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Several carbon blacks and carbon nanofiber were treated with heat at six hundred degree. The effect of reinforcement of rubber composites was investigated. The acidic functional groups in the filler surface decreased due to the heat treatment. The decrement of generation of CO and CO2 on carbon-base nanofillers was confirmed. The heat treatment of carbon-base nanofillers brought the increment of both storage modulus (E′) in viscoelasticity and tear strength for their rubber composites. The shapes of carbon nanofibers in rubber composite were observed by TEM and SEM photograph. The carbon nanofibers in rubber composites have been cut into about 1/5 of the original ones and they are oriented to the roll direction. In spite of small amount of isodine adsorption, the rubber composite with carbon nanofibers showed higher E′ than that with carbon blacks. Thus, it is indicated that the heat treatment of carbon-base nanofillers will be beneficial for improving reinforcement of rubber composites.

Carbon fiber reinforced plastics (CFRP) have been well developed for many engineering structural components in the aircraft, automotive and modern space industries with high specific rigidity and high specific strength. But it is poor in vibration and noise reduction as same as many metal materials. In this research, in order to improve the damping properties of CFRP, the innovative CFRP/SDR sandwich composite materials with damping rubber sheet were developed, and the mechanical and damping behaviors were investigated by three-point bending test, center vibration method and dynamic mechanical analysis (DMA), respectively. As a result, it is shown that the mechanical and damping properties of the developed 8 types of CFRP/SDR sandwich laminates depend deeply on the fiber orientation of lamina, the property of rubber sheet and its layer number and sequence. Among these materials, the optimal sequence for the CFRP and SDR sheet was obtained, which showed excellent both mechanical and damping properties.

The relationships between the load peaks in load-displacement curves and the failure type of trabecular root in an interlaminar peeling process of a beetle fore-wing of A. Dichotoma were investigated and the interlaminar reinforcement mechanism was analyzed by using FEM. The peeling model with trabecular structure was proposed and the geometrical parameters for the model were determined by in-situ microscope observation. It was shown that the proposed model could be used to predict failure type of the trabecular root and to make clear the interlaminar reinforcement of a fore-wing. It was also found that the load peaks in a peeling process were proportional to the diameter of a trabecula, and depended on the failure type of the trabecular root. The principal stress at the peeling tip was very converged without the trabecula, but could eased by trabecula structure. It was shown that the fracture type of the trabecular root could be predicted by FEM model analysis.

An interlaminar peeling test was conducted for an A. dichotoma beetle fore-wing with the interlaminar reinforcement mechanism being investigated. The load-displacement curves indicated the presence of many load peaks with the number of load peaks being equal to the number of trabeculae found in the chitin fiber laminae. This result suggested that each trabecula fracture contributed to a single load peak, which then combined to provide the interlaminar strength. The increment of interlaminar strength due to the trabecular in the chitin fiber laminae was approximately 30 times in a local region and 3 times in a whole region larger compared to that of the chitin fiber laminae without trabeculae. The chitin fibers were found to be connected between the chitin fiber laminae with the trabeculae being curved and continuous, whilst the trabeculae bonded chitin fiber laminae were distributed in two dimensions within the chitin fiber lamina plane. Furthermore, a strong reinforcement mechanism in nature was clarified with a model for the reinforcement mechanism being proposed.

The fracture behavior and interfacial properties of single fiber composites (SFC) containing a single optical fiber are examined by acoustic emission and a polarized microscope in a monotonous tensile and bending test. As a result, in both tests, initial and main AE events occur in an earlier loading region, and near the peak loading point, respectively. Fiber fragment length can be expressed by Weibull distribution. However, the differences in these two tests are clearly seen in AE activity patterns, amplitude distributions, power spectra, and fiber fragment distributions. the shape parameter of a Weibull distribution in the bending test is 5.7, which is about twice as large as that in the tensile test. This means a smaller dispersion of fiber fragment length in the bending test than in the tensile one. A transition of failure modes due to tensile, compressive, or shear stresses or a combination of these is found by changing the fiber position along the thickness direction of a specimen in the bending test. Variance of AE characteristics and fracture behavior at a fiber breakage can also be observed for different fiber positions.

The fracture behavior and crack propagation process of carbon-fiber-reinforced laminate composites are examined by in situ SEM, and acoustic emission (AE) signals are measured simultaneously. As a result, the fractures of matrix, fiber-matrix interface and bridge fiber give rise to AE signals, and the patterns of AE event count rate are found to depend strongly on the fiber orientation in a laminate. The direction of crack propagation is along the fiber orientation even for cross laminates and crack propagation is terminated by the reinforced fibers. The amplitude of the AE signal is low at the period of initial crack occurrence, but becomes high and the number of AE events increases rapidly as the crack propagates. This means that microfractures in the material increase during crack propagation. This result can also be confirmed by the results of an AE power spectrum analysis. Furthermore, by matching AE signals to the fractographs, it is found that AE activity is weak and has a low amplitude in the region of a flat fracture surface, while it is strong and has a high amplitude in the rough surface region, especially for a unidirectional material A.

It is well known that the interfacial property is an important factor for the strength of fiber-reinforced composites. The temperature dependence of the interfacial property and fracture mechanisms of a single fiber composite are examined by acoustic emission. Two kinds of materials, thermosetting and thermoplastic resins, are used. The fracture surfaces are observed with a polarized microscope. The interfacial shear strength of the fiber/matrix is calculated using AE events which are almost equal to the number of fiber breakages. As a result, it is confirmed that the fracture mechanisms of SFC are different when the temperature is varied. The debonding length increases and the interfacial shear strength decreases with increasing temperature for all specimens. However, it is found that the thermoplastic resin becomes extremely brittle with decreasing temperature and the fiber breakages contribute to the fracture of the composite directly.

The temperature dependence of fracture mechanisms on two typical structures, a short-fiber-reinforced material and a chopped-strand material with a thermoplastic matrix, were examined by AE monitoring and SEM. It was found that the matrix became brittle as the testing temperature decreased from 60°C to -20°C, and this gave rise to different fracture behaviors of the materials used. In a short-carbon-fiber-reinforced material, matrix cracking and fiber breakage were the main fracture forms at -20°C and 0°C, whereas pull-out became the main form at 20°C and 60°C. In a chopped-strand-reinforced material, cracking between chopped tapes and debonding of fiber/matrix in a chopped tape became marked with increasing testing temperature. In particular, at 60°C, the matrix became more ductile and this resulted in decreased interfacial strength, then pull-out of fiber strands and chopped tapes occurred

The fracture behavior and crack propagation process of carbon-fiber-reinforced thermosoftened plastic (CFRTP) materials are examined under SEM in situ, and acoustic emission signals are also measured simultaneously. As a result, in the model materials fiber breakages do give rise to AE signals. In CFRTP materials, the relationships between fracture factors and AE parameters can be made clearer since the fractography technique is combined with the method of acoustic emission in real time. It is found that the crack suspended after a rapid propagation, and this phenomenon recurred although the tensile load in the experiment was increased monotonously. Corresponding to this phenomenon of crack propagation/suspense, the characteristics of AE events and power spectrum varied sensitively. Furthermore, it was shown that the degree of damage of materials during the fracture process can be evaluated by using AE cumulative energy and analysis of power spectra.