Environmental stress cracking in polyimide composites and adhesives

High residual stresses and minimal crosslinking in some modern high performance composites and adhesives may enhance susceptibility to environmental stress cracking in the presence of organic solvents. Cross-ply laminates of several polyimide-based composite materials are subjected to various solvents and liquids which might be encountered during aircraft service conditions. Extensive matrix microcrackingis observed for several composite / liquid combinations. Unidirectional composite specimens subjected to such liquids for various exposure conditions also show strength reductions for certain combinations. Solvent resistance of a modern high performance polyimide adhesive is also determined. The most recent versions of the polyimide show improved resistance to environmental stress cracking.