DYE PENETRANT INDUCED MICROCRACKING IN HIGH-PERFORMANCE THERMOPLASTICPOLYIMIDE COMPOSITES

The possibility of spurious microcracking in three high performance th ermoplastic polyimide composite materials due to zinc iodine dye penet rant was studied. The material systems were IM7/LaRC(TM)-IAX, IM7/LaRC (TM)-IAX2, and IM7/LaRC(TM)-8515. Specimens from each material system were subjected to one of three immersion tests. The first immersion te st involved soaking composite specimens previously prepared with diffe rent polishing techniques in dye penetrant. In the second test, specim ens were soaked in the individual components of the dye penetrant. The final test involved soaking the specimens in one of six immersion liq uids followed by soaking in dye penetrant. Results showed that the com posite materials have sufficiently high thermal residual stresses to d rive microcracking in the presence of dye penetrant without external m echanical loading. There was no evidence that the different polishing techniques had an effect on dye penetrant induced stress cracking. The individual components of the dye penetrant did not produce microcrack s in the composites. Some combination of the components must be presen t to induce microcracking. Observations also revealed that polishing h ad an effect on the microcracking process of the composites that were initially soaked in immersion liquids then dye penetrant.