Shear and Tensile Fracture Analysis of HDPE and PP-Experimental Results Combined with Simulation

Abstract: For the past many years, packaging have been designed just to preserve food items and to catch the attention of the customers by concentrating on the design rather than making it easy to open. But now companies like Tetra Pak are focusing on the flexibility of packaging design by making it user friendly without compromising the design quality. To predict the overall opening performance, it is required to understand the general mechanical and fracture behavior of a material. This thesis project focused on the study of two polymer materials, Poly Propylene (PP) and High Density Poly Ethylene (HDPE) which are used to manufacture screw caps of the food packaging. Further fracture study will enable to understand how the material will behave under shear opening. Physical experiments were performed on both materials for finding Tensile and Shear properties of the material. Dog bone shape for the case of continuum, 1mm and 2mm centered crack have been tested under Mode I loading, and tensile material model for Abaqus was constructed. Properties i.e. fracture toughness and energy release rate was determined for both of the materials by using Modified Strip Yield Model (MSYM). Whereas specially designed shear specimen has been loaded under Mode II to construct shear material model for simulation. Finally numerical simulation results have been validated against physical results of torque opening of screw cap which fracture under Mixed Mode (Tensile and Shear) with the aim of replacing experimentation by simulation. The results were compared for both materials and more favorable material for screw cap production was determined.