Ductile failure prediction during the flow forming process

Abstract

Flow forming is an incremental metal-forming technique used for manufacturing thin-walled seamless tubes where a hollow metal material flows axially along the mandrel by a rotating mandrel and multiple cylinders. Flow formed materials are frequently used in the aviation and defence industry and it is crucial to examine the influence of the process on the material in terms of ductile fracture. However, the process requires in-depth failure analysis considering different process parameters and materials. The current study is concerned with investigating the ductile fracture behavior during flow forming process which includes complex stress states in terms of stress triaxiality and Lode parameter. Ductile fracture is simulated through the modified Mohr-Coulomb model. A user material subroutine (VUMAT) has been developed to implement the plasticity behavior and the damage accumulation rule. The model is validated through finite element (FE) simulations performed in Abaqus/Explicit and using the experimental data in Granum et al. (2021). The validated framework is applied to a finite element model of flow forming process with single and three rollers. The incremental forming with three rollers significantly reduces the damage accumulation. The initial results show a highly damaged region outer and inner surfaces of the workpiece after 40% thickness reduction ratio, and the forming limit is predicted as about 40-45%. The modeling framework is planned to be applied using various process parameter for different materials.