, the lens within the intact eye was preserved for 24 h by: (i) freezing at −80°C (n = 12), (ii) freezing at −20°C (n = 12), and (iii) refrigeration at +8°C (n = 12). In the remaining groups, the lenses were immediately extracted and treated as follows: (iv) kept intact, no storage (n = 12), (v) decapsulated, no storage (n = 21), and (vi) immersed in Minimum Essential Medium (MEM) at +8°C (n = 12) for 24 h. Frozen lenses were thawed at room temperature. Each lens was compressed between two glass lamella and subjected, first to a period of relaxation during which the compression force was recorded and second to an oscillating micro-compression while the deformation was recorded with a total of 256 subsequent B-scans via optical coherence tomography. The corresponding axial strain was retrieved via phase-sensitive image processing and subsequently used as input for an inverse finite element analysis (iFEA) to retrieve the visco-hyperelastic material properties of the lenses.ResultsAfter freezing at temperatures of −80°C and −20°C, the cortical strains increased by 14% (p = 0.01) and 34% (p < 0.001), and the nuclear strains decreased by 17% (p = 0.014) and 36% (p < 0.001), compared to the lenses tested immediately after postmortem, respectively. According to iFEA, this resulted from an increased ratio of the nuclear: cortical E-modulus (4.06 and 7.06) in −80°C and −20°C frozen lenses compared to fresh lenses (3.3). Decapsulation had the largest effect on the material constant C10, showing an increase both in the nucleus and cortex. Preservation of the intact eye in the refrigerator induced the least mechanical alterations in the lens, compared to the intact fresh condition.DiscussionCombining iFEA with optical coherence elastography allowed us to identify important changes in the lens mechanics induced after different preserving ex vivo methods.

Resilient mounts are essential for anti-vibration and shock absorption applications, making accurate predictions of their static and dynamic behaviors critical for effective design and mechanical performance. This study investigates static and dynamic characteristics of resilient mounts to predict their effects. Tension, compression, and shear tests were performed under quasi-static loading conditions to obtain stress-strain cycle curves. This study includes a review of the Yeoh hyperelastic model, which consists of three parameters, and discusses the calibration of these parameters to describe the hyperelastic material behavior. The parameters were validated through numerical analysis by comparing them with experimental results from quasi-static tests on the resilient mount. The dynamic behavior was further analyzed using modal analysis and frequency response simulations under various preload conditions. Results show that increasing preload significantly shifts the transmissibility curves and resonance peaks to lower frequencies. This study offers valuable insights into static and dynamic characteristics of resilient mounts, contributing to the design and optimization of vibration isolation systems for naval applications.

This paper presents static modelling and simulation of a spherically-shaped hyperelastic balloon actuator subjected to an angular rotation with an internally applied air pressure. These actuators are extensively used in soft robotics because its safe and flexible nature. The balloon actuator is a pneumatic-type actuator made of a polymeric material. A continuum mechanics-based analytical modelling and Finite element method-based simulation are performed to predict the response of the actuator for a given angular rotation with internally applied air pressure. The proposed modelling framework is subsequently utilised to perform the parametric studies for varying pressure, thickness, and rotational speed of the actuator. Various elastic instability curves are also obtained to examine the critical inflation of the rubber balloon actuator. The analytical findings agree well with the FEM simulations. [ABSTRACT FROM AUTHOR]

Rubber material is widely used in practical engineering due to its good seismic and energy absorption effect. However, the collision of hyperelastic materials is a strong nonlinear problem. It is of great significance to analyze the contact collision and large deformation of hyperelastic materials to improve the buffering performance of the device. The smoothed finite element method (S-FEM) is a weak form of numerical calculation method. Compared with the traditional finite element method, the smoothed finite element method has low requirements on the mesh quality, allows the element to undergo large deformation during the calculation process, where the construction of the smooth domain is more flexible. The S-FEM has high accuracy without additional degrees of freedom. Based on the S-FEM, the double potential method was applied to contact calculation, with both advantages of the S-FEM in calculating large deformation problems and advantages of the double potential method in solving contact force fully used. In comparison with the numerical results of finite element software MSC. Marc, the results of the proposed algorithm were verified with high accuracy and good energy conservation, and the effects of the friction coefficient on the collision body were analyzed. [ABSTRACT FROM AUTHOR]

The thermoforming process is commonly used in industry for the manufacturing of lightweight, thin-walled products from a pre-extruded polymer sheet. Many simulations have been developed to simulate the process and optimize it with computer tools. The development of testing machines has simplified the simulation of this type of process, allowing researchers to characterize the behavior of the material at different temperatures and for large deformation to be closer to the real conditions of the process. This paper presents the results of a study on the modeling of the thermoforming process for an industrial demonstrator made from a high-impact polystyrene (HIPS) polymer. The HIPS shows a mechanical behavior that depends on the temperature and strain rate. In such conditions, a thermo-hyper-viscoelastic constitutive model is used to replicate the thermoforming process of the industrial demonstrator using ABAQUS/Explicit. Its behavior is determined via various experimental tests: uniaxial tensile tests at different temperatures and strain rates and Dynamic Mechanical Analysis (DMA). A comparison between the numerical and experimental results is carried out for the evolution of film thickness. The paper concludes with a discussion of possible improvements to be considered for future simulations of the thermoforming process using Abaqus, which presents complex challenges in terms of contact and material modeling. [ABSTRACT FROM AUTHOR]

The propagation of elastic waves in hyperelastic materials is described by a nonlinear system of partial differential equations (PDEs) governing the material’s motion. Hyperelastic materials are characterized by a strain–energy density function that correlates material deformation with stored elastic energy. For simplicity, we focus on the one-dimensional case where the displacement field, denoted as ϕ(x,t), signifies material deformation along the x-direction at position x and time t. The governing equation for elastic wave propagation in hyperelastic materials is derived from the strain–energy density function and associated stress–strain relations. In this study, Lie symmetry analysis is used to examine a nonlinear system of such equations relevant to the propagation of elastic waves in hyperelastic materials. The resulting equations are solved by applying Lie’s invariance criterion, yielding a ten-dimensional Lie algebra. An optimal system is derived from this algebra, allowing for the identification of invariant solutions under certain conditions. Additionally, the multiplier approach and Ibragimov’s new conservation laws are utilized to obtain the conservation laws for this coupled system of elastic waves. The outcome presented here is innovative and suggests utilizing the Lie symmetry method for investigating hyperelastic materials.

This research article delves into the intricate domain of nonlinear wave dynamics within the framework of a Murnaghan hyperelastic circular pipe. Thus, the current study makes use of some powerful analytical approaches to examine the propagation of nonlinear elastic waves on a Murnaghan hyperelastic circular pipe. The work is exceptional since it allows for the incorporation of double dispersion terms and material nonlinearity in the controlling nonlinear mode. The study entails a thorough examination of the propagation and interaction of solitons within the Murnaghan hyperelastic medium, providing insights into the distinctive nonlinear wave phenomena manifested by circular pipe configurations. Theoretical insights are substantiated by numerical simulations, presenting a comprehensive understanding of the dynamic responses within these elastic structures. In the end, graphical representations of some of the derived solutions have been provided for clarification. In addition, the reported solutions in the study help researchers working in modern fields of engineering and materials science to obtain valuable insights that can inform the design, analysis, and optimization of materials and structures in contemporary applications.

The prevention, control and treatment of cerebral aneurysm (CA) has become a common concern of human society, and by simulating the biomechanical environment of CA using finite element analysis (FEA), the risk of aneurysm rupture can be predicted and evaluated. The target models of the current study are mainly idealized single-layer linear elastic cerebral aneurysm models, which do not take into account the effects of the vessel wall structure, material constitution, and structure of the real CA model on the mechanical parameters. This study proposes a reconstruction method for patient-specific trilaminar CA structural modeling. Using two-way fluid-structure interaction (FSI), we comparatively analyzed the effects of the differences between linear and hyperelastic materials and three-layer and single-layer membrane structures on various hemodynamic parameters of the CA model. It was found that the numerical effects of the different CA membrane structures and material constitution on the stresses and wall deformations were obvious, but does not affect the change in its distribution pattern and had little effect on the blood flow patterns. For the same material constitution, the stress of the three-layer membrane structure were more than 10.1% larger than that of the single-layer membrane structure. For the same membrane structure, the stress of the hyperelastic material were more than 5.4% larger than that of the linear elastic material, and the displacement of the hyperelastic material is smaller than that of the linear elastic material by about 20%. And the maximum value of stress occurred in the media, and the maximum displacement occurred in the intima. In addition, the upper region of the tumor is the maximum rupture risk region for CA, and the neck of the tumor and the bifurcation of the artery are also the sub-rupture risk regions to focus on. This study can provide data support for the selection of model materials for CA simulation and analysis, as well as a theoretical basis for clinical studies and subsequent research methods.

We proposed an approach for interpretable data‐driven modeling of an isotropic incompressible hyperelastic membrane deformation. The approach is based on the response functions in terms of the Laplace stretch and the finite element method, where response functions are partial derivatives of a hyperelastic potential with respect to the chosen strain measure. The Laplace stretch as the strain measure allows us to recover directly the response functions from experimental data and construct automatically data‐driven constitutive relations. All needed formulas were obtained explicitly. We tested our approach for membrane inflation with data‐driven constitutive relations based on the perforated membrane extension tests. [ABSTRACT FROM AUTHOR]

The aim of this paper is to explore the mechanical characteristics of lattice-based airless tires made by three-dimensional (3D) printing technology under a large-deformation regime. The proposed airless tires are designed and fabricated based on the hexagonal lattice geometries under two different orientations. Experimental tests are conducted to investigate the effects of geometrical parameters and the types of lattices on the radial responses of airless tires. A finite-strain beam element is also established to simulate airless tires under various loading states, including radial, longitudinal, torsional, slipping, and rolling conditions. In this respect, a finite-element formulation is developed based on finite-strain hyperelasticity and solved by implementing an iterative Newton–Raphson scheme. Numerical and experimental results confirm that the proposed finite-strain beam element can be used for the analysis of airless tires with complicated lattice geometries under various nonlinearities, such as geometrical, material, and contact phenomenon. The numerical illustrations emphasize the effects of geometrical parameters of lattices and loading parameters on the behavior and mechanical properties of airless tires. The effects of lattice orientations, thickness, number of unit cells, and the coefficient of Coulomb friction between the tire and the ground, as well as loading direction, are investigated. Their implications on the responses of the airless tires with the same weight are highlighted, and pertinent conclusions are outlined. It is also shown that the proposed mathematical model can be used in future efforts for analysis, optimization, and design of lattice-based airless tires with complex geometries. This paper is a numerical/experimental research of the 3D printed lattice-based airless tires under various real loading cases such as radial, longitudinal, torsional, slipping, and rolling conditions. The proposed airless tires are designed/fabricated based on two different orientations of hexagonal lattice geometries. The material used for modeling and fabrication of these airless tires is rubber-like materials (hyperelastic), which can have many reversible deformations. The results show that under real loading conditions, the links of the lattice experience instabilities, such as buckling and snap. It should be mentioned that these instabilities are quite important in practical applications that are investigated in the present work in detail. Moreover, the behavior of lattice-based airless tires under each loading condition is divided into linear behavior and nonlinear behavior. Linear behavior of an airless tire can be predicted by the present model for different geometrical parameters (such as length, thickness, among others). Unlike linear behavior, nonlinear behavior highly depends on load and deformation histories. Therefore, each case needs the optimization and design of lattice-based airless tires. [ABSTRACT FROM AUTHOR]

Harmonic wave excitation in a semi-infinite incompressible hyperelastic 1D rod with the Mooney–Rivlin equation of state reveals the formation and propagation of the shock wave fronts arising between faster and slower moving parts of the initially harmonic wave. The observed shock wave fronts result in the collapse of the slower moving parts being absorbed by the faster parts; hence, to the attenuation of the kinetic and the elastic strain energy with the corresponding heat generation. Both geometrically and physically nonlinear equations of motion are solved by the explicit Lax–Wendroff numerical tine-integration scheme combined with the finite element approach for spatial discretization. [ABSTRACT FROM AUTHOR]

Sophisticated muscle material models are required to perform detailed finite element simulations of soft tissue; however, state-of-the-art muscle models are not among the built-in materials in popular commercial finite element software packages. Implementing user-defined muscle material models is challenging for two reasons: deriving the tangent modulus tensor for a material with a complex strain energy function is tedious and programing the algorithm to compute it is error-prone. These challenges hinder widespread use of such models in software that employs implicit, nonlinear, Newton-type finite element methods. We implement a muscle material model in Ansys using an approximation of the tangent modulus, which simplifies its derivation and implementation. Three test models were constructed by revolving a rectangle (RR), a right trapezoid (RTR), and a generic obtuse trapezoid (RTO) around the muscle's centerline. A displacement was applied to one end of each muscle, holding the other end fixed. The results were validated against analogous simulations in FEBio, which uses the same muscle model but with the exact tangent modulus. Overall, good agreement was found between our Ansys and FEBio simulations, though some noticeable discrepancies were observed. For the elements along the muscle's centerline, the root-mean-square-percentage error in the Von Mises stress was 0.00%, 3.03%, and 6.75% for the RR, RTR, and RTO models, respectively; similar errors in longitudinal strain were observed. We provide our Ansys implementation so that others can reproduce and extend our results. [ABSTRACT FROM AUTHOR]

Red blood cell (RBC), undertaking the significant work of oxygen transport to maintain human life, could shuttle spindly capillaries by their own stretching and contractile properties due to their biconcave discoid shape and hyperelastic responses. In this paper, the coupled fluid-solid module in finite element software COMSOL was used to study the dynamic simulation of RBC when the three factors, including capillary width, plasma viscosity, and blood flow rate were considered. The results implied that the RBC could easily pass through capillary with hole size of 3 μm, and the aqueous shear stress was 4.5 times greater than that in the capillary with 6 μm hole size. Meanwhile, the plasma viscosity of 5.5 mPa·s induced parachute-like formation of RBC. Furthermore, biconcave structure in the center gradually disappeared and turned into bulge along the flow direction. With regard to the study on fluidic velocities in T-shaped and Y-shaped micro-channel, both results indicated that the asymmetric structure caused the falcate shape of RBC. In addition, the higher fluidic velocity in the other branch channel, the easier the convergence leaded to the disappearance of falcate shape and the rod posture lying flat flowing in the solution. [ABSTRACT FROM AUTHOR]

The deformation behavior of an artificial heart valve was analyzed using the explicit dynamic finite element method. Time variations of the left ventricle and the aortic pressure were considered as the mechanical boundary conditions in order to reproduce the opening and closing movements of the valve under the full cardiac cycle. The valve was assumed to be made from a medical polymer and hence, a hyperelastic Mooney–Rivlin model was assigned as the material model. A simple formula of the damage mechanics was also introduced into the theoretical material model to express the hysteresis response under the unloading state. Effects of the hysteresis on the valve deformation were characterized by the delay of response and the enlargement of displacement. Most importantly, the elastic vibration observed in the pure elastic response under the full close state was dramatically reduced by the conversion of a part of elastic energy to the dissipated energy due to hysteresis.

Fracture of compliant materials is preceded by large deformations that reshape initially sharp cracks into rounded defects. This phenomenon, known as elastic crack blunting, is peculiar of rubber‐like polymers and soft biological tissues, such as skin, vessel walls, and tendons. With this work, we aim to provide a discussion on crack‐tip blunting and its implications in terms of tearing resistance and flaw tolerance of soft elastic materials. The characteristic features of the crack‐tip zone in the framework of nonlinear elasticity are reviewed analytically and with the help of finite element analyses on pure shear cracked geometries. Specifically, the strain‐hardening behavior typical of soft biological tissues is addressed, and we illustrate its effect on crack‐tip blunting, in terms of a local radius of curvature at the crack tip. A simplified geometrically nonlinear model, proposed to describe the progressive blunting at the crack tip and its effect on flaw tolerance, is validated through finite element analyses and experimental tests on silicone samples. We show how this can lead to a simplified criterion to define the fracture condition in nonlinear soft materials. [ABSTRACT FROM AUTHOR]

This study describes the basic design, material selection, fabrication, and evaluation of soft pneumatic actuators (SPA) for lower-limb rehabilitation compression therapy. SPAs can be a promising technology in proactive pressure delivery, with a wide range of dosages for treating venous-related diseases. However, the most effective design and material selection of SPAs for dynamic pressure delivery have not been fully explored. Therefore, a SPA chamber with two elastomeric layers was developed for this study, with single-side inflation. The 3D deformation profiles of the SPA chamber using three different elastomeric rubbers were analyzed using the finite element method (FEM). The best SPA-compliant behavior was displayed by food-grade silicone A10 Shore with a maximum deformation value of 25.34 mm. Next, the SPA chamber was fabricated using A10 Shore silicone and experimentally validated. During the simulation in FEM, the air pressure was applied on the inner wall of the chamber (i.e., the affected area). This is to ensure the applied pressure was evenly distributed in the inner wall while the outer wall of the chamber remained undeformed for all compression levels. During the inflation process, pressure will be applied to the SPA chamber, causing exerted pressure on the skin which is then measured for comparison. The simulation and experimental results show an excellent agreement of pressure transmission on the skin for the pressure range of 0–120 mmHg, as depicted in the Bland–Altman plots. The findings exhibited promising results in the development of the SPA chamber using low-cost and biocompatible food-grade silicone. [ABSTRACT FROM AUTHOR]

In order to acquire topographic/morphological images with superior resolution and depth of focus than an ordinary optical microscope, scanning electron microscopy (SEM) is used to take photographs of a surface of materials or specimens at a desired point. In the context of polymer and rubber materials science, SEM investigations frequently try to visualize phase morphology, surface and cross-sectional topography, and surface molecular order, and clarify damage mechanisms. In the case of rubber vulcanizates, test specimens are frequently put through a variety of mechanical property assessment procedures, including tensile, flexing, fatigue, abrasion, and tear tests, in order to finalize compounding parameters for required levels of quality. The damaged surface of the test specimens exhibits distinctive topographical characteristics, which are captured as an SEM picture and associated with relevant strength properties. However, the majority of the time, the relationship between strength attributes and the type of surface topography is qualitative. Surface roughness measurement metrics such as root mean square (r.m.s) roughness, average roughness, and peak-to-valley distance are frequently determined for quantitative research using standard software accessible in an SEM. The primary goal of this research is to use a statistical/spectral-based technique for quantitatively measuring surface topography using SEM. The Mullins stress-softening phenomenon of an isotropic, incompressible, hyperelastic rubberlike material is predicted using a phenomenological model. A simple exponential damage function characterizes the model, which represents deformation-induced microstructural degradation of rubberlike material.

The thermoforming process is commonly used in industry for the manufacturing of lightweight, thin-walled products from a pre-extruded polymer sheet. Many simulations have been developed to simulate the process and optimize it with computer tools. The development of testing machines has simplified the simulation of this type of process, allowing researchers to characterize the behavior of the material at different temperatures and for large deformation to be closer to the real conditions of the process. This paper presents the results of a study on the modeling of the thermoforming process for an industrial demonstrator made from a high-impact polystyrene (HIPS) polymer. The HIPS shows a mechanical behavior that depends on the temperature and strain rate. In such conditions, a thermo-hyper-viscoelastic constitutive model is used to replicate the thermoforming process of the industrial demonstrator using ABAQUS/Explicit. Its behavior is determined via various experimental tests: uniaxial tensile tests at different temperatures and strain rates and Dynamic Mechanical Analysis (DMA). A comparison between the numerical and experimental results is carried out for the evolution of film thickness. The paper concludes with a discussion of possible improvements to be considered for future simulations of the thermoforming process using Abaqus, which presents complex challenges in terms of contact and material modeling.

Soft robotics is an emerging area of research due to its safe interaction with humans; it also has exciting applications, such as wearable soft medical devices for rehabilitation, prosthetics, etc. Soft robots require soft actuators for performing desired movements, including bending, expansion, contraction, and twisting. This work focuses on bending-type multi-chambered extra-soft actuators actuated by pneumatic pressure. The corrugated design of a multi-chambered soft pneumatic actuator (SPA) is analyzed experimentally to observe the radial, longitudinal, and lateral expansions of different chambers, i.e., ballooning of the chambers under the application of air pressure. From the experimental study, it is observed that the ballooning mainly occurs at the free end of the actuator in a cantilever-type boundary condition, which could not be demonstrated by the computational solution using the finite element analysis (FEA). Moreover, it is observed that the effect of ballooning also disturbs the constant curvature profile of SPA. Therefore, a chamber-reinforcement solution is provided for minimizing the ballooning and ensuring the uniform bending of a SPA.

Soft growing robots have received considerable attention because of their unique locomotion. However, the use of a single material for their manufacturing causes numerous problems, because each part of the robot requires different characteristics. This study attempts to solve this fundamental problem from a material perspective, rather than integrating independent solutions. A hyperelastic material is proposed for building a soft growing robot. Several problems associated with conventional soft growing robots are addressed using a hyperelastic material that offers the required properties for each part of the soft growing robot, while maintaining its intrinsic advantages. Two unique features of hyperelastic materials, bulging and shape‐locking, are introduced. The advantages that these two features offer to soft growing robots are investigated and analyzed. A soft growing robot, utilizing these features, can easily achieve shape locking, small tail tension, easy retraction, uniform circular inner channel, and wrinkle‐free curve formation, without additional hardware. The initial concept of the growing and steering mechanisms of a hyperelastic soft growing robot is proposed and demonstrated using a prototype. [ABSTRACT FROM AUTHOR]

The deformation behavior of an artificial heart valve was analyzed using the explicit dynamic finite element method. Time variations of the left ventricle and the aortic pressure were considered as the mechanical boundary conditions in order to reproduce the opening and closing movements of the valve under the full cardiac cycle. The valve was assumed to be made from a medical polymer and hence, a hyperelastic Mooney–Rivlin model was assigned as the material model. A simple formula of the damage mechanics was also introduced into the theoretical material model to express the hysteresis response under the unloading state. Effects of the hysteresis on the valve deformation were characterized by the delay of response and the enlargement of displacement. Most importantly, the elastic vibration observed in the pure elastic response under the full close state was dramatically reduced by the conversion of a part of elastic energy to the dissipated energy due to hysteresis. [ABSTRACT FROM AUTHOR]

A wide variety of hyperelastic rubber-like materials, exhibiting strong nonlinear stress–strain relations under large deformations, is applied in various industrial mechanical systems and engineering applications involving shock and vibration absorbers. An optimal design procedure of an elevator chassis crashing on a hyperelastic shock absorber in a fail scenario, applicable in large-scale mechanical systems or industrial structures of high importance under strong nonlinear dynamic excitation, is presented in this work. For the characterization of the hyperelastic absorber, a Mooney–Rivlin material model was adopted, and a series of in-lab compression quasi-static tests were conducted. Applying a fully parallelizable state-of-the-art stochastic model updating methodology, coupled with robust, accurate and efficient Finite Element Analysis (FEA) software, the hyperelastic behavior of the shock absorber was validated under uniaxial large deformation, in order to tune all material parameters and develop a high-fidelity FE model of the shock absorber system. Next, a series of in situ full-scale experimental trials were carried out using a test-case elevator chassis, representing the crash scenario on the buffer absorber system, after a controlled free fall. A limited number of sensors, i.e., triaxial accelerometers and strain gauges, were placed at characteristic points of the real structure of the elevator chassis recording experimental data. A discrete Finite Element (FE) model of the experimentally tested arrangement involving the elevator chassis and updated buffer absorber system along with all boundary conditions was developed and used in explicit nonlinear analysis of the crash scenario. Steel material properties and the characterized updated Mooney–Rivlin material model were assigned to the elevator chassis and buffer, respectively. A direct comparison of the numerical and experimental data validated the reliability and accuracy of the methodology applied, whereas results of the analysis were used in order to redesign and optimize a new-design elevator chassis, achieving minimum design stresses and satisfying serviceability limit states.

• Finite-element analysis offers insights into needle-TM interactions for middle-ear interventions. • Combined 2D and 3D FE modeling strategy reveals TM deformation during needle insertion. • First-order Ogden hyperelastic model accurately captures TM mechanical nonlinearity. • TM thickness, needle geometry, and material impact needle insertion force and success. • Methodology aids in developing therapeutic and diagnostic technologies for hearing and balance pathologies. The tympanic membrane (TM) is one of the most common routes to access the middle ear and inner ear for the treatment of hearing and balance pathologies. Since the TM is a soft thin biological tissue with small dimensions, using needles seems to be among the most practical interventional approaches. In this study, we proposed a finite-element (FE) analysis of needle-TM interactions that combines a 3D model of the TM and other main middle-ear structures in gerbil, and a 2D model of needle insertion into the TM based on the cohesive zone method (CZM). The TM was modelled using a 1st-order Ogden hyperelastic material and its properties were obtained by fitting to the experimental force-displacement plots of large deformation in the TM under needle indentation. The cohesive parameters were also acquired by calibrating the puncture force against the experimental data of needle insertion into the TM. These FE models were then used to obtain the deformation behaviour of the TM and other middle-ear structures due to the insertion force applied at different locations on the TM. Moreover, we investigated the effect of the TM thickness, the geometry of the needle (i.e., diameter and tip angle), and needle material on the insertion of needles into the TM. We also studied the penetration success of deformable needles. [ABSTRACT FROM AUTHOR]

This paper presents mathematical modelling and simulation founded on an Asymptotic Numerical Method (ANM) for the rubber-like material hyperelastic behaviour. The basic models such as Mooney-Rivlin, and the Gent partial models and the Hybrid Integral Approach (HIA) model are considered. The HIA is a strong nonlinear model developed from the inverse Langevin function approximation is considered here for its efficiency. Explicit formulations of each model are presented as well as the associated asymptotic developments in the frame of the ANM. Various types of boundary conditions effects are analysed for each considered hyperelastic model. The effectiveness of the ANM compared to the Newton-Raphson method is demonstrated and particularly for the HIA model. We present as results stress-strain curves for the implementation of these different models where we specify the influence of the Imposed Displacement for tensile and compressive stresses when the structure is clamped and simply supported. In term of this study, we observe that the complete HIA model present the curves with the difference hardly perceptible when we vary results in term of stress-strain curves with different imposed Displacement. But when strain is high than 5%, the Mooney-Rivlin and the Gent partial models, presents the high disparities with different imposed Displacement. This observation justifying the limitations of partial models in term of characterisation of the behaviour law of hyperplastic materials. [ABSTRACT FROM AUTHOR]

This study explored the impact of hypertension on atheroma plaque formation through a mechanobiological model. The model incorporates blood flow via the Navier–Stokes equation. Plasma flow through the endothelium is determined by Darcy's law and the Kedem–Katchalsky equations, which consider the three-pore model utilized for substance flow across the endothelium. The behaviour of these substances within the arterial wall is described by convection–diffusion–reaction equations, while the arterial wall itself is modelled as a hyperelastic material using Yeoh's model. To accurately evaluate hypertension's influence, adjustments were made to incorporate wall compression-induced wall compaction by radial compression. This compaction impacts three key variables of the transport phenomena: diffusion, porosity, and permeability. Based on the obtained findings, we can conclude that hypertension significantly augments plaque growth, leading to an over 400% increase in plaque thickness. This effect persists regardless of whether wall mechanics are considered. Tortuosity, arterial wall permeability, and porosity have minimal impact on atheroma plaque growth under normal arterial pressure. However, the atheroma plaque growth changes dramatically in hypertensive cases. In such scenarios, the collective influence of all factors—tortuosity, permeability, and porosity—results in nearly a 20% increase in plaque growth. This emphasizes the importance of considering wall compression due to hypertension in patient studies, where elevated blood pressure and high cholesterol levels commonly coexist. [ABSTRACT FROM AUTHOR]

Harmonic wave excitation in a semi-infinite incompressible hyperelastic 1D rod with the Mooney–Rivlin equation of state reveals the formation and propagation of the shock wave fronts arising between faster and slower moving parts of the initially harmonic wave. The observed shock wave fronts result in the collapse of the slower moving parts being absorbed by the faster parts; hence, to the attenuation of the kinetic and the elastic strain energy with the corresponding heat generation. Both geometrically and physically nonlinear equations of motion are solved by the explicit Lax–Wendroff numerical tine-integration scheme combined with the finite element approach for spatial discretization.

Soft growing robots have received considerable attention because of their unique locomotion. However, the use of a single material for their manufacturing causes numerous problems, because each part of the robot requires different characteristics. This study attempts to solve this fundamental problem from a material perspective, rather than integrating independent solutions. A hyperelastic material is proposed for building a soft growing robot. Several problems associated with conventional soft growing robots are addressed using a hyperelastic material that offers the required properties for each part of the soft growing robot, while maintaining its intrinsic advantages. Two unique features of hyperelastic materials, bulging and shape‐locking, are introduced. The advantages that these two features offer to soft growing robots are investigated and analyzed. A soft growing robot, utilizing these features, can easily achieve shape locking, small tail tension, easy retraction, uniform circular inner channel, and wrinkle‐free curve formation, without additional hardware. The initial concept of the growing and steering mechanisms of a hyperelastic soft growing robot is proposed and demonstrated using a prototype.

Despite the exponentially expanding capabilities of robotic systems with the introduction of soft robotics, the lack of practical considerations in designing and integrating soft robotic components hinders the widespread application of newly developed technology in real life. This study investigates the development and performance evaluation of soft-rigid hybrid (SRH) robotic systems employing multilayered bellow-shaped soft pneumatic actuators (MBSPAs) to overcome the common challenges exclusively exhibited in soft robotics. Specifically, we introduce a unique SRH revolute joint enabled by a single thermoplastic polyurethane-MBSPA and rigid components to tackle the limitations of existing soft pneumatic actuators (SPAs), such as restricted payload capacity, vulnerability to external damages, and lack of resilience against outdoor environment. The proposed SRH system entails rigid components encapsulating to protect the MBSPA throughout the entirety of the desired range of motion, and demonstrates improved displacement efficiency, force output, and resilience against external loads. The rigid components also help to stabilize the axis of motion, fostering high durability and repeatable motion. We also extend this concept to a one-degree of freedom SRH prismatic joint. Finite element method modeling is used to estimate the general actuator performance, facilitating the design of MBSPA with limited material information and bypassing trial and error. The wider application of this research targets delicate object handling in industries such as agriculture, encouraging safe and efficient automated harvesting. The article includes thorough actuator performance characterization including displacement, frequency response, durability with life cycle testing up to 25,000 cycles, force output, stiffness, and power density. Performance comparisons with other SPA are provided. A proof of concept 3-point gripper enabled by the proposed SRH joints is capable of gripping objects of various sizes and shapes, with detailed workspace analysis and demonstration showing the gripper's versatility. The SRH system presented here lays a robust foundation for the ongoing advancement of soft robotic technology toward real-life applications, unveiling the potential for a future in which robots operate efficiently in the targeted applications, aiming to integrate seamlessly into workflows with human workers.