|M.Sc Student||Regev Alon|
|Subject||A Comparison of Core and Surface Temperature of a Ductile|
Polymer under High Strain Rate Loading
|Department||Department of Mechanical Engineering||Supervisor||Professor Daniel Rittel|
|Full Thesis text - in Hebrew|
Thermo mechanical coupling has been addressed in many instances, and it has been shown that the plastic energy which is invested in material deformation could be partly transferred to heat. A major problem is that of real time monitoring of the specimen's temperature changes under high strain rate deformation.
There are two main methods for high strain rate measurements of temperature: Infrared detectors (IR), and embedded thermocouples (ETC).
In 1998 Rabin & Rittel conducted a thermal analysis of the specimen's temperature difference between the core and the surface under dynamic conditions. The results were expressed in terms of the Biot and Fourier numbers. From an experimental point of view, one should note that the IR technique provides a surface measurement while the ETC concerns the bulk of the material. So far, there has been no direct measurement aimed at confronting the two techniques, in light of the above mentioned analytical results.
Therefore, the goals of this work are:
(1) Compare the core temperature (ETC) with the surface temperature (IR) of a ductile polymer subjected to impact loading.
(2) Evaluate the Taylor b factors (efficiency of the thermo-mechanical conversion) for each experiment (secondary goal).
The experimental system: (1) The mechanical actuator – A Split Hopkinson Pressure Bar (SHPB). (2) The sampling systems – two strain gages (part of SHPB); An infrared system; ETC in each specimen. (3) The data processing – A Matlab programs.
Calibration of the thermal system: The goal of the calibration is to produce a situation in which the voltage measured with the infrared detector is calibrated against the specimen’s temperature measured by the thermocouple, provided adequate conditions for which the bulk and surface temperatures are identical.
Experiment description: The investigated material was commercial as-received Polycarbonate cylinders. The cylinders’ diameter was 10mm and the thickness was 3, 4 and 5mm. In each specimen, a T-type thermocouple was embedded.
The results: The present study has found that for a ductile polymer, under high strain rate, there is an excellent match between the core and the surface temperatures measured by two distinct techniques.
Discussion and conclusions: (1) It is the first time that simultaneous temperature measurement with IR and ETC is carried out on dynamically loaded polymers. (2) The measurements support Rabin & Rittel's analytical results . (3) The calibration process has to be done at the beginning of every experiment. (4) Several experimental factors that affect the quality of the measurements were systematically identified in this work.