A comprehensive fatigue life predictive model for electronically conductive adhesive joints under constant-cycle loading

This paper describes a novel fatigue life prediction methodology aimed at providing the design engineer an easy fatigue life predictive tool using experimental data for thermo-mechanical load cyclic fatigue under constant maximum load (P-max) and load ratio (R = P-min/P-max = sigma(min)/sigma(max)). This encompasses an integrated approach to joint testing, analysis and modeling. Utilizing the proposed methodologies, we aim to predict the changes in fatigue life of the adhesive, based on the whole spectrum of test variables including temperature, humidity and load ratio. 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 degrees C, 20% relative humidity, 50 degrees C, 90 degrees C and elevated humidity levels. Load-number of cycles (P-N) curves were generated using two specimen geometries at two different load ratios (R), at a cyclic frequency of 150 Hz. Using the experimental data, a life predictive methodology was developed and validated. Furthermore, the usefulness of the above-mentioned fatigue life predictive capability was extended to varying stress states.