Lecture
This lecture covers the empirical constitutive relations used in material science, focusing on the Johnson-Cook model. It explains how to collapse experimental data into single equations, considering factors like temperature, flow stress, and strain rate. The lecture also discusses the parameters involved in curve fitting and the weaknesses of the model. Additionally, it explores the effects of dislocation movement, shear strain, and the velocity of dislocations under applied stress. The presentation delves into the thermally activated motion of dislocations, the obstacles they face, and the role of temperature in overcoming barriers. Finally, it touches on physically based constitutive models, emphasizing the connection between high strain rate behavior and evolving microstructures during deformation.