Multi-scale Intrinsic Flaws in Composite Materials

Abstract

In the present, the intrinsic flaw concept introduced by Waddoups is extended to determination of the intrinsic flaw length in the 10-degree off-axis specimen. The intrinsic flaw will be defined as a fracture mechanics-type planar crack. The experimental testing procedures for fabricating, testing and examining the off-axis specimen are overviewed. A fracture mechanics-based methodology is introduced for calculation of the intrinsic flaw length. The intrinsic flaw length on the homogeneous scale and on the micromechanical scale will be determined and compared for unnotched (no hole) specimens and specimens containing a circular-hole. Variation in fiber volume fraction influences the micromechanical stress field; hence the effect of fiber volume fraction variation on the intrinsic flaw length is determined through a multi-scale, integrated computational approach. The effect of the spatial variation in fiber volume fraction, as observed in micrographs of the free-edge, is discussed. The intrinsic flaw lengths on the homogeneous and micromechanical scales, with and without fiber volume fraction variation are compared. The approach not only quantifies the length scale of critical flaws on multiple-scales but demonstrates an approach for treating the stochastic variation in fiber volume fraction.