The wrinkle generation process of high-strength steel sheets in compression is investigated by finite element method (FEM) simulation and experiment. When a high-strength steel sheet is compressed under a pad with a constant load and initial clearance, there exist two modes in the wrinkle generation process. One is the wrinkle growth mode with the progress of compression upon lifting the pad. The other is the wrinkle disappearance mode, where the wrinkle generated at the early stage of the compression process vanishes with the decrease in clearance between the pad and the sheet resulting from the increase in sheet thickness. The wrinkle disappearance mode is applicable when the pad load is higher than the initial peak value of the wrinkle pushing force in compression.
To calculate the required pad load in the compression of high-strength steel sheets under the wrinkle disappearance mode, a theoretical model based on the balance among the moment due to the compressive force, the moment due to the pad reaction force, and the bending moment of the steel sheet is examined. In the theoretical model, a sine curve and a trapezoidal curve are employed as wrinkle shapes, and the tangential and conversion coefficients are used as the apparent Young's modulus. Calculation results of the theoretical model are compared with the results simulated by the finite element method (FEM). It is confirmed that the theoretical model with the conversion coefficient and trapezoidal curve is practical. With the theoretical model, the calculation equation of the pad load required to realize the wrinkle disappearance mode is proposed.