Evaluation of tread pattern by observing interface between shoe sole and sliding surface

Falls in everyday life can cause serious disability or death especially in older people. Recently, the need for safety against falls has increased, thus shoes are required to have high slip resistance, even on wet surfaces with water or oil. On a smooth surface, most of the friction is adhesive. Adhesion friction is caused by adhesion at the interface where the shoe sole and the road surface are in contact each other. When the surface is wetted with water or oil, the total frictional force is greatly reduced because the contact area is reduced by the intervening liquid film, thereby reducing the adhesive friction. The tread pattern of the shoe sole forms grooves which allow water to escape and promote contact between the shoe sole and the road surface. Therefore, the design of the sole tread pattern has a significant effect on slip resistance on smooth surfaces. The purpose of this study is to evaluate the tread pattern and develop a new tread pattern by observing the sliding state simply under lubrication using specimens that simulate the tread pattern of a shoe sole. The coefficient of friction was acquired by traction tests, and at the same time, visualization of fluid flow by PIV (Particle Image Velocimetry) was attempted. PIV is a method of visualizing fluid flow by tracking the motion of particles dispersed in the fluid.