A design of experiments assessment of moisture content in uncured adhesive on static strength of adhesive-bonded galvanized SAE1006 steel

Abstract As part of a cooperative research program to develop and implement crash-resistant toughened adhesives targeted for future vehicles, this paper summarizes a study of the influence of pre-exposure of uncured adhesive and steel sheets in a humid and elevated temperature environment on quasi-static strength of bonded hot dipped galvanized SAE1006 steel joints. In this study, we use a DOE (design-of-experiment) program called DEXPERT to design the experiment and to analyze the effects of exposure temperature, exposure time, curing temperature and curing time on joint strength of adhesive-bonded galvanized SAE1006 steel. Prior to adhesive curing, the adhesive and galvanized steel coupons were pre-exposed to various relative humidity levels and temperatures. The experimental results were then analyzed by DEXPERT and the relative contributions of each factor on variance in joint strength were calculated. It was found that curing temperature is the most influential factor affecting the strength of adhesive-bonded galvanized SAE1006 steel joints. The curing of a joint at 180 °C can increase the robustness of the process and provides the greatest strength regardless of the variation of other factors. The joint strength curing at 150 °C shows a strong sensitivity to the curing time, while the adhesive cannot cure at 130 °C at all under all conditions. It has also been found that the pre-exposure of adhesive and steel for an hour can slightly decrease the joint strength at high temperature and humidity. Therefore, the effect of long time exposure of the uncured adhesive and steel still needs to be further investigated.