Main Surface Crack Propagation and Crack Initiation and Propagation on Counter Surface under Cyclic Bending

Abstract

Cyclic bending is a dominant loading mode in structures sustaining thermal loads. Numerical analysis was performed for the evaluation of the main elliptical crack propagation and crack initiation and propagation on the counter surface under cyclic out-of-plane bending. Inelastic three-dimensional finite element analyses were conducted taking crack opening and closure into account. When the front surface is in tension, the main crack opens and the compressive strain on the counter surface increases. Thus, deeper the main crack, larger the total strain range on the counter surface and this stimulates crack initiation on the counter surface. As the main crack propagates, the J-integral range at the deepest point decreases for deeper than 40% of the plate thickness. These numerical results explain the previous cyclic bending test results; a crack initiates and propagates on the counter surface and meets the main crack near 1/3 of the plate thickness of the specimen while the main crack grows. The J-integral range of the counter surface crack increase rapidly and becomes larger than that of the main crack. The calculated crack propagation rates in both longitudinal and depth directions of the main and the counter surface cracks based on the J-integral ranges were close to the experimental ones.