Hyperelastic Material Model Research Articles

Frequency domain analysis of pre-stressed elastomeric vibration isolators

Two types of elastomeric vibration isolators used for equipment vibration isolation in aerospace vehicles are considered for the present study. These isolators are constructed using elastomers mounted in steel encasings. These isolators are initially deformed statically and dynamic loads are applied on the deformed configuration. To capture the static deformation, equivalent static load corresponding to its load rating and specified displacements are created. Static deformation is computed using Finite Element methods with four node axi-symmetric element which include the geometric non-linear effect for steel and with standard Yeoh hyper-elastic material model for elastomers (Muhammed and Zu, 2012) [1]. Yeoh material constants are derived from uni-axial tension test data of the elastomer specimen. These isolators are subjected to harmonic and random excitations in the pre-deformed state. For numerical analysis, elastomeric constants at dynamic conditions are obtained as complex function of frequency using Dynamic Mechanical Analyzer (DMA) for a range of frequencies. The standard material model of Yeoh is modified incorporating frequency dependant material characteristics and damping in the range of frequencies of interest. A multiplicative non-separable variables law is derived for Yeoh material model to include the effect of static pre-stress, based on the methodology given in literature (Nashif et al., 1985; Beda et al., 2014) [2,3]. The modifications of Yeoh model suitable for frequency domain analysis is the novelty in the present study. In the analysis, while dynamic loads are applied, the configuration is updated considering initial static loading. The frequency response of the isolators is computed using material properties evaluated at progressive dynamic strains until a match in natural frequency is observed. Appropriate damping corrections are then incorporated to match the test observed transmissibility. Then updated material properties are used to compute the random response which showed good agreement with results of experiments, validating the approach taken for the development of this model.

Orientation and depth dependent mechanical properties of the porcine cornea: Experiments and parameter identification

The porcine cornea is a standard animal model in ophthalmic research, making its biomechanical characterization and modeling important to develop novel treatments such as crosslinking and refractive surgeries. In this study, we present a numerical model of the porcine cornea based on experimental measurements that captures both the depth dependence and orientation dependence of the mechanical response. The mechanical parameters of the established anisotropic hyperelastic material models of Gasser, Holzapfel and Ogden (HGO) and Markert were determined using tensile tests. Corneas were cut with a femtosecond laser in the anterior (100 μm), central (350 μm), and posterior (600 μm) regions into nasal-temporal, superior-inferior, and diagonal strips of 150 μm thickness. These uniformly thick strips were tested at a low speed using a single-axis testing machine. The results showed that the corneal mechanical properties remained constant in the anterior half of the cornea regardless of orientation, but that the material softened in the posterior layer. These results are consistent with the circular orientation of collagen observed in porcine corneas using X-ray scattering. In addition, the parameters obtained for the HGO model were able to reproduce the published inflation tests, indicating that it is suitable for simulating the mechanical response of the entire cornea. Such a model constitutes the basis for in silico platforms to develop new ophthalmic treatments. In this way, researchers can match their experimental surrogate porcine model with a numerical counterpart and validate the prediction of their algorithms in a complete and accessible environment.

Constitutive modeling of particle reinforced rubber-like materials

The present study is focused on the constitutive modeling for the mechanical behavior of rubber reinforced with filler particles. A filler-dependent energy density function is proposed with all the continuum mechanics-based necessities of an effective hyperelastic material model. The proposed invariant-based energy function comprises a single set of material parameters for a material subjected to several modes of loading conditions. The model solution agrees well with existing experimental results. Later, the effect of varying concentrations of filler particles in the rubber matrix is also studied.

Constitutive modeling of rubber-like materials: an alternative material model

ABSTRACT This article proposes an alternative strain energy density function to describe the hyperelastic behavior of rubber-like materials under various deformations. This proposed strain energy function fulfilled all the necessary characteristics of a hyperelastic material model. This function consists of four material parameters and represents an invariant-based material model. Also, the material parameters are kept constant for the different modes of loading conditions. The model solution based on the proposed energy function is mathematically simple and well suited for all stretching ranges. The model solution is further tested with the existing experimental data and compared with the results of available model solutions. The findings of the model solution agree well with both experimental and theoretical results available in the literature.

Oligodendrocyte tethering effect on hyperelastic 3D response of axons in white matter

A novel finite element model is proposed to study the mechanical response of axons embedded in extracellular matrix when subjected to tensile loads under purely non-affine kinematic boundary conditions. Ogden hyperelastic material model describes the axons and the extracellular matrix material characterizations. Two axon-glia tethering scenarios in white matter are studied a single oligodendrocyte (single-OL) with multiple connections a multi-oligodendrocyte (multi-OL) one. In the multi-OL tethering configuration, resultant forces are randomly oriented as distributed glial cells arbitrarily wrap around axons in their immediate vicinity. In the single-OL setup, a centrally located oligodendrocyte myelinates multiple axons nearby. Tethering forces are directed towards this oligodendrocyte, resulting in greater directionality and farther-reaching stress distribution. The oligodendrocyte connections to axons are represented by a spring-dashpot model. The material properties of myelin served as the upper limit for the parameterization of the oligodendrocyte stiffness (“K"). The proposed FE models enable realization of connection mechanisms and their influence on axonal stiffness to determine resultant stress states accurately. Root mean square deviation analysis of stress-strain plots of different connection scenarios reveal an increasing axonal stiffness with increasing tethering, indicating the role of oligodendrocytes in stress redistribution. In single-OL submodel, for the same number of connections per axons, RMSD values increased as “K" (the oligodendrocyte spring stiffness) values were set higher. RMSD calculations reveal that for a “K" value, single-OL model yielded slightly stiffer models compared to multi-OL. The current study also addresses the potential geometrical limitations of multi-OL model by randomizing and adding connections to ensure greater responsiveness. Cyclic bending stresses noticed in both submodels suggest the risk of axonal damage accumulation and repeated load failure.

Experiments and hyperelastic modeling of porcine meniscus show heterogeneity at high strains.

Constitutive modeling of the meniscus is critical in areas like knee surgery and tissue engineering. At low strain rates, the meniscus can be described using a hyperelastic model. Calibration of hyperelastic material models of the meniscus is challenging on many fronts due to material variability and friction. In this study, we present a framework to determine the hyperelastic material parameters of porcine meniscus (and similar soft tissues) using no-slip uniaxial compression experiments. Because of the nonhomogeneous deformation in the specimens, a finite element solution is required at each step of the iterative calibration process. We employ a Bayesian calibration approach to account for the inherent material variability and a Bayesian optimization approach to minimize the resulting cost function in the material parameter space. Cylindrical specimens of porcine meniscus from the anterior, middle and posterior regions are tested up to 30% compressive strain and the Yeoh form of hyperelastic strain energy density function is used to describe the material response. The results show that the Yeoh form is able to accurately describe the compressive response of porcine meniscus and that the Bayesian calibration and optimization approaches are able to calibrate the model in a computationally efficient manner while taking into account the inherent material variability. The results also show that the shear modulus or the initial stiffness is roughly uniform across the different areas of the meniscus, but there is significant spatial heterogeneity in the response at high strains. In particular, the middle region is considerably stiffer at high strains. This heterogeneity is important to consider in modeling the response of the meniscus for clinical applications.

Stiffness Adaptation of a Hybrid Soft Surgical Robot for Improved Safety in Interventional Surgery.

Minimally invasive instruments are inserted per-cutaneously and are steered toward the desired anatomy. The low stiffness of instruments is an advantage; however, once the target is reached, the instrument usually is required to transmit force to the environment. The main limitation of the constant stiffness is predetermined maneuverability and cap of force transmission. Whereas, a highly flexible device can be safely steered through the body but is not suitable for payload limit, while a highly stiff device can have relatively high loads but cannot be steered in highly tortuous trajectories. To overcome this limitation, an adaptive stiffness soft robot was proposed, and the effects of the chamber pressure on the stiffness of the soft robot were investigated. To this end, a single-chamber pneumatic soft robot with one tendon was designed and fabricated. Afterward, a continuum mechanics model based on the nonlinear Cosserat rod model with hyperelastic material model and large deformation kinematics of the robot was developed. The shooting method solved the model as a boundary value problem with Dirichlet and Neumann boundary conditions. The results of the model showed stiffness adaptation feasibility with simultaneous tendon-driving and pneumatic actuation. Thus, to validate the theoretical findings, a series of experimental studies were performed with pressure in the range of 33 to 44 kPa and tendon tensions in the range of 0 to 2.7 N. The theoretical and experimental results for tip displacement and stiffness showed similar trends with a maximum error of 8.25%.

Valve interstitial cells under impact load, a mechanobiology study

Understanding the relationship between mechanobiology and the biosynthetic activities of the valve interstitial cells (VICs) in health and disease under severe dynamic loading conditions is of particular interest. The purpose of this study is to further understand the mechanobiology of heart valve leaflet tissue and the VICs under impact forces. Two novel computational and experimental platforms were developed to study the effect of impact load on the VICs to monitor for apoptosis. The first objective was to design and develop an apparatus to experimentally study viability (apoptosis) of the porcine heart valve leaflet tissue VICs in the aortic position under controlled impact forces. Apoptosis was assessed based on terminal transferase dUTP nick end-labelling (TUNEL) assay. The second objective was to develop a computational platform to estimate the stress and strain fields in the vicinity of VICs when the tissue experiences impact forces. A nonlinear finite element (FE) model with an anisotropic, hyperelastic and heterogeneous material model for the matrix and cells was developed. Preliminary results confirm that interstitial cells are successfully resistant to impact loads up to 30 times more than normal physiological conditions. Additionally, the structure and composition of heart valve leaflet tissue provides a mechanical shield for VICs protecting them from excessive mechanical forces such as impact loads. Although, the entire tissue may experience excessive stresses, which may lead to structural damage, the stresses around and near VICs remain consistency low. Results of this study may be used for heart valve leaflet tissue-engineering, as well as further understanding the mechanobiology of the VICs in health and disease.

Non-linear analysis of orthotropic hyperelastic plate using VAM

An asymptotically accurate zeroth-order constitutive relation between 2D strains and stress tensor for an orthotropic hyperelastic material is derived using the Variational Asymptotic Method (VAM). Material nonlinearity is encompassed through the hyperelastic material model while geometric nonlinearity is by allowing finite displacements and rotations. Moderate strains of order 20% are considered. The small parameters such as the ratio of thickness to characteristic dimension, and maximum allowable strain (0.2) separate strain energy density into different orders. The analysis starts with the 3D strain energy density function and is divided into the thickness analysis (1D) and mid-surface analysis (2D). The 1D analysis leads to analytical expressions for warping functions, constitutive relations, and recovery relations. The 2D analysis is based on a non-linear finite element method that takes the constitutive relation as its input and obtains 2D displacements. The recovery relation converts them to 3D field variables i.e. displacements, strains, and stresses. The theory is applied to a square clamped plate subjected to uniformly distributed pressure. The results are accurate and obtained in a computationally efficient manner.

A Prestressed Intracellular Biomechanical Model for the Platelet to Capture the Disc-to-Sphere Morphological Change from Resting to Activated State

This paper proposes a biomechanical platelet model with an intracellular prestressed assumption. The platelet structure is composed of a membrane cortex and a marginal band (MB). The membrane cortex is assumed in a spherical shape in its initial state and modeled using spring-network elements widely used for the similar membrane structure of red blood cells. The MB is modeled as one solid torus, which employs the hyperelastic material model, and is confined inside the cortex through a contact model. In the initial equilibrium state, the platelet has a stable, flat, and discoid shape. Upon activation, the possible mechanism of the unbinding rate of crosslink between the microtubules (MTs) is assumed to break the homogeneous stiffness of the MB, which causes the platelet to have a disc-to-sphere morphological transition. The numerical results and the experimental images of the MBs show good agreement. The proposed model provides a novelty in relating the mechanical property changes of the MB to the platelet morphological changes upon activation, thus, can provide a possible engineering tool to reveal the intriguing behavior of platelet upon activation.

Hyperelasticity models extending Hooke’s law from small to moderate strains and experimental verification of their scope of application

Lagrangian formulations of Hill’s linear isotropic hyperelastic material models based on the one-parameter (r) Itskov family of strain tensors (including the Hencky, Pelzer, and Mooney strain tensors generating the H, P, and M material models, respectively) were developed. Explicit basis-free expressions for fourth-order elasticity tensors were obtained for these material models. These expressions use the right Cauchy–Green deformation tensor. The developed formulations of isotropic hyperelastic material models were implemented in the commercial finite element MSC.Marc code. Simple tension stress–strain diagrams were obtained for dog-bone shaped flat specimens made of Duothane QA965 polyurethane. The experimental data were used to fit the parameters E and ν (having the meaning of Young’s modulus and Poisson’s ratio for specimens at small strains) for the H, P, and M material models and the parameters C1 and C2 for the Mooney–Rivlin (M–R) isotropic incompressible material model included in the library of standard material models of the MSC.Marc code. For the investigated material, the H and M material models were shown to adequately reproduce stress–strain diagrams up to 50% elongation, and the P and M–R models up to 150% elongation. In addition, cylindrical specimens were made of the same polyurethane and tested for simple torsion (with constrained edges) and generalized torsion (with edges free to move in the longitudinal direction). In both problems, the resultant moments obtained by computer simulations using the P and M–R material models agree well with the experimental data on rod torsion up to buckling; computer simulations using the H and M material models give less satisfactory agreement with the experimental data. Similar qualitative agreement is obtained between the experimental and simulated resultant axial force and axial elongation; however, in this case, the quantitative agreement is less satisfactory than for the resultant moment.

Association of 3-Year All-Cause Mortality and Peak Wall Stresses of Ascending Thoracic Aortic Aneurysms in Veterans

Risk of aortic dissection in ascending thoracic aortic aneurysms is not sufficiently captured by size-based metrics. From a biomechanical perspective, dissection may be initiated when wall stress exceeds wall strength. Our objective was to assess the association between aneurysm peak wall stresses and 3-year all-cause mortality. Finite element analysis was performed in 273 veterans with chest computed tomography for surveillance of ascending thoracic aortic aneurysms. Three-dimensional geometries were reconstructed and models developed accounting for prestress geometries. A fiber-embedded hyperelastic material model was applied to obtain circumferential and longitudinal wall stresses under systolic pressure. Patients were followed up to 3 years following the scan to assess aneurysm repair and all-cause mortality. Fine-Gray subdistribution hazards were estimated for all-cause mortality based on age, aortic diameter, and peak wall stresses, treating aneurysm repair as a competing risk. When accounting for age, subdistribution hazard of mortality was not significantly increased by peak circumferential stresses (p=0.30) but was significantly increased by peak longitudinal stresses (p=0.008). Aortic diameter did not significantly increase subdistribution hazard of mortality in either model (circumferential model: p=0.38; longitudinal model: p = 0.30). The effect of peak longitudinal stresses on subdistribution hazard of mortality was maximized at a binary threshold of 355kPa, which captured 34 of 212(16%) patients with diameter <5 cm, 11 of 36(31%) at 5.0-5.4 cm, and 11 of 25(44%) at ≥5.5 cm. Aneurysm peak longitudinal stresses stratified by age and diameter were associated with increased hazard of 3-year all-cause mortality in a veteran cohort. Risk prediction may be enhanced by considering peak longitudinal stresses.

Analysis of factors influencing on performance of solid tires: Combined approach of Design of Experiments and thermo-mechanical numerical simulation

Excessive loading conditions and internal heat build-up are the major causes of failures in solid resilient tires. Both operational and design related factors can affect tire performance including internal stress generation and heat build-up. In spite of their limitations, experimental techniques are still the most common method of identifying the factors that affect tire performance. This study explores a combined approach of numerical modelling and Design of Experiments (DoE) to identify the impact of several key design and operational factors on the performance of solid tires under different temperature levels. First, 3D Finite Element (FE) static and thermal models of the solid resilient tires are developed by incorporating suitable temperature dependent hyperelastic material models and relaxation properties. The temperature-dependent mechanical behaviours of rubber material are obtained by using Dynamic Mechanical Analyzer (DMA) and the William Landel Ferry (WLF) parameters. The developed FE thermal model is used to predict the tire performance, including the tire blasting region, which is then validated with experimental data. Secondly, a two-level fractional factorial DoE analysis is developed using response readings of maximum stresses, deformations and contact pressure obtained from the validated FE thermal model. The factors used in the DoE include the number of rubber layers, applied load, rolling speed, ramp angle and aperture level. The results provide optimal operational and design parameters of the solid resilient tire at different environmental temperatures and show the potential for considerable stress reduction with minimal changes to tire deformation and contact area. These results highlight the capability of the combined FEM and statistical design approach to drastically reduce the number of physical experiments required for obtaining optimal tire performance thus saving significant time and cost.

Hyperelastic parameter identification of human articular cartilage and substitute materials

Numerical simulations are a valuable tool in the field of tissue engineering for cartilage repair and can help to understand which mechanical properties affect the behavior of chondrocytes and contribute to the success or failure of surrogate materials as implants. However, special attention needs to be paid when identifying corresponding material parameters in order to provide reliable numerical predictions of the material's response. In this study, we identify hyperelastic material parameters for numerical simulations in COMSOL Multiphysics® v. 5.6 for human articular cartilage and two surrogate materials, commercially available ChondroFillerliquid, and oxidized alginate-gelatin (ADA-GEL) hydrogels. We consider several hyperelastic isotropic material models and provide separate parameter sets for the unconditioned and the conditioned material response, respectively, based on previously generated experimental data including both compression and tension experiments. We compare a direct parameter identification approach assuming homogeneous deformation throughout the specimen and an inverse approach, where the experiments are simulated using a finite element model with realistic boundary conditions in COMSOL Multiphysics® v. 5.6. We demonstrate that it is important to consider both compression and tension data simultaneously and to use the inverse approach to obtain reliable parameters. The one-term Ogden model best represents the unconditioned response of cartilage, while the conditioned response of cartilage and ADA-GEL is equally well represented by the two-term Ogden and five-term Mooney-Rivlin models. The five-term Mooney-Rivlin model is also most suitable to model the unconditioned response of ADA-GEL. For ChondroFillerliquid, we suggest using the five-term Mooney-Rivlin or two-term Ogden model for the unconditioned and the two-term Ogden model for the conditioned material response. These results will help to choose appropriate material models and parameters for simulations of whole joints or to advance mechanical-stimulation assisted cartilage tissue engineering in the future.

Equilibrium-based convolution neural networks for constitutive modeling of hyperelastic materials

Recently, various machine learning methods have been developed to model the stress-strain constitutive behavior of materials. In these methods, a large database of multi-axial stress versus strain curves is indispensable for training and cross-validation. However, it is usually formidable to experimentally obtain such curves by noting that, although strain can be easily measured, stress can only be extracted for limited specimens with a simple and uniform stress field upon loading. Moreover, most developed approaches are based upon supervised learning and ignore known physical laws, resulting in limited interpretability and generalization. In this paper, an equilibrium-based convolution neural network (ECNN) is proposed to model the constitutive behavior of hyperelastic materials. Only strain and externally applied force are taken as input for training while the hard-to-measure stress is considered as internal variables. Therefore, a large database can be easily generated with a single non-uniformly deformed specimen with spatially dependent strain. The equation of equilibrium is embedded in the architecture of the ECNN as a constraint to implicitly establish the correspondence between the internal variables and the stress components and, consequently, the constitutive stress–strain relationship. Moreover, the ECNN is unsupervised by noting that training is not against the output stress. Numerical and experimental examples are presented to show that the developed ECNN can faithfully extract the stress corresponding to local strain, model the multiaxial stress-strain constitutive behavior of hyperelastic materials, and surrogate equation-based conventional constitutive models of hyperelastic materials.

Fluid‐Structure Interaction Study of Coronary Artery Disease Biomechanics

Coronary artery disease (CAD) kills 1 in 7 in the United States. Atherosclerosis and thrombosis are both disease states that are impacted by biomechanical conditions in the blood vessels. Platelets and vascular endothelial cells are known to respond to their mechanical environments, which can be altered around a coronary stenosis. Certain pertinent mechanical parameters, such as vascular wall shear stress and strain, can be difficult or impossible to measure directly in vivo.Computational fluid dynamics (CFD) models and Fluid‐Structure Interaction (FSI) models are often used to assess coronary artery biomechanics. In this study, we developed three FSI models based on the computed tomography data from a patient: a normal model, a severe stenosis model with a 71% diameter occlusion (which would be a candidate for intervention), and a mild stenosis model (50% diameter occlusion, which would not be considered clinically severe). Our hypothesis was that the high‐resolution FSI model could reveal small changes in coronary biomechanics at the cellular level (microscopic scale), which may be used as a biomarker/indicator for endothelial cell and platelet activation at the early stage of disease development. FSI simulations were conducted in COMSOL Multiphysics. Time‐dependent velocity and pressure boundary conditions were applied at the inlet and outlet of the fluid domain, respectively. A five‐parameter Mooney‐Rivlin hyperelastic material model was used to model the material properties of the artery. A time‐dependent pressure boundary condition was applied to the outside of the vessel, mimicking squeezing of the cardiac muscle in areas of myocardial bridging. In the region of interest, a spatial resolution of less than 40 µm was achieved. This is comparable to the size of vascular endothelial cells (which can range in size from 20‐100 µm), allowing us to capture hemodynamic and solid mechanical behavior at the cellular level. In the normal geometry, wall shear stress (WSS) values peaked at 1.51 Pa. In the 71% stenosis throat, transient WSS could reach 200 Pa, while in the 50% stenosis throat, the maximum WSS was less than 5 Pa. In the recirculation zone of the 71% stenosis, WSS peaked at 4.66 Pa, while in the recirculation zone of the 50% stenosis WSS reduced to 0.83 Pa, which is pathologically low. Time‐averaged wall shear stress (TAWSS) was 0.62+0.002 Pa (average + standard error) in the normal model, 1.60+0.004 Pa in the 50% stenosis model, and 7.47+0.017 Pa in the 71% stenosis model. Time‐averaged wall shear stress gradient (TAWSSG) was 0.018+6.25*10‐5 N/m in the normal model, 0.150+3.4*10‐4 N/m in the 50% stenosis model, and 0.970+0.002 N/m in the 71% stenosis model. Radial strain in the normal, 71% stenosis throat, 50% stenosis throat, 71% recirculation zone, and 50% recirculation zone peaked at 7.5%, 4.0%, 6.3%, 0.5%, and 5.1% respectively, and the circumferential strain peaked at 8.9%, 4.4%, 6.6%, 0.6%, and 4.2% respectively. In summary, we were able to develop mesoscopic FSI models that can provide microscopic hemodynamic information at the cellular level. Such information can be used in the in vitro models to study biomechanical pathways associated with coronary artery atherosclerosis and thrombosis; it may also be used as biomarkers at the early stage of atherosclerosis development.

Effects of gripper location and blank geometry on the thermoforming of a carbon-fiber woven-fabric/polyphenylene sulfide composite sheet

The effects of gripper location and blank geometry on the thermoforming of a pre-consolidated carbon-fiber woven-fabric/polyphenylene sulfide (PPS) thermoplastic composite sheet (deformed into a U-beam geometry) are investigated both experimentally and numerically. The thermoforming experiments and simulations are performed at constant tool (160oC) and sheet (315oC) temperatures by using four thermoplastic composite blanks, which are different in geometry and inserted into the blank holder using gripping springs. Thermocouples are inserted on the composite sheet and forming molds in order to monitor the temperature variations during thermoforming. Thermoforming process is simulated in Ls-Dyna; the composite sheet is modeled using the Anisotropic Hyperelastic Material Model (MAT_249). An optimum punch speed and a spring constant are initially determined through numerical simulations. Afterward, the numerical thermoforming processes of four different blanks are implemented separately. Results reveal that the simulations show good agreements with the experiments in terms of defects formation and the maximum shear angles between the fiber directions on the final thermoformed U-beam geometry. When the blank is attached with eight springs from the lugs to the blank holder, the deformation and distortion of the net edge of the sheet are avoided, resulting in significant reductions in the extent of defect formation.

A PORCINE FORELEG FINITE ELEMENT MODEL FOR SURFACE WAVE CHARACTERIZATION

Injuries from BB shots are responsible for thousands of injuries each year, with many resulting in contusions or superficial embedments to the extremities. To help better understand the injury biomechanics of BB shots, a porcine foreleg finite element model was selected for comparison with some documented porcine ballistic experiments. The model was created by segmenting a porcine leg computerized tomography (CT) scan into the major bones, skin, and soft tissues, and then generating a mesh from the resulting geometries. A previously published hyperelastic material model was incorporated to represent the skin’s non-linear mechanical behavior. The pig leg model was used to simulate the skin response to 87.1 and 114.6 m/s stainless steel BB shots. The simulation matched the non-penetrative behavior from the experiments, predicting peak dynamic deformations of 12.6 and 25.4 mm respectively. MatLab was used to collect the movement of surface nodes and reconstruct continuous surfaces every 0.5 ms. The position and speed of the impact-induced wave was non-linear and did not depend on the BB initial velocity. Future work is needed to compare the simulation results against experimental digital image correlation (DIC) data, increase the time and spatial resolution of simulated sampling surface, and eventually include dynamic material data to account for skin damage with increasing BB initial velocity.

Design and structural analysis of non-pneumatic tyres for different structures of polyurethane spokes

NPTs have vast applications because of no tyre puncture, no need for air pressure, low rolling resistance, and also have higher flexibility for design and recyclability. In this research work, different structures of polyurethane (PU) spokes have been designed and analyzed under radial loading conditions which include structures like honeycomb with varying cell angles, simple spoke, and trapezoid type by keeping in view that the cell wall thickness and somehow the mass of the structures remain the same. Based on the Mooney-Rivlin hyper-elastic material model and performing 2D non-linear static structural analysis on different types of NPTs using ANSYS, it has been observed that the simple spoke structure has the lowest spoke stress and deformation values of 2.01 MPa and 11.7 mm, while HC–A1 has the least value of strain energy of 2.58 mJ, at a load of 2500 N. The above results show that the straight spoke structures like simple spoke and trapezoid type have a high load-carrying ability than the honeycomb type NPTs under same boundary conditions. While honeycomb NPTs have higher fatigue life as compared to straight-spoke NPTs.

Interdisciplinary Methods for Zoonotic Tissue Acellularization for Natural Heart Valve Substitute of Biomimetic Materials.

The goal of this work was to create a bioactive tissue-based scaffold using multi-disciplinary engineering materials and tissue engineering techniques. Materials & methods: Physical techniques such as direct laser interference lithography and proton radiation were selected as alternative methods of enzymatic and chemical decellularization to remove cells from a tissue without degradation of the extracellular matrix nor its protein structure. This study was an attempt to prepare a functional scaffold for cell culture from tissue of animal origin using new physical methods that have not been considered before. The work was carried out under full control of the histological and molecular analysis. Results & conclusions: The most important finding was that the physical methods used to obtain the decellularized tissue scaffold differed in the efficiency of cell removal from the tissue in favour of the laser method. Both the laser method and the proton method exhibited a destructive effect on tissue structure and the genetic material in cell nuclei. This effect was visible on histology images as blurred areas within the cell nucleus. The finite element 3D simulation of decellularization process of the three-layer tissue of animal origin sample reflected well the mechanical response of tissue described by hyperelastic material models and provided results comparable to the experimental ones.