THE EFFECTS AND NONDESTRUCTIVE EVALUATION OF DEFECTS IN THERMOPLASTICCOMPRESSION-LOADED COMPOSITE CYLINDERS

Measurements and predictions of the effects of voids and ply waviness on compression and interlaminar shear properties of thermoplastic-matr ix composites are presented. Correlations between ultrasonic C-scan lo ss to voids and to compression strain-to-failure are described. The da ta are drawn from a database of seventy-six cylinders and cylinder sec tions fabricated by DuPont Advanced Material Systems since 1988 using an insitu consolidation filament winding and tape laydown process. Com posites with graphite (AS-4 and IM-7) or S-2 glass fibers in polyether etherketone (PEEK) or polyetherketone-ketone (PEKK) thermoplastic matr ices are included. Property measurements are from various mechanical a nd external hydrostatic compression pressure tests on cylindrical shel ls intended for marine submersible applications and on autoclave or co mpression-molded flat panels. Performance data show the negative impac t of voids and ply waviness on mechanical properties and cylinder perf ormance. NDE data show a correlation between ultrasonic loss and void content only over a broad void content range; over the important O% to 2.0% range, no correlation is observable. Data directly relating C-sc an loss with compression strain-to-failure show a continuous loss of p erformance with increasing void content.