Accelerated aging versus realistic aging in aerospace composite materials. I. The chemistry of thermal aging in a low‐temperature‐cure epoxy composite

Samples of an aerospace‐grade epoxy composite (M20/IM7) are subject to long‐term (∼ 1 year) thermal aging at temperatures of 70°C, 120°C, 170°C, and 200°C (in air) and the changes to the chemical and physicochemical structure of the composite are analyzed by a range of different techniques, including gravimetric analysis, FTIR, DSC, and DMA to compare the effects of different severities of degradation treatment. The results show that at the lower temperatures, the oxidative degradation changes are very selective for chemical defect groups, particularly near the sample surfaces. However, at the higher temperatures, combinations of further cure reactions and generalized oxidative degradation changes (again from the surface inwards) make for a highly complex ageing pattern for this particular composite material.