Sand erosion is a phenomenon wherein solid sand particles impact on materials causing damage to the material surface. Aircraft jet engine is exposed to many particles from takeoff to landing, because sucking in a considerable amount of air and sand. Aircraft jet engine operating under such an environment suffer from degraded performance and have a shorter lifespan. Therefore, it is necessary to estimate the amount of damage caused due to the shape and material of the aircraft engine airfoil at the design stage. In this study, a sand erosion prediction method for evaluating the lifespan of engine structural material was proposed. First, sand erosion experiments in which the erosion rate was calculated by varying the impact velocity and impact angle for the A7075-T7351 and Ti-6Al-4V plates were conducted. Second, the erosion rate on the surface was predicted by applying the erosion rate equation to a two-dimensional airfoil. Subsequently, erosion rates of the calculated A7075-T7351 and Ti-6Al-4V two-dimensional airfoil were examined and compared. Finally, the validity of the prediction was confirmed by a verification experiment.

Various materials, such as natural wood, plywood, and wood laminate, have been studied for application in table tennis rackets. The performance of each the rackets is evaluated independently by every manufacturing company; however, their performance criterion is unclear owing to their qualitative evaluation. The correlation between the natural frequencies and the coefficient of restitution has already been studied for metal baseball bats. However, this correlation has been barely studied for table tennis rackets. This study conducted natural frequency measurements for several kinds of rackets and investigated the impact of a ball against a racket at different speeds. First, the correlations among the impact velocity, coefficient of restitution, and damage to a ball were investigated by means of colliding the ball against a rigid wall to estimate the characteristics of the ball. Furthermore, the natural frequencies and coefficients of restitution of the rackets were measured using rackets with and without rubber in cantilever state by fixing grip part of the racket. Finally, the effect of natural frequency on the racket's coefficient of restitution was investigated.

A highly efficient joining method using ultrasonic welding is required for the manufacturing and processing of thermoplastic carbon fiber-reinforced plastic (CFRP) structures. Herein, the application of resin mesh as a sheet-like energy director is proposed, and its feasibility is assessed. The relationship between the welding conditions and the tensile shear strength was investigated using single lap joint specimens prepared by ultrasonic welding. The fracture surface observations indicated that resin mesh melting occurred from the end of the specimen, whereas the unmelted zone remained at the center of the welding surface. It was necessary to supply a sufficient amount of resin to the welding surface and select a resin mesh suitable for the welding conditions to minimize variations in the bonding strength. Under the welding conditions used herein, the specimens with the coarsest resin mesh showed an average tensile shear strength of 34 MPa and a coefficient of variation of 0.1. From these results, it was concluded that the application of a sheet-like energy director for the ultrasonic welding of thermoplastic CFRP is a promising method to achieve a practical level of bonding strength.

　静止軌道上のテザー型太陽発電衛星においては，発電面への太陽光照射角度変化による太陽電池の発生電力変化とそれによるRF増幅部への供給電力変動を要因としたDC-RF変換効率変動が起こる．そこで従来研究により，試作したRF増幅部を用いて，静止軌道上における供給電力変動を考慮したDC-RF変換効率変動が予測された．本研究では，RF増幅部を断続的に動作させることで，効率変動を抑制し，高効率を維持するシステムについて検討したので報告する．

According to the report by the Japan Sports Council, there are about 40,000 cases of insurance compensation for eye injuries in school sports activities at primary, junior and senior high schools in a year. Besides, there have been 259 cases of blindness and other sequelae caused by accidental injuries in baseball play over the past decade. However, there is no suitable eye guard, even more no specification for eye protection on playing baseball in Japan. In contrast to baseball, there is an obligation to wear an eye guard in women's lacrosse game, and there are eye guard product specifications in ASTM F3077. Therefore, this study explores the product development and design of baseball eye guards through the baseball impact resistance evaluation using both impact and free-fall experiments on women’s lacrosse eye guards. As for the performance evaluation, this study mainly focused on whether the ball contacts to the eye point of the face model or not, the maximum load transmitted to the face model, and the deformation amount of the eye guards after the collision of a ball. Additionally, the correlation between the two experimental evaluation, impact and free fall method was also discussed. In terms of the peak value of the load, there were some differences between the results of the two experiments. On the other hand, the deformation amount of the eye guard were commensurate between the two experiments at the same impact energy. It provides a sufficient basis for the development of baseball eye guard product specifications.

The performance of a table tennis racket is often stipulated using an unique standard for the manufacturer. However, the performance criteria for restitution characteristics still have been unclear due to lack of qualitative evaluation by each manufacturer. For metal baseball bats, a formula that can easily estimate the coefficient of restitution (COR) for the bat has been proposed. Similarly, it is important to establish a method that can control the COR at the design stage for table tennis rackets. In this study, first, to understand the restitution characteristics of the table tennis ball used in the official game, an impact test was conducted on a pseudo-rigid wall at low to high velocity. Then, for 15 types of rackets, the COR of the racket body (with and without rubber) was measured. Additionally, the natural frequency and flexural rigidity of the racket body without rubber were measured. Furthermore, these experimental data revealed relationships between the COR and both of the impact velocity and natural frequency of the racket. A formula for the COR was derived similar to that for a baseball bat, and developed by considering the flexural rigidity. The effect of rubber on the COR was also investigated. Consequently, the effects of ball’s impact velocity, racket’s natural frequency and racket’s flexural rigidity on the COR of the racket were clarified. From these results, an equation that can estimate and control the COR of the racket at the design stage was developed.