The University of Tokyo

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A damage mechanics analysis was used to derive the energy release rate associated with matrix cracking and average stress of cracked plies. Matrix crack density as function of laminate stress was predicted based on both energy and average stress criteria. Laminate strain increment caused by matrix cracking was also derived as a function of applied laminate stress and matrix crack density, and the relation between laminate stress and strain could be predicted considering matrix cracking.Microscopic damage progress under static tensile loading was observed to study the effect of matrix resin, stacking sequence and temperature, experimentally. The analytical prediction of matrix crack behavior and the relation between laminate stress and strain were compared with the experimental results obtained. Analytical predictions for matrix crack behavior were in good agreement with experimental results. However, analytical prediction underestimated the laminate stress, because strain increment associated with matrix crack opening displacement is overestimated in this analysis. An advantage of the present predictive method is that it can be applied to laminates with arbitrary stacking sequences.Microscopic damage progress behavior in quasi-isotropic CFRP laminates under fatigue tensile loading was also observed. The effect of stacking sequence on microscopic damages was investigated. Damage mechanics analysis was used to derive the energy release rate associated with matrix cracking. Matrix cracking behavior was modeled using modified Paris-law approach.Microscopic damage progress in cross-ply laminates under thermal fatigue loading was also investigated. Matrix cracks initiated in both O° and 90° plies and the number of cracks increased as the number of cycles increased. It was found that modified Paris law approach was effective far thin plies and average stress approach was effective for thick plies.