This paper deals with an active vibration control of a new smart board designed by mounting the piezoelectric fibers with metal core on the surface of the CFRP composite. These complex fibers function as sensor and actuator in the CFRP board. A finite element model of a cantilever and a reduced order model for controller design are established. The piezoelectric fibers each have unevenness in the actuator outputs. Therefore, the liner fractional transformation (LFT) is formulated considering the unevenness of the actuator outputs as the perturbation. Next, the controller considering the perturbation and the robust stability is designed by using μ synthesis. The control performance of the proposed method is verified by experiment and it is shown that the use of piezoelectric fibers is effective in the vibration control.

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In this study, micro damage initiation and propagation behavior of woven fabric composite after fatigue loading was investigated. In order to detect the micro damage under static tensile loading, acoustic emission (AE) technique was employed. The AE generating stresses were defined as the initiation and propagation of the micro damage. In case of static loading, Kaiser effects were confirmed above the AE generating stress. After fatigue loading, the residual properties were same as virgin material in case that fatigue stresses were kept lower than the AE generating stress. On the other hand, the residual properties, especially the AE generating stress were drastically decreased at the higher fatigue stresses range.

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Experimental investigations of CFRP laminates by using carbon fiber (CF) stitching were carried out for evaluating CF stitching effect. The used CF stitch thread is TR 40-1K (612d), in-plane fiber of the CFRP is T700 12K, and resin is TR-A31 for resin transfer molding. Various stitch densities of the CF stitched CFRP laminates for double cantilever beam (DCB) tests were employed here. An insert type of loading fixture which was developed by National Aerospace Laboratory of Japan (NAL) was employed in DCB tests. Pull-out tests of a single carbon stitch thread in the CFRP laminates were also carried out. It is clarified from the DCB test results that the relationship between the volume fraction of CF stitch thread (V_ft) and G_l shows a mostly linear function. Moreover, this increase slope of V_ft-G_l curve indicates higher one than CFRP stitched by Kevlar-29 1000d. Single CF stitch thread pull-out tests showed that there are two fracture modes of the CF stitch threads in the CFRP laminates, and that a difference in the shape of the load-displacement curve corresponds to these fracture modes. However, there is no big difference in the total energy consumption amount in these different fracture modes. Moreover, CF stitch thread pull-out test results indicate that the energy consumed per unit area of the CF stitch thread was larger than Kevlar-29 1000d stitch thread. This finding agrees with the fact that Interlaminar toughness improvement of CFRP laminate for mode I by CF stitching is more effective than that by Kevlar-29 1000d stitching shown in V_ft-G_l relationships.

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The purpose of this study is to find out the tensile behavior of Carbon Fiber Reinforced Polymer (CFRP) sheets at different temperatures. Ordinary epoxy resin to be softened and modified in a higher temperature than the glass transition temperature (T_g) which is investigated by DMA (Dynamic Mechanical Analyzer) tests. First, tensile behavior of non-impregnated carbon fiber sheets and epoxy resin is studied. Moreover the tensile behavior of CFRP sheets with both ordinarily used epoxy resin and newly developed epoxy resin that has higher heat-resistant behavior with higher than T_g is investigated experimentally. The specimens are stretched in lengths of 130 mm and 2, 000 mm to investigate the size dependency. Through the experimental investigations, the tensile strength, stiffness and ultimate strain under different temperature levels and size dependency are identified. It is considered that the temperature dependency of FRP tensile behavior is also a noticeable concern in FRP bonding techniques.

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