Over the wide range of the loading rates, fracture toughness test have been carried out for the GFRP material. Fracture toughness based on the stress singularity is significantly affected by the loading rate, while one based on the strain singularity is less affected by the loading rate. Fracture toughness based on the strain can explain the fracture behaviors of viscoelastic materials, but to explain the loading rate effect completely, the debonding process between the glass fiber and the polymer matrix must be taken into account.

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Macroscopic elastic properties of porous compacts prepared by applying uniaxial pressure in powder sintering are numerically estimated, with their biomedical application in mind. The estimation is based on a three step simulation method similar to the previous one. It is found that the compaction by the pressure and the sintering lead to increase in the macroscopic elastic moduli in the pressure direction, which is made to coincide with that of gravity in packing. It is also found that these moduli are larger than those in the direction normal to the pressure by 20% to 40%. Those for the less sintered compacts whose porosity ranges from approximately 32% to 37% fall in those of human cortical bone and show similar behavior to those of artificial implants.

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Carbon tool steel substrates were quenched after TiN coating by dc magnetron sputtering, and the effects of substrate post-quenching on the mechanical properties of TiN films were investigated. The residual stress of TiN film was decreased by substrate post-quenching, and the hardness of TiN film also decreased. On the other hand, the adhesive strength determined by the scratch test and the substrate hardness were improved by substrate post-quenching. The improvement in the adhesive strength could be explained by the following three effects of substrate post-quenching: decrease of residual stress, increase in substrate hardness, and the formation of a diffusion layer between the film and the substrate caused by the elevated temperature in substrate post-quenching.

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This study develops a new inverse analysis technique for estimating damage patterns in notched composite laminates using an embedded fiber Bragg grating (FBG) sensor. The damage pattern near the notch was investigated by using a layer-wise finite-element model with cohesive elements for cracks and delamination. The reflection spectrum of the FBG sensor was simulated from the strain distribution obtained along the gage length. We approximated the typical damage pattern (splits, transverse cracks, and delamination) near the notch using some variables; these were then estimated through mathematical programming by minimizing the differences of spectrum shapes between the inputs (e.g. experiments) and the estimations. This damage identification procedure was applied to numerical examples, i.e. simulation results, for a notched CFRP cross-ply laminate. The damage patterns estimated from the calculated reflection spectra were almost identical to those obtained by the simulation. Finally, we estimated the damage pattern of a notched laminate from a measured reflection spectrum of an embedded FBG sensor and demonstrated the capability of the developed identification procedure for practical applications.

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The progressive miniaturization and integration of electronic devices has made interfacial fracture between thin films of several nanometers thickness an important consideration. The present paper attempts to clarify the mechanism of the damage process along an interface between multi-layered films during nanoscratch tests. Using the edge of a Berkovich-type indenter, a nanoscratch test was performed on sub-micron films of Si₃N₄/Cu/TaN fabricated on a silicon substrate. Initiation of damage occurs near the Si₃N₄/Cu interface before the tip of indenter reaches the interface. This implies that Si₃N₄ is weak in terms of interfacial resistance to failure. A spot-like damaged area appears under the scratched line, and the size of this area is several nanometers or less. Critical values measured in the nanoscratch tests and three-dimensional non-linear finite element analysis reveal that shear stress concentration appears behind the indenter; this agrees qualitatively with the behavior of the spot-like damage area as observed under an optical microscope. In order to examine the validity of the damage mechanism, another nanoscratch test was performed by moving the indenter in the opposite direction. Critical load is greater than that in the original test due to the difference in the shape of the indenter, but stress analysis reveals that initiation of spot-like damage occurs when the two tests are equal in terms of peak stress acting on the interface.

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In order to improve the service life of the artificial acetabular cup in a total hip replacement, it is important to determine the best material and design, and to assess the mechanical behavior around the cup. In this study, electronic speckle interferometry (ESPI) and the two-dimensional finite element method (FEM) are employed to investigate the mechanical behavior. The influence of the cancellous bone and cup thickness on mechanical behavior around the cup was investigated. Good agreement of the cup model was found between the ESPI measurements and FEM predictions. The following results were obtained. (1) Cancellous bone with a porous structure can be measured by the ESPI method. (2) There are discontinuities of the displacement distribution in the transverse direction in each boundary region of the cup, bone cement and cancellous bone. (3) The maximum shear stress exists in the boundary region of the cup and bone cement.

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A unified criterion is proposed that allows one to predict the effects of phase difference and mean stress on the fatigue strength of components containing small holes under combined loading. Combined axial and torsional fatigue tests were conducted using annealed JIS S35C steel and quenched/tempered JIS SCM435 steel specimens containing a small hole of either 100 μm or 500 μm in diameter. The phase differences between axial and torsional loads were 0° and 90°. Non-propagating small cracks were observed to emanate in the radial direction from the holes at the fatigue limit. Moreover, these cracks were always in the plane of maximum principal stress. This indicates that a crack on this specific plane plays an important role in the determination of fatigue strength. A criterion was proposed on the basis of the assumption that at the threshold level, the time-variation in the Mode I stress intensity factor of a crack under multiaxial cyclic loading is equal to that under uniaxial cyclic loading. A predictive method for the determination of fatigue strength under combined loading conditions was also presented making use of this criterion. This method is useful in practice since no fatigue tests are necessary in making predictions. Good agreement between experimental results and predictions was obtained.

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High-order Lamb waves of symmetric mode are applied to flaw detection in steel plates. In inspection of thin plates, Lamb wave of the lowest symmetric mode is preferable, because effect of the velocity dispersion, which distorts the waveform, is small in the low frequency region. However, for thick plates, the frequency should be lowered and the wavelength becomes large. Then, the flaw detectability is reduced. In this study, we suggest to make use of high-order Lamb wave at frequency of its maximum group velocity in order to avoid the interference with the other modes. Electromagnetic acoustic transducers (EMATs), each of which consists of an electromagnet and a meander line coil, are designed for three modes of Lamb wave in 6mm-thick steel plate, using theoretically obtained dispersion curves. Optimum magnetic field strength is investigated, ensuring that the wave generation and detection are based on the magnetostriction. Dispersion curves are measured by sweeping the excitation frequency, which reveals the optimum frequency. Echoes from drilled holes are detected to discuss the flaw detectability of each mode.

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A single-fiber pull-out model composite for an aramid/epoxy system was specially designed to measure the stress distribution of the aramid fiber embedded in the matrix using micro-Raman spectroscopy. The stress transfer length of the fiber obtained was about 400-500 μm, which was equal to the result of FEM analysis. Just after the initiation and propagation of the fiber/matrix interfacial debonding, the fiber was broken, and the fiber in the matrix had the axial tensile residual stress. The tensile residual axial stress showed the maximum at around the tip of the interfacial debonding. The stress was reduced after the specimen was kept in air at 80°C for 44h, and it became almost equal to zero after being immersed in deionized water at 80°C for 44h. This behavior agreed with the result of FEM analysis, in which the friction coefficient was introduced in the fiber/matrix interface. The axial residual stress was caused by the friction between the fiber and matrix, due to the compressive stress acting between the resin and the fiber, which was caused by the difference of the coefficient of thermal expansion.

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It is important to know the impact fracture behaviors in the safety design of the brittle material board. However, the three-dimensional analysis for the impact fracture behaviors of the brittle material board is not done over the current. In this research, the impact penetration fracture when the impact body collides with the center of the brittle material board is analyzed by PFC3D. It is the general three-dimensional program that uses the Distinct Element Method (DEM). DEM is suitable for the analysis of the fracture behavior of the non-individual body and the break-up body. The analytical results are compared with the experimental one and the validity of analytical results are checked. By this research, it is obvious that the penetration speed and the loss energy increase as the impact velocity, radius and mass of the impact body increase. Moreover, the relations between the parameters of impact body and fracture behavior are clarified.

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