Three-dimensional (3D) printing is an efficient and sustainable technology useful in various manufacturing fields. The aim of this study was to investigate the applicability of thermoplastic polyurethane (TPU) as a 3D printing material and the conditions related to the use of TPU as personal protective equipment. The tensile strength, shock absorption, and compressibility were evaluated for different infill and thickness conditions. An increase in the infill rate led to an increase in the tensile strength, regardless of the sample thickness. Similarly, the compression energy increased as the infill increased. Both the shock absorption and compression properties increased as the thickness decreased under identical infill conditions. The actual shock absorption test data were compared to the results of structural analyses, which confirmed the potential for predicting impact deformation through the analysis of the tensile characteristics and the basic properties of a 3D printed material.
Novel materials have been recently developed for coping with various environmental factors. Generally, to improve the thermal comfort to humans in cold environments, securing an air layer is important. Therefore, this study analyzed the thermal properties of 3D spacer technical materials, 3D printed using thermoplastic polyurethane, according to the structural changes. Four 3D spacer technical material structures were designed with varying pore size and thickness. These samples were moved into a cold climate chamber (temperature 5 ± 1 °C, relative humidity (60 ± 5)%, wind velocity ≤0.2 m/s) and placed on a heating plate set to 30 °C. The surface and internal temperatures were measured after 0, 10, 20, and 30 min and then 10 min after turning off the heating plate. When heat was continuously supplied, the 3D spacer technical material with large pores and a thick air layer showed superior insulation among the materials. However, when no heat was supplied, the air gap thickness dominantly affected thermal insulation, regardless of the pore size. Hence, increasing the air gap is more beneficial than increasing the pore size. Notably, we found that the air gap can increase insulation efficiency, which is of importance to the new concept of 3D printing an interlining.
To develop baseball catcher leg guards, 3-dimensional (3D) methodologies, which are 3D human body data, reverse engineering, modeling, and printing, optimized guard design for representative positions. Optimization was based on analysis of 3D body surface data and subjective evaluation using 3D printing products. Reverse engineering was used for analysis and modeling based on data in three postures: standing, 90° knee flexion, and 120° knee flexion. During knee flexion, vertical skin length increased, with the thigh and knee larger in anterior area compared to the horizontal dimension. Moreover, 120° knee flexion posture had a high radius of curvature in knee movement. Therefore, guard designs were based on increasing rates of skin deformation and numerical values of radius of curvature. Guards were designed with 3-part zoning at the thigh, knee, and shin. Guards 1 and 2 had thigh and knee boundaries allowing vertical skin length deformation because the shape of thigh and knee significantly affects to its performance. Guard 2 was designed with a narrower thigh and wider knee area than guard 1. The guards were manufactured as full-scale products on a 3D printer. Both guards fit better in sitting than standing position, and guard 2 received better evaluations than guard 1. Additional modifications were made and an optimized version (guard 3) was tested. Guard 3 showed the best fit. A design approach based on 3D data effectively determines best fitting leg guards, and 3D printing technology can customize guard design through immediate feedback from a customer.
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