ABSTRACT
In an effort to obtain fracture toughness parameters for a predictive scheme to estimate the remaining life of a bonded joint, double cantilever beam, end notch flexure and crack lap shear tests were performed to obtain the Mode I, Mode II, and mixed mode strain energy release rates, respectively. Testing was performed at room temperature on Ti-6A1–4V titanium joints bonded with an adhesive (FM®x5) based on a polyimide developed at the NASA-Langley Research Center (LaRC™-PETI-5). To enhance the durability of the joints, a Sol Gel chemical pretreatment process was performed on the surface of the titanium adherends. Specimens cut from a bonded sheet were tested in the as-received state, as well as isothermally exposed for 5,000 hours at 177°C, and isothermally exposed to a hot/wet environment (80°C, 90%+ relative humidity). Isothermal exposure at I77°C reduced the fracture toughness of the bonded joints, however environmental exposure to the hot/wet condition was most detrimental.
