Studies indicate that injury risks in tennis depend on the playing surface type. In order to assess loading during tennis specific movements, plantar pressure parameters are determined and analyzed. So far, only comparisons between whole stride sequences on different surfaces have been performed showing some inconsistent results. We assumed that on the more slippery clay higher vertical forces are required to accelerate, and that on hard-court higher loadings occur during deceleration. Hence, we analyzed the influence of the playing surface on respective types of steps. Eight experienced male tennis players performed two different tennis specific movements on clay and hard-court. We used a Pedar-X insole measurement system for determining selected plantar pressure parameters for the whole foot as well as for the forefoot and rear foot area. Steps were categorized as accelerating or decelerating regarding the path of the center of pressure during impact of the foot on the ground. For accelerating steps, a multivariate analysis revealed significant differences (Pillai-Spur; p < .05) for both repeated factors as well as their interaction for both playing conditions. All loading parameters were significantly higher in the forefoot area on clay for one of the two playing conditions investigated. For decelerating steps, the multivariate analysis revealed significant differences for both repeated factors for one playing condition. Higher values were observed for all loading parameters in the rear foot area in both playing conditions on clay. Running styles during tennis specific movements depend on the court surface. Separate analyses of acceleration and deceleration steps may help revealing high-risk parts and periods.
Nowadays, additive manufacturing techniques such as the Fused Filament Fabrication appear to be among the most promising additive manufacturing methods for enabling modern industry to produce components of high geometrical complexity. The main characteristic of this method is the deposition of thermoplastic polymers that can be further reinforced with chopped and/or continuous fibers that attributes to the product some unique structural characteristics. Nevertheless, the process is susceptible to a variety of defects that are derived from the fabrication process parameters, such as porosity, insufficient fiber impregnation with the polymer and fiber disorientation. On the other hand, since the applicability of the process depends on the development of numerical tools for assessing the effects of these defects, the accurate detection and quantification of them is a crucial part of it. In the present work, these defects are studied experimentally by implementing an X-Ray computed tomography testing campaign. The manufacturing defects, as a form of initial damage, are identified using well-established techniques while a complete analysis of the distribution of porosity is presented for various zones of Onyx, Onyx/Carbon and Onyx/Glass fiber reinforced structures. Finally, the tendency of the overall pore content to increase with increasing number of continuous fiber reinforcement was identified as well as porosity variations in printing direction are presented.
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