STUDY ON UNIAXIAL RATCHETING OF POLYCARBONATE

Observations are reported in uniaxial cyclic tests (strain-controlled cyclic programs and asymmetrical stress-controlled cyclic programs) on polycarbonate (PC) at room temperature and ambient moisture. The cyclic deformation behaviors of PC are discussed under different loading levels, loading histories, stress rates, and peak stress holds. It can be found that PC shows a slight cyclic softening, and exhibits obvious ratcheting during the stress-controlled cyclic loading with non-zero mean stress. Ratcheting strain increases with the increases of mean stress and stress amplitude, but the effect of the mean stress on the ratcheting is much higher than that of stress amplitude. Loading history has an obvious effect on the ratcheting, but has little effect on the cyclic softening presented in the strain-controlled cyclic tests. The ratcheting strain of PC increases when the stress rate decreases or peak stress hold time increases, which shows a pronounced time-dependence of ratcheting.