In this study, bending and transverse shear properties of plain weave fabric composite laminates are investigated considering the intra-lamina inhomogeneity through finite element analysis. Using the homogenization procedures, efective Reissner–Mindlin plate bending and transverse shear properties of the composite laminate are calculated. Assuming the number of laminations is infinite, effective 3D continuum properties of the composite (elastic properties as a bulk material) are also calculated. Then, the effect of the number of laminations on the laminate bending stiffness and the transverse shear stiffness, in other words, the effect of the intra-lamina inhomogeneity on the laminate stiffness, is investigated. Through the numerical investigation, it is found that if the number of plies of the laminate is very small, bending stiffness and transverse shear stiffness of the laminate are significantly reduced compared to those evaluated using effective 3D continuum properties.

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This paper presents machining quality and characteristics of circular piercing hole produced by punch press in thermosetting CFRP laminates. First, a hole was produced by using a punch with flat surface at room and elevated temperatures. After the piercing process, damages and burrs on the surfaces and the cutting planes around the hole were microscopically observed. Internal damage such as delamination was then observed using radiography. Second, the quality of the hole was examined through roundness measurement using three coordinate measuring machine. Finally, piercing process mechanism was discussed from antiplane load and displacement diagrams and cutting planes observations of the specimen during the piercing process. It was proved from X-ray radiography and quality evaluation of the hole after the piercing process at elevated temperature that the least amount of delamination was generated although the roundness was low. It was presumed from the piercing process mechanism that the roundness becomes low because the face parallel to fiber direction in the middle layers was preferentially cut.

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It is important to understand the contribution of the ratio of in-plane and out-of-plane properties in order to clarify the flexural deformation of out-of-plane anisotropic material like CFRTP (carbon fiber reinforced thermoplastics) in detail. Since, in specifically, E1/G13 of CFRTP would be very large, in case that CFRTP is applied vehicle structure, it becomes important to know the influence of out-of-plane properties on structural deformation behavior. From the point of reliability design, additionally, the information of the time-dependence of flexural behavior is greatly helpful to analyze and design some kinds of structural parts. In this study, a theoretical model on time dependent flexural elastic modulus of CFRTP was tried to construct by time-temperature superposition principle on viscoelastic properties of matrix resin. The theoretical model was verified by dynamic three point bending test using the polypropylene-based discontinuous CF mat reinforced thermoplastics (CMT) with in-plane isotropic. As a result, it was quantitatively clarified that the time dependence of flexural stiffness of CMT is due to viscoelastic property of matrix resin. And the contribution of out-of-plane shear modulus to flexural modulus was also clarified quantitatively. These results indicate that the time and temperature dependence of flexural modulus of CMT is able to be predicted by Young’s modulus and out-of-plane shear modulus influenced from viscoelastic property of just matrix resin, volume fraction of fiber and coefficient configuration of reinforced-fiber. It is also clarified that out-of-plane properties affect flexural stiffness strongly at high temperature or low strain rate condition.

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Crack length dependencies of intralaminar and interlaminar crack growth resistances were evaluated under static and fatigue loadings for CF/Epoxy laminates. The crack length dependency for intralaminar crack growth was more significant than that for interlaminar crack growth due to larger amount of bridging fibres. On the other hand, there was no significant difference in stress shielding effect derived from bridging fibres at a crack tip under static and fatigue loadings for both interlaminar and intralaminar crack growths. Then, the mechanism of the formation of fibre bridging is different from that for CF/PEEK where the difference between static and fatigue was clear. Fracture surface observations reveal that plastic deformation of matrix resin and damaged zone size are probably the key factors for the different stress shielding effect between for static and fatigue loadings.

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