Stress concentration and fracture analysis of perforated woven composite plates

Abstract

A micromechanical three-dimensional finite element model of the single-layer unit cell of 2/2 twill weave fabric composite is established and an homogenization process is implemented. Detailed geometry of the finite element model is developed by using the ANSYS Parametric Design Language (APDL) in order to facilitate the variation of the weave and yarn configurations. Standard tensile and in-plane shear tests with modifications are performed for the 2/2 twill weave T300 carbon/epoxy woven fabric composite laminates. Satisfactory correlation between the predicted and experimental results is obtained and the finite element model of unit cell is validated. Micromechanical three-dimensional finite element models of the 2/2 twill weave woven fabric composite laminates with drilled holes and moulded-in holes are developed for the stress analysis. All the perforated laminates have a nominal size of 150 mm x 25.4 mm x 1.31 mm. Hole sizes of 3 mm, 6 mm and 9 mm diameters are chosen in the current study. In order to simulate the single-layer models as thin and relatively thick laminates, models without and with surface constraints are also analyzed. From each of the drilled hole and moulded-in hole models, the location of failure initiation for the laminate and the corresponding stress concentration factors are determined. For the drilled hole models, a fibre breakage failure criterion for predicting the ultimate tensile notched strength of fibre dominated composites is proposed. While for the moulded-in hole models, a progressive failure analysis in conjunction with a newly developed "maximum notched strength method" are also proposed to predict the failure modes and notched strengths of laminates. Standard tensile tests with modifications are performed for this particular type of woven fabric composite. The notched strengths from the proposed numerical procedure are slightly higher than the experimental results.