Effect of Strain Rate on Adhesively Bonded Lap Joints with Similar and Dissimilar Adherends

Abstract

Adhesively bonded joints provide several benefits, such as uniform stress distribution than conventional methods such as mechanical fastening. Hence, the knowledge of stresses inside the adhesive layer of an adhesively-bonded joint is essential for design analysis and joint strength prediction. In this thesis, the effect of strain rate on adhesively bonded single lap joints of similar and dissimilar adherends (Aluminum and Carbon fiber composites) with a number of adhesives was investigated. The experiments were conducted based on three different sets of substrate combinations that included 1) Al6061 –Al6061, 2) Al6061–CFRP and, 3) CFRP-CFRP using three different adhesives that included a high strength epoxy, a quick set epoxy, and a urethane-based adhesive. The manufactured single lap joints were initially tested under tensile loading conditions using a screw-driven universal tensile machine to achieve strain rates of 0.0015 s-1 and 0.15 s-1. Furthermore, these joints were subjected to dynamic loading conditions at strain rates of 15 s-1 and 150 s-1 on a servo-hydraulic universal testing machine. Here, the bond strength and peak loads were determined. Furthermore, using the digital image correlation (DIC) system, the local and global strain distributions were investigated within the adhesive bond line. Finally, low magnification and optical microscopy analyses were conducted to identify the resulting failure modes. Initial results revealed a clear effect of strain rate on the peak load and shear lap strength. In addition, DIC analysis revealed evidence of strain concentrations at the lap ends as well as major strain distributions within the bond line. Furthermore, a combination of adhesive and cohesive failure modes was evident after low magnification analysis. Finally, it is clear that these results can be utilized for comparative analysis and design purposes of adhesive joints of similar and dissimilar materials that may be subjected to various strain rates.