The strength of Polymethyl Methacrylate (PMMA) depends on temperature and rate of loading (strain rate), according to published literature. PMMA becomes brittle at low temperatures, ductile at higher temperatures, and exhibits a brittle behavior at elevated strain rates from strain hardening. We are exploring if the high strain rate mechanical behavior of PMMA can be verified by using a miniaturized Kolsky bar system. Given significant temperature and rate dependent data in published literature, PMMA may serve as a good verification material to establish confidence in the highest achievable strain rate for new and miniaturized Kolsky bar systems.
To evaluate the highest strain rate for our Kolsky bar system at Penn State University, computational and experimental results are compared to published literature. A computational model of our physical system with 3.16 mm diameter bars is created in Abaqus and retains the main components of the physical system: the incident bar, transmission bar, striker bar, and cylindrical sample. The Kolsky bar setup is restricted to only allow movement in the axial direction. Similar to previous published work on PMMA, we assume a Johnson-Cook (JC) model to capture the mechanical behavior of PMMA. The JC model constants are found through a fit of the published data. The sample will have a range of dimensions, retaining a length to diameter ratio of at least 0.5 to promote accurate results while maximizing the strain rate.
The simulation output of the axial stress and strain acting on the sample over time of the impact is used to create a true stress vs true strain graph for comparison to published research data and experimental data. The mechanical response of high strain rates, deformation mechanisms, and mode of failure using quantitative computed tomography are also examined. This work aims to rigorously examine the range of applicability for experimental measurements using miniaturized Kolsky bar systems.
2025-04-09 09:00:00
