Plateau Stages Research Articles

Quasi-static compression response of a novel multi-step auxetic honeycomb with tunable transition strain

Auxetic honeycombs with multi-step deformation have received widespread attention due to their multifunctionality and superior mechanical properties. To improve the tunability of the auxetic honeycomb, a novel multi-step auxetic honeycomb (MSAH) is proposed by combining star-rhombic parts with crossed thin walls. MASH is characterized by multi-step deformation, and its stress-strain curve has three significant plateau stages. The strain during the transition between different deformation steps can be adjusted by designing unit cells with different geometrical parameters. In the compression process, the ordered contact of the cell walls of MASH is the critical reason for realizing the multi-step deformation. The quasi-static compression finite element model of MASH is established and verified by experiments. Quasi-static compression response and deformation mechanism of MASH are studied. Then, the effects of geometrical parameters on the compression response of MASH are investigated. The results show that the wall thickness has a greater effect on the compressive stress, and the cell-wall angle determines the deformation mode of MASH. Furthermore, the transition strain of MASH is theoretically analyzed and verified by numerical simulations. This study provides a reference for designing multi-step deformation honeycombs and applying multi-stage energy absorbers.

Size shrinkage and compressive behaviour of Al2O3 honeycomb structures fabricated via Digital Light Processing technology

Al2O3 ceramic have excellent chemical inertness, superior heat resistance, and excellent corrosion resistance, so they are considered ideal materials for manufacturing high-performance components such as thermal end devices in aerospace, heat dissipation panels in electronic communication, and exhaust filters in the automotive industry. Digital Light Processing (DLP) is a useful technology to fabricate complex Al2O3 ceramic components. However, the size shrinkage effect of DLP-fabricated components need to be investigated deeply before its further application. In this work, we utilized DLP technology to fabricate Al2O3 ceramic honeycomb structures and systematically investigated their microstructure, size shrinkage, and mechanical properties. Our findings revealed that the Al2O3 ceramic grains exhibit flake-like structures with an average diameter of 1–2 μm, and the ceramic particles are tightly bonded. The shrinkage rates in the X and Y axes were 7.54 % and 7.42 %, respectively, while the Z-axis exhibited a more significant shrinkage of 13.04 %. This anisotropic shrinkage in different direction was attributed to accumulation of the interlayer bonding under gravity action during debinding and sintering process. The compressive stress-strain curve of the honeycomb structures demonstrated a typical brittle compressive behavior, including elastic, stress plateau, and brittle fracture stages. The honeycomb structures exhibited an elastic modulus of 54.49 ± 1.22 MPa and a compressive strength of 10.22 ± 0.42 MPa. The fracture analysis indicated that the fractures region of honeycomb structures initiated at the corners of the honeycomb structures, indicating their easy-broken compared to the walls. These findings provide valuable guidance for the high-precision and high-performance manufacturing of complex Al2O3 ceramic components.

New descriptions of the larval and pupal stages of Orthocladiusnitidoscutellatus and Psectrocladiusnevalis from Xizang, China (Diptera, Chironomidae).

Tibetan Plateau is one of the most typical areas of biodiversity in the world because of its unique environmental and regional units, which breed unique biological communities and concentrate on many unique and rare wild animals and plants. Research on Chironomidae in the Tibetan Plateau is relatively weak. At present, the identification of Chironomidae species mainly depends on male adults, while identification of larvae and pupae is relatively difficult and there is less research on them. During the investigations of insect diversity in the Tibetan Plateau, larval and pupal stages of Orthocladiusnitidoscutellatus Lundström, 1915 and Psectrocladiusnevalis Akhrorov, 1977 were described and illustrated. Matching and identification of larval and pupal stages were based on DNA barcodes. Neighbour-joining trees were reconstructed, based on known Orthocladius and Psectrocladius COI DNA barcodes, respectively.

Dynamic mechanical response, energy absorption capacity, and constitutive modeling of polypropylene fiber-reinforced foamed concrete under high temperature

This study utilized a modified split Hopkinson pressure bar apparatus to subject polypropylene fiber-reinforced foamed concrete (PPFRFC) to substantial deformation loading at high temperatures and strain rates. Based on experimental results, the study systematically investigated the coupled effects of temperature and strain rate on the dynamic mechanical behavior of PPFRFC across a broad range of strain rates (0.001 s−1 to 1300 s−1) and temperatures (25 °C–600 °C). The findings revealed that elevated temperatures significantly affected various mechanical parameters including peak stress, plateau stress, elastic modulus, densification strain, dynamic increase factor (DIF), and energy absorption. Notably, with increasing temperature, the strain rate amplified the peak stress, plateau stress, and energy absorption, whereas its influence on the elastic modulus diminished. Microstructural examination revealed the absence of notable cracks in the pore walls after high-temperatures exposure. However, degradation of the cement matrix results in a loose skeleton structure within the pore walls, leading to a considerable reduction in material strength. Finally, a constitutive model was developed, considering the coupling effects of temperature and strain rate. This model accurately describes the mechanical response of the PPFRFC across various stages, including the elastic, plateau, and densification stages, as well as the stress drop behavior in the transition stage. Moreover, it effectively reflects the influence of strain rate and temperature coupling effects on the material's mechanical properties.

A novel elliptical annular re-entrant auxetic honeycomb with enhanced stiffness

Auxetic structures have sparked a lot of interest due to their excellent mechanical characteristics and unusual negative Poisson's ratio influence. However, the large porosity property results in low stiffness, which limits their application scope. Current approaches to augment stiffness often result in diminished auxetic performance. Therefore, it is challenging to simultaneously enhance the auxetic, stiffness and energy absorption capacity of auxetic structures. To address this issue, this paper proposes a novel elliptical annular re-entrant honeycomb (EARE) by introducing an elliptical annular structure into a conventional re-entrant honeycomb (RE) cell, which can provide extra longitudinal support without hindering lateral deformation. The plateau stress, Poisson's ratio and energy absorption properties of the EARE are investigated by quasi-static compressive tests and finite element modeling. The results show that the EARE honeycomb has two plateau stages due to the supporting effect of the elliptical annular structure. Compared with the conventional RE honeycomb with the same wall thickness, the EARE honeycomb not only exhibits a stronger auxetic effect embodied in the Poisson's ratio reduced by 5.19%, but also has a higher average plateau stress and a higher specific energy absorption of 171.63% and 28.03%, respectively, which significantly improves the stiffness and energy absorption performance. The parameterized analysis reveals that by appropriately adjusting the geometric parameters, the stiffness, energy absorption, and auxetic effect of the EARE honeycomb can be enhanced. The research findings address the conflict between auxetic performance and honeycomb stiffness, providing new insights into the optimization of honeycomb structure design.

Finite element analysis on global and local deformation behavior of 3D spacer fabric

Three-dimensional spacer fabric is a type of one-piece sandwich structure consisting of two outer layers and vertical and inclined spacer monofilaments. It behaves like a cushioning material, having linear, plateau, and densification stages under compression. This article elucidates the compression mechanism of a typical spacer fabric in terms of global deformation, local deformation, and internal contact behavior of spacer monofilaments through finite element simulation. While the linear stage is post-buckling of spacer monofilaments with tight constraints, the plateau stage is a combination of post-buckling, torsion, rotation, and contact of spacer monofilaments. The densification stage is attributed to the contact between spacer monofilaments and outer layers, which decreases the effective length to bear the load and enhances the constraints on the spacer monofilaments. The vertical spacer monofilaments with almost triple the normal strains of the inclined ones contribute more to compression resistance.

Mechanical response and energy absorption of bridge block with negative Poisson's ratio

A new negative Poisson's ratio (NPR) block is proposed as girder falling restrainer for bridge structures, which is anticipated to have high energy absorption, high bearing capacity and intensified stiffness inherited the advantages of negative Poisson's ratio structure. The monotone loading test and the FE simulation are employed to investigate the deflection, the load-displacement response, the energy absorption of the block. The sensitivity of the block to the critical geometric parameters is revealed. The FE simulation is also employed to investigate the response of honeycomb NPR blocks. The monotone loading experiment shows that the proposed monomer NPR block has a three-step deformation process and consequently three plateau stages. The stiffness and the plateau load are small in the initial stage but can be significantly increased without significant oscillations in the following stages. The transitional displacements of the block are affected mainly by the folded angle and the length of the steel plates in the NPR monomer while the plateau loads are affected mainly by the thickness and the length of the plates. The total energy absorption of the NPR monomer in the block is more sensitive to the plateau load. The layer of the honeycomb affects mainly the transitional displacement of honeycomb NPR blocks. Cell number in each layer affects both the plateau loads and the transitional displacements.

A New Analytical Model for Predicting Steam-Assisted Gravity-Drainage Performance in the Plateau and Decline Stages

Summary Analytical models have been widely used to study the steam-assisted gravity-drainage (SAGD) process. Existing analytical models for this process either underperform or are limited in their applicability. In this paper, a new analytical model is developed to address these shortcomings. The new model consists of three major components. First, an equation for predicting oil production rate during the plateau stage was developed. This equation allows for permeability anisotropy in the reservoir, which is neglected in the majority of existing analytical models. Second, a novel and concise equation for calculating oil production rate during the decline stage was derived. This equation for the first time provides a general relationship between oil production rate during the decline stage and the properties of the reservoir together with key operating conditions and simultaneously mitigates the shortcomings of the majority of existing models (e.g., inapplicable in the decline stage of the SAGD process). Third, new correlations representing heat loss from the steam chamber to the overburden and heat transfer to oil-undepleted zone ahead of the chamber interface were derived; new predictive equations for estimating steam/oil ratio (SOR) in the plateau and decline stages of SAGD were obtained. The new model has been validated against a 2D scaled laboratory experiment and a set of field data. The results of this validation show that the new model predicts the oil production rate and SOR over the lifetime of an SAGD operation (excluding the short steam rise period) reasonably well. Predictions from the new model were also compared with several existing analytical models: The new model provided a closer match to actual measurements than other models. This robust model is grounded in more physics and incorporates reservoir geology and well operating conditions. It enables better understanding of the SAGD process and significantly improves the prediction of SAGD performance. Hence, it can be used to design new SAGD projects, predict existing projects, and optimize existing projects.

Dynamic response of cross steel reinforced concrete filled steel tubular columns under impact under fire

To explore the impact response of cross steel-reinforced concrete-filled steel tubular (CSRCFST) columns under fire, a finite element model using ABAQUS software was generated. After validation against test results, parametric studies were carried out to investigate the effects of impact load as well as time of fire exposure on the impact resistance of CSRCFST columns. The numerical results show that the impact behavior of post-fire CSRCFST columns can be divided into three stages: peak stage, plateau stage, and softening stage. For CSRCFST columns, the peak and plateau stages are important, which absorbed 32.4% and 67.6% of the impact kinetic energy, respectively. After two hours of fire exposure, the stiffness and peak impact load of the column decreased by 93.7% and 71.7%, respectively. However, the peak mid-span deflection and residual deflection increased by 6.5% and 20.1%, respectively. When the drop weight tripled, the maximum deflection and residual deformation of the midspan increased by 2.8 and 3.2 times, respectively. However, the peak impact load increases only by 14.5%. When the impact energy is the similar, the maximum midspan deflection of the specimen is almost identical, whereas a larger impact momentum reduces the peak impact force but increases the impact force at the plateau stage. By increasing fire duration, the behaviors of the column deteriorate seriously, with 85% reductions in peak impact force and 39% increase in maximum midspan deflection. In addition, the effects of impact velocity are also significant regarding each stage.

Single-base methylome analysis reveals dynamic changes of genome-wide DNA methylation associated with rapid stem growth of woody bamboos.

CG and CHG methylation levels in the rapid shoot growth stages (ST2-ST4) of woody bamboos were obviously decreased, which might regulate the internode elongation during rapid shoot growth, while CHH methylation was strongly associated with shoot developmental time or age. DNA methylation plays a critical role in the regulation of plant growth and development. Woody bamboos have a unique trait of rapid stem growth resulted from internode elongation at the shooting period. However, it is still unclear whether DNA methylation significantly controls the bamboo rapid stem growth. Here we present whole-genome DNA methylation profiles of the paleotropical woody bamboo Bonia amplexicaulis at five newly defined stages of shoot growth, named ST1-ST5. We found that CG and CHG methylation levels in the rapid shoot growth stages (ST2-ST4) were significantly lower than in the incubation (ST1) and plateau stages (ST5). The changes in methylation levels mainly occurred in flanking regions of genes and gene body regions, and 23647 differentially methylated regions (DMRs) were identified between ST1 and rapid shoot growth stages (ST2-ST4). Combined with transcriptome analysis, we found that DMR-related genes enriched in the auxin and jasmonic acid (JA) signal transduction, and other pathways closely related to plant growth. Intriguingly, CHH methylation was not involved in the rapid shoot growth, but strongly associated with shoot developmental time by gradually accumulating in transposable elements (TEs) regions. Overall, our results reveal the importance of DNA methylation in regulating the bamboo rapid shoot growth and suggest a role of DNA methylation associated with development time or age in woody bamboos.

Two plateau characteristics of re-entrant auxetic honeycomb along concave direction

Auxetic honeycombs usually feature a single plateau stress, which hinders their multifunctional applications. In this work, we aim at investigating the two plateau characteristics of re-entrant honeycomb (REH) with negative Poisson’s ratio (NPR) in the concave direction through experimental, numerical and theoretical methods. A series of REH prototypes with different geometric parameters were fabricated by utilizing the additive manufacture (AM) technique, and were tested under quasi-static crushing. It was found that due to the transitional rectangle structures formed during crushing, the REH specimens exhibit a two-step deformation mode and thus have two plateau stresses in the stress–strain curves. The second plateau stress of the baseline specimen is more than twice the first plateau stress. Both the numerical and the theoretical predictions agree well with the experimental results. Detailed parameter analysis showed that larger cell wall thickness, smaller straight wall length and smaller inclined angle lead to larger first and second plateau stresses. In addition, the effect of crushing velocity on the crushing behavior of the REH was discussed. Under dynamic crushing, no critical strain is found to divide the first and second plateau stages, and the two plateau characteristics disappear. This study may provide guidelines for the design of multifunctional honeycombs with two plateau stages.

Design and quasi-static responses of a hierarchical negative Poisson’s ratio structure with three plateau stages and three-step deformation

To solve the problems that the existing negative Poisson’s ratio (NPR) structures only exhibit single plateau stage and irregular deformation modes, a novel hierarchical NPR structure called rotating star-circle structure (RSCS) was proposed. We respectively replaced the hinges and the rigid solid square in the classical rotational rigid square with the beam-like links and star-circle substructure. Through the quasi-static experiment, the FE modeling was validated. According to energy conservation, a theoretical model was established to predict the equivalent elastic modulus. The FE analysis was carried out to verify the theoretical model. The deformation modes and compression responses were studied by the FE method. It was found that there were three-step deformation and three plateau stages. Further, the deformation mechanisms were revealed based on the deformation modes and mechanical responses. Additionally, the parameters study showed that the geometric configuration significantly affected the deformation modes and mechanical responses. Compared with other auextic structures in the SEA, the RSCS exhibited better energy absorption. Lastly, we proposed a general design method based on the equal chord division to construct the multi-plateau structure. This research was a reference for the multi-functional application of the NPR structure and improving their energy absorption.

In-plane crushing behavior and energy absorption of a novel graded honeycomb from hierarchical architecture

Nature's bio-organisms are typically hybrid structures composed of hierarchical and functionally graded micro-architectures, which are lightweight and of high mechanical performances. Inspired by nature, an innovative graded hierarchical honeycomb is proposed in this study to enhance its crashworthiness behaviors. The structure is created by replacing cell walls of regular honeycombs with triangular and hexagonal sub-structures and varying the hierarchical length ratio in each layer. The in-plane crushing performances of the graded hierarchical honeycombs are comprehensively analyzed and compared with their uniform hierarchical counterpart. The former exhibits a progressive deformation model under different impact velocities and three plateau stages can be observed under in-plane crushing loads through theoretical predictions. The triangular sub-structure presents better energy absorption than the hexagonal sub-structure, and its specific energy absorption is enhanced by up to 32.2% as compared to the uniform hierarchical honeycomb. The present study suggests that the combination of hierarchy and gradient is an effective strategy to improve the dynamic crushing behaviors of honeycombs, which can be further explored in protective devices to enhance their impact resistance.

Pseudo-ductile effects in ±45∘ angle-ply CFRP laminates under uniaxial loading: Compression and cyclic tensile test

The capacity of symmetric ±45∘ angle-ply laminates of carbon fibre reinforced polymer to hold large strains before final failure is studied in uniaxial tensile and compressive loading. In particular, [±45]2S and [±45]4S laminates are tested under tension and compression respectively. Both present a three-staged stress–strain response with a first linear evolution followed by a plateau and a final strain hardening. Thanks to the Loading–Unloading–Reloading tensile test, the pseudo-ductile process is analysed in terms of the strain energy. In the first two stages the percentage of the total energy recovered in each cycle follows a similar correlation than the relation of the apparent tensile stiffness with the initial one. Therefore, assuming a similar pattern in both tensile and compressive loading cases, the mechanical response during the linear and plateau stages undergoes a progressive damage with a stiffness reduction related to the dissipated energy. However, a damage model that includes the influence of the fibre’s reorientation would not predict the re-stiffening of the third stage. In this work the last stage of strain hardening is assumed to follow a different pattern because of the microstructural changes of the matrix during the plateau stage. These are promoted by strain localisation processes both under tension and compression, with dimensional changes in perpendicular to the loading direction that are observed thanks to the strain fields obtained by Digital Image Correlation. Finally, the main differences between both loading cases are evidenced with the help of the final failure modes.

Modeling and ex vivo experimental validation of liver tissue carbonization with laser ablation

ObjectiveThe purpose of this study was to model the process of liver tissue carbonization with laser ablation (LA). MethodsA dynamic heat source model was proposed and combined with the light distribution model as well as bioheat transfer model to predict the development of tissue carbonization with laser ablation (LA) using an ex vivo porcine liver tissue model. An ex vivo laser ablation experiment with porcine liver tissues using a custom-made 1064 nm bare fiber was then used to verify the simulation results at 3, 5, and 7 W laser administrations for 5 min. The spatiotemporal temperature distribution was monitored by measuring the temperature changes at three points close the fiber during LA. Both the experiment and simulation of the temperature, tissue carbonization zone, and ablation zone were then compared. ResultsFour stages were recognized in the development of liver tissue carbonization during LA. The growth of the carbonization zone along the fiber axial and radial directions were different in the four stages. The carbonization zone along the fiber axial direction (L2) grew in the four stages with a sharp increase in the initial period and a minor increase in Stage 4. However, the change in the carbonization zone along the fiber radial direction (D2) increased dramatically (Stage 1) to a long-time plateau (Stages 2 and 3) followed by a slow growth in Stage 4. An acceptable agreement between the computer simulation and ex vivo experiment in the temperature changes at the three points was found at all three testing laser administrations. A similar result was also obtained for the dimensions of coagulation zone and ablation zone between the computer simulation and ex vivo experiment (carbonization zone: 2.99± 0.10 vs. 2.78 mm2, 67.39± 0.09 vs. 63.53 mm2, and 90.53± 0.11 vs. 85.15 mm2; ablation zone: 68.95± 0.28 vs. 65.29 mm2, 182.11± 0.24 vs. 213.81 mm2, and 244.80± 0.06 vs. 251.79 mm2 at 3, 5, and 7 W, respectively). ConclusionThis study demonstrates that the proposed dynamic heat source model combined with the light distribution model as well as bioheat transfer model can predict the development of liver tissue carbonization with an acceptable accuracy. This study contributes to an improved understanding of the LA process in the treatment of liver tumors.

Compressive and Energy Absorption Properties of Pyramidal Lattice Structures by Various Preparation Methods.

Metallic three-dimensional lattice structures exhibit many favorable mechanical properties including high specific strength, high mechanical efficiency and superior energy absorption capability, being prospective in a variety of engineering fields such as light aerospace and transportation structures as well as impact protection apparatus. In order to further compare the mechanical properties and better understand the energy absorption characteristics of metal lattice structures, enhanced pyramidal lattice structures of three strut materials was prepared by 3D printing combined with investment casting and direct metal additive manufacturing. The compressive behavior and energy absorption property are theoretically analyzed by finite element simulation and verified by experiments. It is shown that the manufacturing method of 3D printing combined with investment casting eliminates stress fluctuations in plateau stages. The relatively ideal structure is given by examination of stress–strain behavior of lattice structures with varied parameters. Moreover, the theoretical equation of compressive strength is established that can predicts equivalent modulus and absorbed energy of lattice structures.

Nanosecond dielectric barrier discharge on a curved surface in atmospheric air: streamer evolution and aerodynamic perturbations

A curved nanosecond-pulsed dielectric barrier discharge actuator is proposed to fit the flexibly complex surface shape of air vehicles. Streamer evolution and aerodynamic perturbations driven by a single-pulse voltage applied on the anode, where the pulse width is 35 ns and the peak voltage is 14 kV, are numerically studied. Continuity equations that consider 15 species and 34 reactions are solved based on the drift–diffusion approximation. The electron temperature is obtained using the local mean energy approximation method. Discharge characteristics during the voltage-rise, plateau and decay stages are discussed, respectively. The streamer is initiated at 2.2 ns. The maximum electric field is progressively located at the head of the streamer, between the electrodes and in the dielectric layer during the three voltage stages, while the maximum value of electron density is settled at the downstream tip of the driven anode. The electron number density at the streamer head increases at the voltage-rise stage, keeps constant during the voltage-plateau stage, decreases at the beginning of the voltage-decay stage and then increases due to the quenching effect of the excited species. Compared with the discharge on a flat surface, the initial discharge propagation velocity is smaller, while it decreases more slowly during the entire applied voltage. The simulated deposited energy matches the analytical solution well. Aerodynamic perturbations are investigated by solving the compressible Navier–Stokes equations. The ambient air is rapidly heated to the maximum temperature of 1883 K within 0.04 μs. The temperature rise remains greater than 1000 K for 0.32 μs and greater than 500 K for 21.6 μs. A ‘semiring-like’ compression wave is formed from the discharge region; the propagation speed decreases as it propagates away from the wall and then converges to 345 m s−1 at 13 μs. High-speed flows are rapidly induced at the beginning, and two vortexes are formed successively due to the interaction between the flow induced by the actuator and the backflow induced by the compression wave.

Effects of cell size vs. cell-wall thickness gradients on compressive behavior of additively manufactured foams

Graded foams show great potential in impact protection and blast resistance applications but a limited experimental study on their compressive behavior has been reported. Thus, this paper investigates the gradient effect on the compressive behavior of foams experimentally and numerically. The cell size graded foam (SGF) and the cell-wall thickness graded foam (TGF) are both built by the Voronoi method and then fabricated by the additive manufacturing technique. Meanwhile, uniform foams with different cell sizes (SUF) and cell-wall thicknesses (TUF) are also produced to be compared with graded foams. Quasi-static and dynamic compressive tests are conducted respectively by using a universal testing device and a direct-impact Hopkinson pressure bar. Experimental results reveal that SGFs deform continuously from lower to higher density regions and hence possess a gradually increasing plateau stage in the stress-strain curve. TGFs show three stepwise plateau stages because of their three layers with different cell-wall thicknesses. Moreover, SUFs and TUFs with constant relative density present similar mechanical properties despite their different cell morphologies. Several empirical formulae are proposed for uniform foams and fit well with experimental data. Further simulation is verified by experimental results and indicates that TGFs with adequate layers also possess a gradually increasing plateau stage just like SGFs. It means that the strength of each layer in a graded foam depends on its local density rather than cell morphology.

Solid-State Supercritical CO2 Foaming of PCL/PLGA Blends: Cell Opening and Compression Behavior

The foaming behavior of poly(e-caprolactone)/poly (lactic-co-glycolic acid) (PCL/PLGA) blends and the effect of composition on porous structure, compression property and biocompatibility are investigated. Various portions of PLGA are added into matrix PCL at dispersion phase by melt blending. A solid-state batch foaming process is used based on supercritical CO2 as a physical blowing agent. With the PLGA content increased from 5 to 30 wt%, storage modulus and complex viscosity of PCL from rheological tests are improved significantly. Foaming tests reveal that incorporation of PLGA facilitates foaming of PCL by increasing viscosity. With an increase of PLGA content, pore size clearly decreases, and the open–cell content first increases and then decreases slightly. The maximum open-cell content value is greater than 86% for foamed 10 wt% PLGA. Moreover, uni-axial compression testing shows that dispersed PLGA improves the compressive stress distinctly. Cell structure evolutions at linear elasticity, plateau, and densification stages in compression tests are also investigated. Cell viability results demonstrate that there are more and denser live HUVECs detected on scaffold with increase of PLGA content. Compression strength of PCL/PLGA scaffold has more contributions to cell viability than that of porosity and open-cell content.

Mechanical behaviors of MoS nanowires under tension from molecular dynamics simulations

As a new class of one-dimensional (1D) transition-metal monochalcogenides (TMMs) nanowires (NWs), the recently synthesized MoS NWs exhibit potential applications in two-dimensional integrated circuit. However, their mechanical behaviors remain almost unexplored. In this paper, the mechanical behaviors of MoS NWs under tensile loading are studied by classical molecular dynamics simulations together with first-principles calculations. A novel phase transformation is observed in the MoS NWs when the strain applied to them is larger than a critical value, which results in tension-induced hardening in their tensile modulus. Due to the existence of phase transformation, a complicated mechanical response is observed in MoS NWs during the entire loading process, which successively experiences the linear, plateau, stress hardening and fracture stages. The influence of various factors including the strain rate and temperature on the mechanical properties of MoS NWs such as phase transformation, Young’s modulus, fracture strength and fracture strain are also examined. The mechanical properties of MoS NWs obtained in this paper will be beneficial to their future applications in the semiconducting field. It is also expected that the results of the tension-induced phase transformation and its influence on the material properties observed in the present MoS NWs can be further extended to other 1D TMMs such as MoTe and SnSe NWs, since these 1D TMMs are found to possess the similar structure.