Expansion Strain Research Articles

Effect of strain on the reactivity of graphene films

The effect of strain on the adsorption of atomic species (Cl, H, N, and O) on pristine and nitrogen-doped graphene is studied using density functional theory. Expansive strain increases surface reactivity by destabilizing graphene π orbitals, which is similar to the shift in the d-band center observed on stretched metal surfaces. However, compressive strain leads to the formation of nanoripples that strongly bind atomic species at ridge sites, which is fundamentally different from adsorption on compressed metal surfaces. Our findings suggest that strain can be used as an effective means of manipulating graphene’s reactivity, which is explicitly shown here for the oxygen reduction reaction.

Reversible visible/near-infrared light responsive thin films based on indium tin oxide nanocrystals and polymer

In this study, we design a novel thermo- and photo-responsive nanocomposite film prepared by depositing indium tin oxide nanocrystals via the coating of amphiphilic copolymer on polycaprolactone substrates (INCP). The INCP film shows reversible surface morphology change properties by changing temperature as well as turning ON/OFF NIR laser. Especially, as the temperature changes from 25 to 75 °C, the film could regulate light transmittance from 75 to 90% across the visible and near-infrared region (500–1,750 nm). In addition, the film also exhibits excellent recycle and thermal stability at different temperature. Our results reveal that reversible surface morphology change properties are caused by curvature adjustment of film, which is owing to the coupling effect between copolymer and PCL with different thermal expansion strains. Our results suggest a possible strategy for the preparation of smart responsive materials in the future, which provides a reference for the development of new energy-saving materials.

3D-printed graphene/polymer structures for electron-tunneling based devices

Designing 3D printed micro-architectures using electronic materials with well-understood electronic transport within such structures will potentially lead to accessible device fabrication for ‘on-demand’ applications. Here we show controlled nozzle-extrusion based 3D printing of a commercially available nano-composite of graphene/polylactic acid, enabling the fabrication of a tensile gauge functioning via the readjustment of the electron-tunneling barrier width between conductive graphene-centers. The electronic transport in the graphene/polymer 3D printed structure exhibited the Fowler Nordheim mechanism with a tunneling width of 0.79–0.95 nm and graphene centers having a carrier concentration of 2.66 × 1012/cm2. Furthermore, a mechanical strain that increases the electron-tunneling width between graphene nanostructures (~ 38 nm) by only 0.19 Ǻ reduces the electron flux by 1e/s/nm2 (from 18.51 to 19.51 e/s/nm2) through the polylactic acid junctions in the 3D-printed heterostructure. This corresponds to a sensitivity of 2.59 Ω/Ω%, which compares well with other tensile gauges. We envision that the proposed electron-tunneling model for conductive 3D-printed structures with thermal expansion and external strain will lead to an evolution in the design of next-generation of ‘on-demand’ printed electronic and electromechanical devices.

Penetration of pressure-injected lithium nitrite in concrete and ASR mitigating effect

The objective of this study is to clarify optimal conditions for suppressing the expansion of ASR-deteriorated concrete by pressure-injecting a lithium nitrite solution. To investigate the ASR-mitigating effect of lithium nitrite, concrete mixtures with two types of reactive aggregates were impregnated with lithium nitrite by pressurized injection at three steps of ASR. The effects of different timings on the penetration of lithium nitrite driven by the pressure gradient and on the suppression of expansion were examined through tests.The expansion rate started to decrease immediately after injecting a lithium nitrite solution into the concrete in the propagation period (PP) with severe ASR cracking and an expansion strain of 2000 micro. With a lithium-sodium molar ratio of 0.6 or more, further expansion was significantly reduced. On the other hand, expansion continued even after application of lithium nitrite when the solution was injected into the concrete in the early propagation period (EPP) with slight ASR cracking and an expansion strain of 400 micro, and the final strain eventually exceeded that of the concrete that had been subjected to the lithium injection in the PP.It is assumed that the lithium nitrite solution migrates through ASR cracks first because of the pressure gradient and then diffuses into the bulk mortar. The degree of expansion could also be affected by at which stage of ASR the lithium ions reach the reactive aggregates and the ASR gel.

Impact of origination of expansion on three-dimensional expansion crack propagation process due to DEF evaluated by mesoscale discrete model

In this study, DEF expansion crack propagation process under different restraint condition was numerically investigated by mesoscale discrete model, which describes concrete material with coarse aggregate phase and mortar phase using 3D-Rigid Body Spring Model. The purpose of this study is to clarify the impacts of origination of expansion and aggregate on characteristic DEF expansion such as localized expansion crack and cracks localized at the ITZ between paste and aggregate. In this analysis, Single Aggregate Model and Multi-Aggregate Model were constructed to verify expansion crack propagation process and interaction between aggregate and mortar phases precisely. As a result of Single Aggregate model, it was confirmed that expansion crack tends to be localized as expansion phase ratio is lower, and cracks localized at the ITZ is appeared at the early stage of expansion. By using Multi-Aggregate Model, the analytical results of expansion crack propagation process, stress distribution change, and expansion strain change under different restraint condition were coincided with experimental observation. In addition, it was found that origination of expansion strongly influences to DEF expansion. In terms of aggregate, the existence of aggregate and grain size distribution slightly inhibit expansion strain development and crack volume development, and their impacts on DEF expansion, however, seems to be small. This is because cracks localized at the ITZ generates at the early stage of expansion process and the stress transfer mechanism between mortar and aggregate phase disappears.

Bulk and interfacial properties of milk fat emulsions stabilized by whey protein isolate and whey protein aggregates

Whey protein is widely used in the food industry as an emulsion stabilizer because of its outstanding emulsifying ability. Recent studies have shown that heat-induced whey protein aggregates may also have potential to stabilize emulsions. The interfacial behavior of whey protein and whey protein aggregates adsorbed at the milk fat-water interface has not been well investigated, especially not in the nonlinear regime, which is highly relevant for the preparation of products such as recombined dairy cream.In this study, the interfacial properties of milk fat-water interfaces stabilized by whey protein isolate (WPI) and whey protein aggregates (WPA) at different bulk concentrations (0.1 wt% - 4.0 wt%) were studied by Large Amplitude Oscillatory Dilatation (LAOD). Lissajous plots were used to analyse the nonlinear response of the interfaces as a function of strain amplitude and frequency. The elastic modulus was quantified based on the tangent modulus at zero instantaneous strain in expansion and in compression. Bulk stability of creams stabilized with the mentioned proteins was studied by determining creaming rate, droplet size distribution, ζ-potential and viscosity of the continuous phase.At low concentrations (<2.0 wt%), WPI-stabilized cream had smaller oil droplets than WPA-stabilized cream, indicating that at these concentrations WPI had better emulsifying ability. For concentrations higher than 2.0 wt%, WPA was a better emulsifier in terms of creaming stability because of the higher viscosity of the continuous phase of the emulsions. Both WPI and WPA could prevent coalescence equally well if the concentration was higher than 0.5 wt%. LAOD measurements showed that at a protein concentration of 0.1 wt%, there was little difference between WPI- and WPA-stabilized interfaces. At 4.0 wt%, WPI showed abrupt intra-cycle yielding followed by a predominantly viscous behavior at large expansion. The WPA interfacial layer had a larger maximum linear strain, and showed a more gradual softening in expansion and mild strain hardening in compression. We hypothesize that WPI formed denser and more brittle (quasi-) 2d structures at the interface, while the interfaces formed by WPA might have a thicker and more stretchable 3d structure. The WPA-stabilized emulsion was less resistant to coalescence upon drastic stirring, which can be explained with its different large deformation behavior, and is relevant for applications where the cream is subjected to large deformations (whipping or stirring).

Resistance improvement of cement mortar containing silica fume to external sulfate attacks at normal temperature

This paper investigates the resistance performance and resistance enhancement mechanism of cement mortar containing silica fume (SF) exposed to external sulfate attacks (ESA) at a temperature of 20 °C. The visual inspection, strain development, and mechanical performance of specimens made of 100% high sulfate-resistant Portland cement of grade 42.5 (P•HSR 42.5), 100% ordinary Portland cement of grade 42.5 (P•O 42.5), and binary blends of P•O 42.5 and SF, respectively, are evaluated using the mortar bar test. The mortar bars are exposed to a 5% Na2SO4 solution for 12 months and measured up to 12 months. The deterioration products are studied in terms of their types, amounts, and micro-structures by the means of x-ray diffraction (XRD), thermo gravimetric analysis (TGA), scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), and mercury intrusion porosimetry (MIP). The results show cement mortars, which contain different dosages of SF (i.e., 3% and 5% by weight of cementitious materials), that have no visual damage after 12 months of exposure to ESA. The exponential increase in the expansion strain of P•HSR 42.5 cement mortars and P•O 42.5 cement mortars are observed, with strain values reaching up to 5825 × 10−6 and 8824 × 10−6, respectively, after 12 months of immersion. However, it is noteworthy that the tendency of increase in the expansion strain of cement mortar containing SF becomes a hyperbolic curve. Specifically, the expansion strain of cement mortar containing 3% and 5% SF are only 65.0 × 10−6 and 29.0 × 10−6, respectively, after 12 months of immersion. The resistance improvement mechanism of SF in cement mortars may be because the SF can effectively reduce the formation of the deterioration products, namely, ettringite (AFt) and gypsum. On the other hand, SF can significantly refine the pore structures, causing a drastic increase in the incidence of harmless pores (<20 nm). The pore structure refinement effect of SF plays a critical role in enhancing the resistance performance of cement mortars exposed to ESA. Therefore, cement containing appropriate SF will significantly improve the resistance performance of cement mortars exposed to ESA.

Influence of Restrained Condition on Mechanical Properties, Frost Resistance, and Carbonation Resistance of Expansive Concrete.

This paper presents the results of an experimental investigation of the effect of the restrained condition on the mechanical properties, frost resistance, and carbonation resistance of expansive concrete with different water–binder ratios. In this study, length change ratio test, expansion strain test, compressive strength test, mercury intrusion porosimetry test, underwater weighing test, freezing–thawing test, and accelerated carbonation test were performed to evaluate the mechanical properties, pore size distribution, total porosity, and durability of expansive concrete under both restrained and unrestrained conditions. The test results indicate that the length change ratio and expansion strain of the expansive concrete were controlled by the restrained condition. The compressive strength of expansive concrete was enhanced by the triaxial restraining when the amount of expansive additive was 40 kg/m3 of concrete. Two hypotheses were described to explain the change of pore structure change expansive mortar. The results also indicate that the carbonation resistance and frost resistance were improved by the uniaxial restrained condition. Furthermore, the effect of the restrained condition must be considered to evaluate not only the experimental results of the expansive concrete with a high EX replacement level but also the expansive concrete combining other cement replacement materials.

Analytical Model for Restraint Strains and Self-stressed in Expansive Concrete Filled Steel Tubes (ECFST) estimation

In this paper, a modified strains development model (MSDM) for expansive concrete-filled steel tube (ECFST) was formulated and verified on the experimental data, obtained from testing specimens on the expansion stage. The modified strain development model for restraint strains and self-stresses values estimation in concrete with high expansion energy capacity under any type of the symmetrical and unsymmetrical finite stiffness restraint conditions was proposed. Based on proposed MSDM a new model for expansive concrete-filled steel tubes is developed. The main difference between this model and other previously developed models consists in taking into account in the basic equations an induced force in restrain that is considered as an external load applied to the concrete core of the member. For verification of the proposed model-specific experimental studies were performed. As follows from comparison results restrained expansion strains values calculated following the proposed model shows good compliance with experimental data. The values predicted by the proposed MSDM for concrete-filled steel and obtained experimental data demonstrated good agreement that confirms the validity of the former.

Intrinsic adsorption behaviour related to the structural and mechanical properties of flexible metal-organic frameworks Co(bdp)

The Co(bdp) family has been widely investigated for the adsorption properties of gas molecules such as hydrogen, nitrogen, and methane. In this paper, the structural and mechanical properties of the Co(bdp) family, including Co(bdp), Co(bdp)-p-F2, Co(bdp)-Me2, and Fe(bdp), were studied based on first-principles theory. Using the methane adsorption behaviours of the Co(bdp) family as references, the adsorption properties of the Co(bdp) family were analysed by studying the structural properties. The adsorption properties can be estimated by analysing the accessible porous channel and ligand arrangement of the frameworks. This study can guide the design of flexible organic frameworks for specific adsorption or separation requirements. The effects of mechanical pressure and adsorbate molecules on the structural transition were analysed to reveal the mechanism of the structural transition of Co(bdp) when adsorbing gas molecules. The applied mechanical pressure from 0 to 50 bars will not result in a structural transition. The structural transition from the collapsed phase to the expanded phase induced by adsorbate molecules was simulated by applying expansion strains to the collapsed Co(bdp) phase. An intrinsic barrier of 13.15 eV per unit cell is present in the structural transition of Co(bdp). The energy necessary to overcome the energy barrier can be provided by the adsorbate molecular insertion. The simulation method in the present study is potentially applicable to the structural transition analysis of other flexible metal-organic frameworks.

Strategy to design high performance TiB2‐based materials: Strengthen grain boundaries by solid solute segregation

AbstractTiB2 exhibits a unique combination of excellent properties that make it promising candidate for applications in extreme environments, where retention of strength at high temperatures is essential. Tailoring grain boundary properties by segregation is believed a prominent way to design high‐temperature performance of ceramics. In this work, segregation tendencies of solute elements, including Sc, Y, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, in TiB2 grain boundaries and the strengthening/weakening effects induced by segregations are investigated by first‐principles calculations. The results reveal that small atoms tend to segregate to grain boundary sites with local compression strains, while large atoms prefer grain boundary sites with local expansion strains. Deteriorated grain boundary strength is usually caused by additional expansion strain induced by segregation, while improved grain boundary strength results from either enhanced local bonding induced by segregation of small atoms or increased fracture strain due to segregation of large atoms. Cr and V, especially Cr, exhibit strong segregation tendency and improvement on grain boundary strength, which provides useful guidelines for the design of high performance TiB2‐based materials.

Роль фононов в стабильности металлических наночастиц

A novel model of a metallic nanoparticle is proposed. The model represents the nanoparticle as a hollow sphere. The existence of a nanohollow inside a particle is related to the behavior of phonons. The strain in the walls of a particle when it's heated is calculated utilizing the theory of a thick-walled shell. We show that in the transition to the elastic state, the expansion strains at the surface of a nanoparticle become sufficient for melting. The dependency of melting temperature on the size of a nanoparticle is discussed.

Micromechanical modelling of damage induced by delayedettringite formation in concrete

A multi-scale poromechanical model of damage induced by Delayed Ettringite Formation (DEF) as a consequence of progression of micro-cracks at the fine aggregate scale is developed. The aim is to link the DEF-induced expansion at both the microscopic and macroscopic scales to the loss of stiffness of the mortar and the increase of its diffusion coefficient. At the microscopic scale, mortar is assumed to be constituted of three phases: cement paste, sand and micro-cracks. Damage is assumed to be driven by a free expansion of cement paste due to ettringite crystallization pressures in small capillary pores, at a lower scale. The corresponding homogenised poroelastic properties are estimated along with the diffusion coefficient by resorting either to a Mori-Tanaka scheme or to a self-consistent scheme, as a function of paste and aggregate properties as well as on the density of micro-cracks. The latter is assumed to be an evolving internal variable in order to model DEF-induced damage in the mortar. As the DEF-induced expansive free strain in the cement paste is restrained by the sand particles, internal stresses arise in the mortar. The corresponding free energy can be partially released by an increase in the micro-cracks density by analogy with the energy restitution rate of linear elastic fracture mechanics. The role of the damage criterion adopted on the thermodynamic force associated with micro-cracks density increase is investigated.

The Study on Early‐Age Expansion and Shrinkage Model of Massive Self‐Compacting Concrete Pumped in Steel Tube Column

Massive self‐compacting concrete pumped in steel tube columns has been used more and more widely in super high‐rise buildings and bridge engineering at present. The early‐age expansion and shrinkage performance of its core mass concrete is an important index to ensure the stress state of triaxial compression and structural safety. However, no relevant reports have been found. In view of the actual building with the height of 265.15 meters, the early‐age expansion and shrinkage tests of the massive self‐compacting concrete pumped in full‐scale columns with the height of 12.54 m and 12.24 m and diameter of 1.3 m and 1.6 m were carried out by means of strain gauges embedded in concrete‐filled steel tubes (CFSTs). The early‐age variation regularity of the vertical and horizontal expansion and shrinkage strains for the core concrete with the diameter of steel tube, development time, temperature, the pouring pressure, expansion stress, and so on is given. The calculation model of its early‐age deformation strains is presented in this paper, which is in good agreement with the experimental results. It provides the basis of experimental and theoretical analyses for shrinkage compensation of massive self‐compacting concrete pumped in steel tube columns.

Shear resistance of self-stressing concrete elements expanded under 2D restraint conditions

An analytical design model for estimation the shear resistance of plane self-stressing concrete elements with orthogonal reinforcement is presented. The design model is based on the strut-and-tie model concept and takes into consideration the restrained expansion strains and selfstresses as a result of self-stressing concrete expansion. The results of theoretical investigations were finally compared to the experimental ones showing the suitability of proposed design method.

Ductile fracture of AISI 304L stainless steel sheet in stretching

The present study focuses upon the numerical investigation of fracture initiation of austenitic stainless steel, AISI 304L, during a forming process leading to an expansion strain path. Hence, a combined experimental and numerical approach was tested. Monotonic tensile tests up to fracture were carried out. Load-extensometer displacement curves and a major strain distribution were measured. Numerical simulations of the tensile test up to rupture were carried out to calibrate damage parameters of several macroscopic fracture criteria.Numerical simulations of the Erichsen test were also carried out to verify the validity of the determined parameters of the ductile fracture criteria. The numerical predictions of the strain field, the onset of fracture, and the fracture location were compared with the experimental results. The simulation results show that the Rice-Tracey or Brozzo fracture criteria are reliable predictors of the onset of fracture of AISI 304L in the Erichsen test. More precisely, the Rice-Tracey criterion is the most effective to predict the ductile fracture in this case.

Monitoring corrosion of steel bars in reinforced concrete based on helix strains measured from a distributed fiber optic sensor

Corrosion of steel bars compromises the safety and service life of reinforced concrete structures. This study develops an in-situ corrosion monitoring method for reinforced concrete with a distributed fiber optic sensor through experimentation. Reinforced concrete beams instrumented with distributed fiber optic sensors were prepared. A constant current was impressed to the beams immersed in a NaCl solution for accelerated corrosion. The distributed fiber optic sensor was deployed in a helix pattern on the steel bar to measure expansive strains generated by corrosion of the steel bar. The corrosion process of the steel bar was assessed in an electrochemical test. The strain measured from the sensor was utilized to evaluate the volume of the corrosion products surrounding the steel bars and predict the cracking of the concrete cover. To investigate the deterioration process of reinforced concrete, different levels of concrete cover thickness (28 mm, 35 mm, and 43 mm) and water-to-cement ratio (0.4, 0.5, and 0.6) were studied. The relationship between the mass loss of steel bars and the volume of corrosion products is established to provide a method for evaluating the effects of steel corrosion on the deterioration of reinforced concrete.

Impact of left atrial appendage occlusion on left atrial function-The LAFIT Watchman study.

Left atrial (LA) strain and strain rate (SR) analysis by two-dimensional speckle tracking echocardiography is a novel way of LA function assessment. From prior study, we know that LA appendage closure with LARIAT appears to improve LA function. The purpose of this study was to assess the impact of LAA closure via Watchman device on LA function via strain and volumetric analyses using two-dimensional speckle tracking echocardiography(2D-STE). Twenty-five patients who underwent Watchman device implantation (WDI) were included. LA function parameters (volumetric, strain indices) were calculated from apical four chamber views with the reference point set at QRS using 2D-STE before and after WDI. LA expansion index, strain and strain rate during ventricular systole represent LA reservoir function. Passive emptying fraction, strain and strain rate during early ventricular diastole represent LA conduit function. Mean age was 76 ± 6.9years with 60% males. There was significant improvement in conduit function (LA passive emptying fraction; post 28.6 (21.9-35.9) vs pre 21.0 (13.8-34.7), p= 0.032), reservoir function (LA expansion index; post 75.3 (52.3-98.0) vs pre 58.1 (37.8-85.2), p= 0.026), and booster function (LA active emptying fraction; post 13.3 (9.7-29.9) vs pre 12.6 (8.8-25.5), p= 0.04) by volumetric indices. No significant improvement was noted with strain indices in conduit function (SRe; post - 0.56 (0.43-0.93) vs pre - 0.58 (0.46-0.87); p= 0.518) and reservoir function (SRs; post + 0.58 (0.28-0.40) vs pre + 0.52 (0.35-0.86); p= 0.851). WDI resulted in discrepancy of volumetric and strain indices in LA function assessment.

Thermal expansion and fatigue properties of automotive brake rotor made of AlSi–SiC composites

Al-9Si- SiC or Al-12Si-SiC composites reinforced with 10 or 20 wt% SiC particles were synthesized by stir casting method. The composites were used to produce automotive brake rotors. Microstructures of the brake rotors made of the composites revealed uniformly distributed SiC particles, primary phase (α-Al) and modified eutectic Si. Grain refining was also observed due to the addition of SiC particles. Coefficient of thermal expansion (CTE) and thermal strain responses during heating and cooling cycles between room temperature and 350 °C of the composites were investigated. Al-12Si and its composites exhibited lower CTE and near zero residual strain. Thermal fatigue studies were carried out on the brake rotors made of the composites as well as commercially available brake rotor made of cast iron, for comparison. After 80 cycles, hardness measurements, microstructure investigations and x-ray diffraction (XRD) analysis were carried out. The results showed that the strain and temperature followed the same path on cooling as on heating, indicating that both hysteresis loop and residual strain were absent. At the same time, the crystallinity of the brake rotor made of the composite was enhanced by the exposure to thermal cycling, while it was deteriorated in case of break rotor made of cast iron on the long run.

Strain field measurements over 3000 °C using 3D-Digital image correlation

With the development of aerospace and fusion engineering, understanding the mechanical behavior of materials under high-temperature conditions has become increasingly important. However, few studies are devoted to the ultra-high temperature range of 2000–3000 °C. In this study, with the aim of developing non-contact measuring techniques of mechanical deformation under ultra-high temperature, a high heat flux (~300 MW) comprehensive experimental platform is established, which includes a vacuum chamber, a three-dimensional digital image correlation (3D-DIC) system, infrared radiation thermometers and an electron beam heating system. Using the electron beam heating technique, the tungsten specimen can be heated to over 3000 °C. Owing to the use of a vacuum chamber, the thermally induced airflow disturbance at high temperature can be completely removed. Tantalum carbide (TaC) powder is chosen as the speckle material and speckle fabrication technology is developed to adapt ultra-high temperatures under vacuum conditions. In order to suppress the blackbody radiation at high temperature, three schemes based on blue light sources, self-radiating light sources and a dual wavelength optical filter technique are designed for three temperature ranges from room temperature to 3067 °C. Afterwards, full-field thermal deformation of the tungsten specimen above 3000 °C was determined based on the above strategies using the 3D-DIC technique. The feasibility and accuracy of the proposed methods are verified by comparing the measurement results with the thermal expansion strain data and model from available databases and literature. The standard deviations in different temperature intervals are 50 με for 25–1200 °C, 100–200 με for 1200–1800 °C and less than 500 με for 1800–3067 °C. The proposed methods and technologies are expected to lay a foundation for further developments in strain field measurements at ultra-high temperature.