Currently, in various industrial fields, much attention is paid to carbon fiber reinforced plastic (CFRP) that is composed of carbon fibers and plastic. CFRP has excellent mechanical properties with the higher specific strength and specific rigidity as compared with metallic materials, and has excellent electrical and thermal properties. Therefore, it is actively used in the aerospace field, automobile industry, and sports field where high-strength and light-weight materials are requested. Especially, in aerospace field, the overall weight of the main wing and fuselage in Boeing 787 was reported to have a considerable decrease due to the adoption of CFRP. However, because CFRP is a laminated reinforced material, its interlaminar strength and fracture toughness are remarkably low compared with the in-plane mechanical properties of CFRP. For this reason, when out-of-plane loads are applied, internal damages, such as delamination etc., occur easily in the CFRP laminates. Such delamination causes a remarkable decrease in CFRP's compressive strength, and might cause the destruction of CFRP. Also, it is difficult to predict the position of the delamination occurrence and to discover it from the surface of CFRP laminates. Therefore, the nondestructive inspection methods using ultrasonic wave or X-ray have been used for the detection of delamination in CFRP laminates. But even if it is possible to discover it, its restoration is very difficult. In addition, after occurrence of delamination, it may grow further under the working environment afterward, which may lead to a bigger deterioration of material strength. Therefore, it is an extremely important topic to achieve high mechanical strength and fracture toughness between layers of CFRP laminate.
Recently, carbon nano tube (CNT) discovered by Iijima and Endo et al. is anticipated as a new material of nanotechnology. CNT has excellent mechanical, thermal, electrical, chemical resistance, and electromagnetic properties. Therefore, it is already applied as a negative-electrode material of lithium battery, a hydrogen storage material, and an exploratory needle of scanning probe microscope. Moreover, in various types of CNT, much attention is paid to vapor grown carbon fiber (VGCF) whose practical applications are most expected due to establishment of its massive production technology. VGCF has the advantage with good dispersibility, because the fiber diameter of VGCF is higher than that of CNT. The improved mechanical, electrical, and thermal properties are confirmed in the resin with addition of VGCF as reinforced filler.
In this thesis, interlaminar mechanical properties of CFRP laminates are improved by adding VGCF between layers in CFRP laminates. The influence of VGCF addition on mechanical properties of CFRP is examined by the experiment and the numerical analysis. It is shown that VGCF is effective for improvement of interlaminar mechanical properties of CFRP laminates.
edited by Naoki HORI