Volume 7, Issue 4 (April 2010)
Variability in the Material Properties of Polymer Matrix Composites for Marine Structures
The test results from a composite material round robin manufacturing study are presented. The objective of the study was to investigate material property variability when different manufacturers were used to fabricate identical composite parts. The study was part of an ongoing Office of Naval Research project to determine the causes of material property variability of E-glass/vinyl-ester structural composites fabricated with a vacuum-assisted resin transfer molding process. The manufacturers that participated in the study consisted of five industrial composite fabricators that either had experience with U.S. naval fabrication projects or possessed commercial marine fabrication experience. The materials specified for the study were a 24 oz woven roving E-glass fabric and a rubber-toughened vinyl-ester resin system. The tests performed included constituent volume, tension, compression, in-plane shear, and flexure. The material coupon tests were performed on 5.1 mm (0.20 in.) thick cross-ply laminates in a warps parallel lay-up. A three-dimensional digital image correlation system was used to measure strain during testing to reduce the variability often experienced when using conventional foil strain gauges on heavy woven fabrics. The results of the testing indicated that compression had the most variability in both strength and modulus, which was attributed to the waviness of the fabric, while the flexural strength and tensile modulus had the least amount of variability.