The Effect of Thermal Aging on the Failure Behavior of Adhesive- Bonded Single-Lap Joints

The effects of thermal aging on the failure behavior of single-lap bonded joint composites were investigated experimentally. The single-lap bonded joints specimens were made of [0]₈ layered woven glass fiber/epoxy composite plates joined together by adhesive. Two different thermal aging processes were applied to adhesive- bonded single-lap joints specimens. In the first process, temperatures of 75, 100, and 150°C were applied during the aging time of 4 h. In the second process, a constant temperature of 150°C was applied for aging times of 2, 4, and 8 h. Additionally, this study was carried out in a temperature-controlled oven, without considering humidity, using three different adhesive thicknesses (0.2, 0.4, and 0.6 mm) and three different overlap lengths (15, 30, and 45 mm). After the thermal aging process, the specimens were subjected to a tensile test to determine the failure loads. Furthermore, the hardness values of both the adhesive and the composite plate were investigated under the conditions of 4 h at 150°C. The failure loads and microstructural changes determined were compared with the results for control specimens kept at room temperature (25°C). It was found that the increase in hardness values positively affected the strength of both the adhesive and the composite. With increasing the thermal aging time, temperature, and overlap length, the failure loads increased by 8.4 to 79.1%, 14.4 to 79.1%, and 9.5 to 50.9%, respectively. However, an increasing the adhesive thickness resulted in a decreasing the failure loads by 4.6 to 23.8%.