Expansion Strain Research Articles

Synergistic effects of ettringite-based expansive agent and polypropylene fiber on early-age anti-shrinkage and anti-cracking properties of mortars

Effects of the ettringite-based expansive agent (EA) and polypropylene (PP) fiber on early-age anti-shrinkage and anti-cracking behaviors of mortar are comprehensively investigated in this paper. Combined with mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analyses, its mechanism of the combination of EA and PP fiber on shrinkage and cracking restriction behavior of mortars is also proposed. The results indicate that the drying shrinkage resistance and cracking resistance behavior of the specimens with the combination of EA and PP fiber, are better than those of the specimens with single EA and PP fiber, while their residual expansion strain in autogenous shrinkage is lower than that of the specimens with single EA. The results of MIP and SEM analyses confirm that the formation of self-compressive stress generated by reinforcing effects of PP fiber and well three-dimensional network structure of ettringite distribution during expansion stage will partly offset the shrinkage force during shrinkage stage. Therefore, the combination of EA and PP fiber is prone to create a non-cracking shrinkage-compensating concrete in real construction.

Temperature and pressure-induced strains in anhydrous iron trifluoride polymorphs.

Various structural configurations of iron trifluoride appear at the nanoscale and macroscopic size, either in the amorphous or crystalline state. The specific atomic organization in these structures crucially alters the performance of FeF3 as an effective cathode in Li-ion batteries. Our detailed first-principles computational simulations examine the structural strains induced by temperature and stress on the four anhydrous polymorphs observed so far in FeF3 at ambient pressure. A wealth of data covering previous experimental results on their equilibrium structures and extending their characterization with new static and isothermal equations of state is provided. We inform on how porous apertures associated with the six-octahedra rings of the HTB and pyrochlore phases are modified under compressive and expansive strains. A quasi-auxetic behavior at low pressures for the ground state rhombohedral phase is detected, which is in concordance with its anomalous structural anisotropy. In contrast with the effect of temperature, this structure undergoes under negative pressure phase transitions to the other three polymorphs, indicating potential conditions where low-density FeF3 could show a better performance in technological applications.

Phase-field simulations of cover cracking in corroded RC beams

Corrosion of steel reinforcement bars is a crucial issue for the reinforced concrete structures. Being one of the most common deterioration mechanisms, corrosion severely affects the serviceability and durability of the structure as the steel reinforcement suffers from a reduction of the cross section and deterioration of the mechanical properties. Additionally, due to the steel oxidation process, residual material is formed, and the volume occupied by the reinforcement increases, leading to cracking and spalling of the concrete cover. A predictive model coupling concrete carbonation process and phase-field approach for brittle fractures is proposed to simulate the carbonation induced corrosion of rebar and the subsequent cracking phenomenon. First, a Fick diffusion law is used to describe the carbon dioxide (CO2) diffusion within the concrete which leads to a generalized corrosion process. As the corrosion evolves, the steel mass loss is converted into expansion strain due to the formation of residual material, and the damage evolution within the concrete cover is determined. After validation against examples from the literature, numerical simulations are performed, presenting a phase-field strategy capable to describe the cover cracking of corroded RC beams.

The modified early age strains development model for the case of two-way restraint conditions

This paper proposes a design model (2D MSDM) for assessment the early-age stress-strain parameters of two-axially restrained expansive concrete elements. The analytical model allows defining the restrained expansion strains and corresponding self-stresses in case of arbitrary restraint conditions in orthogonal directions by taking into consideration the elastic-plastic behavior of concrete during the expansion period. The results of solution according to the proposed model were compared with the experimental results of expansive concrete elements with orthogonal confinement carried out by authors and other researchers.

Analysis of Thermo-Hydro-Mechanical Coupling of Coal and Gas with Absorption/Desorption Thermal Effect

Coal adsorption/desorption gas can cause temperature changes. Moreover, the pressure difference between the high gas pressure area and the low gas pressure area in the coal may affect the coal adsorption/desorption gas thermal effect. To study the effect of adsorption/desorption thermal effect on the evolution law of coal and gas outburst precursor information under different pressure differences, the adsorption/desorption thermal effect experiments were carried out. And the thermo-hydro-mechanical coupling model was established, which reflects the interaction between coal and gas. Under the action of ground stress, pore pressure, adsorption expansion stress, and thermal expansion stress, the model includes the dynamic evolution of coal porosity and permeability, gas adsorption-desorption-diffusion-seepage, and energy accumulation and dissipation. Using the coupling model, the mechanism of adsorption/desorption thermal effect on the evolution of outburst precursor information and the mutual coupling relation between coal and gas is analyzed. The experimental results show that the relation between pressure difference and coal sample temperature variation is linear, and the pressure difference has a quadratic parabolic relation with the temperature accumulation of coal sample. As the pressure difference increases, the temperature variation of the coal sample gradually increases, but the temperature accumulation gradually decreases. Numerical simulation results show that as the pressure difference increases, the changes in coal temperature and gas pressure gradually decrease, and the thermal expansion strain caused by the adsorption/desorption thermal effect decreases, and the permeability increases. Comparing the calculation results with or without the adsorption/desorption thermal effect, the volumetric strain, temperature, and permeability of the coal have significant changes when the adsorption/desorption thermal effect is considered, and the gas drainage volume increases as the pressure difference increases. The effect of thermal expansion strain caused by adsorption/desorption thermal effect on gas seepage is greater than the effect of temperature change on gas seepage.

Transformation temperatures, mechanical properties and residual stress of two low-transformation-temperature weld metals

Two low-transformation-temperature weld metals, 12Cr6Ni and 8Cr10Ni weld metals, were devised and their martensite start temperatures were 245°C and 225°C, respectively. Despite a small difference of 20°C in martensite start temperature, the martensite finish temperature of the former was 100°C, while the one of the latter was below room temperature. The difference in martensite finish temperature was due to the stacking fault energy. Lower stacking fault energy accelerated martensitic transformation, thus elevating martensite finish temperature. Owing to difference in martensite finish temperature, the microstructures, mechanical properties and residual stress of low-transformation-temperature weld metals varied correspondingly. Furthermore, experimental and finite-element study indicated that volume expansion strain and martensitic transformation temperature range strongly affected residual stress.

Calculation of Expansion Stresses and Strains in Concrete under Sulfate Crystallization Attack in Dry–Wet Cycles Environments

AbstractThis paper analyzed the deterioration model of concrete in dry–wet cycles and sodium sulfate solution. The calculation method of stress transformation from dry–wet cycle and salt crystalliz...

Influence of geogrid reinforcement on the thermal expansion of reactive powder concrete

The influence of geogrid on the thermal expansion of reactive powder concrete (RPC) was experimentally investigated. Eighteen RPC prisms of dimensions 75 × 75 × 280 mm were tested at a temperature of 27 ± 4°C and a relative humidity of 50 ± 10% for 103 days. Triaxial geogrid having equilateral triangular openings with a side length of 35 mm was used as a reinforcement layer. The triaxial geogrid was placed at a depth of 37.5 mm from the surface of the RPC prism. Test results illustrate that the triaxial geogrid reinforcement significantly reduces the thermal expansion strains of RPC. In addition, the thermal expansion strains of RPC decrease with increasing the number of triaxial geogrid layers. The triaxial geogrid reinforcement could reduce the rate of thermal expansion of the RPC specimens compared with the unreinforced RPC specimens. An empirical equation was developed in this study for determining the thermal expansion strains of RPC reinforced with a single or a double triaxial geogrid layer.

Hydration-induced chemical expansion of BaCa(1+y)/3Nb(2−y)/3O3−δ∙xH2O (BCN) and other proton-conducting perovskite oxides

Thermal expansion and chemical strain caused by water uptake were measured for BaCa(1+y)/3Nb(2−y)/3O3−δ∙xH2O (BCN) perovskite-type oxides by dilatometric and X-ray diffraction methods. To describe the total and chemical expansion, we proposed a simple geometric chemical strain model based on the relative change in ionic radii upon hydration. The model calculations agree well with the experimental data for BCN oxides, for which the values of the linear chemical expansion coefficient, β, were found to be around 0.038 per mole of water-filled oxygen vacancies. Next, the model was applied to different perovskite-type proton-conducting oxides with existing literature data on chemical expansion. For example, the values of β, estimated using the model, are around 0.036 and 0.031 for BaZr1−yMyO3−δ and BaCe1−yMyO3−δ, respectively (M = rare-earth metal, Y or Sc). These values are close to those obtained by others using either density functional theory (DFT) calculations or direct experimental measurements, especially given the rather large scatter in the data reported in the literature. The latter is most probably related to the kinetic limitations since, unlike the most oxygen exchange phenomena, humidification of oxides happens at lower temperatures where the slow kinetics of water uptake plays an important role.

Modeling of irradiation-induced thermo-mechanical coupling and multi-scale behavior in a fully ceramic-microencapsulated fuel pellet

Fully ceramic microencapsulated (FCM) fuels with enhanced accident tolerance can provide an increased retention of fission products. In this study, a new method to model their irradiation-induced thermo-mechanical behavior is established. A fuel performance code called Thermo-mechanical Analysis of Inert Matrix Fuels (TMAIMF) is developed based on ABAQUS platform to enable the researchers to allow for all the irradiation effects in the three-dimensional large-deformation constitutive models of the involved materials. Especially, the important gas-release-induced thermal-mechanical effects are considered for the porous carbon layer. Finite element analysis is implemented for the thermo-mechanical coupling and multi-scale behavior in a FCM pellet, with the non-spherically symmetric thermal-mechanical interactions among all the coating layers in a TRISO particle, the TRISO particles and the matrix taken into account. Numerical simulation results indicate that (1) the irradiation shrinkage and gas-induced effective expansion strain in the porous carbon layer are responsible for the accommodation of kernel swelling, so the deformations of FCM pellets are dominated by the thermal expansion and irradiation swelling of SiC matrix; (2) the gas-induced effective expansion strains in the porous carbon layer together with the irradiation creep strains occurred in various materials protect the pellet from cracking during the whole irradiation process, with highly efficient heat transfer maintained. This study supplies a fundamental basis for advanced fabrication and optimization of FCM fuel pellets.

Strain-Induced Cracking Behavior of Coating/Substrate Systems and Strain Tolerant Design for Thick Coatings

The life span for a coating attached to its substrate is basic support for their desired protective function. Therefore, it is necessary to find out the causes responsible for the failure of coatings during service. This paper developed a finite element model to investigate the cracking behavior of plasma-sprayed ceramic coatings induced by the mismatch strain of thermal expansion between coating and substrate. Crack propagation affected by coating thicknesses was realized by the virtual crack closure technique (VCCT). The residual stresses (σ22 and σ12) and the strain energy release rate (SERR) induced at the tip of pre-crack in ceramic coatings are calculated. Results show that the σ22 and σ12 at the tip of the pre-crack increases continuously with the thickening ceramic coatings. The SERRs at the tip of the pre-crack in top-coat (TC) were increased with the thickness of ceramic coatings, resulting in the propagation of cracks. The crack length increases with the thickening of ceramic coatings. The crack propagation and coalescence lead to coating spallation, which is one of the main failure modes for plasma sprayed ceramic coatings during service. Given that, strain tolerant design was developed by inserting vertical pores in coatings. It was found that the SERRs were decreased with the increase in the number of vertical pores, as well as their depth. Moreover, the coatings with vertical pores appear to be crack-resistant, in particular for the thicker coatings. This suggests that the strain tolerant design is helpful to extend the life span of thick coatings, which makes a fundamental contribution to the design and preparation of advanced protective coatings in future applications.

Effects of SiO2 Filler in the Shell and Wood Fiber in the Core on the Thermal Expansion of Core-Shell Wood/Polyethylene Composites.

The influence of nano-silica (nSiO2) and micro-silica (mSiO2) in the shell and wood fiber filler in the core on the thermal expansion behavior of co-extruded wood/polyethylene composites (Co-WPCs) was investigated to optimize the thermal expansion resistance. The cut Co-WPCs samples showed anisotropic thermal expansion, and the thermal expansion strain and linear coefficient of thermal expansion (LCTE) decreased by filling the shell layer with rigid silica, especially nSiO2. Finite element analysis indicated that the polymer-filled shell was mainly responsible for the thermal expansion. The entire Co-WPCs samples exhibited a lower thermal expansion strain than the cut Co-WPCs samples due to protection by the shell. Increasing the wood fiber content in the core significantly decreased the thermal expansion strain and LCTE of the Co-WPCs. The Co-WPCs whose core layer was filled with 70% wood fiber exhibited the greatest anisotropic thermal expansion.

Dynamic fragmentation of a Zr-based metallic glass under various impact velocities

The dynamic fragmentation of ZrCuNiAl bulk metallic glass (BMG) subjected to various impact velocities was investigated in argon atmosphere. The results demonstrated that the ZrCuNiAl metallic glass generated debris after impact. The cumulative mass distribution curves of ZrCuNiAl BMG samples after impact under various velocities were obtained; the results showed that the cumulative mass of BMG samples conforms to the Schuhmann power function distribution. The characteristic fragment size λ governing the fragment distributions was determined by fracture toughness and expansion strain rate. The results demonstrated that characteristic fragment size decreases with an increase in impact velocity, which was well described by the model. A relationship between the cumulative mass distribution and the impact velocity of Zr55Cu30Ni5Al10 alloy was obtained based on energy principles. This formula is feasible to predict the cumulative mass distribution of Zr55Cu30Ni5Al10 alloy after impact under a wide velocity range.

Research on internal monitoring of reinforced concrete under accelerated corrosion, using XCT and DIC technology

Reinforcement corrosion and induced cracking of concrete is the major durability problem for concrete structures in the marine environment. And the evolution of expansion stress produced by reinforcement corrosion is a crucial parameter for the cracking of concrete. However, it’s difficult to directly measure the expansion stress by traditional measurement techniques since reinforcement is embedded in the concrete. In this study, concrete specimens mixed with seawater and reinforced by two kinds of steel bars, Q235 carbon steel bar and corrosion-resistant steel bar, were subjected to accelerated corrosion. X-ray computed tomography (XCT) was used to in situ and in real-time monitor the corrosion process of concrete, what digital image correlation (DIC) is for analyzing the inner expansion strain variation of reinforced concrete. The results show that the images collected by XCT can directly reflect the cracking position and the whole corrosion process of reinforced concrete. Meanwhile, the internal strain evolution can also be quantitatively calculated via DIC based on CT images. And the feasibility of combing XCT and DIC can be verified by the existing corrosion expansion cracking model. The correction coefficient of the non-uniform corrosion of carbon steel bar and corrosion resistance steel bar is KS1 = 9.3 × 10−4, KS2 = 2.4 × 10−4, respectively. The corrosion expansion stress that causes the initial corrosion expansion and cracking of the concrete is 2.5 Mpa and 3.0 Mpa, respectively. Furthermore, it can be observed that the uneven corrosion of steel bars, as well as the compressive stress or tensile stress caused in different parts of concrete. Additionally, the corrosion delay effect of corrosion resistance steel bar is not obviously under potentiostatic accelerated corrosion.

Alkali–silica reaction, delayed ettringite formation and corrosion effects on a bridge pier

Premature concrete deterioration in certain bridge piers in Texas, USA, has been attributed to the deleterious effects of alkali–silica reaction and delayed ettringite formation. A semi-empirical expansion model was used to estimate the maximum possible expansion strains from these causes. The compatibility-based strut-and-tie method was used to model the force–deformation behaviour of a bridge pier with and without such deterioration. The beneficial effects of prestressing forces in the reinforcement, along with modified cover and core concrete properties to account for coupled deterioration and confining action, were incorporated into the model of a bridge pier with deterioration. The model showed that large expansion strains and hence excessive cracking could be expected. However, the analysis showed that the load-carrying capacity of the deteriorated bridge pier was above its required design load capacity. The overall force–deformation response of the deteriorated bridge pier was slightly stronger and stiffer but had less displacement ductility. However, reinforcement corrosion in the beam–column joint significantly decreased its load-carrying capacity, ductility capacity and energy absorption. Even though these deterioration had a beneficial effect on the structure in the short term, severe reinforcement corrosion due to excessive cracking adversely affected the structure.

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.