Effect of manufacturing process on mixed-mode fracture toughness of woven fabric composites

Abstract

Effect of manufacturing processes on delamination fracture toughness and resistance to growth of T300/934 plane weave fabric carbon/epoxy laminate was evaluated. Three manufacturing processes, namely, autoclave molding (ATM), compression molding (CM), and vacuum assisted compression molding (CMV) were used. Split edge delaminated specimens and mixed-mode bending test apparatus were used to measure delamination fracture toughness. All panels were fabricated and specimens prepared and tested under dry condition and displacement control. Mixed-mode tests for G/G,, ratios of 1/4, 1/1, 2/1, and 4/1 were conducted. Fracture tests were stable for mode-l and G,/GM > 1.0 and unstable for mode-ll and G/GM < 1/4. Average G,. for ATM composites for G/G,, loading of 1/0, 4/1, 2/1, 1/1,1/4 and 0/1 was 282.0, 336.3, 374.8, 390.5, 632.2, and 663.8-J/m2 respectively. Average G0 for CM composites for G/G,, loading of 1/0, 4/1, 2/1, 1/1, 1/4 and 0/1 was 375.5, 381.9, 439.6, 504.4, 746.1, and 933.8-J/m2 respectively. Delamination fracture toughness and resistance to delamination growth of ATM and CMV composites were nearly same for all loading conditions. However, the delamination fracture toughness of CM composite is about 14 to 40 % larger than ATM composites, due to larger resin thickness ahead of the delamination front. In both ATM and CMV, vacuum was used to remove entrapped air and any volatile gases between and within the plies, which resulted in laminated composites having nearly identical flexural modulus and delamination fracture properties.