In recent years, biodegradable plastics which have low effect on environment have been developed. However, many of them have lower mechanical properties than conventional engineering plastics. Reinforcing them with a natural fiber is one of reinforcing methods without a loss of their biodegradability. In the present study, we use a bamboo fiber as the reinforcement and polybutylenesuccinate (PBS) as the matrix. We fabricate long fiber unidirectional composites and cross-ply laminate with different fiber weight fractions (10, 20, 30, 40 and 50wt%). We conduct tensile tests to evaluate the mechanical properties of these composites. In addition, we measure bamboo fiber strength distribution. We discuss the experimentally-obtained properties based on the mechanical properties of the constituent materials. Young's modulus and tensile strength in unidirectional composite and cross-ply laminate increase with increasing fiber weight fraction. However, the strain at fracture showed decreasing tendency. Young's modulus in fiber and fiber transverse directions are predictable by the rules of mixture. Tensile strength in fiber direction is lower than Curtin's prediction of strength which considers distribution of fiber strength. Young's modulus in cross-ply laminate is predictable by the laminate theory. However, analytical prediction of Poisson's ratio in cross-ply laminate by the laminate theory is lower than the experimental results.

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A method for identification of a crack on the surface of material by means of direct-current electrical potential difference method of multiple-point measurement type was proposed and the related experiments were carried out to verify the method. The geometry of the crack was given by the two-dimensional location of the crack center, the surface and inward angles, the length and the depth of the crack. The experiments were carried out for metal plates with various surface cracks made by electric discharge machining. When most of the area of electric potential disturbance by the crack was included in the measurement area, the geometry of the crack was successfully evaluated by the proposed method based on the potential differences measured at multiple locations around the crack.

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In this paper, the debonding initiation and propagation in the bundled fibers-matrix composite is studied by utilizing a finite element method, which incorporates the bilinear cohesize zone model. The cohesive zone model parameters are adjusted so that the mechanical response of the model fits to that obtained in an experiment. Furthermore, the model performance is verified against three additional experimental datasets. The study reveals that for this particular specimen and loading condition, the interface debonding stably propagates until the applied load reaches its maximum. After the maximum applied load, the debonding propagates rapidly, and finally, the bundled fibers breaks completely.

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Although several studies have examined stress singularity at the edge of an interface, few have focused on shear loading. The present paper analyzes a stress singularity in a shear loading that should be useful in the electronic device machining process. In the present study, the enriched finite element method is applied to analyze the intensity of singularity in two-dimensional joints under a shear loading. The stress fields in dissimilar materials (bi- and three-material joints) described by one and two real intensities of singularity are investigated. In addition, the intensity of singularity in the joints with various model geometries and material properties are investigated and discussed.

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This study investigated damage detection in holed CFRP laminates by using a newly developed technique for visualizing ultrasonic waves. This technique provided a moving diagram of propagating waves with non-contact scanning by a pulsed laser. Its measurement scheme overcame the difficulties of sensitivity in conventional methods and enabled us to observe ultrasonic waves on CFRP laminates. We observed two types of ultrasonic waves propagating on the CFRP laminate in the measured snapshots. These waves were identified as the S₀ and the A₀ Lamb modes by the dispersion curves, confirming the validity of the visualization technique for composite laminates. Furthermore, ply cracks and delamination, as well as the damage during manufacturing, were observed near the hole in the loaded specimens, and we successfully visualized the Lamb waves scattered by the delamination. The region of wave scattering agreed with the damage observed by soft X-ray radiography. These inspection results demonstrated the usefulness of the visualization technique in inspecting composite laminates.

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This paper deals with fatigue damage and life prediction of CFRP cross-ply laminates. Fatigue tests are carried out on CFRP unidirectional and cross-ply laminates under the on-axis and off-axis directions. On the unidirectional laminate, fiber breakage and fiber-peeling develop before the final fracture under on-axis fatigue, while the final fracture suddenly occurs by cracking along the fiber direction under off-axis fatigue. On the cross-ply laminates, ply-cracking in 90° plies and fiber-peeling in 0° plies develop under on-axis fatigue, while ply-cracking and delamination lead to the final fracture under off-axis fatigue. Based on the comparison of damage behavior and S-N curves between unidirectional and cross-ply laminates, possibility of fatigue life prediction of CFRP cross-ply laminates is discussed.

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This paper simulates the macroscopic thermal conductivities of randomly-packed, sintered balloons for various degrees of sintering and for a wide range of the balloon inner/outer diameter ratio. Although this problem was already studied by Ono et al., we found some errors in their paper, including a critical one. Thus, we re-examine the same theme and correct all errors. Furthermore, we extend its contents and discuss the results in more detail. For practical purposes, we present all the macroscopic conductivities in terms of a simple expression of two balloon's geometrical parameters. “Specific” macroscopic thermal conductivities (i.e., those per weight) are precisely estimated and found to have a peak when the balloons have the diameter ratio larger than approximately 0.8.

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Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×10⁷ cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

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Micro computed tomography (μCT) is quite useful in the nondestructive evaluation of devices with complicated internal structures. However, a large difference in x-ray absorption coefficients of the materials produces streak and star pattern artifacts in a CT image. These artifacts, which are called “metal artifacts”, make it difficult to inspect an image of the device. Hence, this study strives to develop a new reconstruction method that reduces the artifacts from images. In this paper, we first discuss the cause of the artifacts using CT data of a sample. Next, we propose a CT reconstruction algorithm to reduce the artifacts. The basic idea of the algorithm is that it corrects the projection data. The shapes of high density parts such as metals are extracted by a threshold method and projection data are replaced to consistent values. Finally, we apply the method to select devices, and confirm that the method is applicable to nondestructive inspections.

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The evaluation of impact damage properties and strength of C/C composites is becoming important, due to its low impact strength. In this study, the impact damage is evaluated by using the impact load-deflection diagrams and absorbed energy of specimens on a drop weight impact test. The measured impact load is decomposed in approximation components and detail components by multiple-resolution analysis based upon the wavelet transform. And then the possibility of wavelet analysis for estimating the impact damage is studied. The results are as follows: (1) The Daubechies' wavelet is useful for smoothing the impact load signals by multiple resolution analysis in wavelet transform. (2) In the low impact energy that most of the damage does not occur, the approximation component result demanded by wavelet analysis accords with the wave pattern of numerical one that is removed free vibration component.

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