13th International Conference on the Technology of Plasticity (ICTP 2021): Microstructure & Damage Development II
Program Organizers: Glenn Daehn, Ohio State University; Libby Culley, The Ohio State University; Anupam Vivek, Ohio State University; Jian Cao, Northwestern University; Brad Kinsey, University of New Hampshire; Erman Tekkaya, TU Dortmund; Yoshinori Yoshida, Gifu University

Tuesday 9:15 AM
July 27, 2021
Room: Virtual: Room B
Location: Virtual

Session Chair: Irene Beyerlein, University of California, Santa Barbara


Analysis of Cross-hardening by High Resolution Orientation Imaging: Till Clausmeyer1; Gregory Gerstein2; Florian Gutknecht3; Florian Nürnberger2; 1Instiute of Forming Technology and Lightweight Components (IUL), TU Dortmund; 2Leibniz Universität Hannover; 3Instiute of Forming Technology and Lightweight Components (IUL), TU Dortmund University
    Sheet metals undergo several loading path changes in sheet-bulk metal forming (SMBF). Ferritic steels an other materials exhibit cross-hardening after orthogonal loading path changes. Cross-hardening is induced by the interaction of currently active dislocations with persistent dislocation structures which have formed during previous loading. The analysis of persistent microstructures requires transmission electron microscopy (TEM) or electron contrast channelling imaging (ECCI). An alternative approach is to apply high-resolution electron backscatter diffraction (EBSD) to detect inter- and intragranular misorientations. These provide information of the substructure in sequences of uniaxial pre-straining followed by simple shear. Such methods are used to detect orthogonal strain path changes in components manufactured by sheet-bulk metal forming. The microstructural evidence is compared with macroscopic stress strain data for the steel DC04.

Assessment of Calibration Strategies and Model Predictions for Damage in Formed Components: Alexander Schowtjak1; Oliver Hering1; Rickmer Meya1; A. Erman Tekkaya1; Till Clausmeyer1; 1Institute of Forming Technology and Lightweight Components (IUL), TU Dortmund University
    The existence and evolution of voids affect component properties such as mass density, strength and elastic stiffness. Material models for the prediction of such properties need to be calibrated. In this work, an efficient and robust methodology for the parameter identification that enables an accurate prediction of the void area fraction is presented. A parameter identification scheme based on macroscopic quantities is applied to a Lemaitre damage model. This model is used to predict the void evolution in the process chain of calibre rolling with subsequent forward rod extrusion. Additionally, a parameter identification strategy based on experimental void analysis is performed for a Gurson-Tvergaard-Needleman model and applied to air bending. Both strategies are analysed with regard to their prediction qualities in terms of void evolution based on high-resolution scanning electron microscopy measurements. The predicted mass density and strength are compared to experimental data to assess the quality of prediction.

Influence of Specimen Preparation Methods on the Mechanical Properties and Superplastic Behavior of AA5083 Sheets: Mohammad Dastgiri1; Leo Kiawi1; Iman Sari Sarraf1; Daniel Green1; 1University of Windsor
    Edge quality has a considerable effect on characterization of sheet materials. In this study, AA5083 sheet specimens were prepared using 4 different methods: shear, wire-EDM, waterjet cutting and conventional milling. Mechanical properties were determined from tensile tests carried out at 450°C and quasi-static strain rates. Optical microscopy and scanning electron microscopy were used prior and after tension tests to analyze the relation between the quality of the edge and mechanical properties. It was found that milled specimens resulted in considerably greater values of total and uniform elongation. Moreover, milling by removing material in smaller increments also leads to slightly greater elongation values. The microscopic investigation revealed that specimens whose edges have lower arithmetic mean roughness (Ra) have greater values of elongation. The SEM investigation also revealed that micro-cracks are more prevalent at the edges of specimens that have a greater surface roughness.

An Extended GTN Ductile Fracture Model for a Broad Range of Stress States: Hongfei Wu1; Xincun Zhuang1; Zhen Zhao1; 1Shanghai Jiao Tong University
    This contribution provides an extended GTN model for predicting damage and fracture of metallic materials under high, low and negative stress triaxiality loadings. In this proposition, two internal damage variables are introduced into GTN model in order to affect the hydrostatic stress and deviatoric stress contributions. The first damage variable is void volumetric damage due to the nucleation, growth, inner-necking of primary voids and nucleation of secondary voids. The void shear damage is proposed as the second damage variable taking the void rotation, distortion and secondary nucleation into account. A novel effective damage is constructed to combine these two damage contributions during the deformation. The extended GTN model has been implemented into ABAQUS/Explicit and the parameters are calibrated through the inverse analysis under different stress states. The validity of the new model is assessed by comparing numerical prediction with experimental measurements.

The Local Strain Evolution for Structured Sheet Metals during Uniaxial Deformation: Evgeniia Ermilova1; Alexander Nikitin1; Sabine Weiss1; 1Technical University of Brandenburg at Cottbus-Senftenberg
     Structured materials can be progressive alternatives to commonly used flat sheets because of their higher bending stiffness and stability compared to flat sheet metals, made of the same alloy. The application of sheet metals requires accurate information regarding their strength and deformation behavior. Such data are not commonly available and have to be measured by specific test set ups and implementation of tests. The aim of this work is to obtain new knowledge about deformation mechanisms of structured sheet metals. Structured sheet metals (SSM) made of conventional deep-drawing steel DC04 were investigated by means of tensile tests. The influence of the structure type arrangement on the deformation behaviour was analyzed. The evolution of local strains was analyzed by means of strain gauge measurements as well as 3D-displacement measurements with an ARAMIS high resolution camera-system. Local orientation changes in different structural elements were measured using the electron backscatter diffraction technique.