Evaluation of shock attenuation properties of sport surfaces with two-dimensional model

Abstract

Shock attenuation property of sports surfaces is especially important not only for the athlete's performance but also for injury prevention. To evaluate the properties of the sports surfaces, some sports governing bodies often adopt friction tests and shock attenuation tests to determine the horizontal and vertical characteristics, respectively. Although the diagonal impacts are often observed in athletic sports, shock attenuation test treats only the vertical impact test. Therefore, we developed a two-dimensional impact test device for examining the two-dimensional cushioning characteristics of sports surfaces in previous studies. To produce a simultaneous two-dimensional force against a test specimen, we incorporated a parallelogram linkage in the measuring system. The weight is dropped onto the upper side of the parallelogram linkage with various height and various initial angles. Initial angle controls the ratio of vertical/horizontal impact forces. In previous studies, FR (Force Reduction) values are calculated from experimental un-cushioned and cushioned forces for evaluating the shock attenuation properties. Additionally, to evaluate the maximum deformation during the impact, a biaxial accelerometer is attached to the sensor unit. Although FR values are simple and easy to calculate from the experimental data, it needs a vast cost because there are huge number of combinations of impact angles, magnitude of impacts and impact durations if the tests should be covered for various human activities. Therefore, in previous studies, we proposed the vertical viscoelastic model which can represent the behavior of sports surfaces during the impact for evaluating the shock attenuation properties. In this study, we propose the two-dimensional viscoelastic model of sport surfaces for evaluating the two-dimensional cushioning properties. Finally, proposed model can be used for estimating the impact forces from the experimental data.