Abstract

Tests were conducted on the heel portions of new and worn running shoe midsoles, to investigate the effect of distance covered on shock absorbency and material microstructure. Shock absorbency, as measured by the area under a load-deformation curve, was found to reduce with distance covered. However, the percentage reduction was dependent on the rate of application of load to the midsole, reducing as the rate increased. Scanning electron microscopy indicated that the material microstructure deteriorated with distance covered. The appearance of holes or splits in the cell walls of the microstructure was observed in all worn samples, and this effect was generally more significant in the shoes worn for the greatest mileage. In addition, cellular collapse was found in the midsoles worn for 1,100 miles, (1,760 km), the cells being deformed from a spherical to a cylindrical shape, with the long axis of the cylinder being perpendicular to the direction of stressing. The reduction in shock absorbency with distance covered, has been explained in terms of the determination of the material microstructure. Verf.-Referat