Finite element modelling of unbending tests with damage approach and experimental verification

This work deals with numerical simulation of unbending operations of parts previously bent in press tools. The aim is to predict the location and time of cracking during the unbending process. To this end, a fully coupled constitutive model of elastic-plasticity and ductile damage has been developed and implemented for the implicit solver of ABAQUS. The framework of the constitutive model is already described in textbooks, such as Lemaı̂tre and Chaboche, Mechanics of Solid Materials, 1990. The significant difference between the present model and the one proposed by Lemaı̂tre and Chaboche for metals is the evolution rule for damage variable. However, the stress update algorithm for the constitutive model is presented and the consistent tangent operator is developed, which is needed for implicit FEA. Materials tests have been performed to identify the constants in the constitutive model, and bending–unbending tests have performed for validation purposes. The bending–unbending test is indeed interesting as a validation case for damage and fracture models. Simulations are finally performed and compared with the experiments, and good agreement is found between experimental and numerical force–displacement curves.