| Description |
The use of adhesively bonded composite joints is increasing in many industries, including the aerospace industry. As a result, there is increasing interest in using coupon- level testing to assess the performance of adhesives and surface preparation procedures for use in composite bonded joints. This investigation focused on the development of coupon- level test methods to evaluate the environmental durability of adhesively bonded composites. Three candidate test methods were investigated: the static wedge test, the back-bonded double cantilever beam test, and the traveling wedge test. The static wedge test, previously standardized for use with metal adherends, was modified to address complications resulting from variable flexural rigidities of the composite adherends. The back-bonded double cantilever beam test uses thin adhesively-bonded composite adherends that are moisture saturated prior to secondary bonding to composite doublers to produce the desired double cantilever beam specimen thickness. In the traveling wedge test, a metal wedge is attached to the crosshead of a test machine and driven through the adhesive bondline of the test specimen under a constant displacement rate. An attractive feature of the traveling wedge test is the increased bond area that can be assessed. Additionally, methods were investigated for estimating the adhesive bondline fracture toughness using the three candidate test methods. Fracture toughness values obtained using each test method were compared to those from conventional double cantilever beam testing. Finally, several different composite adherend surface preparation iv methods were used to evaluate the capabilities of each candidate test method to assess the performance of adhesively bonded joints under environmental conditions as well as to investigate environmental durability. |
