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Design of NiTi-based shape memory microcomposites with enhanced elastocaloric performance by a fully thermomechanical coupled phase-field Model

The non-transforming intermetallic Ni3Ti phase generated in NiTi matrix by additive manufacturing was previously reported to create elastocaloric composites with a great coefficient of performance (COP) between 11 and 22 [Hou et al., Science 366 (6469) (2019) 1116–1121]. In this work, we use a fully thermomechanical coupled phase-field model to design microarchitectures with very high COP considering the effects of all the possible non-transforming intermetallics (Ni4Ti3, Ni3Ti, and Ti2Ni) in NiTi.

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Superelasticity and shape memory effect in zirconia nanoparticles

In this work, superelastic and shape memory properties of single crystalline and polycrystalline yttria stabilized tetragonal zirconia (YSTZ) nanoparticles are studied by atomistic simulations. N. Zhang and M. Asle Zaeem. Superelasticity and shape memory effect in zirconia nanoparticles. Extreme Mechanics Letters 46 (2021) 101301 (8 pages).

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Effects of Cleavage Plane and Material Strength on Fracture of Polycrystalline Brittle Materials: A Phase-Field Modeling Study

A modified phase-field model for fracture is presented which includes the material strength and cleavage planes to quantitatively predict the crack propagation path and the mechanical response in polycrystalline brittle materials. Computational Materials Science 197 (2021) 110642 (11 pages).

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Nanotwin-induced strengthening in silicon: A molecular dynamics study

Mechanical performance of silicon nanopillars with homogeneous and gradient nanotwinned structures are investigated through a series of molecular dynamics simulations. The most observed Σ3 twin boundary (TB) with two preferable (lowest surface energy) planes of {111} and {001} are used to generate homogeneous and gradient nanotwinned structures. Simulations of compression and tension of nanotwinned pillars reveal an extra strengthening behavior due to the addition of Σ3 TBs when compared to the single crystalline nanopillar without any TBs.

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Quantitative prediction of rapid solidification by integrated atomistic and phase-field modeling

Dear iMechanica colleagues, I am pleased to share with you our newest paper on qauntitative prediction of rapid solidification. S. Kavousi, B. Novak, D. Moldovan, and M. Asle Zaeem. Quantitative prediction of rapid solidification by integrated atomistic and phase-field modeling.

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Quantitative Phase-Field Modeling of Solute Trapping in Rapid Solidification

A quantitative phase-field model is developed for prediction of solute trapping for solidification velocities relevant to additive manufacturing. S. Kavousi and M. Asle Zaeem, Quantitative phase-field modeling of solute trapping in rapid solidification.  Acta Materialia 205 (2021) 116562 (11 pages). 

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Phase-field modeling of crack propagation in polycrystalline materials

A phase-field model based on a modified form of the regularized formulation of Griffith’s fracture theory is presented to investigate intergranular and transgranular crack propagations in polycrystalline brittle materials. Grains and grain boundaries are incorporated in the crack initiation and propagation model based on a phase-field model for grain growth, in which the elastic anisotropy varies based on the grain orientation angle, and the grain boundary energy is related to the misorientation angle of the adjacent grains.

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A new planner BCN lateral heterostructure with outstanding strength and defect-mediated superior semiconducting to conducting properties

Motivated by the recent synthesis of boron-carbon-nitride (BCN) monolayers with different atomic compositions, we propose a novel planar BCN lateral heterostructure with a combination of graphene and hexagonal boron nitride (h-BN) counterparts. Density functional theory (DFT) and classical molecular dynamics (CMD) simulations are integrated to examine the effects of defects (vacancy and Stone-Wales (SW) defects) and temperature on the physical properties of the BCN heterostructure.

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Strain-induced work function in h-BN and BCN monolayers

Thomas, M.S. Manju, K.M. Ajith, S.U. Lee and M. Asle Zaeem. Strain-induced work function in h-BN and BCN monolayers.  Physica E: Low-dimensional Systems andNanostructures 123 (2020) 114180 (9 pages) 

Abstract

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Fatigue-resistant high-performance elastocaloric materials made by additive manufacturing. Science 366 (6469) (2019) 1116-1121

H. Hou, E. Simsek, T. Ma, N.S. Johnson, S. Qian, C. Cissé, D. Stasak, N. Al Hasan, L. Zhou, Y. Hwang, R. Radermacher, V.I. Levitas, M.J. Kramer, M. Asle Zaeem, A.P. Stebner, R.T. Ott, J. Cui, I. Takeuchi. Fatigue-resistant high-performance elastocaloric materials made by additive manufacturing. Science 366 (6469) (2019) 1116-1121.

Abstract

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Effects of solidification defects on nanoscale mechanical properties of rapid directionally solidified Al-Cu Alloy: A large scale molecular dynamics study

Directional solidification of Al-11 at % Cu is investigated by molecular dynamics (MD) simulations utilizing second nearest neighbor modified embedded atom method (2NN-MEAM) interatomic potential. The condition for directional solidification is produced by imposing dissimilar temperatures at the model boundaries along the [1 0 0] solidification direction to create a temperature gradient. During solidification, the solid-liquid front travels through the Al-Cu liquid along the [1 0 0] direction towards the high temperature end.

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Nanoscale self-healing mechanisms in shape memory ceramics

Shape memory ceramics, such as yttria-stabilized tetragonal zirconia (YSTZ), offer unique properties including ultra-high operating temperatures and high resistance to oxidation. However, they are susceptible to formation of defects during manufacturing and/or by mechanical deformation. To completely take advantage of their shape memory properties, it is necessary to fully understand the nano-structural evolution of defects under external stimuli. In this study, defect evolution behaviors in YSTZ nanopillars are investigated by atomistic simulations.

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Competition between formation of Al2O3 and Cr2O3 in oxidation of Al0.3CoCrCuFeNi high entropy alloy: A first-principles study

We studied the oxidation behavior of face-centered cubic Al0.3CoCrCuFeNi high entropy alloy through first-principles calculations. Three surface orientations were chosen for oxidation, and all the possible combinations of atomic positions at these surfaces were considered. The adsorption energy of oxygen adhesion to the studied surfaces was the lowest for the sites with more neighboring Cr atoms, and the second most favorite site for oxygen adsorption had more neighboring Al atoms.

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Evolution of solidification defects in deformation of nano-polycrystalline aluminum

Formation of solidification defects and their evolution in uniaxial tensile deformation of solidified polycrystalline aluminum (Al) were investigated by molecular dynamics (MD) simulations. First, solidification process was simulated both isothermally and with different quench rates. At the initial stages of nucleation, coherent twin boundaries and/or fivefold twins formed depending on the quench rate or the undercooling temperature.

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A PostDoc/Research Assistant Professor Position is available immediately on DFT/Phase Field Modeling at the Colorado School of Mines

A PostDoc/Research Assistant Professor Position is available immediately on DFT/Phase Field Modeling at the Colorado School of Mines. The applicants should have a PhD degree in Mechanical Engineering, Materials Science or in a relevant field, with a strong background in DFT calculations and phase-field modeling. The project involves simulating structures/phases, kinetics and nano/microstructural evolution in advanced manufacturing. Please send your CV with 2-3 of your recent and reverent publications to zaeem@mines.edu (Prof. Asle Zaeem).

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A Review of Computational Modeling Techniques in Study and Design of Shape Memory Ceramics

Shape memory ceramics are a unique family of shape memory materials with a wide variety of applications, such as ultra-high energy dissipation and high-temperature actuation. Along with significant progress in the experimental study of zirconia-based shape memory ceramics in recent years, computational simulations have exhibited powerful capabilities in revealing nano/microstructure-dependent deformation and failure mechanisms in these materials.

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