Theoretical Method to Predict the First Microcracks in a Scarf Joint

Abstract

ABSTRACT In this work, we have calculated the theoretical threshold (F d) of the first microcracks in the scarf joint. This threshold is particularly important because it marks the end of the elastic behavior of the bonded structure. At this point, the mechanical behavior of the adhesive is nonlinear and becomes dependent on the type of loading applied (dynamic tests, fatigue). Our method takes into account the geometrical variations of the joint as the scarf angle varies. We have used and adapted to our study a theoretical model based on the asymptotic-expansion method. The comparison between the theoretical values and the experimental thresholds determined by strain gauges and acoustic-emission techniques showed that the model accurately forecasts the microcracking of the joint provided that the scarf-angle value is more than 10°. When α is smaller than 10°, the theoretical model can no longer predict the very complex micromechanical behavior at the extremities of the joint, where the sharp ends of the adhesive layer and the metallic adherends coexist and react among themselves.