AEM Seminar: Friday, October 24th - Prof Curt Bronkhorst, Dept Mechanical Engineering, University of Wisconsin - Madison

[Molly Schmitz]

University of Minnesota

Aerospace Engineering and Mechanics
Fall 2025 Seminar Series

Friday, October 24, 2025

209 Akerman Hall

2:30pm-4:30pm

AEM Seminar: 

Modeling the Statistical Thermomechanics of High-Stress Triaxiality Porosity-based Ductile Damage

Abstract: 
Porosity-based ductile damage within polycrystalline metallic materials is known to be strongly dependent upon microstructural details for light to moderate shock loading conditions. This is presumed to be dictated by spatially distributed stress conditions and defect pore nucleation strength due to the statistical aggregate nature of the material. During shock loading, in addition to pore nucleation and growth, the material deforms via finite elastic and plastic mechanisms. The power delivered to the material during shock loading is distributed to each deformation mechanism as stored and dissipated power with change of temperature by both Thompson-Joule and plastic power dissipation effects. A new finite deformation probabilistic porosity-based ductile damage model for high triaxiality conditions is presented which represents pore nucleation by a new combined probability distribution for stress and pore nucleation strength distributions. This nucleation model is derived from experimental and computational physics data. A new isotropic plasticity model is included in the damage model which accounts for both thermally activated and phonon-drag regimes of dislocation motion with dislocation density as the primary state variable. This model accounts for both stored energy via an effective temperature measure and thermal energy via kinetic-vibrational temperature. This formulation also proposes an expression for the Taylor-Quinney factor which is guided by second-law restrictions. Porosity growth is represented by a thick-walled sphere unit cell approach which allows for inertial resistance to growth and facilitated
by plastic deformation. A governing equation for thick wall sphere growth due to applied external pressure is derived which also accounts for surface energy and kinetic energy. Closure of this governing equation is achieved with a reduced-order model of inertial power as a function of loading conditions. This reduced-order model is derived from a thick-walled sphere computed database by employing the isotropic plasticity model to perform varying initial temperature and strain rate condition thick-walled sphere calculations. The finite deformation ductile damage model is thermodynamically consistent and accounts for energy partitioned to finite-elasticity, dislocation slip plasticity, dislocation energy storage, kinetic energy, surface energy, and thermal energy. The physics computation work will be presented and connections with experiments will be made. Results for the ductile damage model will also be presented and compared with plate-impact experiments conducted on high-purity tantalum.

Biography:
Dr. Curt A. Bronkhorst is Harvey D. Spangler Professor of Applied Mechanics at the University of Wisconsin – Madison in the Department of Mechanical Engineering and associate appointments in the Nuclear Engineering Department and Materials Science and Engineering
Department. Prior appointments include Senior Scientist in the Theoretical Division at Los Alamos National Laboratory and Senior Scientist at Weyerhaeuser Company. He is director of the Army Research Laboratory funded Center for Extreme Events in Structurally Evolving
Materials and guest scientist at Los Alamos National Laboratory. Bronkhorst is emeritus Honorary Commander for the Wisconsin Air National Guard 115th Fighter Wing. He is fellow of the American Society of Mechanical Engineers and a vice-chair of the ASME Materials
Division Executive Committee. He is Associate Editor of the International Journal of Plasticity and also president of Northland Partners, LLC. The Theoretical and Computational Mechanics of Materials Group Website: https://uwtcmmg.engr.wisc.edu/

*Refreshments to follow in 209 Akerman Hall 

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Molly Schmitz (She/Her/Hers)

Principal Accountant, Purchasing & Payroll Specialist, Graduate Program Coordinator

Department of Aerospace Engineering & Mechanics, University of Minnesota - Twin Cities