1,721,201 research outputs found
Electronic signal for mechanical failure in two-dimensional <i>g</i>-SiC
No full textIt is non-trivial to identify mechanical failure using first-principles calculations as only long-wave phonons are used in these models due to size limitations. Here, we propose a new criterion to predict the mechanical failure by electronic bandgap closure in graphene-like two-dimensional silicon carbide (g-SiC) monolayer. The electronic bandgap decreases with strain and closes beyond the ultimate strain. This mechano-electronic coupling suggests that the onset of the zero bandgap and the correlation between electronic bandgap and ultimate strain could be used to predict the ideal mechanical failure of g-SiC monolayers
Atomistic Insights into the Irradiation Resistance of Co-Free High Entropy Alloy FeMnNiCr
No full textWe have investigated the displacement cascade irradiation resistance behavior of a cobalt-free high entropy alloy FeMnNiCr using molecular dynamics simulations. The results show that defects in FeMnNiCr form in small clusters, and their migration is significantly inhibited, leading to a higher defect recombination rate and a lower number of residual defects compared to Ni. Additionally, FeMnNiCr exhibits a longer thermal peak life and lower thermal conductivity compared to Ni, providing a longer time for defect migration and combining. The migration of defect clusters in FeMnNiCr displays three-dimensional properties, attributed to its high chemical disorder. After prolonged irradiation, defects in FeMnNiCr stabilize as small clusters, whereas point defects in Ni tend to form large defect clusters and evolve into dislocations. Considering the feature of absence of the element cobalt, our results imply that FeMnNiCr has great potential in application in nuclear energies
Reduced plastic dilatancy in polymer glasses
No full textAmorphous solids in general exhibit a volume change during plastic deformation due to microstructure change during plastic relaxation. Here the deformation dilatancy of alkane polymer glasses upon shearing is investigated using molecular static simulations at zero temperature and pressure. The dilatancy of linear alkane chains has been quantified as a function of strain and chain length. It is found that the system densities decrease linearly with respect to strain after yield point. In addition, dilatability decreases considerably with increasing chain length, suggesting enhanced cooperation of different deformation mechanisms. An analytic model is introduced for dilatability based on the atomistic study. The entanglement chain length is predicted as 43 for alkane polymers from the model, agreeing well with experiments. The study provides insights of correlations of the physical properties and chain length of polymers which might be useful in material design and applications of structural polymers.</p
Insights into scratching force in axial ultrasonic vibration-assisted single grain scratching
No full textUltrasonic vibration-assisted grinding is typically used for ultra-precision machining of hard and brittle materials in aerospace, medical and semiconductor industry. Single grain scratching force is a key to understand its mechanism. Herein, a scratching force model of axial ultrasonic vibration-assisted single-grain scratching was proposed, based on the deformation of chips, friction, and material pile-up forces of a single grain during scratching. The single-crystal silicon carbide was selected as the model material. The molecular dynamics method was employed to simulate single-grain scratching. The scratching forces obtained from the simulations were consistent with the theoretical model with a difference of 4.13 %. The period of the normal force and tangential force is half of that of the vibration and the axial force. The discrepancies are 11.26 % and 4.05 % in tangential and normal directions, respectively, referring to experiment. Axial ultrasonic vibration-assisted scratching facilitates the cyclical removal of brittle and ductile phases, which corroborates the conclusion about the periodicity of the force. Our insights might be helpful in the arrangement of grains on the surface of the grinding wheel and advanced machining design
Effects of size and shape of hole defects on mechanical properties of biphenylene: a molecular dynamics study
No full textThe distinctive multi-ring structure and remarkable electrical characteristics of biphenylene render it a material of considerable interest, notably for its prospective utilization as an anode material in lithium-ion batteries. However, understanding the mechanical traits of biphenylene is essential for its application, particularly due to the volumetric fluctuations resulting from lithium ion insertion and extraction during charging and discharging cycles. In this regard, this study investigates the performance of pristine biphenylene and materials embedded with various types of hole defects under uniaxial tension utilizing molecular dynamics simulations. Specifically, from the stress-strain curves, we obtained key mechanical properties, including toughness, strength, Young's modulus and fracture strain. It was observed that various near-circular hole (including circular, square, hexagonal, and octagonal) defects result in remarkably similar properties. A more quantitative scaling analysis revealed that, in comparison with the exact shape of the defect, the area of the defect is more critical for determining the mechanical properties of biphenylene. Our finding might be beneficial to the defect engineering of two-dimensional materials
AAC theory for ultrasonic vibration-assisted grinding
No full textUltrasonic vibration-assisted grinding (UVG) has several advantages, such as small grinding force, good surface quality, and high grinding efficiency, outperforming conventional grinding (CG). However, it is sensitive to process parameters, making optimal processing parameters crucial and a major challenge. Therefore, in this study, we introduce a model based on the AAC theory, which uses only three quantities (vibration Angle, contact Area, and influence Coefficient of adjacent abrasive particles) to assess the forces during UVG. These three quantities depend on the movement trajectory, mutual contact relationship between the workpiece and abrasive particles, and spacing between abrasive particles. The effects of these three quantities on the scratch force were examined using molecular dynamics (MD) simulations. The reduction ratios of forces (tangential and normal directions) gradually increased with increasing angle, while the differences in the force reduction ratios for the different contact areas were not significant. As the influence coefficient increased, the reduction ratio of the tangential force increased and then flattened, and the reduction of the normal force increased and then slightly decreased. Spearman's correlation analysis shows that the vibration angle has the most effect on the reduction ratio of the scratch force. And the AAC theory was verified by UVG experiments
Stable and 7.7 wt% hydrogen storage capacity of Ti decorated Irida-Graphene from first-principles calculations
No full textSolid-state hydrogen storage is crucial for the widespread applications of hydrogen energy. It is a grand challenge to find appropriate materials that provide high hydrogen density and ambient temperature stability. Herein, we investigated the potential of Ti-decorated Irida-Graphene, a promising effective hydrogen storage system, as a novel hydrogen storage material using first-principles calculation. Irida-Graphene is a two-dimensional isomer of carbon consisting of tri-, hexa-, and octagon rings of carbon. Ti atoms are tightly bounded to the hexagonal rings. Binding energy analysis reveals that a single Ti atom in the primitive unit-cell of Ti-decorated Irida-Graphene is capable to bind up with 5H2 molecules and the average adsorption energy was-0.41 eV/H2. It indicates the gravimetric density of 7.7 wt%. The stability is attributed to Kubas-type interactions and ensured by a 5.0 eV diffusion energy barrier that prevents the Ti-Ti clustering. Further, ab initio molecular dynamics simulations results illustrate that the system remains stable at 600 K, higher than the desorption temperature of 524 K, implying the stability of the system during hydrogen recharge and discharge. The exceptional hydrogen storage performance suggests that Ti-decorated IridaGraphene is an outstanding candidate for hydrogen storage materials.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
Effect of low-frequency optical phonons on the thermal conductivity of 2H molybdenum disulfide
No full textPhonon engineering is a novel and effective approach to tailor the thermal conductivity for the thermoelectric performance and heat dissipation. In general, the acoustic phonons rather than the optical phonons are dominant in heating carriers. Here we report an unprecedented large contribution, 47% overall, from the low-frequency optical phonons to the in-plane thermal conductivity in 2H molybdenum disulfide, revealed by low-wave-number high-pressure Raman technology assisted with first-principles calculations. The analysis of phonon dispersion curves and Gr??neisen parameters of individual phonon modes reveals that the large contribution originates in a joint effect of the large group velocity of low-frequency optical phonons and their strong anharmonic effects. The joint effect is continuously maintained when pressure increases, up to 20 GPa. Our work provides new insights into the optical phonon transport, paving the way for the phonon engineering and thermal management
Element-dependent evolution of chemical short-range ordering tendency of NiCoFeCrMn under irradiation
No full textThe evolution of short-range order (SRO) structures under irradiation has a great impact on the mechanical properties of high-entropy alloys. In this study, the atomistic mechanism of the evolution of SRO during and after cascade collisions was investigated in NiCoFeCrMn by multiscale modeling using molecular dynamics and lattice kinetic Monte Carlo simulations. SRO structures could be destructed by cascade collisions in short time and recovered by atomic diffusion in a much longer time. The destruction rate depends on the primary knock-on atom energies in cascade collisions and shows a universal law with respect to the number of replacement-per-atom. The vacancy diffusion simulations reveal that the SRO recovery rates of different element pairs vary significantly due to the distinct diffusion rates. Consequently, the SRO state under irradiation differs from that in thermodynamic equilibrium due to the difference of destruction and recovery rate for each element pair. The evolution of SRO is a result of the competition between the destruction and recovery mechanisms and depends heavily on the irradiation conditions
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