張 月琳

American football is a sport that requires high safety precaution for players because it entails very fast and powerful movements. The players’ helmets are one of the most important means of ensuring their safety, and so the mechanical design of these helmets is extremely difficult for the manufacturer. Therefore, in this report, the mechanical behavior of the pad material is measured experimentally and then it is formulated by theoretical simulation for design of the helmet numerically. Then, an analysis of the collision problem of the helmet is carried out using the characteristics of the pad material obtained in these mechanical tests. Numerical analyses are carried out by changing the material characteristics and movement of physical model while keeping the structure of the helmet and head constant. LS-Dyna is used in the numerical simulation because of its availability in crash analysis. In the analysis results, it was first confirmed that the optimum characteristics of the pad material can be defined by the mechanics of plateau stress. With these results, the concept of a usage limit due to deterioration of the pad material is discussed in addition to the suggestion of helmet specifications according to the physique and exercise capacity of the football players.

The strain distribution of the facial skin surface at the local area near eyes at the instant of blinking are measured for evaluating the effect of cosmetics products. The motion of the skin at the local area as well as the whole face is observed using multiple digital high-speed cameras. Images of the typical blink motion are extracted from the mass of the local images by evaluating the blink motion in the whole face images. Two-dimensional digital image correlation is used for measuring strain. Irregularities and textures of the skin near the eyes are utilized as random patterns in digital image correlation. The strain distribution and its variation with time under various condition of skin such as bare skin, skin care, and foundation are obtained. The effect of cosmetic product on the skin behavior is elucidated by performing the series of the measurement for several subjects.