Fatigue Life Evaluation of the A-7E Arresting Gear Hook Shank

This paper describes a program conducted to develop criteria, based on test results, to safely extend the service life of the A-7E arresting gear hook shank. Fracture mechanics techniques provided a method for assessing the significance of proof testing and correlating proof loads with remaining life under operating loads. Additional tests were performed to validate the proof-test criteria. The proof load developed in this program defined the maximum possible flaw size that could exist in the structure and provided data for establishing remaining life under operating loads. In addition, local yielding resulted in residual stresses that maximized crack growth retardation. As a result, an increase in fatigue life was produced by periodically inserting the proof load into the operating load spectrum. The primary impact of this program was to demonstrate that the proof test interval for the hook shank could be extended from 100 to 550 arrested landing cycles, and that the total service life could be extended from 500 to an indeterminate number of arrestments.