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15 pages, 5456 KB

Open AccessArticle

Influence of an Engineered Notch on the Electromagnetic Radiation Performance of NiTi Shape Memory Alloy

by Anu Anand, Rajeev Kumar, Shatrudhan Pandey, S. M. Mozammil Hasnain and Saurav Goel

Materials 2024, 17(7), 1708; https://doi.org/10.3390/ma17071708 - 8 Apr 2024

Viewed by 1676

This work explores the influence of a pre-engineered notch on the electromagnetic radiation (EMR) parameters in NiTi shape memory alloy (SMA) during tensile tests. The test data showed that the EMR signal fluctuated between oscillatory and exponential, signifying that the specimen’s viscosity damping coefficient changes during strain hardening. The EMR parameters, maximum EMR amplitude, and average EMR energy release rate remained constant initially but rose sharply with the plastic zone radius with progressive loading. It was postulated that new Frank–Read sources permit dislocation multiplication and increase the number of edge dislocations participating in EMR emissions, leading to a rise in the value of EMR parameters. The study of the correlation between EMR emission parameters and the plastic zone radius before the crack tip is a vital crack growth monitoring tool. An analysis of the interrelationship of the EMR energy release rate at fracture with the elastic strain energy release rate would help develop an innovative approach to assess fracture toughness, a critical parameter for the design and safety of metals. The microstructural analysis of tensile fractures and the interrelation between deformation behaviours concerning the EMR parameters offers a novel and real-time approach to improve the extant understanding of the behaviour of metallic materials. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Alloys)

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16 pages, 5697 KB

Open AccessArticle

An Investigation of Spiral Dislocation Sources Using Discrete Dislocation Dynamics (DDD) Simulations

by Luo Li and Tariq Khraishi

Metals 2023, 13(8), 1408; https://doi.org/10.3390/met13081408 - 6 Aug 2023

Cited by 4 | Viewed by 2158

Abstract

Discrete Dislocation Dynamics (DDD) simulations are a powerful simulation methodology that can predict a crystalline material’s constitutive behavior based on its loading conditions and micro-constituent population/distribution. In this paper, a 3D DDD model with spiral dislocation sources is developed to study size-dependent plasticity in a pure metal material (taken here as Aluminum). It also shows, for the first time, multipole simulations of spirals and how they interact with one another. In addition, this paper also discusses how the free surface of a crystalline material affects the plasticity generation of the spiral dislocation. The surface effect is implemented using the Distributed Dislocation Method. One of the main results from this work, shown here for the first time, is that spiral dislocations can result in traditional Frank–Read sources (edge or screw character) in a crystal. Another important result from this paper is that with more dislocation sources, the plastic flow inside the material is more continuous, which results in a lowering of the flow stress. Lastly, the multipole interaction of the spiral dislocations resulted in a steady-state fan-shaped action for these dislocation sources. Full article

(This article belongs to the Special Issue Deformation of Metals and Alloys: Theory, Simulations and Experiments)

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9 pages, 3064 KB

Open AccessArticle

Dislocation Dynamics Model to Simulate Motion of Dislocation Loops in Metallic Materials

by Xinze Tan, Enhui Tan and Lizhi Sun

Metals 2022, 12(11), 1804; https://doi.org/10.3390/met12111804 - 24 Oct 2022

Viewed by 2294

Abstract

Dislocation dynamics has been an intensive research subject in materials science and engineering due to the significant roles it plays in plastic deformation and the hardening of metals, fracture mechanics, and the fabrication of semiconductor thin films. However, a long-standing problem from the three-dimensional dislocation dynamics is that the motion and interaction of dislocation loops heavily depend on the loop-segment sizes, which substantially reduces the accuracy of simulation. We herein propose a new three-dimensional dislocation dynamics model together with its physical background. The proposed model incorporates the inherent interactions among differential dislocation segments. The simulation results on motion of Frank–Read sources demonstrate that the proposed model can resolve the paradoxical segment-dependent phenomenon in dislocation dynamics. Full article

(This article belongs to the Special Issue Computer Methods in Metallic Materials)

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12 pages, 2414 KB

Open AccessReview

Emission of Dislocations from Grain Boundaries and Its Role in Nanomaterials

by James C. M. Li, C. R. Feng and Bhakta B. Rath

Crystals 2021, 11(1), 41; https://doi.org/10.3390/cryst11010041 - 31 Dec 2020

Cited by 21 | Viewed by 5497

Abstract

The Frank-Read model, as a way of generating dislocations in metals and alloys, is widely accepted. In the early 1960s, Li proposed an alternate mechanism. Namely, grain boundary sources for dislocations, with the aim of providing a different model for the Hall-Petch relation without the need of dislocation pile-ups at grain boundaries, or Frank-Read sources inside the grain. This article provides a review of his model, and supporting evidence for grain boundaries or interfacial sources of dislocations, including direct observations using transmission electron microscopy. The Li model has acquired new interest with the recent development of nanomaterial and multilayers. It is now known that nanocrystalline metals/alloys show a behavior different from conventional polycrystalline materials. The role of grain boundary sources in nanomaterials is reviewed briefly. Full article

(This article belongs to the Special Issue Crystal Plasticity at Micro- and Nano-scale Dimensions)

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7 pages, 1780 KB

Open AccessArticle

Geometrically Necessary Dislocations on Plastic Deformation of Polycrystalline TRIP Steel

by Joan Josep Roa, Sebastián Suárez, Agustina Guitar, Gemma Fargas and Antonio Mateo

Crystals 2019, 9(6), 289; https://doi.org/10.3390/cryst9060289 - 3 Jun 2019

Cited by 8 | Viewed by 3731

Abstract

In this study, the main deformation behavior in terms of geometrically necessary dislocations (GND) was investigated on a transformation induced plasticity (TRIP) stainless steel by using sharp indentation at nanometric length scale. Results evidence that austenitic grains display an isotropic behavior on terms [...] Read more.

(This article belongs to the Special Issue Mechanical Behaviour of Austenitic Stainless Steels)

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10 pages, 14562 KB

Open AccessArticle

Nanoindentation-Induced Pile-Up in the Residual Impression of Crystalline Cu with Different Grain Size

by Jiangjiang Hu, Yusheng Zhang, Weiming Sun and Taihua Zhang

Crystals 2018, 8(1), 9; https://doi.org/10.3390/cryst8010009 - 26 Dec 2017

Cited by 28 | Viewed by 6856

Abstract

Nanoindentation morphologies of crystalline copper have been probed at the grain scale. Experimental tests have been conducted on nanocrystalline (NC), ultrafine-grained (UFG), and coarse-grained (CG) copper samples with a new Berkvoich indenter at the strain rate of 0.04/s without holding time at an indentation depth of 2000 nm at room temperature. As the grain size increases, the height of the pile-up around the residual indentation increases and then exhibits a slightly decrease in the CG Cu. The maximum of the pile-up in the CG Cu obviously deviates from the center of the indenter sides. Our analysis has revealed that the dislocation motion and GB activities in the NC Cu, some cross- and multiple-slip dislocations inside the larger grain in the UFG Cu, and forest dislocations from the intragranular Frank-Read sources in the CG Cu would directly induce this distinct pile-up effect. Full article

(This article belongs to the Special Issue Crystal Indentation Hardness)

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