Multiaxial Distortional-Hardening Plasticity to Advance Forming Process Modeling

University Of New Hampshire, Durham NH

Investigators

Abstract

Sheet metal forming processes are among the most flexible and energy-efficient manufacturing processes, corresponding to approximately 7 percent of the US Gross Domestic Product. Transformation of the sheet into a useful component typically occurs in multiple steps, with the part transferred from one forming die to the next, progressively obtaining a more complex shape. While these multi-step processes enable the creation of complex components, they also increase the cost due to the number of dies and presses needed. Also, from a scientific point of view, the multiple steps cause repeated loading and unloading of the materials, which is very challenging to model in a computationally-efficient way. This research aims to create a material model suitable for repeated loading and unloading, to enable science-based process and die design, minimize the number of necessary steps, reduce waste and thus enhance the competitiveness of American manufacturing. Since the automotive industry is one of the major users of multi-step sheet forming, this research will also enable the use of modern, difficult-to-form steels and aluminum alloys in auto-bodies, yielding safer and environmentally friendlier cars. The work will be performed in collaboration with 2 Korean universities (whose work is funded by the Korean National Research Foundation), and this collaboration will allow access to equipment and expertise not otherwise available in the US. Graduate and undergraduate students and Research Experience for Teachers (RET) participants and their students will benefit from the industrial focus of this project, as well as its international dimension. To provide industry with a robust and computationally-efficient material model suitable for severe strain-path changes, including repeated loading and unloading, this research will: 1) create a unique machine for biaxial tension/compression of sheets and perform multiaxial plasticity experiments, 2) use this dataset to evolve the recent (2011) Homogeneous Anisotropic Hardening (HAH) plasticity model and create the extended-HAH one, to capture the experiments, and 3) conduct multi-step forming experiments and simulate them with the extended-HAH model, to further inform its evolution and validate its performance. Two families of materials, advanced high strength steels and aluminum alloys, will be investigated in this research, both of which are of interest to various weight-sensitive applications, but have widely varying responses to severe strain-path changes. Beyond the specific forming processes studied here, the creation of a robust and computationally-efficient material model to describe severe strain-path changes is expected to benefit the modeling of all multi-step plastic deformation processes in industry, as well as low-cycle fatigue and cyclic plasticity.