Modeling the behaviour of polymeric materials under uniaxial and multiaxial cyclic loadings

The aim of this PhD thesis is to model the mechanical behaviours of polymeric materials subjected to not only monotonic loadings, but also cyclic loadings. Viscoplasticity theory (VBO) based on the concept of overstress is used as the material model. The material used in the modeling, especially commonly used in the field of biomechanics (prosthesis applications), is ultra-high-molecular-weight polyethylene (UHMWPE). UHMWPE has been widely used as knee and hip prosthesis material under the cyclic loading. Defining the mechanical properties and modeling the material behaviours of UHMWPE are very important in design of prosthesis. In this study, the ratcheting observed the cause of failure in polymeric material under the cyclic loading is investigated. Observing that the present VBO model cannot model the ratcheting perfectly, theory of viscoplasticity was modified. Numerical results were compared with experimental results.