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YIELD STRESS UNDER REPEATED LOADING AFTER APPLYING DIFFERENT DEFORMATION PATH FOR LARGE TENSION AND SHEAR

This paper describes the yield phenomenon when a repeated loading is applied to the structure after giving a large pre-strain on it. In the series of our previous research, focusing on the fundamental deformations such as tension or shear, changes of yield stress as the number of repetition increases have been investigated experimentally by using test specimens of annealed pure copper. In the determination of yield stress value, the method by using slope of stress-strain curve at yield has been used instead of proof stress. As a consequence, it has been found that if the type of pre-deformation and the type of deformation in repeated load are the same, yield stress at the pre-deformation side has a declining tendency as compared with opposite side. Therefore, it is predicted that the yield stress under repeated loading after applying a large deformation is closely related to the loading history in large deformation previously applied. Thus, in this study, in order to clarify the influence of pre-deformation on the yield behavior under repeated loading, the experiments are performed by changing the order of tension and shear in pre-deformation. Consequentially, it is clarified that the declining tendency of yield stress under repeated loading is closely related to the yield surface anisotropy, which is formed during the second half of the pre-deformation.