Describing the plastic deformation of aluminium softball bats

Hollow aluminium bats were introduced over 30 years ago to provide improved durability over wooden bats. Since their introduction, however, interest in hollow bats has focused almost exclusively around their hitting performance. The aim of this study was to take advantage of the progress that has been made in predicting bat performance using finite elements and apply it to describe bat durability. Accordingly, the plastic deformation from a ball impact of a single-wall aluminum bat was numerically modelled. The bat deformation from the finite-element analysis was then compared with experiment using a high-speed bat test machine. The ball was modelled as an isotropic, homogeneous, viscoelastic sphere. The viscoelastic parameters of the ball model were found from instrumented, high-speed, rigid-wall ball impacts. The rigid-wall ball impacts were modelled numerically and showed good agreement with the experimentally obtained response. The strain response of the combined bat-ball model was verified with a strain-gauged bat at intermediate ball impact speeds in the elastic range. The strain response of the bat-ball model exhibited positive correlation with the experimental measurements. High-speed bat-ball impacts were performed experimentally and simulated numerically at increasing impact speeds which induced correspondingly increased dent sizes in the bat. The plastic deformation from the numerical model found good agreement with experiment provided the aluminium work hardening and strain rate effects were appropriately described. The inclusion of strain rate effects was shown to have a significant effect on the bat deformations produced in the finite-element simulations. They also helped explain the existence of high bat stresses found in many performance models.     

我国网球项目奥运备战运动员技、战术水平跟踪监测及比赛胜负规律分析

运用电视、录像、临场观察和数理统计等方法,对国家女子网球队奥运备战运动员主要比赛过程进行跟踪监测,研究分析我国女子网球运动员技战术水平和实力现状,正确定位我国女子网球整体水平,并从众多的统计数据中揭示网球项目比赛规律。     

篮球运动中防守无球队员能力培养刍议

现代篮球运动，防守技战术愈发重要，本文对篮球运动中防守无球队员能力培养问题进行了研究，提出了在今后的训练和比赛的过程中要不断提高防守意识，加强能力培养，强化日常训练，使该技术动作得到加强与提高。