Crack Arrest Fracture Toughness of 7075-T6 Aluminum Alloy

The plane-strain fracture toughness KIc represents the resistance of a material against crack initiation. The material toughness in the case of a run-arrest event involves a special “material property” called the crack arrest toughness KIa, which within certain limitations, is a measure of the ability of a material to arrest a fast running crack under linear elastic conditions. It has been indicated that KIa is a material property independent of specimen geometry, but this is not a universal belief. Whether or not KIa is a material property is still being debated. The objectives of this project were to measure the crack arrest fracture toughness of 7075-T6 aluminum alloy and to determine the effect of specimen size and thickness on KIa. The tests were performed in accordance with a proposed ASTM procedure developed for high-toughness and mediumstrength steels. Specimens that were used in this program exceeded the proposed minimum linear elastic size requirement of ferritic steel specimens by a factor of 4 between 2 and 10. KIa showed a slight dependence on test parameters such as stress intensity at crack initiation, specimen thickness, and crack jump lengths. However, KIa was not a strong function of the stress intensity at crack initiation K0. The mean value of KIa was an adequate representation of the crack arrest toughness value within the test matrix. The average KIa was only 10% lower than the average plane-strain fracture toughness KIc.