Phonons, Electrons and Dislons: Exploring the Relationships Between Plastic Deformation and Heat: Session II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Aashish Rohatgi, Pacific Northwest National Laboratory; Sean Agnew, University of Virginia; Thomas Bieler, Michigan State University
Monday 2:00 PM
March 15, 2021
Room: RM 42
Location: TMS2021 Virtual
Session Chair: Thomas Bieler, Michigan State University; Sean Agnew, University of Viriginia; Aashish Rohatgi, Pacific Northwest National Laboratory
2:00 PM Invited
Do Moving Dislocations Induce Lattice Instabilities?: Benat Gurrutxaga-Lerm1; 1University of Birmingham
'Phonon radiation' is caused by the breaking and rebuilding of bonds as dislocations glides. In this talk, I will discuss how phonon radiation is associated with fundamental lattice instabilities triggered by the moving dislocation in the lattice. Complementary models based on lattice dynamics and molecular dynamics(MD) will be used to explain them. Lattice dynamics offer mathematical understanding, showing the existence of breakdown velocities at which moving dislocations trigger lattice resonances; MD simulations offer a way of understanding how the lattice responds to them.In particular, two phenomena are observed at resonance: significant local heating, and a kinematic generation mechanism, which results in a new pair of dislocations being generated. A repetition of this process in cascade ultimately results in an avalanche of further dislocations. These instabilities offer a physical rationale for local plastic softening of the sort relevant in phenomena such as adiabatic shear banding.
2:20 PM Invited
Thermal and Strain Rate Effects on
Plasticity and Fracture of Gen 3 Steels
: Louis Hector1; 1General Motors Global Technical Center
Plasticity of multiphase Gen 3 steels involves martensitic transformation, or the diffusionless transformation of metastable retained austenite to martensite. Martensitic transformation is sensitive to thermal and strain rate effects in stamping and impact, both important for automotive. Elevated temperatures can slow transformation and interfere with the dynamic regulation of work hardening to delay plastic instability. This presentation will focus on recent experimental and computational research aimed at quantifying thermal and strain rate effects on Gen 3 steel plasticity and fracture with multi-length scale methodologies spanning atomistic to engineering. Results show effects of different deformation modes and strain paths on martensitic transformation, formability and fracture over a range of temperatures. The presentation will conclude with a discussion of future high-quality experimental data needs under various thermal and deformation conditions to support development of new Gen 3 steels as well as microstructure-based constitutive model development for Gen 3 steel automotive component simulations.
2:40 PM Invited
Thermo-mechanics of Large Deformation Shear Banding : Curt Bronkhorst1; Charles Lieou2; Hashem Mourad2; Veronica Anghel2; 1University of Wisconsin, Madison; 2Los Alamos National Laboratory
Shear banding is a form of ductile damage where the relationship between plastic work and material temperature is critical. We present a new physical model for the plastic deformation of metallic materials which accounts for softening due to increased dislocation mobility with heating and dynamic recrystallization. This model is based upon a new partitioned-energy thermodynamic framework which assigns the energy of cold work to atomic configurational stored energy and kinetic-vibrational energy. With specific energies assigned to dislocation line length and grain boundary area, second law considerations for any given loading condition lead to either increased plastic deformation by dislocation glide or the creation of new grain boundaries in recrystallized form. The theory is used to describe specific experiments performed on stainless steel alloys loaded dynamically. Computational results compared to experiments strongly suggest the prominence of dynamic recrystallization during adiabatic shear banding.
3:00 PM
Thermomechanical Conversion in Metals: Dislocation Plasticity Model Evaluation of the Taylor-quinney Coefficient: Charles Lieou1; Curt Bronkhorst2; 1Los Alamos National Laboratory; 2University of Wisconsin-Madison
Using a partitioned-energy thermodynamic framework which assigns energy to that of atomic configurational stored energy of cold work and kinetic-vibrational, we derive an important constraint on the Taylor-Quinney coefficient, which quantifies the fraction of plastic work that is converted into heat during plastic deformation. Associated with the two energy contributions are two separate temperatures -- the ordinary temperature for the thermal energy and the effective temperature for the configurational energy. We show that the Taylor-Quinney coefficient is a function of the thermodynamically defined effective temperature that measures the atomic configurational disorder in the material. Finite-element analysis of recently published experiments on the aluminum alloy 6016-T4, using the thermodynamic dislocation theory (TDT), shows good agreement between theory and experiment for both stress-strain behavior and temporal evolution of the temperature. Our results suggest a value of the differential Taylor-Quinney coefficient which differs between materials and increases with increasing strain.
3:20 PM
Unified Analysis of Temperature Fields Arising from Large Strain Deformation and Friction in Manufacturing Processes: Harish Dhami1; Priti Panda1; Debapriya Mohanty2; Anirudh Udupa2; James Mann3; Koushik Viswanathan1; Srinivasan Chandrasekar2; 1Indian Institute of Science; 2Purdue University; 3M4 Sciences Corporation
We consider the contact between a sliding wedge/tool and a metal surface prototypical of material removal and deformation processing operations such as forming, cutting and wear. We show how heat generated at the contact is partitioned into each of the bodies involved - tool, workpiece, removed chip and surrounding fluid (if any). By performing thermal analysis and heat partition via temperature matching on global and local scales, we show how temperature fields in all four bodies can be easily calculated. The analysis framework involves a heat source moving over a body (Jaeger), and energy partition at the contact into tool, workpiece, fluid and chip/wear particle (Blok). We present temperature solutions for two cases – incremental forming and grinding - while providing a simple method for solving the thermal problem in other deformation processing applications.
3:40 PM
Shear Bands, Thermal Profiles and Microstructure Stability in Large-strain Deformation of High Entropy Alloys: Shwetabh Yadav1; Dhruvil Shah1; Andrew Kustas2; Nicolas Argibay2; Ping Lu2; Dinakar Sagapuram1; 1Texas A&M University; 2Sandia National Laboratories
We study the stability of plastic flow and microstructure in CoCrFeNiMn high entropy alloy under large strain and strain rate conditions. A 2D cutting (shear) apparatus is used to impose large shear strains in a single deformation pass under high strain rates > 103 per second. A clear transition in the flow from homogeneous type to localized shear banding, upon increasing the strain rate, is demonstrated. Using high-resolution TEM characterization, we show that shear bands exhibit a highly-refined nanocrystalline microstructure and possess exceptional phase stability despite extreme local deformation conditions (strains > 10, strain rates of 105–106 per second). Planar heat source models are used to analyze deformation-induced heating effects in the vicinity of shear bands and interpret microstructure observations in terms of the characteristic diffusion times and thermal length-scales.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.