The analysis of metal-forming processes

A complete stress and deformation analysis of metal-forming process is necessary in order to assess the onset of metal-forming defects such as the initiation of cracks, the generation of high residual stresses or the occurrence of local flow abnormalities. Rigid-plastic theory can only predict stresses in the regions exhibiting significant current plastic flow so that to evaluate stresses throughout the material it is necessary to carry out an elastic-plastic analysis. A finite-element computer program to evaluate complete stress and deformation distributions has been developed and applied, bringing new insights to the assessment of metal forming processes. The plastic part of an elastic-plastic deformation is that remaining when the stress, and hence the elastic strain, is reduced to zero. Elastic deformation is that produced in this purely plastically deformed material by the action of stresses up to yield. The associated exact finite-deformation kinematics shows the almost universal assumption that the total rate of deformation is the sum of elastic and plastic rates to be in error. An incremental elastic-plastic theory is developed using the nonlinear kinematics. The theory is contrasted with that in common use and anomalies in the latter are discussed.