In order to investigate the effect of biodiesel fuel on a fatigue crack growth behavior of a squeeze cast Al alloy, AC4CH-T6, rotating bending fatigue tests were carried out using plain specimens in biodiesel fuel based rapeseed oil. The results were compared with those in mineral oils of light oil and turbine oil and in ambient air. Fatigue life was longer in turbine oil and shorter in biodiesel fuel than in air. Fatigue life in each environment tested was mainly occupied by the growth life of a crack smaller than 1mm, meaning that the difference in fatigue strength affected by environment was mainly yielded in the growth process of a small crack. The crack growth rates were suppressed in turbine oil and accelerated in biodiesel fuel in comparison with those in air. Biodiesel fuel contained much water dissolved from air in the early stage of fatigue process. In biodiesel fuel, there are both effects of the suppression of crack growth due to wedging effect of oil and the acceleration due to corrosion causing by dissolved water, and the former effect was larger than the latter one causing the decrease in fatigue life.

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In order to detect damages in rotating components, a non-contact AE (Acoustic Emission) monitoring system was developed. The system was composed of an air-coupled ultrasonic sensor and a digitizer with a noise reduction function. Noise in the AE signal is reduced in real time by using a spectral subtraction method and ε-filter. The SN ratio of the AE signal was improved by approximately 11.8 dB. The developed system was next applied for monitoring bending fatigue in a rotating component. AE signals were detected at 90% or more to fatigue life and amplitude of AE signals increased with increasing the rotating cycle. Source of most AE signals was estimated that they were caused by contact of crack surface due to cyclic loading. However, some AE signals were generated by crack progression in other experiment.

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Resin composites as dental restorative materials were investigated with respect to compressive strength. Columnar specimens were prepared by light curing process, and compression tests were performed under various conditions. Then stress-strain curves, fracture stress, fracture strain and elastic modulus were estimated. In the preparation of specimens, light curing time was changed, and the dependence of compressive strength on the light curing time was investigated. Furthermore, after preparation of specimens by adequate light curing process, specimens were immersed in water at the temperature of 37 degrees C, and the dependence of compressive strength on the water immersing period was investigated, too. Variation of density and wear resistance as well as compressive strength were investigated, and effects of the light curing time and the water immersing period on mechanical properties were discussed. Shrinkage of specimens and variation of mechanical properties according to the polymerization depending on light curing time were clarified, and degradation of mechanical properties according to the absorption of water depending on water immersing period was clarified, too. Finally, cross sections of specimens were observed by SEM micrograph, and internal defects and their development depending on applied compressive stress and water immersing period were clarified.

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Beginning in 2012, judo has been selected to be a compulsory course in junior high schools in Japan. However, the number of participants, in particular beginners, who die or are injured in judo is higher than that for other sports. For this reason, there is a fear that there will be a drastic increase in the number of judo-related accidents leading to death or injury in junior high schools. The most serious form of head injury is acute subdural hematoma (ASDH). The purpose of the present study is to compare ASDH occurrence indices and to evaluate the effectiveness of using head protectors. Based on measurements of head acceleration during falling, the Head Injury Criterion (HIC), maximum angular acceleration and angular velocity variation range were calculated. The results indicated that the relative displacement between the brain and skull was most strongly correlated with the angular velocity variation range, which is thus a candidate evaluation index for ASDH. The results also suggest that in order to prevent ASDH, a head protector should be made of shock absorbing materials with a small coefficient of restitution, so as to reduce the rebound velocity of the skull after occipital impact.

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The extended finite element method (XFEM) using a crack tip element (TIP element), which is enriched through only the Heaviside function, is applied to crack and its propagation analysis in two-dimensional elastic problems. In the proposed method, two-kind of signed distance functions are utilized in order to express crack geometry implicitly and finite elements, which has interaction with crack, are appropriately partitioned according to the level set values and then integrated numerically for derivation of stiffness matrix. The results by XFEM using TIP elements were compared with those by the conventional XFEM using both the asymptotic bases and the Heaviside function. It was shown that the TIP element provides appropriate stress intensity factors and crack propagation path.

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The extended finite element method (XFEM) has an advantage that an arbitrary shaped crack and its extension can be treated easily. But it is also pointed out that the results of the fracture parameter have significant errors that come from the existence of 'blending elements'. In the standard formulation of XFEM, the nodes in the element including the crack tip have enriched additional degrees of freedom. The nodes in the outer region have usual degrees of freedom, i.e. 2 in the two dimensional problem. The elements in the region surrounding the crack site have nodes with enriched freedom at the crack side and normal freedom at the outer region side. These elements are called 'blending elements'. In this paper, a new Hermite element with three nodes has been formulated and applied to a crack problem with XFEM. Errors of fracture parameters calculated by the M-integral method were discussed from the point of view of the effect of the blending elements. Stress intensity factor of CCT specimen has a 10% of error with a simple formulation. It decreases down to 0.5% by considering the improvement of XFEM proposed by Shibanuma et. al.

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