Advances in Fatigue Test Technology

The report summarizes work directed at the verification of currently used compliance relationships for the wedge-open-loading (WOL) specimen geometry frequently used in fatigue crack propagation testing. An overview is given of compliance curve fitting procedures. A new procedure is proposed which appears to offer significant advantages. Compliance calibration results are presented for Ti-6Al-4V(RA) and Ti-6Al-4V(Beta) alloys. Analytical procedures for obtaining the stress intensity calibration function (C sub 3) from experimental compliance results were compared and the proposed three parameter fit was found to be superior. The advantages of this proposed data analysis procedure are: small numbers of constants, relationship between normalized compliance (compliance x modulus x thickness) and normalized crack length (crack length/specimen width) is differentiable and invertible, consistency with physical reasoning, and discussion of possible differences in compliance due to material differences can be restricted to a single parameter.