Development and Validation of the Instrumented Traveling Wedge Test for Mode I Fracture of Adhesively Bonded PMCs

Abstract

To date, methods for characterizing bondlines in adhesively bonded polymer matrix composites (PMCs) have relied on adapting tests for bonded metals or tape laminate composites. These test methods have not been accepted as standard due to the lack of quantitative information connecting the observed bondline failure (e.g., fracture growth), the specimen geometry, and applied loading. The ITW test method is a mode I fracture test designed to characterize long (>150 mm) adhesive bondlines between PMC adherends. In this work, the ITW test is further developed to allow for the extraction of fracture toughness using a J-integral approach. It is then validated by comparing ITW results to those obtained using a traditional DCB configuration where the loading is applied via hinges. In both cases, J-integral data reduction was used. Close agreement between the ITW and DCB test results suggests the ITW test is equivalent to the DCB method. Additionally, the ITW’s ability to detect bondline variability was assessed by testing specimens manufactured with variable bondline toughness. Gradual changes in bond toughness were introduced by tapering the adhesive thickness along the specimen bondline. Dramatic changes in bond toughness were produced by using two adhesives with noticeably different fracture toughness in the same bondline. The ITW was shown to be capable of detecting subtle and dramatic changes in bondline toughness.