Tensile Properties and Plane-Stress Fracture Toughness of Thin Film Aerospace Adhesives

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Abstract
Tensile and Mode I plane-stress fracture toughness tests were performed at room temperature on three film-type aerospace adhesives, two epoxies and one polyimide. Specimens were cut from cured sheets. Tensile modulus, strength, failure strain, and fracture toughness values were obtained for supported versions of the epoxy films which contained a non-woven carrier (“scrim”) cloth and for the polyimide which contained a woven carrier cloth. The same tensile and fracture properties were obtained for unsupported versions of the epoxies and for the supported polyimide subjected to thermal cycling or isothermal exposure. The polyimide adhesive displayed a higher tensile strength and fracture toughness than the epoxy adhesives. Isothermal exposure for 5,000 hours to a hot/wet (71°C [160°F], > 90% relative humidity [rh]) environment was the most detrimental condition for all of the adhesives. The presence of a scrim cloth reduced many of the tensile and fracture properties of the epoxy adhesives.