Theoretical and experimental analysis of the scarf joint bonded structure:Influence of the adhesive thickness on the micro-mechanical behavior

In this work, we have studied the influence of the adhesive thickness on th e micromechanical behavior of a scarf joint bonded structure loaded in unia xial tension. Adherends are made of mild steel containing 0.18% Carbon (Fre nch Standard XC 18), the adhesive is a two-component epoxy resin with a 580 0 MPa elastic modulus. The experimental method is based on strain gauge mea surements and acoustic emission. It makes it possible to determine the foll owing zones: - the areas of the joint where the start of microcracks occurs (threshold f ill); - the areas where crack propagation occurs (threshold Fg) up to the failure (threshold Fv), The experimental results confirm the good correlation betw een the different thresholds. They also show that there is an optimal adhes ive thickness close to 0.1 mm, which confers to the scarf joint the greates t resistance to microcrack initiation and crack extension. We have compared our experimental measurements with the main theories in this domain to det ermine their limits and their fields of application, particularly in the an gular singularities regions near the ends of the lap.