A novel cumulative fatigue damage model for electronically-conductive adhesive joints under variable loading

Abstract

This paper describes a novel cumulative fatigue damage life predictive model aimed at providing the design engineer an easy fatigue life predictive tool using experimental data. This encompasses an integrated approach of joint testing, analysis, and modeling. For this purpose, joints were prepared using stainless steel adherend specimens and a commercial silver-filled electronically conductive adhesive, and tested under monotonic and cyclic fatigue conditions, at 28°C, 20% relative humidity. Load–number of cycles (P–N) curves were generated for these specimens using load ratio R = 0.1 and R = 0.5 (R = P min/P max = σmin/σmax) at a cyclic frequency of 150 Hz. Fatigue life and failure behaviors due to cumulative fatigue damage were assessed using a novel experimental program. Experimental results revealed that most of the fatigue damage occurs during the latter part of the fatigue process and the combination of lower load ratio and higher maximum applied load has the most detrimental effect on the failure of the joint. Finally, a novel analytical model for fatigue life prediction under variable cyclic conditions was proposed using experimental data and a detailed stress analysis.