Biomechanical Evaluation on Selective Laser Sintering Cellular Structures Applied to the Shoe Midsole – a Dynamic Finite Element Analysis

• Main Authors: ZHENG, YU-CHENG, 鄭宇晟
• Other Authors: CHEN, WENG-PIN
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/ux6rd4

碩士 === 國立臺北科技大學 === 機械工程系機電整合碩士班 === 107 === As the advancement of additive manufacturing technology, many internationally renowned shoe brands have developed new footwear by utilizing additive manufacturing technology. The footwear made by additive manufacturing technology is featured with cellular midsole structure. It is also aimed to have better biomechanical performance during heel strike and midstance phases of gait. It has been reported in literature that the cellular structure with characteristic of negative Poisson’s ratio (auxetic structure) has better capabiliity to withstand compressive load and higher fracture toughness. Such structure may be a good candidate for shock absorption applications. The purpose of this study was to design different auxetic structures and to apply them for shoe midsole design. Dynamic finite element (FE) analysis was used to investigate the biomechanical effects of such cellular midsole structures on the foot during gait cycle. Three types of cellular, auxetic structures were designed and named: Type A, B and C structures with porosity ratios of 59%, 68% and 70% respectively. The FE models of the cellular structures were generated with both solid and beam elements by using HyperMesh pre-processing software. Then, LS-DYNA FE software was used to analyze the cellular structures under compression loading. The test specimens of the cellular structures were fabricated with TPU (Thermoplastic polyurethane) material by using a selective laser sintering 3D printer. The compressive mechanical properties of the cellular structure specimens were obtained by following the ASTM D3575-14 standards and were compared with the finite element analysis results. The shock absorption test of the cellular structures were also conducted with ASTM F1976-13 standard. In order to investigate the biomechanical effects of the cellular structure when used as shoe midsole, three different cellular pads were created using beam elements and then combined with a 3D finite element foot model for dynamic FE analysis during gait loadings. From the compression tests, the force-displacement results from the mechanical tests and FE analyses were compared. Pearson's correlation ratios in between the FE analysis results by using solid elements and beam elements were calculated for each of the three types of cellular structures. The correlation ratios showed that the mechanical properties were highly correlated among these three types and were all greater than 0.80. The energy absorption test values of Type A, B and C structures were 0.338 J, 0.485 J and 0.735 J, respectively. Therefore, Type C structure has the best shock absorption capability. The dynamic finite element analysis results showed that the peak plantar pressure during gait on the calcaneus area were 456.48 kPa, 417.72 kPa and 400.30 kPa, respectively. In the cellular structures analysis, it was demonstrated that the beam element model could effectively replace the solid element model and greatly reduce the analysis time. It was found that the Type C structure had the best shock absorption and plantar pressure reduction capabilities, the Type B structure had the best effect of stress distribution on the cellular structure during the dynamic gait cycle. In the present study, the complex cellular structures can be reasonably represented by simplified beam elements for finite element analysis. Also, the biomechanical characteristics of the foot using dynamic finite element analysis can be evaluated as well. This study can provide a useful reference for future studies on cellular structured midsole designs.