Papers by Keyword: Hyperelasticity

Abstract: Classical linear contact mechanics, formulated with small strain and displacement assumption, struggles to accurately describe experiments involving rubbers and elastomers. Indeed, under high loads, these materials undergo large deformations and exhibit constitutive behaviors that deviate from a linear relationship between stress and strain. In such cases, it is essential to move beyond linear elasticity to account for nonlinearity caused by large deformations and displacements. Despite efforts to develop numerical tools capable of incorporating these non-linearities in contact problems, our understanding of their impact on contact mechanical responses remains limited. In this study, we investigate the basic case of normal contact between a wavy rigid indenter and a flat, deformable substrate. We examine the influence of geometric non-linearities, arising from large deformations and displacements, alongside material non-linearities, under both frictionless and frictional interfacial conditions. To this end, we developed a finite element model, and we compared its predictions with those of Westergaard’s fully linear theoretical model. The results indicate that even in frictionless contact scenarios, non-linearities produce a mechanical response that differs significantly from predictions based on linear theory. This discrepancy becomes more pronounced as the aspect ratio of the wavy indenter increases, thereby invalidating the small-displacement assumption inherent in linear models. Moreover, the presence of friction, coupled with geometric non-linearities, induces contact hysteresis during loading and unloading cycles a phenomenon often attributed to other interfacial behaviors such as adhesion and plasticity.

Abstract: Industrial use of composite materials requires an increasingly advanced knowledge of technical textiles mechanical properties to control the manufacturing process and guarantee the performances of the finished products. Among the qualities that influence greatly the shaping process, theshear deformability is key for the forming of complex composite parts with double curves geometries. On the other hand, the stiffening of the behavior as the shearing rise is responsible for the occurrence of the wrinkling defect. This shearing behavior of the textile reinforcement is difficult to determinebecause it is non-linear and it coexists with a tensile stiffness of the fibers that is several orders of magnitude higher. Furthermore, shear and tension are coupled due to the weaving of the textiles. Now, few experimental methods have been proposed to measure the tension behavior of fabric as a function of its shear level because dedicated devices are needed for this investigation, capturing the shear-tension coupled behavior of fabric is then a difficult task. This paper deals with the robotization of the fabric shear-tension effect characterization. A KUKA robot associated with a force/torque sensor is utilized, taking advantage of its benefits in the ability to control the state of yarn tensions during shear tests while keeping track of the desired trajectory as enabled by the hybrid position-force control feature. This ensures precise positioning of a sample fabric and accurate contact forces. An anisotropic hyperelastic constitutive model for fabrics, based on the continuum theory of mechanics that takes into account the shear-tension coupling effect was formulated analytically and numerically simulated using Matlab software. An experimental test was then implemented to validate the proposed model. The results from a uni-axial tensile test and shear test under constant uni-axial tensile loading were obtained and analyzed to characterize the test sample. The model parameter identification was performed and presented in detail.

Abstract: The deformation of the human breast, especially that of the female, under variable pressure conditions, has been a recent focus for researchers, both in the computational biomechanics, computational biology and the health sector. When the deformation of the breast is large, it hampers suitable cyst tracing as a mammographic biopsy precontrive data. Finite element methods (FEM) has been instrumental in the currently studied practices to trail nodules dislocation. However, the effect of breast material constitution, especially that of a fibrocystic composition, on the biomechanical response of these nodules has gained less attention. The present study is aimed at developing a finite element fibrocystic breast model within the frame of biosolid mechanics and material hyperelasticity to model the breast deformation at finite strain. The geometry of a healthy stress‐free breast is modelled from a magnetic resonance image (MRI) using tissues deformations measurements and solid modelling technology. Results show that the incompressible Neo-Hookean and Mooney-Rivlin constitutive models can approximate large deformation of a stressed breast. In addition to the areola (i.e. nipple base), the surrounding area of the cyst together with its interface with the breast tissue is the maximum stressed region when the breast is subjected to compressive pressure. This effect can lead to an internal tear of the breast that could degenerate to malignant tissue.

Abstract: In order to find hyperelastic material model constants, data fitting technique is often used. For this task, the data is collected through different laboratory tests, namely, the uniaxial, the biaxial and the pure shear. However, due to the difficulty in getting biaxial data, often only uniaxial data was used for the fitting. Despite frequent use, it was established that this practice creates erroneous results. With a view to improve the data fitting results and at the same time to overcome the difficulty of collecting primary biaxial data, uniaxial data was used to generate a secondary biaxial data set. The data derived through this method was then tested with four common models as to examine the compatibility of the method. Subsequently, real biaxial data was used to compare with the data fitting results obtained through the proposed method. As results indicated combined data fitting for both instances were very much identical with respect to all tested models. Cases where somewhat higher deviation observed between experimental curves and data fitted curves for biaxial data, gave similar results for adjusted data driven data fitting too. However, such deviation could be attributed to mismatch between models with the particular material behaviour rather than the generated data.

Abstract: Mechanical behavior of a rubber bushing of a stabilizer of a passenger car is studied in this article. An analysis of behavior of the bushing loaded in the axial direction is performed. An identification of the critical points in the bushing body and, especially, in the interface between the bushing and the stabilizer bar for later optimization of the whole system of the stabilizer fixing in the car construction is the aim of this work. An advanced FEM system including such effects as a strongly nonlinear strain/stress relation of material of the bushing (hyperelasticity), large displacements, large deformations, and contact between the bushing and the stabilizer bar was used for the numerical analysis.

Abstract: A new constitutive equation for rubber-like materials model was proposed. The model is based on the Arruda-Boyce (AB) 8-chain non-Gaussian molecular network to which two new terms were added. Taking into account the effects of molecular chain entanglement and the topological constraint on the transverse motions of a single chain, the new added components combine the phenomenological theory of elasticity for rubber vulcanizates at large deformation and the tube theory for topological constraint. The new model contains five parameters which are obtained by fitting the uniaxial Treloar extension data, the predictions from the proposed model for equi-biaxial extension and pure shear are in good agreement with test data. Moreover, compared with some available models, the proposed model is more suitable for characterization of the uniaxial tension mechanical behavior of carbon black particles filled rubber material.

Abstract: Skin is an important organ which provides multiple functions. Thus, if skin fails i.e. due to burns or diseases, body will lose the protection provided by skin against infections and the harmful outer environment. Due to that, synthetic skin is seen as a very important alternative in the future. A number of studies have been carried out to understand skin’s basic functions and behaviour as its mechanical properties and behaviour are important in various fields. Nevertheless, to date no breakthrough has been reported. Therefore, this paper aims to briefly review and outline a framework which ultimately will lead to the synthesising silicone-hydrogel materials that potentially becoming a skin substitute. The newly synthesised composite materials will be tested mechanically to characterise its behaviour based on Ogden hyperelastic model. It could be emphasised that the present study is significant and will contribute to the body of knowledge in the area of skin mechanics.

Abstract: Modeling large nonlinear elastic deformation of elastomers is an important issue for developing new materials. Particularly, this is very promising for design and performance analysis of dielectric elastomers (DEs). These “smart materials” are capable of responding to an external electric field by displaying significant change in shape and size. In this paper, finite element method (FEM) was used to simulate the mechanical behavior of soft elastomers on uniaxial tension. Experimental data from uniaxial tensile tests were used in order to calibrate hyperelastic constitutive models of the material behavior. The constitutive model parameters were evaluated in ABAQUS/CAE. The 3D-model simulation results of a dumbbell shaped specimen at uniaxial tension shows very good correspondence with experimental data.

Abstract: In this paper concepts and behaviour of plasticity, hyperelasticity and hyperplasticity are explained and clarified. Description of hardening models and hyperplastic models is provided too. The theoretical overview presented in this paper covers the crucial prerequisite for creating and applying hyperplastic material models into practice, either for simulation purposes or for real world application.

Abstract: During the last decades, automotive industry has to meet many environmental constraints and to reduce the cost and the energy conception. Giving their mechanical properties and low manufacturing cost, thermoplastic multilayered materials have proven to be an adequate solution for such applications. In this paper, the particular combination of Thermoplastic PolyOlefin (TPO) sheets and Polypropylene (PP) foams is considered. The mechanical behavior of each material is studied and the multilayered material response is predicted and compared to measurements at a 120°C temperature. Despite the transversely isotropic behavior of the TPO sheets and the very high stretch ranges, the obtained results are very convincing and the used models proved to be very reliable.