The effects of process parameters on the properties of resin transfer molded composites
A series of composite panels were fabricated by resin transfer molding (RTM), varying materials and process conditions. Reinforcements used included a fiberglass woven material, and AS-4 carbon in both sized and unsized plain weave fabrics. Vinyl ester, epoxy, and cyanate ester resins were pressure injected into these fabrics. The epoxy panels were processed with varying injection temperatures and pressures.
A density-based technique was used to measure the fiber volume fraction and void content of the composite panels. Optical photomicrographs were used to verify the accuracy of the void calculations. Mechanical tests included compression strength, inplane and interlaminar shear strengths, and impact. Compression after impact tests were performed and compared to undamaged compression strengths.
The compression, inplane shear, and interlaminar shear strengths of the epoxy composites were higher than the vinyl ester composites. Similarly, cyanate ester systems with similar reinforcements outperformed the epoxy composites in these tests. In impact testing, the graphite fabric/ epoxy resin composite retained the lowest portion of original strength after impact. The cyante esters retained the most strength, but vinyl ester composites suffered less damage. Vinyl ester composites made with unsized carbon fibers performed better in interlaminar shear, and in impact tests, than those with sized fibers. The variation of injection temperature had little effect on either void content or strength of the epoxy composites. Increases in injection pressure did produce a higher void content in epoxy laminates, but no significant change in strength was observed.