Collaborative Research Center Transregio 188 – Damage Controlled Forming Processes
German Research Foundation (DFG)
Prof. Dr.-Ing. A. Erman Tekkaya
Dr.-Ing. Frauke Maevus
The Collaborative Research Center TRR 188 aims at fundamentally understanding the damage mechanisms during forming and their effects on product properties in order to be able to predict the damage quantitatively and adjust it specifically with regard to component performance. Starting point is the observation that different process routes for the manufacturing of a forming component from a given semi-finished product lead to the same final geometries, but different properties and damage. Thus, it is basically possible to influence the damage evolution along the forming process chain from the semi-finished product to the finished component by selecting and designing the forming processes. If not only the nominal material properties are used in the design, but the damage caused by the forming process is taken into account in the same way as other production-induced properties, this leads to a paradigm shift in both process and component design. Instead of a process design based on the manufacturability or the maximum failure-free formability of the material (“formability”), there is a “damage-based” process design that pursues a failure analysis with regard to the use of the component and the achievement of maximum performance (“usability”). When dimensioning the components, the targeted adjustment and precise quantification of the damage level enables a significant reduction in safety factors. As a result, novel lightweight products can be realized which are characterized by a reduced mass compared to the state of the art, at the same time guarantying the functional reliability of the components during the utilization phase.
To achieve this goal, an interdisciplinary consortium of production engineering, material science, materials testing technology, and mechanics develops new methods and technologies for a quantitative prediction (project area “Modeling”), assessment (project area “Characterization”), and control (project area “Process Technology”) of the damage, taking into account the materialphysical relationships.
Project areas of the TRR 188
The indispensable prerequisite for a damage-based design of forming processes are powerful modeling approaches that can map the underlying microscopic damage mechanisms and predict the properties of components manufactured by forming technologies including the damage. Since there are no generally applicable approaches for any forming processes and process sequences so far, new theoretical model approaches at meso/micro and macro level are developed in TRR 188.
For the development and validation of these models, the physical damage mechanisms located on different length scales must be precisely resolved. To characterize these mechanisms, innovative and high-resolution measuring methods, such as in-situ testing technology in electron microscopy, are used. Since the ductile damage is usually dispersed in the material volume, additional alternative methods which can characterize the damage states nondestructively in the material volume are tested. To evaluate the component’s performance at the macro level, modified load increase tests are used to characterize and quantify the interaction of ductile and cyclic damage mechanisms.
The prerequisite for the control and targeted adjustment of the damage is knowledge of how the load paths can be influenced in the various sheet metal and bulk forming processes and how these load paths affect the damage. In addition, the influence of the forming history on the damage development along the process chain must be determined in order to be able to make statements about the accumulated damage in the finished component and Project areas of the TRR 188 the resulting component properties. The characterization methods mentioned above are used to investigate the initiation and development of damage as well as the relationships between process parameters and the resulting state of damage. The modeling methods for the quantitative prediction of the damage provide important clues for the development of damage-controlled processes.
The basis for the joint, interdisciplinary development of methods and technologies is a precise definition of damage and its mechanisms. As the literature shows, the different disciplines use different definitions and terms. Therefore, the TRR 188 has set itself the task of developing a comprehensive, uniform understanding of damage and making it publicly accessible in the form of a basic lecture. In addition to this lecture, the various other research results of the TRR 188 were presented and discussed at scientific and indus-try-related symposia in the national and international environment. These included CIRP, ICTP, ECCM, IDDRG, ESAFORM, GAMM, MSE, various DVM working group meetings, and the 1st Industrial Colloquium organized by TRR 188 in Dortmund.
The research is carried out by scientists from TU Dortmund University (Coordinating University) and RWTH Aachen University. Specifically, the Institute of Forming Technology and Lightweight Components (IUL), the Institute of Mechanics (IM), and the Department of Materials Test Engineering (WPT) from the Faculty of Mechanical Engineering in Dortmund are involved as well as the Chair of Structural Mechanics (BM) from the Faculty of Architecture and Civil Engineering. At RWTH Aachen University, the participating institutes are the Metal Forming Institute (IBF), the Steel Institute (IEHK), and the Institute of Physical Metallurgy and Metal Physics (IMM) from the Faculty of Georesources and Materials Technology as well as the Laboratory for Machine Tools (WZL) from the Faculty of Mechanical Engineering and the Central Facility for Electron Microscopy (GFE). In addition, there is the Chair of Mechanical Design and Manufacturing at BTU Cottbus-Senftenberg and the non-university institute Max-Planck-Institut für Eisenforschung GmbH (MPIE) in Dusseldorf. The interdisciplinary consortium is supported by an industrial advisory board counseling the TRR 188. The research association receives important impulses for further research activities by the experiences and suggestions from industrial practice.