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Describing the plastic deformation of aluminium softball bats 总被引：1，自引：1，他引：0
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. 相似文献
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The procedures used to produce a research-based teaching evaluation system, containing low-inference indicators of effective and ineffective teacher behavior, included instrument development, content validation, and field testing. An extensive reliability study produced estimates for three types of consistency: intercoder agreement (r = 0.85), stability across teaching situations r = 0.86, and discriminant reliability among teachers (r = 0.79). The norming component of the study conducted in 45 schools, generated over 1200 observations of current teacher practice at all grade levels and in various subject areas. The results indicated the substantially generic nature of these behaviors; only grade level and instructional method (interactive, lecture, and independent seatwork) produced meaningful differences among groups of teachers. In addition, the average teacher used most of the effective behaviors (70%), and a few of the ineffective behaviors (8%) during observation. These results support the instrument's value in teacher training, remediation, and evaluation. 相似文献