Date of Award
Spring 4-15-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Mechanical Engineering
First Advisor
John Borg
Second Advisor
John Moore
Third Advisor
Le Zhou
Abstract
The shock-induced α → ε → α phase transition in iron-based alloys is critical for understanding material behavior under high strain rate loading, such as in impacts or explosions. However, the influence of elevated temperatures on this transition remains underexplored in low carbon steels. This thesis uses plate impact experiments with a light gas gun to investigate the effects of preheating up to 200°C on the Hugoniot, spall strength, and phase transition of a low carbon steel. Shock-recovery experiments with momentum trapping rings were used to preserve samples for post-shot analysis including optical microscopy, microhardness, X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). Results showed that in the α phase, spall strength increased with temperature due to dislocation drag while the Hugoniot elastic limit decreased. Previously, this behavior has only been observed for pure metals, not alloys. The α phase Hugoniot parameters s and C0 decreased at 200°C compared to room temperature. CTH simulations utilizing those results for the Mie–Grüneisen equation of state showed an improved fit to experimental data at elevated temperatures. The α → ε phase transition onset occurred between 12.9 and 13.6 GPa at room temperature, with minor reductions to 11.8 and 12.6 GPa at 200°C. Recovered samples exhibited a lower hardness and microstrain in the phase transitioned region compared to the region remaining α phase. This is attributed to this material’s beginning structure of tempered martensite compared to previous work that has only considered annealed ferrite.