Apparent strain of a pipe at plastic bending buckling state

An expression for apparent strain of a pipe at plastic bending buckling status is proposed in the present paper. The material of the pipe is considered as a rigid-perfectly plastic one, and the cross section of the pipe during the pipe-bending process assumes to be elliptic gradually. The energy rate for the pure bending of the elliptic pipe is proposed firstly, and the energy rate of cross-sectional ovalizing of the pipe is derived afterward. Furthermore, both the energy rates are combined to analyze the pipe bending buckling. As a result, an apparent strain expression of a pipe at the plastic bending buckling status is proposed. The predicted result of the new strain expression of pipe bending at buckling status is compared with the available test data and shows that the new formula is reasonable.