Volume 26, Issue 3 (May 1998)
Evaluation of the Fracture Toughness of the Deep-Carburized Layer
The composite nature of case-hardened materials, meaning the existence of the gradients of microstructure, toughness, and residual stresses, ensures that the fracture in the case layer is quite different from that of homogeneous materials. In this paper a new method to evaluate the fracture toughness of the deep-carburized layer is discussed. This method uses the “pop-in” phenomenon that happens when the crack propagates through the carburized layer. The results show that the “pop-in” phenomenon is caused by the gradient distribution of the fracture toughness, the microstructure, and the residual stresses in the carburized layer. The KIC-X (distance from notch) distribution curve calculated from the load and the crack length at the “pop-in” point is the basis for the evaluation of the fracture toughness.