Session: 03-01-01: Mechanics of Penetration, Shockwaves, and High-Strain-Rate Events: Modeling and Experiments

Paper Number: 99701

99701 - Analysis of the Thermal Response of Polycarbonate Resulting From High Velocity Impact 

Glassy polymers are becoming an increasingly popular solution for safety applications where transparency and light-weight are desired. Examples include safety glasses and face shields. In most cases, these safety solutions are designed to go through large plastic deformation in order to absorb the energy of the incoming projectile. It is well known that as a polymer undergoes plastic deformation, a portion of the mechanical energy is converted into thermal energy. High speed impacts from any incoming projectile will subject the polymer plates to deformations at estimated strain rates anywhere from 1000 to 10,000 (/sec) depending on the conditions of the impact. At these high rates, the thermal energy that is generated from the mechanical work does not have time to dissipate into the environment or diffuse within the sample, so the process can be considered nearly adiabatic. This is expected to cause significantly high rises in the temperature of the specimen. Since the mechanical properties of polymers are highly dependent on the temperature, the rate and magnitude of temperature rise will cause significant changes in the behavior of the polymer chains. In this work, we investigate the thermal response and thermal gradient of polycarbonate under impact loading and high strain rates. The thermal response of the polymer will be studied using direct impact experimentation, as well as high-rate testing equipment (split Hopkinson pressure bar; SHPB) and several thermal measurement methods including IR thermography, a high speed IR sensor, and thermocouples. In recovery split Hopkinson pressure bar technique it is ensured that the sample is only loaded once and only to a desired total level of deformation. This allows for post-mortem analysis of the specimen with known and controlled deformation history. Additionally, the temperature rise in the sample can be measured using a number of techniques over the course of the loading, unloading, and immediately after, until the conduction to the bars remove heat and/or the measurement is no longer viable. Finally, in direct impact experiments, the deformation history at a selected few number of points may be collected via phononic Doppler velocimetry (PDV), while the overall final full-field deformation can be measured accurately after the test. Similarly, the temperature rise may be measured with very high time resolution locally using the high speed IR sensor, while the final temperature distribution may be captured using an IR thermography cameras at a lower rate. The knowledge and data generated from such experiments will be used for modeling the response of the polymers to consider both the rate and temperature effect on the material response.

Presenting Author: Alexander Krueger University of Massachusetts, Lowell

Presenting Author Biography: Alex Krueger is a PhD student at UMass Lowell with research focus on mechanics and physics of polymer under extreme loading conditions.

Authors:

Alexander Krueger University of Massachusetts, Lowell
Daniel Schmidt Luxembourg Institute of Science and Technology (LIST)
Alireza Amirkhizi University of Massachusetts Lowell