Buckling and wrinkling of rectangular hollow sections curved in three-point-roll bending

Curved aluminium extrusions are applied in a wide range of industrial applications. Because extrusions are initially straight, an additional process is required to curve the product. Undesired wrinkling of the plate part at the inner radius is frequently observed during the curving process. Wrinkling has already been extensively studied for the rotary-draw bending process. This paper aims at predicting the conditions for which wrinkling of a hollow section can occur during the three-point-roll bending process. It is shown that the most important condition for wrinkling is that buckling of the compressed plate part at the inner radius occurs. An analytical prediction model for buckling is presented, which predicts the critical bending radius as a function of the plate slenderness. The analytical model is validated with a finite element model, which in turn is validated with an experiment. Both the finite element model and the experiment confirm that wrinkling does not occur if the applied radius exceeds the model predicted critical radius.