Investigation on mechanical properties and finite element analysis of HDPE/EPR filled with CNT irradiated nanocomposites

Abstract

Shoe outsoles experience the most fatigue flexing effect during movement, thus initiating cracks with time. This crack will lead to changes in the mechanical property of the shoe outsole, where the effect of loading is dependent on the mechanical properties of the shoe outsole. Currently, ethylene vinyl acetate (EVA) is used to fabricate shoe outsoles. Due to a decaying problem, radiated high-density polyethylene (HDPE)/ethylene propylene rubber (EPR) filled with carbon nanotube (CNT) are now chosen to replace the current material (EVA) for outsole shoes. EPR possesses superior properties such as higher flexural strength as compared to EVA. Furthermore, when CNT is added as nanofiller to a material, it can increase the lifetime of the material. Electron beam (EB) irradiation can also improve the mechanical property of the outsole. The aim of this study is to fabricate an irradiated HDPE/EPR filled with CNT nanocomposite outsole. The materials were prepared through a blending process involving HDPE, EPR and CNT materials, which are then compression moulded to a size 5 female outsole. The outsole was exposed to EB irradiation for the cross-linking process and its mechanical property characterised via a tensile and flexing test. The tensile fracture specimen was observed morphologically under SEM. Initially, the outsole was modelled in ABAQUS software with the exact design as the fabricated ones. Then, it was compared experimentally for model validation. After that, the outsole was modelled at thicknesses of 4.05 mm, 4.55 mm, 5.05 mm, 5.50 mm, 5.55 mm and 6.05 mm for size 4, 5 and 6. It was found that EB irradiation indeed improved the flexibility of the outsole, but the outsole became stiff with the addition of CNT. The most suitable material to fabricate the outsole was found to be the irradiated HDPE/EPR blend. The obtained numerical results were close to the experimental ones, which are 95% similar to each other. The numerical result simulations enable the prediction of experimental data. The results of finite element analysis (FEA) show that the outsole should be fabricated at a size 6 with a base thickness of 3.05 mm and a tread pattern thickness of 1 mm. This combination of thicknesses gives the best results such as the longest fatigue lifetime, minimum stress applied, and the lightest weight, at 51 g. This project has yielded highly significant results, which future researchers and fabricators can use for predicting the best material to replace the current material for shoe outsoles. The method to determine the fatigue lifetime and the flexibility of the outsole using different materials can also be replicated, and subsequently, will save cost and time required in the fabrication of the outsole.