Expansion Strain Research Articles

Early-age strains and stresses in bi-axially restrained expansive concrete elements

Practical application of expansive concretes in reinforced concrete structures needs the rational design model for assessment the early-age stress-strain parameters of self-stressing concrete elements under any restraint conditions during the expansion stage. Various strategies are used to calculate the restrained expansion strains and self-stresses but, in most cases, disregarding the elastic-plastic behaviour of expansive concrete at early ages. It’s noticeable that in case of bi-axial restraint conditions both the elastic-plastic parameters of expansive concrete and the influence of restraint in orthogonal directions should be taken into consideration. To achieve a reliable solution a design model for estimation the restrained expansion strains and self-stresses in self-stressed structural elements under bi-axial restraint conditions (2D MSDM) at expansion stage has been developed. The proposed design model is based on the MSDM for the case of uniaxial restraint arrangement. The validation of 2D MSDM was confirmed by the experimental results of expansive concrete elements under 2D confinement carried out by authors as well as obtained by other researchers.

Performance of Concrete Structure after Fire Disaster Based on Thermal Stress Coupling Field Analysis

Concrete is a kind of non-combustible material, but its mechanical properties are quite sensitive to temperature, once the temperature exceeds the limit temperature of steel and concrete, the structure of the building will be broken, therefore it’s an urgent task to study the fire resistance, bearing capacity and stability of the concrete structure after fire disaster, and to respond to these questions, this paper studied the performance of concrete structure after fire disaster based on thermal stress coupling field analysis. At first, this paper gave the method for collecting displacement changes of each surface of concrete structure under high temperature during the experiment, and analyzed the thermal expansion strain of the concrete under thermal stress coupling effect. Then, to investigate the changes in the stability of concrete structure under high temperature, this paper simulated the thermal stress coupling of concrete structure after fire. After that, parameters of the concrete structure under high temperature were selected to further simulate the fire disaster temperature field of the concrete structure under high temperature and construct the corresponding heat conduction differential equations of the structure. At last, this paper analyzed the experimental results, proposed conclusions, and verified the effectiveness of the proposed parameter calculation method.

Drying shrinkage and thermal expansion of metakaolin-based geopolymer concrete pavement reinforced with biaxial geogrid

The most often used material in concrete pavement slabs is ordinary Portland cement concrete (OPC). Many of OPC pavement slabs crack due to drying shrinkage and thermal expansion of OPC before applying traffic loads. Geopolymer concrete is an environmentally friendly type of concrete that achieves early strength without the need of moisture curing and can be strengthened further by heating. Metakaolin – based geopolymer concrete (GPC) present a suitable behavior against volumetric changes in previous researches. Biaxial geogrid layers can be an effective and durable alternative for steel reinforcement to reduce cracks propagation and volumetric changes in concrete. In this research, biaxial geogrid reinforced GPC was investigated to evaluate its drying shrinkage and thermal expansion properties which affect cracks propagation due to thermal volumetric changes in concrete pavement slabs. Geogrid reinforcing in GPC and OPC displayed a suitable performance against drying shrinkage and thermal expansion. Biaxial geogrid reinforcement in GPC resulted in about 48% reduction in drying shrinkage strains and 45% reduction in thermal expansion strains.

Strain effect on adsorption and reactions of AHx (A = C, N, O, x ≤ 3) on In2O3(110), TiO2(110), and ZrO2(101) surfaces.

More and more attention has been paid to strain-based regulation of catalytic activity. To guide regulation of catalytic performance via strain engineering, adsorption and reactions of AHx (A = C, N, O, x ≤ 3) were investigated on uniformly strained In2O3 (110), rutile TiO2 (110), and tetragonal ZrO2 (101) from -2% to 4%. The results show that adsorption energies vary linearly with strain; expansive strain enhances the adsorption of most adsorbates. Unlike the adsorbate scaling relations that are central atom dependent, the adsorbate scaling relations on strained surfaces are central atom independent. C-H/O-H bonds are elongated/shortened with expansive strain, and adsorption energies of CHx generally change more than those of OHx and NHx, which can be rationalized with effective medium theory and pertinent bond energies. Thermodynamically, In2O3(110)/ZrO2(101) is the most active/inactive. The estimated variation of rate constants at 300K from 0% to 2% strain based on the Brønsted-Evans-Polanyi relationship demonstrates great strain regulation potential of catalytic performance on these oxide surfaces. Finally, it is demonstrated that strain tends to facilitate the reactions whose sum of the stoichiometric number is positive, which can be used as a rule to guide strain engineering for heterogeneous catalysis.

Thermal and electric field induced phase transitions of Na0.5Bi0.5TiO3 single crystals

The phase transitions of unpoled and poled Na0.5Bi0.5TiO3 (NBT) single crystals were studied using structural, hysteresis loops, polarizing-microscope, dielectric, mechanical (the first measurement), thermal expansion strain and calorimetric measurements. It was found that phase transitions in NBT are first-order and clearly demonstrate ferroelastic aspects. Both rhombohedral-tetragonal and tetragonal-cubic transformations are accompanied by a softening of mechanical properties like in improper ferroelastic transitions. It was concluded that the difference in the internal friction between unpoled/poled states and between [001]c/[111]c poled states can be associated with a difference in the density of mobile ferroelastic twin walls in these states.

A length scale insensitive phase‐field model for fully coupled thermo‐mechanical fracture in concrete at high temperatures

AbstractFracture in concrete at high temperatures involves complex thermo‐mechanical couplings and arbitrary crack evolution, imposing great challenges to its computational modeling. This work addresses a length scale insensitive phase‐field cohesive model for fully coupled thermo‐mechanical fracture in concrete at high temperatures. Both the thermal expansion and transient creep strain are accounted for in the kinematics. Based on the underlying phase‐field cohesive model for fracture in solids at ambient temperature, the temperature‐dependent mechanical properties of concrete, that is, Young's modulus, tensile and compressive strengths and fracture energy, and so forth, are all incorporated. In addition to the cracking‐induced mechanical damage mechanism represented by the crack phase‐field, the thermal deterioration mechanism is also considered by a temperature‐dependent thermal damage variable. The numerical implementation of the proposed model into the multi‐field finite element method is then briefly addressed. Several representative numerical examples, for example, thermally induced cracking in energy storage structures, thermal shock in quenched concrete plates, mode‐I and mixed‐mode failure of notched beams at high temperatures, and so forth, are presented for the validation. The effects of various expressions for the transient creep strain (TCS) on the global behavior of concrete structures are also studied. As in those purely mechanical problems, both the predicted crack pattern and global responses for all examples are insensitive to the incorporated phase‐field length scale. Being able to capture the fully coupled thermo‐mechanical fracture in concrete, the proposed phase‐field cohesive model, combined with a reliable hydro‐chemo‐thermal analysis, is promising in assessing the integrity and safety of concrete structures at high temperatures like fire scenarios.

Strain Profile in the Subsurface of He-Ion-Irradiated Tungsten Accessed by S-GIXRD

The strain profile in the subsurface of He-ion-irradiated W was figured out by unfolding the synchrotron-grazing incidence X-ray diffraction (S-GIXRD) patterns at different incidence angles. The results show that for 2 × 1021 ions/m2 He2+-irradiated W, in addition to a compressive strain exists in the depths of 0–100 nm due to mechanical polishing, an expansion strain appears in the depth beyond 100 nm owing to irradiation-induced lattice swelling. This work provides a reference for the study of irradiation damage in the subsurface by S-GIXRD.

Revisit the Progress of Binders for a Silicon-Based Anode from the Perspective of Designed Binder Structure and Special Sized Silicon Nanoparticles

Si-based anodes have the advantages of high energy density and abundant reserve. However, their severe volume change during the charge–discharge process leads to particles’ pulverization and electrode destruction, which hinder their commercial application. Nanostructured Si is effective at relieving the expansion strain, and binders with a small proportion have been proven to play a pivotal role in maintaining the Si-based electrode integration. Si nanoparticles of various sizes show different particuological behaviors, including distribution, aggregation, etc. Moreover, the binders with specific molecular structure also have unique bonding characteristics with Si particles of different sizes. Except the aforementioned aspects, the process techniques of Si nanoparticles and binders also greatly affect the electrode. Though some pioneering reviews about the progress of binders for Si-based anodes have been published, in order to boost the practical application of Si-based anodes, it is urgent to revisit the previous investigations to clarify the correlation of the particle size, binder structure, and process techniques.

Modelling concrete slabs subjected to localised fire action with OpenSees

PurposeReinforced concrete slabs in fire have been heavily studied over the last three decades. However, most experimental and numerical work focuses on long-duration uniform exposure to standard fire. Considerably less effort has been put into investigating the response to localised fires that result in planarly non-uniform temperature distribution in the exposed elements.Design/methodology/approachIn this paper, the OpenSees for Fire framework for modelling slabs under non-uniform fire exposure is presented, verified against numerical predictions by Abaqus and then validated against experimental tests. The thermal wrapper developed within OpenSees for Fire is then utilised to apply localised fire exposure to the validated slab models using the parameters of an experimentally observed localised fire. The effect of the smoke layer is also considered in this model and shown to significantly contribute to the thermal and thus thermo-mechanical response of slabs. Finally, the effect of localised fire heat release rate (HRR) and boundary conditions are studied.FindingsThe analysis showed that boundary conditions are very important for the response of slabs subject to localised fire, and expansive strains may be accommodated as deflections without severely damaging the slab by considering the lateral restraint.Originality/valueThis work demonstrates the capabilities of OpenSees for Fire in modelling structural behaviours subjected to non-uniform fire conditions and investigates the damage pattens of flat slabs exposed to localised fires. It is an advancing step towards understanding structural responses to realistic fires.

Finite element analysis on the diffusion-reaction-damage behavior in concrete subjected to sodium sulfate attack

The deterioration of concrete caused by sodium sulfate attack (SSA) is a process of volume expansion and cracking layer by layer, causing the external solution to flow directly into concrete. Taking ettringite type of SSA as an example, this paper studies the SSA-induced deterioration of concrete. Based on Fick’s law and reaction kinetic theory, the diffusion-reaction model of sulfate ion in concrete is proposed. Introducing the crack density coefficient, the chemical damage of concrete is characterized by expansion strain caused by sulfate products, and then the condition of boundary movement is further established. Using the finite element method, the Crank-Nicolson-Galerkin scheme governing equation of diffusion-reaction model is developed. On the basis of model validation, a numerical simulation is performed to analyze the temporal-spatial variation of sulfate ion and damage degree in concrete. The result show that, the SSA-induced cracking of concrete obviously lags behind the ion diffusion and chemical reaction.

Developing a heterogeneous ensemble learning framework to evaluate Alkali-silica reaction damage in concrete using acoustic emission signals

The monitoring and evaluation of Alkali-silica reaction (ASR) damage in concrete structures are required to ensure the serviceability and integrity of concrete infrastructures such as bridges and dams. The innovation of this paper lies in the development of an automatic ASR monitoring and evaluation approach by leveraging acoustic emission (AE) and a heterogeneous ensemble learning framework. In this paper, ASR was monitored by AE sensors attached to a concrete specimen, which was placed in a chamber with high humidity and temperature. The recorded AE signals were filtered and divided by four ASR phases according to signal strength, crack width and expansion strain. A heterogeneous ensemble network including convolutional neural networks (CNN) and random forest models was employed to learn different features from AE signals and classify the AE signals into their corresponding phases. The results suggest that the proposed model has a high performance and classifies the signals into the assigned phases with high accuracy.

Three-dimensional modeling of the mechanical behavior of a single pile in unsaturated expansive soils during infiltration

In this paper, a novel coupled hydro-mechanical model for unsaturated expansive soils and a constitutive model for unsaturated pile-soil interfaces are implemented into ABAQUS for performing 3-D finite element analysis of single piles in expansive soils during infiltration. Some key features of coupled thermal–mechanical model from ABAQUS are used to formulate coupled hydro-mechanical model developing five independent user-material subroutines. User-defined field subroutine (USDFLD) is used to access the stress and strain and transfer these values to other subroutines. Three subroutines including user-defined material subroutine (UMAT), user-defined thermal material subroutine (UMATHT), and user-defined thermal expansion subroutine (UEXPAN) are developed and used to calculate the stress-deformation, the hydraulic behavior, and the expansion strain, respectively. In addition, an unsaturated soil-structure interface model is implemented into user-defined friction behavior subroutine (FRIC) to calculate the friction stress between soil and pile. The program is successfully validated using experimental results performed on a single model pile in an expansive soil. The modeling results are consistent with the experimental results which suggest that a decrease in matric suction can contribute to the reduction in the shaft friction as more load is transferred to the pile resulting in an increase in the pile head settlement and pile base resistance. The modeling approach presented in this paper is promosing and can be extended by the practitioners in the rational design of pile foundations in expansive soils.

Experimental investigation of the uniaxial tensile properties and thermal deformation of the ETFE membrane at different temperatures

This study focused on the mechanical properties of the ethylene tetrafluoroethylene (ETFE) membrane at temperatures between −20 and 140 °C, the thermal expansion performance from the ambient temperature of 25 °C to 140 °C, and the thermal deformation performance from the ambient temperature of 25 °C to 80 °C. According to the experimental study, the mechanical properties, the glass transition temperature, the coefficient of thermal expansion (CTE), and the thermal deformation strain model of ETFE at different temperatures were obtained. Finally, the thermal deformation mechanism is proposed, namely that the thermal deformation strain is equal to the thermal expansion strain and elastoplastic strain produced by the change of the strain–stress relationship.

Insights to compressive strength, impermeability and microstructure of micro-expansion steel slag cement under constraint conditions

This work aims at evaluating the influence of steel slag as partial replacement of cement on the mechanical properties and impermeability of cement-based materials under constraint conditions. The results show that, compared with the raw steel slag, the setting time of the wet-grinding steel slag system is shortened, and the free expansion rate is increased. When the wet-grinding steel slag content is 10%, the compressive strength of the specimen (constraint) after 28 days of curing is the highest, reaching 68.5 MPa, which is 9.3% higher than that of the free curing specimen, and the impermeability is also the best. Under the constraint conditions, the expansion strain produced by steel slag leads to the compact sample structure and reduced porosity, which is conducive to the mechanical properties and compactness of the pore structure of cement paste.

Modification of hexachiral unit cell to enhance auxetic stent performance

Stents possess disadvantages such as foreshortening and dogboning. Material selection alongside topological modifications are two main approaches to overcome these issues. Stents with negative Poisson’s ratio, also known as auxetic property, can lead to promising performance improvement. Therefore, in this study, three stents were designed by improving a hexachiral unit cell and underwent numerical and experimental investigations using CoCr 605 L and SS 316 L alloys. The modified auxetic stents presented higher auxeticity and NPR of −0.64 and −0.69. Higher radial expansion, stress tolerance and yield strain of these modified stents help them overcome drawbacks of non-auxetic stents.

Estimation of restrained expansion strain of reinforced expansive concrete considering mixture and curing conditions

Several standards have been used as guidelines for expansive concrete design. However, all of these standards still do not consider several factors that affect the level of expansion such as the incorporation of fly ash, curing temperature, and curing condition. The main objective of this study is to estimate the restrained expansion strain of reinforced expansive concrete by including several factors which affect level of expansion. This research determines the effective free expansion strain of expansive concrete, which is the expansion strain after eliminating the loss of expansion due to the effects of pores filling by expansive products and compression creep during early age restrained expansion. This effective free expansion strain is used as the input of finite element (FE) analysis to estimate the restrained expansion strain. A reduction factor is introduced to account for the loss of expansion. It was found that by the application of the proposed reduction factor, the tested restrained expansion results of specimens with various mixture and curing conditions can be predicted satisfactorily.

Research on mixed alkaline-earth effect in non-alkali glass substrates for TFT-LCDs

Herein, we used CaO to replace MgO to investigate the effect of mixed alkaline-earth effect on structure and properties of the non-alkali glass substrates which were synthesized by the traditional melting technology. The results show that with the replacement of CaO for MgO, the stability of the glass network structure decreases due to the decrease of the bridging oxygens. In terms of the comprehensive properties, the glass density, molar volume, thermal expansion coefficient, strain and softening points, and chemical stability all show a near-linear increase or decrease. However, due to the mixed alkaline-earth effect, some other properties including the crystallization peak temperature, thermal stability, and mechanical properties show a negative deviation from linearity, and the extremum locates at the CaO content of 6 mol%. Based on the results, this research can provide a significant guidance for the property control of non-alkali glass substrates.

Field Investigation and Finite Element Analysis on Expansion and Shrinkage Strains of Expansive Concrete Structures

Field Investigation and Finite Element Analysis on Expansion and Shrinkage Strains of Expansive Concrete Structures

Electrochemo-mechanical analysis of solid oxide fuel cell using surrogate model and substitution approach

In this paper, we incorporate the surrogate model and substitution approach into electrochemo-mechanical analysis of plate shaped solid oxide fuel cell (SOFC). A local structure which is called in-plane unit structure (IPUS) is extracted from the plate shaped SOFC. The oxygen potentials of the IPUS as training data are obtained from the electrochemical potential analysis. A surrogate model using proper orthogonal decomposition is constructed from the oxygen potential of the IPUS obtained from the electrochemical potential analysis, and the distribution of oxygen potential in plate shaped SOFC is predicted by the surrogate model. The reduced expansion strain is calculated from the predicted oxygen potential. Then, a substitution approach using numerical plate testing is applied to analyze macro deformation considering mechanical behavior and thermal and reduced expansion.

Expansive Strain Distribution and Its Estimation Methods for Expansive Concrete Applied to Full Size Slabs and Wall Rails

Expansive Strain Distribution and Its Estimation Methods for Expansive Concrete Applied to Full Size Slabs and Wall Rails