Time to Failure Testing in Shear of Wood–Adhesive Bonds under Elevated Temperatures

At present, the evaluation of wood–adhesive bonds lacks a method that is able to predict the long-term load carrying capacity in shear of a bond in a comparatively short testing time. For this reason, a new test approach was investigated to determine the time to failure of wood–adhesive bonds. In our research, lap joint specimens were prepared with a melamineurea- formaldehyde (MUF) adhesive at two mixing ratios (100/100 and 100/20 [resin/hardener]). The specimens were subjected to tensile shear stresses at load levels between 30 and 90 percent of their mean wet short-term strength while being immersed in water at temperatures of 608C and 908C. The time to failure and the wood failure percentage were determined. The analysis showed good correlations between time to failure and load level as well as between time to failure and temperature. The adhesive mixing ratio, however, showed no influence on the failure characteristics. The wood failure percentage highly depended on the test duration. With prolonged test duration, the mode of failure increasingly changed from wood failure to adhesion failure. Overall, the test method proved to be promising for a detailed performance evaluation of wood–adhesive bonds.