Serrated plastic flow in slowly-deforming complex concentrated alloys: universal signatures of dislocation avalanches

Under plastic flow, multi-element high/medium-entropy alloys (HEAs/MEAs) commonly exhibit complex intermittent and collective dislocation dynamics owing to inherent lattice distortion and atomic-level chemical complexities. Using atomistic simulations, we report on an avalanche study of slowly-driven model face-centered cubic (fcc) NiCoCrFeMn and NiCoCr chemically complex alloys aiming for microstructural/topological characterization of associated dislocation avalanches. The results of our avalanche simulations reveal a close correspondence between the observed serration features in the stress response of the deforming HEA/MEA and the incurred slip patterns within the bulk crystal. We show that such correlations become quite pronounced within the rate-independent (quasi-static) regime exhibiting scale-free statistics and critical scaling features as universal signatures of dislocation avalanches

Effects of Lateral Wedge Insole on Static and Dynamic Balance in Patients with Moderate Medial Knee Osteoarthritis

BACKGROUND AND OBJECTIVE: Knee osteoarthritis (OA) is associated with diminished joint proprioception, balance deficits and increased risk of falls. Patients with medial knee osteoarthritis are at higher risk of balance deficits and falling due to the development of secondary varus deformity. Therefore, it is of great clinical importance to identify the treatment methods that could improve balance in knee OA. The purpose of this study was to evaluate the effects of Lateral Wedge Insole (LWI) on static and dynamic balance in patients with moderate medial knee osteoarthritis. METHODS: Thirty patients with moderate medial knee OA participated in this semi-experimental interventional study. Patients were recruited from orthopedic and rheumatology clinics of the university. For each patient, the static and dynamic balance were assessed in two conditions including wearing shoes with flat insole and wearing shoes with lateral wedge insole, using a Prokin stabilometer. The balance variables were the anteroposterior and mediolateral velocity and standard deviation of the center of pressure (COP) displacement, and total stability indices. Patients performed two familiarization trials, then, three actual trials with at least 30 s interval for each test. FINDINGS: Wearing LWIs resulted in significant decreases in the anteroposterior (static:1.78mm/s, dynamic:6.63mm/s) and mediolateral velocity of COP (static:1.53mm/s, dynamic:5.58mm/s) in compression to wearing shoes with flat insole (p<0.001). The anteroposterior (static:1.04 mm, dynamic:1.57mm) and mediolateral SD of the COP (static:1.58mm, dynamic:2.02mm) were also decreased after using LWIs (p<0.007). Except for the anteroposterior stability index, other balance indices were also significantly improved (p<0.05). CONCLUSION: Our findings suggest that using a LWI improve static and dynamic balance in patients with moderate medial knee OA

Atomistic simulations of dislocation plasticity in concentrated VCoNi medium entropy alloys: Effects of lattice distortion and short range order

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Shear banding instability in multicomponent metallic glasses

| openaire: EC/H2020/857470/EU//NOMATEN Funding Information: This research was funded by the European Union Horizon 2020 research and innovation program under Grant Agreement No. 857470 and from the European Regional Development Fund via Foundation for Polish Science International Research Agenda PLUS Program Grant No. MAB PLUS/2018/8. Publisher Copyright: © 2022 American Physical Society.The shear-banding instability in quasistatically driven bulk metallic glasses emerges from collective dynamics, mediated by shear transformation zones and associated nonlocal elastic interactions. It is also phenomenologically known that sharp structural features of shear bands are typically correlated to the sharpness of the plastic yielding transition, being predominant in commonly studied alloys composed of multiple different elements, that have very different atomic radii. However, in the opposite limit where elements' radii are relatively similar, plastic yielding of bulk metallic glasses is highly dependent on compositional and ordering features. In particular, a known mechanism at play involves the formation of short-range order dominated by icosahedra-based clusters. Here, we report on atomistic simulations of multicomponent metallic glasses with different chemical compositions showing that the degree of strain localization is largely controlled by the interplay between composition-driven icosahedra-ordering and collectively-driven shear transformation zones. By altering compositions, strain localization ranges from diffuse homogenized patterns to singular crack-like features. We quantify the dynamical yielding transition by measuring the atoms' susceptibility to plastic rearrangements, strongly correlated to the local atomic structure. We find that the abundance of short-range ordering of icosahedra within rearranging zones increases glassy materials' capacity to delocalize strain. This could be understood on the basis of structural heterogeneities that are enhanced by the presence of local order. The kind of plastic yielding can be often qualitatively inferred by the commonly used compositional descriptor that characterizes element associations, the misfit parameter da, and also by uncommon ones, such as shear-band width and shear-band dynamics' correlation parameters.Peer reviewe

glassDef dataset: metallic glass deformation

&lt;p&gt;The glassDef dataset contains a set of text-based LAMMPS dump files corresponding to shear deformation tests on different bulk metallic glasses. This includes FeNi, CoNiFe, CoNiCrFe, CoCrFeMn, CoNiCrFeMn, and Co5Cr2Fe40Mn27Ni26 amorphous alloys with data files that exist in relevant subdirectories. Each dump file corresponds to multiple realizations and includes the dimensions of the simulation box as well as atom coordinates, the atom ID, and associated type of nearly 50,000 atoms.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Load glassDef Dataset in Python&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;The glassDef dataset may be loaded in Python into Pandas DataFrame. To go into the relevant subdirectory, run cd glass{glass_name}/Run[0-3]/ where &ldquo;glass_name&rdquo; denotes the chemical composition. Each subdirectory contains at least three glass realizations within subfolders that are labeled as &ldquo;Run[0-3]&rdquo;.&lt;/p&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;&gt; cd glassFeNi/Run0; python&lt;/p&gt; &lt;p&gt;&gt; import pandas&lt;/p&gt; &lt;p&gt;&gt; df = pandas.read_csv(&quot;FeNi_glass.dump&quot;,skiprows=9)&lt;/p&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;One may display an assigned DataFrame in the form of a table:&lt;/p&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;&gt; df.head()&lt;/p&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;To learn more about further analyses performed on the loaded data, please refer to the paper cited below.&lt;/p&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;glassDef Dataset Structure&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;glassDef Data Fields&lt;/strong&gt;&lt;/p&gt; &lt;ul&gt; &lt;li&gt;Dump files: &ldquo;id&rdquo;, &ldquo;type&rdquo;, &ldquo;x&rdquo;, &ldquo;y&rdquo;, &ldquo;z&rdquo;.&lt;/li&gt; &lt;/ul&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;glassDef Dataset Description&lt;/p&gt; &lt;ul&gt; &lt;li&gt;Paper: Karimi, Kamran, Amin Esfandiarpour, Ren&eacute; Alvarez-Donado, Mikko J. Alava, and Stefanos Papanikolaou. &quot;Shear banding instability in multicomponent metallic glasses: Interplay of composition and short-range order.&quot; Physical Review B 105, no. 9 (2022): 094117.&lt;/li&gt; &lt;/ul&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;ul&gt; &lt;li&gt;Contact: [email protected]&lt;/li&gt; &lt;/ul&gt

Dislocation plasticity in equiatomic NiCoCr alloys : Effect of short-range order

Funding Information: This research was funded by the European Union Horizon 2020 research and innovation program under Grant Agreement No. 857470 and from the European Regional Development Fund via Foundation for Polish Science International Research Agenda PLUS program Grant No. MAB PLUS/2018/8. | openaire: EC/H2020/857470/EU//NOMATENEquiatomic NiCoCr solid solutions have been shown by recent experiments and atomistic simulations to display exceptional mechanical properties that have been suggested to be linked to nanostructural short-range order (SRO) features that may arise from thermal treatments, such as annealing or/and aging. Here we use hybrid Monte Carlo-molecular dynamics simulations to gain further insights of thermal effects on the SRO formation as well as the edge dislocation plasticity mechanisms of equiatomic NiCoCr face-centered cubic solid solution. For that purpose, we utilize two well-known NiCoCr interatomic potentials, one of which displays well-documented SRO, believed to be linked to experimental evidence and labeled as the Li-Sheng-Ma potential, while the other (Farkas-Caro) does not. We use these two potentials to discern short-range ordering (from inherent randomness in random solid solutions) and understand how SROs influence dislocation depinning dynamics in various thermal annealing scenarios. In this context, we used robust, scale-dependent metrics to infer a characteristic SRO size in the Li-Sheng-Ma case by probing local concentration fluctuations which otherwise indicate uncorrelated patterns in the Farkas-Caro case in a close agreement with random alloys. Our Voronoi-based analysis shows meaningful variations of local misfit properties owing to the presence of SROs. Using relevant order parameters, we also report on the drastic increase of chemical ordering within the stacking fault region. More importantly, we find that the Li-Sheng-Ma potential leads to excellent edge dislocation depinning strength with low stacking fault width. Our findings indicate an enhanced roughening mechanism due to the SROs-misfit synergy that leads to significant improvements in dislocation glide resistance. We argue that the improvements in alloy strength have their atomistic origins in the interplay between nanoscopic SROs and atomic-level misfit properties.Peer reviewe