Dye Penetrant Induced Micro cracking in High Performance Thermoplastic Polyimide Composites

Abstract

The possibility of spurious microcracking in three high performance thermoplastic polyimide composite materials due to zinc iodine dye penetrant 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 test involved soaking composite specimens previously prepared with different polishing techniques in dye penetrant. In the second test, specimens were soaked in the individual components of the dye penetrant. The final test involved soaking the specimens in one of six immersion liquids followed by soaking in dye penetrant. Results showed that the composite materials have sufficiently high thermal residual stresses to drive microcracking in the presence of dye penetrant without external mechanical 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 microcracks in the composites. Some combination of the components must be present to induce microcracking. Observations also revealed that polishing had an effect on the microcracking process of the composites that were initially soaked in immersion liquids then dye penetrant.