Tensile properties of notched non-crimp fabric VaRTM composites

Abstract

Tensile strength and damage behaviors are investigated for non-crimp fabric VaRTM CFRP composites, which are being applied to aircraft structures, containing stress concentrations such as notch and open-hole, and are compared to that of conventional prepreg/autoclave CFRP laminates. Notched strength normalized by unnotched strength of the VaRTM composites has been found to be comparable to the prepreg laminates, though with some variation. Damage aspect has been also observed to be different from the damage mode in the prepreg laminates. Effects of stitches used in the non-crimp fabric on the notched strength and damage behavior are evaluated. Resin rich region and porosities are found to be existing around the stitch sites, and it is considered that damage onset stress is dependent on the positional relation between the stich sites and the notch tip. In addition, the non-uniform ply thickness and laminate condition, and instability of damage modes in the plates caused by the stiches have been found to result in the variation in their notched strength. Furthermore, point stress criterion that has been used to predict the notched strength of conventional prepreg laminates is applied to the VaRTM composites. It has been confirmed that the criterion is valid for the VaRTM composites to predict their notched strength using same characteristic length as of the prepreg laminates without any modification. © 2012 The Society of Materials Science, Japan.