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 Δ
K levels in polycarbonate, and restrains the formation of discontinuous growth bands which are easily formed at low Δ
K 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.
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