The Novel Coronavirus which emerged in India on January/30/2020 has become a catastrophe to the country on the basis of health and economy. Due to rapid variations in the transmission of COVID-19, an ...accurate prediction to determine the long term effects is infeasible. This paper has introduced a nonlinear mathematical model to interpret the transmission dynamics of COVID-19 infection along with providing vaccination in the precedence. To minimize the level of infection and treatment burden, the optimal control strategies are carried out by using the Pontryagin's Maximum Principle. The data validation has been done by correlating the estimated number of infectives with the real data of India for the month of March/2021. Corresponding to the model, the basic reproduction number Formula: see text is introduced to understand the transmission dynamics of COVID-19. To justify the significance of parameters we determined the sensitivity analysis of Formula: see text using the parameters value. In the numerical simulations, we concluded that reducing Formula: see text below unity is not sufficient enough to eradicate the COVID-19 disease and thus, it is required to increase the vaccination rate and its efficacy by motivating individuals to take precautionary measures.
Cyclic plastic deformation behavior of nanocrystalline body-centered cubic (BCC) iron is investigated using molecular dynamics simulation. The formation of X-junction and Y-junction during ...deformation causes the faster mobility of dislocation, which results in softening behavior of the material. In addition, the generation of vacancy defects behind the moved perfect screw dislocation represents the jerky deformation behavior of nanocrystalline BCC iron. The study also highlights the distribution of atomic strain. The grain boundary sliding may result in local atomic strain distribution at the grain boundary. Whereas the region of maximum defects activity shows a higher distribution of atomic strain. The vivid story of crystalline defects in BCC iron helps to develop a deep understanding of cyclic plastic deformation response in the atomic scale.
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The present analysis focus on the mechanism of deformation in different tensile deformation modes. Uniaxial, plane strain and equi-biaxial tensile deformation modes play a significant role in ...determining the yield stress of the material. Yielding of the material begins with nucleation of 1/6 Shockley partial dislocation and subsequent deformation cause an increase in dislocation line length in the material. Consequently, strain hardening is observed in the RVE of nanocrystalline copper. Nucleation and propagation of dislocations and stacking faults collectively control the strain hardening behavior of the material. Distribution of atomic shear strain and dislocation is found moderately homogeneous in case of equi-biaxial tensile deformation. While the heterogeneous distribution of atomic strain and dislocation is observed in uniaxial and plane strain tensile distribution. Higher grain boundary migration is observed in uniaxial tensile deformation. Moreover, the attractive dislocation traits are noticed during dislocation and grain boundary interaction such as pinning of Shockley partial dislocation and formation of peanut like complex dislocation structure.
The current study investigates the uniaxial tensile deformation and damage mechanism in single-crystal Aluminum (Al) in the presence of soft and hard inclusions. Spherical shaped Magnesium (Mg) and ...Titanium (Ti) are added as inclusions within an Al single crystal. Alteration in mechanical properties has been noticed in the presence of inclusions. Softening has been observed in the presence of Mg; while hardening in the presence of Ti. Low Young modulus of Mg inclusion and lack of dislocation activity results in less deformation, higher stress concentration at the interface, and early void nucleation in Al+Mg system. While high Young modulus of Ti inclusion and substantial dislocation activity prevails the large deformation, lower stress concentration at the interface, and slow fracture in Al+Ti system. The study provides an understanding of the governing fracture mechanism influenced by the inclusion.
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•Alteration in mechanical properties of aluminum is observed due to inclusions.•Nucleation and growth of voids occur in {111} slip planes in SC Al, and near the interface of Al+Ti system.•High-stress concentration causes rapid fracture in Al+Mg; low-stress concentration causes ductile fracture in Al+Ti systems.•Softening and hardening are observed in Al in the presence of inclusions Mg and Ti inclusions, respectively.•Higher dislocation length is observed in Al+Ti system in contrast to SC Al and Al+Mg systems.
This paper examined the Bauschinger effect in single-crystal (SC) and polycrystal (PC) aluminum (Al). The effect of hard Ti inclusion has also been analysed on both systems considering the case of ...the Bauschinger effect. The reversibility effect of 1/6 < 112 > partial dislocation and reduction in defect densities such as dislocations annihilations, stacking fault, and twin are found in the stress reversal in Al. It has been noted that the Bauschinger effect is the consequence of the reversibility effect of 1/6 < 112 > partial dislocation and reduction in defect densities during unloading in Al. Additionally, the development of residual strain has been observed during unloading in PC Al which significantly affects the Bauschinger effect. The presence of inclusion considerably affects the Bauschinger effect in SC Al concerning PC Al. To quantify the Bauschinger effect in various systems, the back stress parameter is calculated, which reveals hard Ti inclusion substantially influences the Bauschinger effect in Al.
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Finite element simulation technique is extensively useful nowadays for die designing by optimizing the springback from the formed state of sheet metal panel. The magnitude of springback is normally ...calculated in finite element simulation by assuming a completely elastic recovery in non-linear kinematic hardening law. Constant values of elastic modulus and Poisson’s ratio are required to estimate the elastic recovery by non-linear kinematic hardening law. Cleveland and Ghosh (Int J Plast 18:769–785, 2002), Li and Wagoner (Int J Plast 1827:1126–1144, 2011), and many other research groups have reported that inelastic strain release during unloading is the main source of extra strain recovery and as a result poor springback prediction by commercial finite element software. In this regard, many theoretical postulates have been proposed to explain such inelastic strain release during unloading. In this work, we show from atomistic simulation that irreversible movement of dislocation, i.e., microplasticity, is the source of inelastic strain release during unloading.
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•Homogeneous crack tip stress and strain fields for copper single crystal.•Inhomogeneous crack tip stress and strain fields for polycrystalline copper.•Nucleation of dislocation from ...crack tip results crack tip blunting.•High stress concentration at grain boundary reduces by dislocation emission.
Molecular dynamics simulation is conducted on single crystal and polycrystalline copper. Two different crack tip orientations (001) -110 and (001) 010 are selected for copper single crystal. For copper single crystal with crack tip orientation of (001) 010, stress is concentrated at the crack tip, and cleavage crack propagation happens due to lack of dislocation activity at the crack tip. For copper single crystal with crack tip orientation of (001) -110, continuous emission of dislocations from crack tip results crack tip blunting and reduction of stress concentration as well. Homogeneous crack tip stress and strain fields are evident for copper single crystals, however, stress and strain fields slightly alter with the generation of dislocations and defects. Crack tip stress and strain distribution are inhomogeneous from the beginning of the deformation for polycrystalline copper. Higher stress concentration at the grain boundary than crack tip results in nucleation of initial dislocations from the grain boundary during plastic deformation.
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•Developed molecular model of sliding contact between two non-Gaussian rough surfaces.•Surface topography changes after sliding motion for each plate spacing (δ).•More increase in ...autocorrelation length signifies more flattening of the surface.•Higher atomic wear and dislocation length are observed for lower plate spacing (δ).
Friction plays a significant role in the wear and tear of sliding metallic surfaces, particularly in gears and bearings employed in nano and micro electro-mechanical systems (NEMS/MEMS). To comprehend the nature of dry sliding friction in mechanical devices, it is crucial to investigate surface interactions at the nano-scale. Molecular dynamics (MD) simulation has been utilized in this study to explore how asperities come into contact at this minute scale. Specifically, the interaction between two non-Gaussian rough surfaces is examined at varying dimensionless spacing (δ/Seq), ranging from 3.6 to 2.7. The von Mises strain, atomic wear, and changes in the atomic arrangement after sliding action are obtained for Cu-Cu (soft-to-soft) tribo-pair at a given sliding speed of 10 m/s. The average friction force on the lower surface increased when the space between surfaces was decreased. More percentage changes in surface topography are found for the lesser dimensionless spacing (δ/Seq) of 2.7. The changes in surface topography parameters during sliding action may have an immense effect on the performance of tribo-pair in NEMS/MEMS. A greater increase in autocorrelation length signifies a more pronounced flattening of the lower surface at the lower dimensionless spacing (δ/Seq).
Abstract
Hybrid halide perovskite solar cells have been recognized as one of the most promising future photovoltaic technologies due to their demonstrated high‐power conversion efficiency, versatile ...stoichiometry and low cost. However, degradation caused by environmental exposure and structural instability due to ionic defect migration hinders the commercialization of this technology. While the experimental studies try to understand the phenomenology of the degradation mechanisms and devise practical measures to improve the stability of these materials, theoretical studies have attempted to bridge the gaps in our understanding of the fundamental degradation mechanisms at different time and length scales. A deeper understanding of the physical and chemical phenomena at an atomic level through multiscale materials modeling is going to be crucial for the knowledge‐based prognosis and design of future halide perovskites. There have been increased efforts in this direction in the last few years. However, the instability fundamentals explored through atomistic modeling and simulation methods have not been reviewed comprehensively in the literature yet. Therefore, this paper is an attempt to present a critical review, while identifying the existing gaps and opportunities in the investigation of the degradation and instability issues of the halide perovskites using computational methods. The review will primarily focus on the instability caused due to the intrinsic ionic defect migration and degradation due to thermal, moisture and light exposure. The findings from the simulation studies conducted primarily using density functional theory, ab initio molecular dynamics, classical molecular dynamics and machine learning methods will be presented.
This article is categorized under:
Software > Molecular Modeling
Structure and Mechanism > Computational Materials Science
Data Science > Artificial Intelligence/Machine Learning
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