Generally the initial fracture is the micro-fracture and the final fractures might be caused by the accumulation of the micro-fractures. A characteristic property of materials is a knee point in the stress-strain curve. In the case of woven fabrics, it is known that the knee point appears in consequence of the initial micro-fracture as transverse cracks. Sun et al. (ref. 1) studied the relation between the tensile properties of the woven fabric composite and the micro-fracture by observing the fracture behavior in detail. One of the main causes of the occurrence of the micro-fracture is artificial miss. When the laminate composites are made by hand-lay up method, the misalignment occurs with very high probability. The misalignments are the gap between the fiber direction and the loading direction. In the materials with the misalignments, the stress at knee point initial fracture and strength would occur at the lower stress. Therefore it is very important that to clarify the influences of the occurrence of initial micro-fractures and these behaviors on the mechanical properties of the woven composites. In this study, off-axis woven fabric composites were considered as woven composites with the misalignments. The purpose of this study was to clarify the effect of the angle between the fiber orientation direction and the loading direction on initial fracture behavior, crack progress and tensile strength in the off-axis tensile test. The observation for single layer and 3 layers laminates were performed.
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