Thermo-Mechanical Characterization of High Impact Polystyrene Sheets Using Uniaxial Stress Relaxation Tests

Thermo-Mechanical Characterization of High Impact Polystyrene Sheets Using Uniaxial Stress Relaxation Tests

In the present study thermo-mechanical properties of high impact polystyrene (HIPS) polymer sheets near its glass transition temperature have been investigated. Its behavior is determined by using uniaxial stress relaxation tests. The tests are performed in both extrusion and transverse directions of the sheets at various temperatures and initial strain magnitudes. By dividing the time dependent relaxation modulus to the initial relaxation modulus, the time dependent stress relaxation modulus is normalized with respect to initial strain. The experimental observations showed that the stress relaxation behavior of HIPS is dependent on the initial strain magnitude and temperature. Moreover, it is found that the properties of HIPS are different at material extrusion and transverse directions such that the material stores more strain energy at transverse direction.