Development of Kolsky Bar Techniques and the Experimental Characterization of Ultra High Molecular Weight Polyethylene Composites
Open Access
- Author:
- Hannah, Thomas
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 12, 2023
- Committee Members:
- Reuben Kraft, Chair & Dissertation Advisor
Charles Bakis, Outside Unit Member
Guhaprasanna Manogharan, Major Field Member
Albert Segall, Outside Field Member
Robert Kunz, Professor in Charge/Director of Graduate Studies - Keywords:
- Kolsky Bars
High Rate Strain Analysis
Composite Analysis
Miniature Kolsky Bars
Finite Element Analysis
Solid Mechanics
Experimental Design
Composite Failure Analysis
High Resolution Imaging
Orthogonal Arrays - Abstract:
- The goal of this work is twofold. One part is to develop both the experimental techniques and advanced finite element modeling techniques necessary for understanding and analyzing data collected using a miniature 3.16 mm diameter Kolsky bar or Split Hopkinson Pressure Bar for high rate experimentation. Additionally, a robust analysis technique to gather statistically significant data is developed to simplify the experimental data gathering process and ensure the significance of the results. The work focuses mainly of the development of the Kolsky equipment and techniques, as well as methods for identifying error sources during testing. Additionally, models of the SHPB system have been generated using the finite element code Abaqus®, and are used throughout the project to aid in system characterization and experimental design efforts. Special attention is paid to the differences between miniature systems and full size ones, especially where data collection rates and sampling frequency are concerned. The use and characterization of paper pulse shapers is also developed to aid in the testing of UHMWPE samples at rates in excess of 10^4 strain per second. The second aspect of this work is to apply these techniques to the characterization of Dyneema® which is a composite consisting of Ultra High Molecular Weight Polyethylene (UHMWPE) fibers set in a polymer matrix, in this case HB26 hard laminate. Additionally, this work entails the design and implementation of full scale high speed impact tests using UHMWPE targets in multiple configurations to examine the variation in response due to a change in initial conditions and to evaluate the change in damage mechanisms. Finally, high resolution Computer Tomography or CT scans are used to evaluate the damage mechanisms observed in both the Kolsky bar testing and the plate impact testing nondestructively and without otherwise effecting the failure surfaces and structures. Mechanisms displayed in the Kolsky experiments are then compared to those observed in the plate impact tests to determine if and where the type of data collected from Kolsky bar tests can be applied to any future modeling efforts of the composite. Three fundamental knowledge gaps to be addressed in this work are: 1) Can a newer generation of “miniature” Kolsky bars generate repeatable and reproducible data? 2) How does Dyneema® respond differently increasing the strain rate from 10^3 strain per second to 10^4 strain per second? 3) Are there similar damage mechanisms seen in small scale Kolsky tests and large scale impact tests, and where could the Kolsky bar data be applied to future modeling efforts?