The flexural static, creep and fatigue fracture behavior of unidirectional CFRP laminates of a general type of thermosetting resin with a PAN-based carbon fiber, were investigated by three-point bending tests over a wide range of temperature and deflection rate. The flexural fracture behavior by the fractographs as well as the strength of the static, the creep and the fatigue loading remarkably depend on the testing rate and temperature. The master curves for these strengths can be produced by using the time-temperature superposition principle. The time-temperature shift factors for the three kinds of strengths were quantitatively in good agreement with that for the stress-strain relation of the matrix resins. Therefore the time and temperature dependences of fracture behavior are mainly controlled by the viscoelastic behavior of the matrix resin.

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Bearing strength tests either with or without lateral constraint were performed for plain weave C/C composites. The tests were conducted with reference to JIS K 7080 which standardized the testing methods for bearing strength of carbon-fiber reinforced plastics. The bearing damage propagation was observed by a soft X-ray and an optical microscopy. Shear cracks were initiated and propagated rapidly at the maximum load when tests were performed without lateral constraint. Tests being performed with lateral constraint, shear cracks were initiated at the relative displacement of 4% of the pin diameter and followed by the stable crack propagation. At the maximum load the crack reached the edge of collar which constrained the specimen laterally. Then the load dropped abruptly. The loads for evaluating bearing strength which are standardized in JIS K 7080 would correspond to the shear crack initiation.

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A simple mechanical model for predicting in-plane elastic moduli and coefficients of thermal expansion of composites using orthogonal 3-D textile reinforcement is proposed in the present work based on the constituent material properties. The theoretical procedure starts after determination of basic mechanical properties of unidirectional composites as the constituents of 3-D textile composites. An establishment of the model automatically leads to the approximate formulae for the prediction. The procedure is constructed by the combination of parallel and serial linkage of the UD composite and pure epoxy blocks. The predicted elastic modulus, in-plane shear modulus and coefficient of thermal expansion of Tyranno^®/epoxy 3-D composite system were compared with experimental results and numerical results obtained from homogenization finite element analysis. An agreement between them is basically excellent. A simple formula to predict elastic and thermal expansion behavior of 3-D composites is well described with some limitation.

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