Shear property of 3D braided composites with various thickness and fiber-angle, which were fabricated using carbon fiber and epoxy resin was measured using V-notch beam specimens (modified Iosipescu method). The shear strength and modulus (τ_ZX, G_ZX respectively) in the plane containing braid axis (Z) were fairly higher than those of the in-plane shear properties of traditional unidirectional (UD) laminates and increased with the braiding angle up to 45°. On the other hand shear property in the plane perpendicular to the braid axis (τ_XY and G_XY) was shown to be as low as out-of-plane property of the UD laminates. Anisotropic shear property of the specimen depending on the load direction was observed. Strength and modulus determined under the load vertical to the braid direction, (G_ZXL, σ_ZXL respectively) were higher than those in the case of horizontal (G_ZXT, σ_ZXT respectively). Especially the shear strength differed by a factor of 3.

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The objective of this study is to statistically evaluate the compressive mechanical properties of a quasi-isotropic carbon/polyimide composite, i.e., T800H/PMR-15 with a stacking sequence (45/0/-45/90)_4S of 32 plies. Compression tests were conducted at room temperature using thirty smooth specimens. Mechanical properties measured are ultimate strength, failure strain, elastic modulus in addition to specimen thickness. Statistical analyses use four kinds of distribution models such as the normal, log-normal, type-I extreme-value, and two-parameter Weibull distributions. These analyses derive the estimates of central tendencies and scatter parameters, and B allowables. The modified Kolmogorov-Smirnov goodness-of-fit tests and graphical plotting techniques are applied to test the goodness-of-fit of each mechanical property data for the four kinds of distribution models. Correla-tion between mutual mechanical properties is examined, and a multiple regression analysis is applied to predict the ultimate strength. Moreover, a simple equation to predict the ultimate strength is derived using the product of the failure strain and elastic modulus.

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