Abstract
Fatigue crack propagation behavior in cold-rolled polycarbonate was studied under constant-amplitude loading and single peak overloading conditions. The results obtained in this experiment are summarized as follows:
(1) Cold-rolling improves the resistance of fatigue crack propagation at low ΔK levels in polycarbonate, and restrains the formation of discontinuous growth bands which are easily formed at low ΔK levels in unrolled polycarbonate.
(2) The acceleration factor of crack propagation due to a single peak overload is markedly lower in cold-rolled specimens than that in unrolled ones, and the fracture surface of acceleration region shows many fine tearing lines in cold-rolled ones in contrast to the granular markings in unrolled ones. This fact suggests that the cold-rolling restrains the craze formation at the crack tip, which causes lower acceleration.
(3) Fatigue crack propagation after a single peak overload shows the so-called delayed retardation in cold-rolled specimens, which contrasts with an undelayed retardation in unrolled ones.
(4) The maximum retardation rate after a single peak overload is lower in cold-rolled specimens than that in unrolled ones. This is considered to be due to the smaller scale of the overload-induced crack tip blunting or orientation hardening near the crack tip in cold-rolled ones.
