Session: 12-23-02: Symposium on Multiphysics Simulations and Experiments for Solids

Paper Number: 145918

145918 - Verification and Validation of a Novel Miniaturized Kolsky Bar Using Published Polymethyl Methacrylate (Pmma) Data. 

The strength of Polymethyl Methacrylate (PMMA) depends on both temperature and rate of loading (strain rate), according to published literature. PMMA becomes brittle at low temperatures and ductile at higher temperatures. At elevated strain rates, PMMA undergoes strain hardening and transitions to a brittle behavior from a ductile behavior. The mechanical behavior of PMMA can be verified through the high strain rates achieved by a miniaturized Kolsky bar system. Given the significant data found in published literature, the temperature and rate dependency, PMMA may serve as a good verification material for establishing confidence in new Kolsky systems, as well as for new users of such devices to establish proficiency in the testing procedure.

In order to verify and validate our in-house Kolsky bar system at Penn State University, our general approach is to compare computational and experimental results to published literature. The computational model, constructed in Abaqus, serves as a ‘digital twin’ of our physical system. In the simulation, there are four main components just like the physical system: the incident bar, transmission bar, and striker bar, as well as the sample. The Kolsky bar setup is restricted to allow movement only in the axial direction. Furthermore, generation of a half symmetry simulation using Abaqus enables the ability to incorporate gravity and axial misalignment and produce results that are similar to the experimental results. Axial misalignment of the bars and gravity are initially modeled using a static analysis to establish contact loads, and pre-stress in the system. Then an explicit dynamic analysis is used to simulate the dynamic loading. The striker bar and sample are not included in the gravity load because the striker is fully supported along its length in the launch tube. In terms of element types, a hex dominated (C3D8) structure is used. Similar to the published results, we assume a Johnson-Cook model for capturing the mechanical behavior of PMMA. The values of the Johnson-Cook model are found through a fit of published data including the yield stress, strain hardening coefficient, strain hardening constant, and the strain rate sensitivity coefficient.

This simulation output provided the axial stress and strain acting on the sample over time of the impact. A true stress vs true strain graph was created and compared to the true stress vs true strain of published data. Experimentally, our in-house Kolsky bar comprises of a 3.16 mm diameter bar and is used to generate axial stress and strain data. In this paper, we present computational and experimental results from our in-house Kolsky bar compared to published literature. The values of axial stress versus strain are compared to the experimental published data. We examined the mechanical response of strain rates, ranging from 0.001 s^-1 to 2200 s^-1. We also explore the deformation mechanisms and mode of failure using quantitative computed tomography (QCT). In summary, this work aims to provide a process to verify and benchmark a Kolsky bar system.

Presenting Author: Ryan Grube The Pennsylvania State University

Presenting Author Biography: B.S. in Mechanical Engineering at PSU. Current graduate student working towards his M.S. in Mechanical Engineering at PSU and works at The Kraft Lab.

Authors:

Ryan Grube The Pennsylvania State University
Thomas Hannah Los Alamos National Laboratory
Valerie Martin Los Alamos National Laboratory
Stephen Ellis Los Alamos National Laboratory
Reuben Kraft The Pennsylvania State University