The Effects and Non-Destructive Evaluation of Defects in Thermoplastic Compression-Loaded Composite Cylinders

Abstract

Measurements and predictions of the effects of voids and ply waviness on compression and interlaminar shear properties of thermoplasticmatrix composites are presented. Correlations between ultrasonic Cscan loss to voids and to compression strain-to-failure are described. The data are drawn from a database of seventy-six cylinders and cylinder sections fabricated by Du Pont Advanced Material Systems since 1988 using an insitu consolidation filament winding and tape laydown process. Composites with graphite (AS-4 and IM-7) or S-2 glass fibers in polyetheretherketone (PEEK) or polyetherketone ketone (PEKK) thermoplastic matrices are included. Property measurements are from various mechanical and external hydrostatic compression pressure tests on cylindrical shells intended for marine submersible applications and on autoclave or compressionmolded flat panels. Performance data show the negative impact of voids and ply waviness on mechanical properties and cylinder performance. NDE data show a correlation between ultrasonic loss and void content only over a broad void content range; over the important 0% to 2.0% range, no correlation is observable. Data directly relating C-scan loss with compression strain-to-failure show a continuous loss of performance with increasing void content.