Dynamic Deformation and Temperature Field Measurement of Metallic Materials
In this dissertation, we first used high-speed X-ray phase contrast imaging and infrared thermal imaging techniques to study the formation processes of adiabatic shear bands in aluminum 7075-T6 and 6061-T6 alloys. A modified compression Kolsky bar setup was developed to apply the dynamic loading. A flat hat-shaped specimen design was adopted for generating the shear bands at the designated locations. Experimental results show that 7075-T6 exhibits less ductility and a narrower shear band than 6061-T6. Maximum temperatures of 720 K and 770 K were locally determined within the shear band zones for 7075-T6 and 6061-T6 respectively. This local high temperature zone and the resulting thermal instability were found to relate to the shear band formation in these aluminum alloys. Secondly, a high-speed laser phosphorescence thermal imaging technique is developed and integrated with the compression Kolsky bar setup. The temperature field measurement during dynamic loading are performed at 100 – 200 kHz frame rate with a spatial resolution of 13 µm/pixel. The dynamic compression of copper shows 312 K temperature rise among the material surface. Experiments with thermocouple are also conducted and the results verifies the laser measurement. In the dynamic shear of aluminums, the temperature evolution during adiabatic shear band formation was observed and the results are compared with infrared measurements. The shear band was found forming at approximately 400 K and 440 K for 7075-T6 and 6061-T6, respectively, while the maximum temperature is measured as 650 K for 7075-T6 and 800 K for 6061-T6. Although the maximum temperature agrees with the infrared results, thermal softening is not considered as the main cause of the ASB formation due to the low temperature when the shear band forms.