Experimental Study of Fretting Crack Nucleation in Aerospace Alloys with Emphasis on Life Prediction

Abstract

A statistically-designed experimental program engendered to validate an analytical approach for the prediction of fretting crack nucleation in 2024-T351 aluminum alloy has been completed. The test results indicate that the near-surface cyclic contact stress and strain field can be juxtaposed with a multiaxial fatigue life parameter relying on uniaxial strain-life constants to predict crack nucleation for a wide range of load intensities and conditions representative of those experienced in riveted joints. With this approach validated, efforts have been initiated to predict fretting-induced fatigue failures in riveted single lap joint structures. Research was targeted at characterizing the conditions at and around the rivet/hole interface, including finite element modeling of both the mechanics of load transfer in riveted joints and the residual stress field introduced during the rivet installation process. Model results and an ancillary set of fatigue tests of single lap joint test articles have identified a strong correlation among riveting process parameters, the mechanics of load transfer, and the subsequent tribological and fatigue degradation of the joints. Final comments are offered regarding the ability of this integrated approach to predict the fatigue performance of riveted lap joint structures.