Oscillatorymechanical spectrometer tests were performed
for HDPE at four temperatures ranging from 160 ◦C to 210◦C to obtain the necessary KBK-Z and WLF non-isothermal material
constants for the numerical simulation runs. These constants
are essentially the relaxation times k and relaxation modulus
coefficients gk at the reference temperature T0. To determine
the material constants at other temperatures than T0, the WLF
equation provides a shift factor 21 given by