Plastic Deformation Under Simultaneous Cyclic and Unidirectional Loading at Low and Ultrasonic Frequencies

Abstract Whenever cyclic strain is superimposed on undirectional loading, the inherent asymmetry of plastic deformation causes an apparent decrease in the externally observable load. This facilitation of deformation can be spectacular at ultrasonic frequencies. Since ultrasound is used for both materials testing and metal forming, the actual stresses reached within the samples must be of concern. The stress dip might be caused by strain-induced recovery, by microstructural changes or by elastic stress relaxation. Aluminum alloy samples were simultaneously exposed to static and vibratory loading at 0.5, 1, 10, 50 and 20 000 Hz. No frequency influence was observed at room temperature. The stress dip is caused by elastic relaxation.