| Abstract Scope |
Ultrasonic softening describes the material flow stress reduction during plastic deformation under ultrasonic vibration. Despite the stress drop consistently observed from various ultrasonically assisted (UA) tension and compression, fundamental mechanisms remain elusive. Besides the stress superposition theory, dislocation movement has been proposed. However, limited experimental validation has been provided so far. In this study, low carbon steel and aluminum alloys are thoroughly studied using UA micro-tensile tests with digital imaging correlation (DIC). The static and dynamic strain aging, reflected as the Luders band and Portevin–Le Chatelier (PLC) band in steel and aluminum, respectively, indicate UA effects on dislocation movement. In steel, UA increases the strain rate of Lüders band. In AA2024-O tempered and T4 treatment, AA2219 with varying grain sizes, UA consistently promotes PLC band formation and increases the propagation speed, which can be attributed to enhanced dislocation movement and unpinning from solute atmosphere at a lower stress. |