Accession Number : AD1015136

Title :   A Modified Constant-Stress Coupon for Enhanced Natural Crack Start during Fatigue Testing

Descriptive Note : Technical Report

Corporate Author : Defence Science and Technology Group Fishermans Bend Victoria Australia

Personal Author(s) : Waldman,Witold ; Kaye,Robert ; Yu,Xiaobo

Full Text :

Report Date : 01 May 2016

Pagination or Media Count : 111

Abstract : This report details the development of a modified constant-stress coupon for use in fatigue testing. This novel coupon design has a significantly greater surface area along the notch boundary that is subjected to the peak stress, and it is useful in studies of the probabilistic growth of in-service fatigue cracks where fatigue life is governed by the most severe defect. The extended region of uniform stress is achieved by shape optimisation of the notch boundary, resulting in the elimination of the highly-localised stress concentration that is a characteristic feature of a traditional dog-bone coupon. The presence of an extensive region of uniform stress increases the incidence of fatigue cracking from small naturally-occurring surface imperfections or discontinuities, as well as more uniformly distributing the fatigue cracking over the region of constant stress. Stress intensity factors have also been computed for simulated crack growth trajectories for edge cracks starting at various locations distributed along the notch boundary. Use of the constant-stress coupon reduces the number of coupons that need to be tested in order to attain desired statistical confidence levels, leading to significant time savings and greatly reduced costs in conducting fatigue testing programs studying the initiation and growth behaviour of small cracks.

Descriptors :   modulus of elasticity , airframes , fatigue tests (mechanics) , fatigue cracking , fatigue life , finite element analysis , fuselages , stress concentration , stress intensity factors , structural mechanics , stress analysis

Distribution Statement : APPROVED FOR PUBLIC RELEASE