【開催予告】2026.11.18 -第203回構材ゼミ- Dr. Alexander R. Umantsev (Department of Chemistry and Physics, Fayetteville State University)
- 日時
-
2026年11月18日（水曜日）13:30-14:30
- 場所
-
NIMS千現地区 先進構造材料研究棟5階カンファレンスルーム
- 講演題目
-
Bifurcation Theory of Plasticity and Damage
- 講演者
-
Prof. Alexander R. Umantsev
Department of Chemistry and Physics, Fayetteville State University, Fayetteville, NC 28301, U.S.A.
Abstract:
Two important trends are taking place simultaneously in the community of materials scientists. On one hand, after accumulating substantial knowledge of phase transformations, researchers began paying more attention to the problem of damage and reliability of the materials in service. On the other hand, mechanicians realized the critical importance of microstructure in the problem of material hardening and failure. All this makes us—theoretically inclined materials scientists—think about theoretical approaches that would combine both trends and allow us to model realistic multiscale and multiphase material behavior from cradle to grave.
In this presentation I will introduce a novel approach to plasticity and damage, which includes all major components of mechanical behavior of ductile materials and covers all regimes of viscoplastic multiaxial loading and unloading [1-4]. The approach is based on the concept of free energy as a function of total strain and internal damage. It helped me to analyze the phenomenon of fatigue and derive a Paris-type equation for the rate of degradation of the specimen as a function of the cyclic plastic work. Also, I will analyze the process of incremental bulk metal forming and show how simulation can be used for the design of new products. I will discuss the process of heating plastically deformed materials and derive expressions for the heat source in plastic deformation, Taylor-Quinney coefficient, and the effect of plastic cooling.
Motion of dislocations is a common mechanism of plasticity in many materials; it deserves special attention. Dislocation mediated deformation is essentially inhomogeneous process, which is manifest in formation of persistent slip bands
and complicated subgrain structures. In this presentation, I will introduce a novel approach to dislocation plasticity and derive an equation of dislocation dynamics. It turns out that the dislocation slip-line and cell-wall structures appear in the theory as ordinary solutions of the equilibrium equations without any arbitrary assumptions. I will also discuss acoustic emission events and stress bursts, which self-organize into the dislocation avalanches and propagate at a speed determined by the conditions of loading. In the compressive creep experiments the avalanches arrange into slow moving slip bands while in the shock compression experiments the avalanches move faster than sound.
References
1. A.R. Umantsev, “Bifurcation Theory of Plasticity, Damage and Failure”, Mater. Today Comm., 26, 102121, 2021; Corrigendum, Mater. Today Comm., 37, 107377, 2023.
https://www.sciencedirect.com/science/article/abs/pii/S2352492821001136
2. A.R. Umantsev, “Thermodynamically Consistent Model of Dislocation-Mediated Plasticity”. Phil. Mag. Part A Mater. Sci. 105 (5-6), 309–330, 2025.
https://doi.org/10.1080/14786435.2024.2408383
3. A.R. Umantsev, “Dislocation Avalanches in Compressive Creep and Shock Loadings” Metals, 15, 626, 2025. https://doi.org/10.3390/met15060626
4. A.R. Umantsev, “Multiscale Theory of Dislocation Plasticity”, Crystals 15 (10), 842 2025. DOI: 10.3390/cryst15100842