EFFECT OF STRESS RATIO AND LOADING CONDITION ON THE FATIGUE THRESHOLD

The fatigue threshold behaviour of cold-worked copper tested under different fatigue loading modes (axial, bending) and conditions (various test frequencies and stress ratios) has been investigated. Emphasis was placed on the determination and evaluation of crack-closure effects as well as the computation of the effective fatigue threshold stress intensity. A special strain gauge technique was used to determine the load displacement curves. A newly proposed closure evaluation method was introduced which permits the explanation of the dependence of the fatigue threshold on stress ratio and loading conditions. The effective fatigue threshold of about 3 MPa square-root m was determined for cold-worked copper. Various evaluation procedures are discussed.