UC Davis

The tensile properties of nano-structured materials are often measured by small-scale samples. Specimens may deviate from the sizes and geometries dictated by conventional testing standards, such as ASTM International. The parametric study of this thesis examines the scaling effects present when altering the dimensions of uniaxial tensile test specimens of high-density polyethylene (HDPE); a thermoplastic polymer that is recyclable, can be 3D-printed, and has a wide range of engineering applications, from pipes, to toys, and bottles. Moreover, polyethylene has also a long track record of radiation protection shielding and is being considered for manned space missions beyond the protection of Earth’s magnetic field. In this thesis, the variation of mechanical properties from ASTM D638 Types I-IV for reinforced and unreinforced plastics, to ASTM D3039 typically used for fiber-reinforced composites are studied. These were water-jet machined and tested on a hydraulic machine. A Monte Carlo method for uncertainty estimation was adopted for the probability distribution of maximum stress at the yield point. Furthermore, the stress-strain behaviors are fitted to an empirical model, used in conjunction with finite element analysis, with the goal of predicting the material response of the tensile test results of several standardized geometries. This project is a useful tool for modeling HDPE’s material response across a range of applications and could be extended to other polymers.