The goal of project B04 is to develop a fundamental understanding of the physical mechanisms of damage formation and evolution in bulk forming processes by the means of the material 16MnCrS5. The processes occurring during forming, such as work hardening, localization of plasticity, and formation of residual stresses, are correlated with the microscopic mechanism of damage evolution, using modern electron microscopy methods. The influence of plastic processes on pore formation, growth, and coalescence depend heavily on the load path (sequence of stress, strain, temperature, and strain rate). The load path-dependent correlation between strain hardening, residual stresses, and local damage occurrence is investigated in this project to predict a controlled, damage-reduced cold forming strategy.

To reach this goal, the early stages of strain hardening and the formation of residual stresses as well as their interaction with existing inclusions and pores are investigated in work packages 1 and 2, using modern electron microscopy techniques in a cross-scaling approach such as EBSD (electron backscatter diffraction), ECCI (electron channeling contrast imaging), and TEM (transmission electron microscopy). This leads to a consistent description of the mechanisms caused by cold forming that result in pore formation and growth. The formation of pores and short cracks at microstructural inhomogeneities and non-metallic inclusions is investigated in work package 3 to understand the influence of strain hardening and softening with regard to the subsequent damage.

Alongside these high-resolution techniques performed on cross-sections of cold formed samples, in work package 4 a large chamber scanning electron microscope (LC-SEM) is used to conduct in situ cyclic bending tests in the low cycle fatigue regime for a time-resolved observation of damage evolution under cyclic loads.

Investigations are performed on plastically strained samples in work package 4, but also on cold-forged components of the bulk metal forming projects A01 and A02. Project B04 delivers input data for the simulations and verification of the models of projects C01, C02, and C03. The cyclic bending tests of project B01, delivering results on the macroscale, will be combined with the results of project B04 to obtain a multiscale characterization.

The results of these investigations will be summarized in mechanism maps in work package 5.

In the second funding period the damage-induced forming processes developed in TRR 188 will be analyzed using the before-mentioned methods. In the third funding period, the new findings will be transferred to a broader material spectrum with high applicability and to the optimization of the forming processes.

 

Project leader
Dr. rer. nat Anke Aretz
Central Facility for Electron Microscopy (GFE), RWTH Aachen University

Dr. rer. nat. Alexander Schwedt
Central Facility for Electron Microscopy (GFE), RWTH Aachen University

Project coordinator
Anthony Dunlap M. Sc.
Central Facility for Electron Microscopy (GFE), RWTH Aachen University