Implementation of Hyperelastic Models for Soft Tissues in FE Program and Identification of their Parameters

J. Bursa, P. Skacel, M. Zemanek (Czech Republic), and D. Kreuter (Germany)


Hyperelasticity, strain energy density, material identification, soft tissues, biaxial tension tests.


Stress-strain behaviour of soft tissues (e.g. arterial walls) is often modelled as pseudoelastic (hyperelastic), i.e. described using various shapes of strain energy density functions, either isotropic or anisotropic ones. Computational modelling of bodies, created of soft tissues, requires solutions to two basic partial problems: Implementation of formulas for calculation of strain energy density into a FE program system; we implemented some isotropic and anisotropic exponential constitutive models in program system ANSYS as user defïned models. Realization of tests under multiaxial stress conditions for identification of parameters of the particular constitutive models. We designed and produced a machine for biaxial testing of hyperelastic materials. This equipment enables us not only uniaxial or equibiaxial tension tests, but also any other biaxial tension tests with independent control of displacement rates in both perpendicular directions. The paper presents the design of the biaxial test rig and an identification of parameters of selected hyperelastic models, based on experimental results of various types of biaxial tension tests carried out with porcine thoracic aortas. Approximations of experimental curves by some particular constitutive models are compared with experimental results. The new constitutive models implemented in ANSYS program system have been verified by calculation of stresses in a two-layer artery model published in [1].

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