TENSILE PROPERTIES AND PLANE-STRESS FRACTURE-TOUGHNESS OF THIN-FILM AEROSPACE ADHESIVES

Tensile and Mode I plane-stress fracture toughness tests were performe d at room temperature on three film-type aerospace adhesives, two epox ies and one polyimide. Specimens were cut from cured sheets. Tensile m odulus, strength, failure strain, and fracture toughness Values were o btained for supported versions of the epoxy films which contained a no n-woven carrier (''scrim'') cloth and for the polyimide which containe d a woven carrier cloth. The same tensile and fracture properties were obtained for unsupported versions of the epoxies and for the supporte d polyimide subjected to thermal cycling or isothermal exposure. The p olyimide adhesive displayed a higher tensile strength and fracture tou ghness than the epoxy adhesives. Isothermal exposure for 5,000 hours t o a hot/wet (71 degrees C [160 degrees F], > 90% relative humidity [rh ]) environment was the most detrimental condition for all of the adhes ives. The presence of a scrim cloth reduced many of the tensile and fr acture properties of the epoxy adhesives.