Safety evaluation of composites with a wrinkled fabric preform under bending

Abstract

Wrinkled fabrics in the preform exert significant influence on the qualities of resin transfer molded composites (RTMCs). The bending properties of composites with wrinkled fabrics were studied using several wrinkled models with different wrinkled lengths and numbers of fabric plies, as well as three different matrices and four different loading rates. It was found that the measured bending properties with a strong matrix are less sensitive to wrinkling than those with a weak matrix. The bending moduli of a composite with wrinkled fabric preform are larger than those of a composite with a non-wrinkled fabric preform even under the same effective fiber volume fraction ($V_{\rm f}^{\prime}$) when the composite is loaded in the middle of the wrinkled region. The bending strengths of the wrinkled models are lower in low $V_{\rm f}^{\prime}$ and higher in high $V_{\rm f}^{\prime}$ than those of a perfect sample. Also, the bending strengths indicate two failure mechanisms as a function of the ratio of the wrinkled length to the span length (L _W/L). Based on the experimental data, safe strength conditions of the wrinkled models that are better than those of a perfect sample are suggested under three-point bending.