Kenichi Yoshioka

Modeling of tensile fatigue damage in resin transfer molded woven carbon fabric composites

Abstract Tension–tension fatigue tests were performed on fabric-based composites processed using resin transfer molding. The composite systems consisted of epoxy and phenolic matrices reinforced with plain weave carbon fabric. The residual strength of open-hole laminates was also investigated for various numbers of fatigue cycles. The results based on the fatigue tests and microscopic observations suggested that considerable damage growth occurred in the early stages of fatigue. In order to examine the property deterioration of the laminates due to the fatigue damage, low frequency cyclic loading tests were carried out, while modulus measurements were performed in situ. Quantitative data were obtained, displaying the reduction in modulus for each material system. Finally, a model to predict the modulus deterioration based on a combination of the crimp model and the shear-lag model was developed. Good agreement between the predictions and the experimental results supported the model, which showed the quantitative effects of transverse cracking and debonding between the yarns on the laminate modulus.

Multiscale approach to predict crack initiation in unidirectional off-axis laminates

Crack initiation in unidirectional off-axis laminates made of carbon fiber and epoxy resin is predicted based on multiscale modeling. This multiscale modeling consists of two finite-element analyses (FEA) on different scales. One is macroscopic FEA, based on the assumption of homogeneous materials, and the other is microscopic periodic unit-cell (PUC) analysis using a micromechanical model. The macroscopic FEA is performed by applying uniaxial tension to off-axis laminates, in which we employ an anisotropic elasto-plastic constitutive law to obtain accurate deformation fields in laminates. In the microscopic PUC analysis, the strain history at a point in laminates obtained from the macroscopic FEA is applied as external forces, and crack initiation is predicted using two failure criteria for the matrix resin. The first is the dilatational energy density criterion under elastic deformation, and the second is a ductile damage growth law under plastic deformation. The simulated predictions are compared with the experiments results.