Mechanical performance of additive manufactured shoe midsole designed using variable-dimension helical springs

Abstract

The mechanical properties such as energy absorption, crushing behavior, and strength-to-weight ratio of graded density structures are significantly better when compared with uniform density counterparts. Graded density structures have been widely investigated due to recent developments in additive manufacturing (AM) technology, which can easily manufacture complex geometries. The study explores the significance of variable-dimension helical spring (VDS) to be used in shoe midsole to improve the stiffness, energy absorption, and energy return. Two novel shoe midsoles are designed using the variable-dimension helical springs and their performance was compared with a third shoe midsole designed using uniform-dimension helical spring (UDS). Variable-dimension shoe midsoles were designed according to the actual pressure distribution applied by the human foot on the midsole. The Multijet fusion AM process was employed for the fabrication of all shoe midsole samples. It is revealed that despite the same mass and bounding box, variable-dimension midsoles have significantly improved mechanical properties compared to uniform-dimension midsole. It is found that the VDS midsole has sixfolds higher force-bearing capacity, and has a lower permanent material setting phenomena when compared to UDS midsole. Moreover, a higher (45%) distortion was found in the UDS midsole after the loading-unloading experiment when compared to the VDS midsole (24%) distortion. A further comparison of the VDS midsole was carried out with the commercially available wave spring-based midsole. Despite about 2-fold higher weight of the wave spring-based midsole, the VDS polymer midsole has higher mechanical properties found in terms of flexibility and force-bearing capacity. Finally, it is concluded that the VDS structure of the midsole can enhance the mechanical properties such as force-bearing capacity, flexibility, and stability with a higher strength-to-weight ratio. This study also proves the feasibility of design and AM of customer-specific shoe midsole.

Investigation of Compression and Buckling Properties of a Novel Surface-Based Lattice Structure Manufactured Using Multi Jet Fusion Technology

“…Fabrication of samples with nylon materials revealed the advantages of mechanical properties, such as printing relatively thin, flexible joints [ 41 ]. The Scanning electron microscope (SEM) micrographs’ details can be found in the picture with magnification in a previous study [ 42 ]. The PA 12 materials’ linear properties mentioned in an earlier study [ 22 ] were also used in the present study.…”

“…The five tensile specimens’ resulting nominal and true stress-strain curves are considered from the authors’ previous study [ 42 ]. The elastic and plastic nominal stress-strain data up to the tensile tests’ necking were converted to true stress-strain data using the equations depicted in [ 43 ].…”

“…In this study, all 24 specimens were fabricated by a multi jet fusion 580 3D printer (HP, Palo Alto, CA, USA) using PA12 materials [ 44 ]. Multi jet fusion fabrication and post-processing details can be found here [ 42 ]. All samples were printed in the same printing batch, same layer height (80 μm), and same speed (1817 cm 3 /h), and were placed near the center of the build unit in the same orientation to minimize the effects of the printing parameters.…”

Parametric investigation of functionally gradient wave springs designed for additive manufacturing

“…Among all, helical springs have been studied the most for its mechanical behavior [20], nite element analysis of closely coiled helical springs [21] ,the effect of various parameters [22] as well as variable dimensions [23] were also investigated. The same author designed and investigated the performance of midsole by using the variable dimension helical springs [24]. Also, helical springs were investigated for the static as well as dynamic characteristics in the application of suspensions of railway vehicles [25].…”

Investigating mechanical properties of 3D printed parts manufactured in different orientations on Multijet printer

“…The optimized results were found at raster angle (90°), horizontal orientation and glossy surface nish. Ali et al [26] compared the two mid soles of helical spring with variable dimensions (VDS) and uniform-dimension helical spring (UDS) mechanical-structure and the commercially available wave spring midsole fabricated on multi jet fusion. Experimental and numerical methods were used to improve energy absorption and strength.…”