The oblique impact of golf balls with a rigid steel target was studied using a high-speed video camera. The video images recorded before and after impact were used to determine the incident and rebound velocities and angles of the balls. The rebound velocity was found to decrease to about 80% of the incident velocity. The rebound angle also showed that it decreases with the incident velocity. The video images during the impact were employed to evaluate the contact time, compression ratio, tangential and angular velocities of the balls. The result showed that the contact time decreases with the incident velocity, while the opposite relation was obtained for the compression ratio. It is found that the tangential and angular velocities increase linearly with the incident velocity. A rigid ball model was also employed to analyze the tangential and angular velocities of the ball during the oblique impact with the target

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Oblique impact tests of a golf ball and a transparent PMMA plate target were carried out to study the dynamic contact behavior. Using a high-speed video camera, the contact behavior was photographed as a function of time. The result showed that the maximum contact area increased linearly with the incident velocity of a ball, while the contact time decreased with the velocity. The video images were also analyzed to study the tangential and rotational velocities during the contact, and compared with the results determined from the steel target and the rigid ball model.

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DMD (Digital Micro-mirror Device) is a new device which has hundreds of thousands of micro-mirrors in one chip. We previously developed a DMD reflection-type CCD camera that we call ‘DMD camera’. In the optical system of the DMD camera, each mirror of the DMD corresponds to each pixel of the CCD. As the result, each DMD mirror works as a high-speed controllable shutter of the corresponding CCD pixel. We applied the DMD camera to the phase analysis and shape or deformation measurement. It is, however, difficult to adjust each mirror of the DMD to each pixel of the CCD exactly, because these sizes are very small. In this paper, we propose a method that can perform accurate adjustment of the optical system for a DMD camera using moiré technique. Furthermore, we also propose a “Phase-shifting moiré method” which can perform phase analysis of the moiré patterns. The proposed technique enables to adjust pixel-to-pixel correspondence within one pixel order of the CCD. These principles and experimental results are shown.

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In some experimental studies for dynamic crack propagation, crack propagation velocities greater than 60% of shear wave velocity of the material have been observed. Mechanism of these fast crack propagations has not been clarified.
In this experimental study, the cracks were critically accelerated by using a multi-loading system. One of the crack propagation velocities reached 74% of the shear wave velocity. Furthermore, the distributions of principal stress gradients near the propagating crack tip are observed using the Coherent Gradient Sensing method. Based on these stress gradient distributions, dynamic stress intensity factors for fast propagating crack tip are estimated.
Two and three dimensional numerical simulations for these fast crack propagations are performed to estimate fracture energy flow and other parameters. The generation phase numerical simulations are achieved based on the experimental results, which are loading histories and crack propagation history. Energy flow to crack tip are visualized by 2-D numerical simulation. In 3-D numerical simulation, the relationship of 3-D fracture roughness and Φtotal parameters are obtained. The increase of the dynamic stress intensity factor with the increase of crack propagation velocity is measured in numerical simulations.

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Phase-shifting digital holography is applied to record the caustics of stationary cracks at arbitrary distances. Stress intensity factors are measured from the reconstruction images of caustics. The measurement results show that stress intensity factors are almost constant in the region where the distance from the crack tip is larger than half a specimen thickness. Also, the stress intensity factors decrease in the three dimensional stress field. These results show that the method is applicable to measure the stress intensity factor of cracks.

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