Modeling of the nonlinear viscoelasticity of polyoxymethylene in tension and compression

An optical measurement technique was used to measure the axial and transverse strain of polyoxymethylene in various uniaxial tensile and compressive loadings. The 3d nonlinear viscoelastic model of Schapery was chosen to describe the time-dependent mechanical behavior. The model equation is solved using a recursive technique, which is used in a nonlinear optimization algorithm to identify model parameters by fitting experimental data. It is shown that the Schapery model is capable of describing the nonlinear viscoelastic relaxation behavior in tension and compression. Furthermore, it is verified that the model determined using stress relaxation data can accurately predict the response to creep and cyclic stress histories. A bending stress relaxation test serves as an exemplary test of a structure with simultaneously occurring compressive and tensile stresses. The model is used in a finite-element simulation of this test to demonstrate its performance in this more complex application.