Strength and failure energy for adhesive interfaces as a function of loading rate

Abstract

Adhesives are used to bond different materials to resist impact and penetration. This adhesive bond layer is a frequent source of failure when subjected to impact loadings. Therefore, it is necessary to measure the cohesive strength and failure behavior, especially at high loading rates. Experimental methods are limited in characterizing the mechanical behavior of adhesive bonds at high loading rate, so a unique experimental method and a specimen geometry was developed to determine the effect of loading rate on the failure (Mode I) of a commercially available adhesive (EPON 828). Four-point bend specimens consisting of two aluminum "wings" bonded together with the adhesive were tested at different loading rates, from quasi-static to high-rate. The high rate loading was performed using a unique modified Split-Hopkinson Pressure Bar (SHPB) setup. Embedded quartz transducers at the loading interfaces were used to measure the applied loads at both sides of the bar-specimen interfaces, which helped to optimize the input stress waves using wave-shapers to conduct valid dynamic experiments. Digital image correlation (DIC) method was used as an optical crack opening displacement (COD) gage to measure the onset of crack opening velocity (COV) to determine the failure initiation point on the load-displacement trace. The experimental results are used to obtain the energy required to initiate failure at different rates of loading. In this paper, the experimental methodology is presented, along with the results from these experiments. These data are being used to develop computational simulation methodologies to investigate the failure of bonded structures during dynamic impact loading. They will also be used to compare potential adhesives in determining the most qualified adhesive for various applications under different environmental conditions as well as different surface morphologies.