Study on the interaction of fatigue crack propagation in hybrid bodies.

Abstract

Interaction of crack growth in hybrid bodies subjected to cyclic loading is investigated using the coupled compact tension specimens model. Coupled CT specimens of 0.45% C steel, JIS S45C and aluminium alloy, A2017-T4, individually precracked to their initial lengths are loaded by common pins in the grip of a fatigue machine. The crack propagation behaviour of coupled specimens fatigued under a stress ratio of 0.05 is compared with that of a single specimen. It is found experimentally that crack growth rate of one of the coupled specimens is accelerated by the plasticity induced crack closure of another specimen. This behaviour is affected by the difference in residual plastic stretch on the crack wall in each specimen. An interaction curve for coupled hybrid specimens is theoretically predicted, and the interaction law is discussed. It is concluded that multiple ended fatigue cracks may propagate with a mechanism such that the increment of total energy release rate in a hybrid body is distributed to each crack with the ratio of the strain constraint factor.