Problems of Fatigue Crack Growth in Strongly Anisotropic Al-Alloys

Abstract

An Al 4114 (8090 type) alloy, a material to be used in aircraft structures, is manufactured by extrusion resulting in a strongly oriented anisotropic microstructure. Fatigue crack growth (FCG) data and mechanisms affecting the FCG process are an important knowledge for an assessment of reliability and safety of structures containing crack-like defects. As a basis, FCG characteristics in the directions of extrusion and the perpendicular one are needed. The FCG properties and mechanisms in the Al 4114 alloy were investigated using CT specimens with side notches to prevent cracking in inappropriate directions caused by the anisotropy. Unlike FCG in the direction perpendicular to extrusion, when dependencies typical for Paris region of stable growth were ascertained, FCG in the extrusion direction was connected with regions of acceleration and retardation resulting in significant scatter. Crack closure measurements and fractographical analyses were performed to explain the irregularities and FCG mechanisms.

Evaluation of AA 2050-T87 Al-Li Alloy Crack Turning Behaviour

“…Developing methods for predicting when crack turning occurs during service and crack propagation behavior is essential to using high strength aluminum-lithium alloys in structural airframe components and various approaches have been presented in literature [1,2,3,4,5]. Current established design methodologies are limited to analysis of Mode I crack behavior and term failure as the point when cracks deviate from the initial fatigue crack path.…”