THE EVALUATION OF LOW-TEMPERATURE ALTERNATE CURE CYCLES FOR 121 deg C (250 deg F)-CURING EPOXY STRUCTURAL FILM ADHESIVES

摘要

Low-temperature cure cycles for adhesively bonded repairs of metallic structure are advantageous for a number of reasons. On-component bonded repairs routinely encounter temperature limitations due to safety considerations and the presence of vulnerable materials or systems in the repair vicinity, such as elastomers and wiring. Reduced cure temperatures decrease thermal residual stresses in aircraft components due to the mismatch in coefficient of thermal expansion between dissimilar materials when performing bonded repairs. Cure temperatures below 100 deg C (212 deg F) also reduce the risk of damaging honeycomb core structures due to entrapped moisture. Aircraft maintainers require a capability to cure several epoxy adhesives lower than the 121 deg C (250 deg F) recommended by the manufacturers. Cytec Engineered Materials' FM~R 73M, 3M~(TM) Company's AF 163-2M, Henkel Products Hysol~R EA 9628 and Hysol EA 9696 adhesives were evaluated using 93 deg C (200 deg F) and 82 deg C (180 deg F) cures. Cure times were established via differential scanning calorimetry to define curing parameters at 93 deg C (200 deg F) and 82 deg C (180 deg F). Tensile lap shear, floating roller peel, and climbing drum peel tests were used to evaluate the corresponding bond strengths. Results obtained in this study proved curing the adhesives at 93 deg C (200 deg F) and 82 deg C (180 deg F) for longer periods of time was feasible but led to reduced mechanical properties.