13th International Conference on the Technology of Plasticity (ICTP 2021): Microstructure Development by Forming III
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
Thursday 9:15 AM
July 29, 2021
Room: Virtual: Room D
Location: Virtual
Session Chair: Johannes Lohmar, RWTH Aachen University
Formability Improvements at Room Temperature of AA5754-H32 via Continuous Bending under Tension (CBT) and Pre-forming Heat Treatment: Jinjin Ha1; Antonio Piccininni2; Yannis Korkolis1; Gianfranco Palumbo2; Marko Knezevic3; Brad Kinsey3; 1Ohio State University; 2Politecnico di Bari; 3University of New Hampshire
Aluminium (Al) alloys play a critical role for the transportation applications where weight reduction is a key aspect; however, the poor formability at room temperature limits their application for complex components. An innovative methodology to overcome this limitation is based on subjecting the material to a local, short-term heat treatment before the stamping to obtain a tailored distribution of properties. In addition, Continuous Bending under Tension uses the action of three rollers to remarkably increase the total elongation to failure. In the present work, the combination of the two approaches is investigated to improve the formability at room temperature of a strain hardenable 5xxx Al alloy, AA5754-H32. Specimens were subjected to both CBT and pre-forming heat treatments. Specimens were then subjected to hardness measurements and tensile tests at room temperature in order to assess the plastic behaviour and evaluate the effect on the material formability.
On Sampling Discrete Orientations for Texture Representation in Aggregates with Varying Grain Size: Aditya Vuppala1; Alexander Krämer1; Johannes Lohmar1; 1Institute of Metal Forming
The amount of orientation difference of crystallites i.e. the texture in a metallic polycrystal governs, plastic anisotropy, electrical and magnetic properties of the material. While the grain size and morphology of polycrystals is often determined via light-optical microscopy, their texture is conventionally analyzed by X-ray diffraction measurements. However, these measurements cannot be correlated. Thus when modeling the texture evolution by means of the CP-FEM method, a sampling of orientations onto grains is required. Here a concept of sampling is introduced that first assigns only the highest weighted orientations generated via an ODF to the few grains of the RVE. This gives an overly sharp texture, especially for inhomogeneous aggregates. Now orientations within the aggregate are rotated in Euler space to match the experimental ODF through an optimization procedure. This enables a re-creation of the measured texture in aggregates with only a few grains and varying grain size.
The Effect of Temperature on Strain-induced Austenite to Martensite Phase Transformation in SS 316L during Uniaxial Tension: Elizabeth Mamros1; M. Bram Kuijer2; Mohammad Ali Davarpanah1; Ian Baker2; Brad Kinsey1; 1University of New Hampshire; 2Dartmouth College
Controlling the microstructure of components is of interest to achieve optimal final part properties, i.e., materials by design. The manufacturing process itself can affect a material’s characteristics by changing the microstructure. For example, past research has shown that an austenite to martensite phase transformation in stainless steel occurs during deformation. Temperature is known to have a significant influence on this phenomenon. In this paper, the effect of temperature on the austenitic to martensite phase transformation in SS 316L under uniaxial tension is investigated. Both a cooling system and a heat exchanger were employed in a uniaxial tension experimental setup to control the temperature. Tensile specimens were strained to fracture at four temperatures of -15°C, 0°C, 10°C, and 20°C. Digital imaging correlation (DIC) and a thermal imaging camera were used for tests at 0°C and above to capture strain and temperature data, respectively. Strain data could not be obtained at -15°C due to the DIC paint flaking during testing. X-ray diffraction was used to measure the weight percent of martensite in both the as-received and the tensile-tested materials.
Energy-dependent Surface Integrity of Stainless Steel AISI 304 after Robot-based Machine Hammer Peening: Robby Mannens1; Lars Uhlmann1; Andreas Feuerhack1; Thomas Bergs1; 1Laboratory for Machine Tools and Production Engineering
Machine hammer peening (MHP) is a high-frequency, incremental surface treatment with a spherical plunger which enables reproducible local plastic forming of metallic surface layers. The elasto-plastic deformation leads to a targeted smoothing or structuring of the surface as well as to the induction of compressive residual stresses and strain hardening. However, since MHP is still a relatively new process, there are still considerably knowledge deficits with regard to the cause-effect relationships of the energy inputs set by the MHP process parameters and the resulting surface integrity of technically relevant alloys. Therefore, the objective of this work is to investigate the peening strategie‘s influence on the surface roughness, the macro and micro hardness, the residual stresses and the microstructure of AISI 304. The results show that MHP leads to smoother and harder surfaces resulting from deformation-induced martensite formation accompanied by high compressive residual stresses, grain refinement and higher dislocation densities.
A Novel Approach to Predicting Surface Properties Generated during Metal Forming Processes: Sergei Alexandrov1; 1Samara National Research University
Thin fine grain layers are often generated in the vicinity of frictional interfaces in manufacturing processes as a result of severe shear deformation. These layers change surface properties of machine parts. The latter affects the performance of structures and machine parts under service conditions. The strain rate intensity factor is the coefficient of the leading singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. The objective of the present paper is to develop a general approach to use the strain rate intensity factor for predicting the evolution of fine grain layers. The paper includes a conceptual approach, experimental results on upsetting and drawing, and a special numerical method for calculating the strain rate intensity factor. The latter is necessary since the strain rate intensity factor appears in singular solutions, and conventional finite element methods are not capable of calculating this factor.
The Evolution of Deformation Microstructures and Strain Hardening during Constrained Sliding with Implications for Metal Forming and Cutting Processes: Darcy Hughes1; 1Sandia National Laboratories (ret.)
A novel apparatus to constrain and extremely deform the subsurface of a metal work piece during sliding was utilized to create an unprecedented average size (crystallite) scale of five nanometers with a high dislocation density near the surface. The depth and degree of subsurface deformation was quantitatively measured and statistically analyzed using high resolution transmission and scanning electron microscopy. Scaling and the principal of grain subdivision enabled a direct link between the deformation microstructure that was graded in size scale with increasing depth below the surface and the decreasing stress and strain. Dislocation mechanisms were demonstrated to dominate the deformation. These observations and analyses indicate that metals and alloys under constrained conditions may continuously refine their size scale and strain-harden. As a result the degree and depth of the deformation, which extends in depth twenty to eighty times the ridge height, far exceeds existing models and wedge experiments.