Investigation of the dragging stress of aluminium under cyclic loading

Abstract

The effect of the variation of the dislocation velocity on the dragging stress of aluminium under cycling loading has been investigated. Hydrogen diffusion around a dislocation was simulated by the finite difference method, and the dragging stress was calculated from the hydrogen distribution. The velocity of the dislocation changed in a sinusoidal manner. The dragging stress depended on the frequency of the sinusoidal velocity variation. In the low-velocity region, the maximum dragging stress decreased with increasing frequency. However, in the mid-velocity region, the maximum dragging stress increased with increasing frequency. The dragging stress did not depend on the frequency in the high-velocity region. A dragging stress model for aluminium with hydrogen under a variable dislocation velocity is proposed. When the frequency is below 0.2 kHz (i.e., in general fatigue tests), the dragging stress–velocity relationship under a constant velocity of the dislocation in the case of aluminium with hydrogen can be used. In the high-velocity region, the dragging stress can be determined using the relationship between the dragging stress and velocity under a constant velocity of the dislocation. The dragging stress under the low-velocity condition can be modelled using an ordinary viscosity model. In the case of actual hydrogen concentration, the dragging stress is thought to be much smaller than 1 MPa.