Uniaxial Tensile Strain Research Articles

Dislocation-Evolution Based Comprehensive Phenomenological Model for Continuum-Scale Description of Stress–Strain and Work-Hardening Behavior

Bridging continuum-scale description of uniaxial tensile plastic stress–strain behavior with adjacent mesoscale deformation models is important and, hence, requires identification of appropriate physical processes and the associated parameters. In this work, a comprehensive phenomenological model (CPM) for true stress–true strain behavior of a polycrystalline material in the plastic regime was developed based on the postulation of physical processes, viz. dislocation nucleation, multiplication, and annihilation, satisfying the statistical perception of dislocation evolution during deformation. Incorporation of these processes through intricate formulations using physical parameters, such as dislocation density, dynamic mean-free-path (MFP), fixed MFP etc. demonstrated a precise fit of a uniform tensile plastic flow curve and of its spin-off work-hardening (WH) behavior, simultaneously. Variation in the calculated parameters for different stress–strain responses of different alloy systems and the sensitivity analyses helped in appreciating the discrete modular nature of the model. Precise fits in both plastic stress–strain and WH responses using the same set of coefficients ensured the CPM to be reliable in simulating realistic uniaxial stress–strain plots from the physical parameters for various alloys. The model advances the understanding of phenomenological modeling especially in terms of incorporation of the dislocation nucleation mechanism in the evolution process, ensuing explicit expression for dislocation evolution with strain and grain size dependence. The present approach is deemed appropriate for linking the length scales in the multiscale description of deformation.

Giant Uniaxial Strain Ferroelectric Domain Tuning in Freestanding PbTiO3 Films

AbstractDimensionality and epitaxial strain have been recently utilized to engineer the interplay between the electrostatic and elastic energies to stabilize exotic ferroelectric domain structures and topological textures in epitaxial heterostructures and superlattices. As the strain state is fixed to the substrate lattice, the strain tunability is discrete and limited, which puts a hard constraint on the exploration and engineering of emergent ferroelectric properties in these thin films and heterostructures. Here, by using water‐soluble Sr3Al2O6 (SAO) as the sacrificial buffer layer, freestanding PbTiO3 (PTO) thin films are synthesized by reactive molecular beam epitaxy to provide ideal flexible systems for continuous strain engineering as they are free of substrate‐imposed clamping. With decreasing thickness below 30 unit cells, the freestanding PTO films show thickness‐dependent reduction of c/a ratio and ferroelectricity as a consequence of strong depolarization effect. Furthermore, continuous uniaxial tensile strain up to 6.4% is applied on these freestanding films, far exceeding the achievable value reported on epitaxial PTO films. Under large tensile strain, a c domain to a domain transition with the polarization flipped from the out‐of‐plane to in‐plane direction is observed. The present work highlights the exceptional tunability of strain and dimensionality in search of emergent phases in freestanding films.

Concrete behavior in steel-concrete-steel panels subjected to biaxial tension compression

Steel-Concrete-Steel (SCS) composite wall is being used for different purposes for its improved performances. Some analytical and finite element models have been presented in the past to predict the behavior of such walls. In this paper, an attempt is made to develop an iterative membrane model to analyze SCS wall panels subjected to in-plane membrane forces in the principal directions. The model accounts for the post-cracking Poisson effects of concrete as the Zhu/Hsu ratio.Individual behaviors of concrete and steel plates in an SCS panel are studied in which confinement in principal tensile direction accompanied by negative uniaxial tensile strain in concrete is observed. To explain this behavior, a detailed perspective for uniaxial strain in principal tensile direction is proposed and the conventional stress-strain trajectory of concrete in tension is extended to incorporate any confinement developed in the concrete. Constitutive law of concrete in compression is also modified to incorporate the observed confining behavior of the concrete.

Surface Functionalization Tailored Electronic Structure and Magnetic Properties of Two-Dimensional CrC2 Monolayers

Spintronics is the promising technology for next-generation information storage due to its low energy consumption, high speed, and high circuit integration density, where the high spin polarization is pursued. The bipolar magnetic semiconductor (BMS) is proposed to easily achieve the reverse spin orientation. Surface chemical modification is a valid method to manipulate the electronic structure of two-dimensional materials. Here, the CrC2 monolayer with single-side and both-side functionalization is investigated by first-principles calculations. The monolayer CrC2 functionalized with O atoms (named 2OX) at both sides shows the bipolar half-metallic characteristics at high symmetry point X, while it is a BMS by being functionalized with H atoms (named 2HX). Under the tensile uniaxial strains along both a (εa) and b (εb) directions, the 2OX model turns into the p-type half-semiconductor, which shows robust characteristics with 100% spin-up polarization against the varied uniaxial strains. Total magnetic anisotropy energy (MAE) of the 2OX model fluctuates with varied uniaxial strain εa and decreases as tensile uniaxial strain εb decreases. The 100% spin-up polarized carriers and 100% spin-down polarized carriers appear in the 2HX model by 0.1 hole doping formula unit (f.u.) and 0.1 electron doping f.u., respectively. The results show that the functionalized CrC2 monolayer has potential applications in two-dimensional spintronics.

Elaboration and characterization of a 200 mm stretchable and flexible ultra-thin semi-conductor film

We describe a process for transferring a 200 nm thick, 200 mm wide monocrystalline silicon (mono c-Si) thin film from a silicon-on-insulator onto a flexible polymer substrate. The result is a stretchable and flexible ultra-thin semi-conductor film that can be subjected to tensile stress experiments. The process uses off-the-shelf 200 mm wafers and standard polymer temporary bonding techniques. The backside substrate and buried oxide are removed using grinding and wet etching processes. No cracks or wrinkles are observed on the film prior to the tensile stress experiments. The stretching of the flexible structure results in up to 1.5% uniaxial tensile elastic strain on the thin mono c-Si film.

Ultra-high mechanical flexibility of 2D silicon telluride

Silicon telluride (Si2Te3) is a two-dimensional material with a unique variable structure where the silicon atoms form Si-Si dimers to fill the “metal” sites between the Te layers. The Si-Si dimers have four possible orientations: three in-plane and one out-of-the plane directions. The structural variability of Si2Te3 allows unusual properties, especially the mechanical properties. Using results from first-principles calculations, we show that the Si2Te3 monolayer can sustain a uniaxial tensile strain up to 38%, the highest among all two-dimensional materials reported. The high mechanical flexibility allows applying mechanical strain to reduce the bandgap by 1.5 eV. With increasing strain, the bandgap undergoes an unusual indirect-direct-indirect-direct transition. We also show that the uniaxial strain can effectively control the Si-Si dimer alignment, which is beneficial for practical applications.

Anomalous Thermal Response of Graphene Kirigami Induced by Tailored Shape to Uniaxial Tensile Strain: A Molecular Dynamics Study.

The mechanical and thermal properties of graphene kirigami are strongly dependent on the tailoring structures. Here, thermal conductivity of three typical graphene kirigami structures, including square kirigami graphene, reentrant hexagonal honeycomb structure, and quadrilateral star structure under uniaxial strain are explored using molecular dynamics simulations. We find that the structural deformation of graphene kirigami is sensitive to its tailoring geometry. It influences thermal conductivity of graphene by changing heat flux scattering, heat path, and cross-section area. It is found that the factor of cross-section area can lead to four times difference of thermal conductivity in the large deformation system. Our results are elucidated based on analysis of micro-heat flux, geometry deformation, and atomic lattice deformation. These insights enable us to design of more efficient thermal management devices with elaborated graphene kirigami materials.

Prediction of Pore Size Characteristics of Needle‐Punched Nonwoven Geotextiles Subjected to Uniaxial Tensile Strains

A modified theoretical model has been proposed to predict the pore size characteristics of nonwoven geotextiles under certain uniaxial tensile strains, considering the difference between the out‐of‐plane Poisson’s ratio and the in‐plane Poisson’s ratio of geotextiles. The pore size distributions (PSDs) and O95 subjected to different levels of uniaxial tensile strains in two needle‐punched nonwoven geotextiles have been investigated by the dry sieving test. The variation of the fibre orientation with tensile strains and the corresponding effect on pore sizes has been evaluated by image analysis. The out‐of‐plane Poisson’s ratio and the in‐plane Poisson’s ratio of geotextiles have been examined. A comparison has been made between the predictions of the original and the modified models. It is shown that the modified model can more accurately predict the decreasing rate of the PSDs, O95, and O98 than the original one. The corrected theoretical O95 and O98 under certain strains can provide a reference for the filtration design under engineering strains. The fibres reorientating to the loading direction result in the increase of the directional parameter with increasing tensile strains, which leads to the decrease of pore sizes. The theoretical PSDs are sensitive to the variation of directional parameter.

Strain-induced band modulation and excellent stability, transport and optical properties of penta-MP2 (M = Ni, Pd, and Pt) monolayers.

First principle calculations utilizing density functional theory were carried out to investigate the electronic, transport and optical properties of penta-MP2 (M = Ni, Pd and Pt) monolayer compounds under applied uniaxial and biaxial tensile strains. With an optimum magnitude of applied strain, we found band gap transitions in penta-MP2 monolayers from zero/narrow to the semiconductor regime, wherein band gaps were noticed to be firmly dependent on the applied uniaxial and biaxial tensile strains. In this study, the PBE approach was used primarily to evaluate electronic properties, from where the identified architectures of penta-MP2 with maximum obtained bandgaps under respective optimum strains were assessed through the HSE06 method of calculation for better estimation of band gaps and optical properties. Prior to HSE calculations, we affirmed our assessment for the stability and reliability of the compounds under uniaxial and biaxial strains of up to 15% through phonon spectrum and elastic calculations. A distinct transition was also noted from semiconductor to metal for all compounds after the applied optimum uniaxial and biaxial strains. The optical absorption spectra in all the stretched penta-MP2 compounds reached the order of 106 cm−1, with significant peaks belonging to the IR and visible regions; this indicates promising applications of these materials in high-performance solar energy and good hot mirror materials. The enhanced I–V responses under uniaxial and biaxial tensile strains using the non-equilibrium Green's function (NEGF) approach confirm the usefulness of the strained state of the considered penta-MP2 monolayers. The results show that tuning electronic properties, I–V characteristics and optical properties of stretched penta-MP2 compounds under tensile strain merits significant future applications in optoelectronic devices and as good hot mirror materials.

Dynamic fracture development in a multiply cracked solid

We have been studying the collective, global behaviour of multiple cracks in solid materials and its connection with each individual, local crack motion. Here, by using a high-speed digital video camera, we examine fracture evolution in a two-dimensional, initially linear elastic rectangular polycarbonate specimen where sets of cracks are prepared and uniaxial tensile strain with a prescribed constant rate is externally applied. We trace local fracture development around every individual crack, and simultaneously, we obtain global stress-strain curves and physical properties like tensile strength of the specimens. By knowing the global characteristics, then, we concentrate our attention to more local, secondary and further fractures caused by the extending main or primary fracture and reversely its influence on the global nature of the multiply cracked specimens. For various different distribution patterns and values of density of initial cracks, we observe the dynamic evolution of the primary fracture and the fracture-induced waves, as well as the generation of the subsidiary fracture. We find that after a total split of the specimen into two by the propagation of the primary fracture, the secondary fracture may be initiated and propagated at a distance from the primary fracture. That is, fracture propagation may jump in multiply cracked solids even without additional external loading. Moreover, in our observations, the secondary fracture moves into the direction opposite to the primary one, and is once arrested and then resumes its propagation with some delay. The secondary and further fractures, or a cluster of fractures, are obviously not owing to additional external energy, but by dynamic waves produced upon enlargement of the primary fracture. The development of the secondary and further fractures in a specimen may be concealed in the global stress-strain relation but may rather appear in a global pattern of dynamic wave radiation such as doublet or a cluster of ruptures in the solid Earth, namely, earthquakes.

Strain engineering in bilayer WSe2 over a large strain range

Both Raman and photoluminescence spectroscopies have been employed to investigate the variation of lattice vibrational and electronic properties of bilayer WSe2 for a large strain range. Upon application of uniaxial tensile strain, the initially degenerate in-plane E2g Raman mode evolves into two discrete modes as a consequence of inversion symmetry breaking. The decrease of direct bandgap energy accompanied by an increase of indirect bandgap energy leads to an indirect-to-direct bandgap crossover, which expectedly occurs at 2% strain. However, under higher strain, a phenomenon of strain relaxation appears in the WSe2 crystal. Such relaxation gives rise to a cease of further redshift of direct bandgap and a significant increase of direct excitonic linewidth. Our findings can provide a deeper understanding in the effects of strain engineering in WSe2 and are believed to be applicable to other layered transition-metal dichalcogenides.

New group V graphyne: two-dimensional direct semiconductors with remarkable carrier mobilities, thermoelectric performance, and thermal stability

The past decades have witnessed the great progress and successes in the research and applications of two-dimensional (2D) carbon materials such as graphene, graphdiyne, and so on. Similar to pure 2D carbon materials, 2D carbon nitride–like h-BN also possesses excellent electronic, mechanical, and optical properties. In this work, stimulated by the chemical tuition of atomic substitution, a new family of monolayer group V graphyne (C16N4, C16P4, and C16As4) with rhombic lattice is designed by replacing some C atoms with group V elements of N, P, or As in 2D graphyne. By using first-principles approach, we investigated their thermal stability, electronic/thermal transport properties, and thermoelectric performance and found that N(P,As)-graphyne monolayers are semiconductors with considerable direct bandgap values of 0.87 eV (0.59 eV, 0.71 eV), respectively. The ab initio molecular dynamics results demonstrate that N(P,As)-graphyne monolayers remain stable up to 1500 K. They all possess high carrier mobilities with the order of 105cm2V−1s−1 for electrons along the zigzag direction. Under the uniaxial tensile strains in the range of 0% to 10%, N(P,As)-graphyne monolayers keep direct-bandgap properties, and the effective mass of carriers can be efficiently tuned. Moreover, the calculated thermoelectric figure of merits at room temperature for the new monolayer group V graphyne are 0.62∼0.69 owing to the low lattice thermal conductivity, which are comparable with some conventional thermoelectric materials. Their excellent electronic transport and thermoelectric performance make N(P,As)-graphyne monolayers promising in high-speed (opto)electronic and thermoelectric devices, and the strain-engineering properties may lead to applications in flexible nanoelectronics.

Shear Load-Displacement Curves of PVA Fiber-Reinforced Engineered Cementitious Composite Expansion Joints in Steel Bridges

The concrete in the transition strips of expansion joints can become damaged prematurely during the service period. Polyvinyl alcohol (PVA) fiber-reinforced engineered cementitious composite (ECC) is a kind of high ductility concrete material, and its ultimate uniaxial tensile strain is more than 3%. It can be used to improve the damage status of expansion joints. Based on previous research results, ECCs were used in the pilot project of bridge expansion joints. Under this engineering background, the shear load-displacement curves of ECC expansion joints were studied through 27 groups of compression-shear tests of ECC/steel composite structures. The shear failure characteristics of ECC expansion joints were analyzed by the digital image correlation method. A shear load-displacement curve model of the composite structures was proposed based on the equivalent strain assumption and Weibull distribution theory. The results show that the failure mode of the composite structure specimens was ECC shear cracking. Stress and strain field nephograms were used to explain the failure characteristics of the composite structure specimens. The calculated curves of the shear load-displacement model of the composite structures were in good agreement with the experimental curves. The work is of great importance to the shear design of ECC expansion joints and their further engineering applications.

Numerical study of thermal conductivity based on phosphorene anisotropy: Including [110] direction and related phosphorus nanotubes

Thermal transport anisotropy is proved as an intrinsic property of phosphorene in armchair (AC) and zigzag (ZZ) direction. Thermal conductivities along the [110] direction (ST) and its perpendicular direction (PS) are systematically studied using molecular dynamics (MD) simulations. Thermal transport tendency from large to small is in the order of ZZ, PS, ST, and AC. The accuracy of MD in describing anisotropy is proved by acoustic phonon dispersion, and the discrepancy of specific thermal conductivity from the first-principle calculation is mainly due to the mismatch of low-frequency optical phonons. There is an enhancement of thermal conductivity with uniaxial tensile strain along ST and PS direction. Potential energy distribution through atom vibration is chosen to describe strain effect from different calculation methods. Nanotubes rolling from phosphorene have a gentle decrease of thermal conductivity with finite length along the same direction. These results shed light on direction-dependent thermal transport properties of phosphorene along with the applicability in MD simulation.

Impact of biaxial and uniaxial strain on V2O3

Using first-principles calculations we determine the role of compressive and tensile uniaxial and equibiaxial strain on the structural, electronic and magnetic properties of V$_2$O$_3$. We find that compressive strain increases the energy cost to transition from the high-temperature paramagnetic metallic phase to the low-temperature antiferromagnetic insulating phase. This shift in the energy difference can be explained by changes in the V-V bond lengths that are antiferromagnetically aligned in the low temperature structure. The insights that we have obtained provide a microscopic explanation for the shifts in the metal-insulator transition temperature that have been observed in experiments of V$_2$O$_3$ films grown on different substrates.

Significance of the particle size distribution modulus for strain-hardening-ultra-high performance concrete (SH-UHPC) matrix design

The distribution modulus, q, of the composite particle size distribution is a key parameter in the particle packing models that are typically used to achieve dense particle packing in ultra-high performance concretes (UHPC). While there are a few studies on the influence of q on the compressive strength of a UHPC in the literature, the effects of q on matrix fracture toughness, workability, and plastic viscosity have not been investigated. These properties are highly important for the micromechanics-based design of strain-hardening UHPC (SH-UHPC) that possess significant uniaxial tensile strain capacity. In this study, the central composite design (CCD) of experiments along with the modified Andreasen and Anderson (A&A) particle packing model were used to investigate the effects of q on the aforementioned matrix properties of SH-UHPC. Along with q, the effects of the type and content of the supplementary cementitious material (SCM) and water/cementitious (w/cm) material weight ratio on the matrix properties were also investigated. A second-order regression model was used to fit the results and identify important trends. Significant effects of q on the matrix properties were observed, mainly due to the influence of q on the particle packing and the aggregate/cementitious paste volumetric ratio. It was concluded that the value of q should be chosen based on the ingredients to achieve target rheological and mechanical properties of the SH-UHPC matrix. The knowledge developed in this study is vital for developing a rational design methodology for SH-UHPC class of materials.

Resident multipotent vascular stem cells exhibit amplitude dependent strain avoidance similar to that of vascular smooth muscle cells

Atherosclerosis is one of the leading causes of mortality worldwide, and presents as a narrowing or occlusion of the arterial lumen. Interventions to re-open the arterial lumen can result in re-occlusion through intimal hyperplasia. Historically only de-differentiated vascular smooth muscle cells were thought to contribute to intimal hyperplasia. However recent significant evidence suggests that resident medial multipotent vascular stem cells (MVSC) may also play a role. We therefore investigated the strain response of MVSC since these resident cells are also subjected to strain within their native environment. Accordingly, we applied uniaxial 1 Hz cyclic uniaxial tensile strain at three amplitudes around a mean strain of 5%, (4–6%, 2–8% and 0–10%) to either rat MVSC or rat VSMC before their strain response was evaluated. While both cell types strain avoid, the strain avoidant response was greater for MVSC after 24 h, while VSMC strain avoid to a greater degree after 72 h. Additionally, both cell types increase strain avoidance as strain amplitude is increased. Moreover, MVSC and VSMC both demonstrate a strain-induced decrease in cell number, an effect more pronounced for MVSC. These experiments demonstrate for the first time the mechano-sensitivity of MVSC that may influence intimal thickening, and emphasizes the importance of strain amplitude in controlling the response of vascular cells in tissue engineering applications.

Effects of external mechanical or magnetic fields and defects on electronic and transport properties of graphene

We report on the results obtained modelling the electronic and transport properties of single-layer graphene subjected to mechanical or magnetic fields and containing point defects. Reviewing, analyzing, and generalizing our findings, we claim that effects of uniaxial tensile strain or shear deformation along with their combination as well as structural imperfections (defects) can be useful for achieving the new level of functionalization of graphene, viz. for tailoring its electrotransport properties via tuning its band gap value as much as it is enough to achieve the graphene transformation from the zero-band-gap semimetal into the semiconductor and even reach the gap values that are substantially higher than for some materials (including silicon) typically used in nanoelectronic devices.

Prediction of Engineered Cementitious Composite Material Properties Using Artificial Neural Network

Cement-based composite materials like Engineered Cementitious Composites (ECCs) are applicable in the strengthening of structures because of the high tensile strength and strain. Proper mix proportion, which has the best mechanical properties, is so essential in ECC design material to use in structural components. In this paper, after finding the best mix proportion based on uniaxial tensile strength and strain, the correlation between these parameters were calculated. Since material properties depend on the content ratios, six mixtures with different Fly Ash (FA) content were considered to find the best ECC mixture called Improved ECC (IECC). Also, The influence of local fine aggregates and FA on the tensile behavior of ECC was considered to introduce IECC which has the best tensile properties. To predict the mechanical properties of ECC based on experimental results, Artificial Neural Network (ANN) was used. Training and validation of the proposed model were carried out based on 36 experimental results to find the best results. Numerical analysis is utilized to find the best mix proportion of ECC in structural design. The results show that the effects of FA and fine aggregates are considerable. Also, The proposed ANN model predicts the tensile strength and strain of ECC with different FA ratios accurately. Furthermore, the model can estimate mechanical properties of ECC in previous experimental results.

Atomistic simulation of mechanical properties of tungsten-hydrogen system and hydrogen diffusion in tungsten

Molecular dynamics simulation is used to systematically investigate mechanical properties of tungsten-hydrogen system and hydrogen diffusion in tungsten. It is found that the tensile strength of tungsten is decreased seriously by the formation of hydrogen bubbles, and the intrinsic mechanism is discussed by deformation dislocations. The present calculation also reveals that the hydrogen clusters in tungsten would be hard to diffuse, and may finally accumulate and form bubbles. In addition, the uniaxial and isotropic tensile strains have different effects on the diffusivity of hydrogen clusters, and the mean square displacements of H clusters diffusing along several directions under uniaxial and isotropic tensile strains are derived and compared with each other. The simulated results agree well with experimental evidence and calculated data available in the literature.