Papers by Keyword: Cyclic Crack Propagation

Abstract: Components in jet engines are subject to time-dependent multiaxial loading. This creates a time-varying mixed-mode stress state at the crack tip. Mixed-mode loading leads to out-of-plane crack propagation and has been treated in previous articles [1,2]. This paper concentrates on coping with the time-dependent character. Key issues are the crack propagation rate and the crack propagation direction in three-dimensional space. In order to determine the prevalent crack propagation direction the dominant loading case is determined based on its crack propagation rate. Then, a mixed-mode equivalent K-factor is calculated for all other loading cases based on the closeness of their associated crack propagation direction with the dominant one. Subsequently, a cycle extraction is performed on the crack propagation rate for all loading cases. The extracted cycles are processed based on their mimimum and maximum equivalent K-factor and the maximum temperature. The mission crack propagation rate consists of the sum of the rate of all extracted cycles.

Abstract: In recent years, increased loading and low weight requirements have led to the need for automatic crack tracing software. At MTU a purely hexahedral code has been developed in the nineties for Mode-I applications. It has been used extensively for all kinds of components and has proven to be very flexible and reliable. Nevertheless, in transition regions between complex components curved cracks have been observed, necessitating the development of mixed-mode software. Due to the curvature of the crack faces, purely hexahedral meshes are not feasible, and therefore a mixture of hexahedral elements at the crack tip, combined with tetrahedral in the remaining structure has been selected. The intention of the present paper is to compare both methods and to point out the strength and weaknesses of each regarding accuracy, complexity, flexibility and computing time. Furthermore, difficulties arising from the out-of-plane growth of the crack such as the determination of the crack propagation direction are discussed.