Expansion Strain Research Articles

Influence of further hydration on UHPC matrix properties

To investigate the evolution laws governing the macroscopic properties of ultra-high-performance concrete (UHPC) matrices under further hydration effect, a further hydration test was performed by varying the cement fineness and slag powder content. The influence mechanism of further hydration on strength was analyzed. The results revealed that the bound water content for further hydration and expansion strain for UHPC matrix with medium fineness cement achieved the minimum values, and the compressive strength reached the lowest value after 21 d of further hydration. Both the bound water content for further hydration and expansion strain showed a tendency to increase with increasing slag powder content, and the higher the slag powder content, the earlier was the peak strength achieved. The volume expansion of further hydration products caused the matrix to crack, and further hydration was manifested as damage effect, resulting in a decrease in strength.

Incorporation of uranium nitride fuel capability into the ENIGMA fuel performance code: Model development and validation

Uranium dioxide (UO2) is the primary fuel form for nuclear reactors but its moderate uranium density and low thermal conductivity have prompted the exploration of alternative materials. Uranium nitride (UN) has emerged as a promising candidate for a variety of reactors, offering higher uranium density and thermal conductivity. This paper details the development and implementation of UN fuel capabilities within the ENIGMA fuel performance code for Light Water Reactor (LWR) applications. The new UN capability in ENIGMA includes correlations for theoretical density at room temperature, thermal conductivity, specific heat capacity, enthalpy, thermal expansion strain, Young’s modulus, Poisson’s ratio, thermal creep strain rate, irradiation creep strain rate and emissivity. Additionally, it incorporates models for densification, solid fission product swelling, fission gas bubble swelling, and fission gas release, along with a modified RADAR model for determining the pellet radial power profile and helium generation. Validation of the UN model was conducted using data from the L414 pin irradiation in the JOYO fast reactor in Japan. Further validation efforts are planned using datasets from JOYO and the Siloé thermal reactor in France. The paper also outlines areas of future work to address experimental data gaps and enhance model accuracy to cover a broader range of cladding materials, manufacturing parameters (including porosity volume fraction) and operating conditions (including fuel temperatures and burnups). Although focused on LWR applications, the work outlined supports the use of UN fuel across various reactor systems.

Performances enhancing of supersulfated cement (SSC) using waste alkaline activators: Red mud and carbide slag

Supersulfated cement (SSC), since its invention, showed lower early-age strength gain, which has limited its practical applications. The urgent issue is how to regulate and enhance its early-age performance. In this context, solid waste materials such as bauxite residue-red mud (RM) and carbide slag residue (CS) from acetylene production by calcium carbide hydrolysis were used to improve the hydration and performance of SSC. By utilizing a range of analytical techniques such as isothermal calorimetry (IC), X-ray diffraction (XRD), backscatter scanning electron images (BSE), and thermogravimetric analysis (TGA), the hydration process, phase assemblages and microstructure of CS/RM-modified SSC were systematically investigated. It’s found that CS, as a calcareous alkaline activator, act as a regulator for adjusting the two main hydration reactions of C-A-S-H deposition and ettringite formation in SSC. The alkaline activator induces the hydration of slag and promotes the formation of hydration products. However, an excessively high dosage of carbide slag delays the primary ettringite formation reaction because it inhibits the dissolution of slag and promotes the formation of outer products. It leads to a looser and more porous paste matrix, resulting in higher expansion strain and poor strength gain at full curing ages. In contrast, red mud improves the hydration rate and enhances the hydration degree of SSC within the studied content (up to 30 wt%). With addition of red mud, SSC hydration is significantly advanced and deepened, resulting in more hydrates, particularly inner products. Red mud facilitates the depolymerization of the slag glass network and promotes the forming of nuclei and growth of hydration products. However, an excessively high red mud content would lead to a looser and more porous paste matrix due to the characteristics of red mud particle itself. An optimal red mud content has been identified as 20 wt%.

A novel method for predicting carburizing and quenching deformation of the gear with the mandrel based on carburizing expansion strain and dynamic thermal boundary conditions of quenching

During the carburizing quenching process, the interaction of multiple physical fields leads to significant nonlinearity in the mechanical properties and physical characteristics of the material, making prediction of carburizing quenching deformation particularly challenging. Based on the phase transformation thermo-elastic-plastic constitutive equation, this paper innovatively incorporated the deformation of interstitial solid solution induced by carburization, and integrated experimental data on material properties for 8620RH, a multi-field model for carburizing quenching was constructed. The accuracy of the proposed deformation prediction model was validated through experiments on cylindrical samples and the calculation results from specialized heat treatment software Dante. Based on the deformation prediction model, considering the flow effect of quenching medium in gear quenching process, and introducing dynamic heat boundary conditions during quenching, a finite element model for predicting carburizing and quenching deformation of the gear with the mandrel was constructed to study the deformation distribution of the gear. The accuracy of the deformation prediction model was verified through the carburizing quenching experiment of the gear with the mandrel. The results show that compared with the classical model which does not consider the carburizing expansion strain and the dynamic thermal boundary conditions, the proposed model demonstrates higher predictive accuracy in torsional deformation and expansion deformation. The research work provides a novel model and method for improving the accuracy of predicting carburizing and quenching deformation in gears.

Origins of enhanced oxygen reduction activity of transition metal nitrides.

Transition metal nitride (TMN-) based materials have recently emerged as promising non-precious-metal-containing electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media. However, the lack of fundamental understanding of the oxide surface has limited insights into structure-(re)activity relationships and rational catalyst design. Here we demonstrate how a well-defined TMN can dictate/control the as-formed oxide surface and the resulting ORR electrocatalytic activity. Structural characterization of MnN nanocuboids revealed that an electrocatalytically active Mn3O4 shell grew epitaxially on the MnN core, with an expansive strain along the [010] direction to the surface Mn3O4. The strained Mn3O4 shell on the MnN core exhibited an intrinsic activity that was over 300% higher than that of pure Mn3O4. A combined electrochemical and computational investigation indicated/suggested that the enhancement probably originates from a more hydroxylated oxide surface resulting from the expansive strain. This work establishes a clear and definitive atomistic picture of the nitride/oxide interface and provides a comprehensive mechanistic understanding of the structure-reactivity relationship in TMNs, critical for other catalytic interfaces for different electrochemical processes.

A coupled phase-field model for sulfate-induced concrete cracking

The performance of concrete will decrease when subjected to external sulfate corrosion, and numerical models are effective means to analyze the mechanism. Most models cannot efficiently consider the effect between cracks and ionic transport because crack initiation and propagation are ignored. In this paper, a coupled chemical-transport-mechanical phase-field model is developed, in which the phase-field model is applied for the first time to predicate the cracking of sulfate-eroded concrete. The chemical-transport model is established based on the law of conservation of mass and chemical kinetics. The phase-field model equivalents the discrete sharp crack surface into a regularized crack, making it convenient to couple with the chemical-transport model. The crack driving energy in the phase-field model is computed by the expansion strain, which can be obtained from the chemical-transport model. The coupling of crack propagation and ionic transport is achieved by a theoretical equation, which considers both the effects of cracking and porosity. Complex erosion cracks can be automatically tracked by solving the phase-field model. The simulation results of the multi-field coupling model proposed in this paper are in good agreement with the experimental data. More importantly, the spalling phenomenon observed in physical experiments is reproduced, which has not been reported by any other numerical models yet, and new insight into the spalling mechanism is provided.

First‐principles calculations to investigate electronic thermodynamic and optical properties of the RbScO2 alloy

AbstractIn this study, we explore the electronic, thermodynamic, and optical properties of the compound RbScO₂ using density functional theory (DFT) and incorporating a U‐correction term, known as the Hubbard correlation energy. This approach enables us to gain an in‐depth understanding of the band structure, density of states, and specific optical properties of RbScO₂. The results reveal that RbScO₂ exhibits an indirect band gap measuring 3.68 eV for GGA+SOC+U. Importantly, this indirect band gap is located at the Γ‐VBM and M‐CBM points of the Brillouin zone. The optical properties of RbScO₂ were studied in the xx, yy, and zz directions, revealing a significant increase in the absorption coefficient with higher photon energies, including a distinct peak in the UV range. Increased absorption was observed along the xx and yy axes under a pressure of 50 GPa. Additionally, the thermodynamic attributes of RbScO₂, including volume, Debye temperature, heat capacity, and entropy, were examined. It was observed that the Debye temperature increases proportionately to the tensile strain but decreases with increasing temperature, suggesting that the expansion strain may increase the compound's mechanical and thermal stability. This study provides valuable information on the characteristics of RbScO2, enriching our understanding of its potential applications.

Analysis of deformation and multi-angle tip contact in a combined mechanism of thin-walled membrane forces and inextensible layers in soft actuators

Soft actuators have extensive applications in operations, are generally made of elastomers, and generate large deformation. It makes accurately predicting their deformation behavior challenging. This study considers the combined effects of chamber sidewall expansion and inextensible layer strain mechanisms on the actuator's bending and tip contact force. We separately model the expansion of the chamber sidewall and the strain in the inextensible layer using the expanding membrane and strain beam theory. The theoretical model presented to predict the contact area of the sidewall expanding membrane under multiple bending conditions. The analytical models for three actuator states are established: 1) Free space; 2) Tip contact at multiple angles; and 3) Grasping state. The proposed theoretical model accurately predicts deformation, force characteristics, and the requisite pressure for object grasping, and its applicability extends to similar soft actuators. Comparative analyses with finite element methods (FEM) and experimental results validate the model's computational efficiency, reduced design variables, and accurate prediction of diverse deformations and tip contact forces. Notably, the model outperforms with shorter computation times. The large and small chamber spacing errors are approximately 10 % and 5 %, respectively.

Impacts of frost heave susceptibility and temperature-changing conditions on freeze-thaw deterioration of welded tuffs

Damage development in rocks by freeze-thaw cycles, a phenomenon that is typical to cold regions, is known to reduce the strength and durability of structures. In this study, a series of freeze-thaw tests were performed on frost and non-frost heave rocks to examine the impact of frost heave susceptibility and temperature-changing conditions on rock behaviors. The freeze-thaw life and uniaxial compressive strength (UCS) of rocks subjected to freeze-thaw cycles were estimated using a model that was based on fatigue damage mechanisms. Furthermore, we proposed a method for estimating the freeze-thaw life of rocks, using expansive strain as an important factor. The results indicated that the Shikotsu welded tuff (a non-frost heave rock) exhibited higher durability than the Noboribetsu welded tuff (a frost heave rock); this may be because the Shikotsu welded tuff had a larger pore radius and more unsaturated pores. The one-dimensional (1D) cooling-heating conditions induced significantly less damage than the three-dimensional (3D) conditions, owing to the continuous migration of free water into the unfrozen zone. The damage model estimated that for the Noboribetsu welded tuff, the freeze-thaw life in the 1D conditions was approximately eight times longer than that in the 3D conditions. Notably, with respect to the Shikotsu welded tuff, a critical freeze-thaw period induced significant expansion, resulting in damage development in the tuff. The freeze-thaw life of each rock sample was estimated based on the magnitude of the volumetric expansive strain. This study contributes to the rational assessment of the stability and durability of rock structures in cold regions.

Effect of Solution-to-Binder Ratio and Molarity on Volume Changes in Slag Binder Activated by Sodium Hydroxide at Early Age.

This research investigates the impact of solution concentration and solution-to-binder ratio (S/B) on the volume changes in alkali-activated slags with sodium hydroxide at 20 °C. Autogenous and thermal strains are monitored with a customized testing device in which thermal variations are controlled. Consequently, both the autogenous strain and coefficient of thermal expansion (CTE) are determined. Heat flow and internal relative humidity (IRH) are also monitored in parallel, making this research a multifaceted study. The magnitudes of autogenous strain and CTE are higher than those of ordinary Portland cement paste. Decreasing the solution concentration or S/B generally decreases the autogenous strain (swelling and shrinkage) and the CTE. The shrinkage amounted to 87 to 1981 µm/m, while the swelling reached between 27 and 295 µm/m and was only present in half of the compositions. The amplitude of the CTE, which increases up to 55 µm/m/°C for some compositions while the CTE of OPC remains between 20 and 25 µm/m/°C, can be explained by the high CTE of the solution in comparison with water. The IRH of paste cannot explain the autogenous strain's development alone. Increasing S/B eliminates the self-desiccation-related decrease.

Field test on thermal control for bridge piers on plateau through energy pile

This study presents a sustainable thermal control method (energy pile technology) for bridge piers in high-altitude regions, addressing the challenges posed by temperature variations in mass concrete structures. The proposed method involves integrating various heat exchange tubes within the pile foundation, pile cap, and bridge pier concrete to harness shallow geothermal energy. This paper summarizes failure cases of bridge structures due to the impact of thermal loads. Through three field tests on a plateau, the feasibility and practicality of the energy pile technology are verified. The system exhibits promising results, achieving a maximum temperature difference reduction of 3.9°C and a reduction of 53.4%. Furthermore, the method has effectively reduced the expansion strain on the sunny side of the bridge piers, with a maximum reduction of up to 44.4%. Importantly, the energy pile technology has minimal impact on the pile foundation, with negligible constrained stress variation. The study evaluates the heat exchange efficiency and energy efficiency of the energy pile-based system, reporting stable heat exchange rates and a comprehensive Coefficient of Performance (COP) reaching up to 4.0. The findings highlight the potential of this sustainable temperature control methodology to enhance the resilience and longevity of critical infrastructure in challenging climates.

Nano-cutting mechanism of ion implantation-modified SiC: reducing subsurface damage expansion and abrasive wear

This study utilized ion implantation to modify the material properties of silicon carbide (SiC) to mitigate subsurface damage during SiC machining. The paper analyzed the mechanism of hydrogen ion implantation on the machining performance of SiC at the atomic scale. A molecular dynamics model of nanoscale cutting of an ion-implanted SiC workpiece using a non-rigid regular tetrakaidecahedral diamond abrasive grain was established. The study investigated the effects of ion implantation on crystal structure phase transformation, dislocation nucleation, and defect structure evolution. Results showed ion implantation modification decreased the extension depth of amorphous structures in the subsurface layer, thereby enhancing the surface and subsurface integrity of the SiC workpiece. Additionally, dislocation extension length and volume within the lattice structure were lower in the ion-implanted workpiece compared to non-implanted ones. Phase transformation, compressive pressure, and cutting stress of the lattice in the shear region per unit volume were lower in the ion-implanted workpiece than the non-implanted one. Taking the diamond abrasive grain as the research subject, the mechanism of grain wear under ion implantation was explored. Grain expansion, compression, and atomic volumetric strain wear rate were higher in the non-implanted workpiece versus implanted ones. Under shear extrusion of the SiC workpiece, dangling bonds of atoms in the diamond grain were unstable, resulting in graphitization of the diamond structure at elevated temperatures. This study established a solid theoretical and practical foundation for realizing non-destructive machining at the atomic scale, encompassing both theoretical principles and practical applications.

Changes in air permeability of restrained expansive concrete under drying condition: contribution of expansive strain

Restraining the expansion of expansive concrete with embedded rebars can exert chemical prestressing, which may affect the durability of concrete structures. This study aims to investigate the durability performance of expansive concrete by understanding the mechanism of air permeability changes while considering the variations in reinforcement arrangements and concrete dimensions. The Torrent’s air permeability test was used to non-destructively evaluate the disparity in air permeability changes of expansive and normal concrete during the drying processes from 28 to 182 days. Additionally, expansive strain changes were continuously monitored to investigate chemical prestress. The experimental test results suggest the immense effect of the change in expansive strain on the air permeability of concrete. This study proposes that the change in microstructure owing to the loss of expansive strain may cause an increase in air permeability. The loss of expansive strain is a distinguished feature that differentiates the mechanism of air permeability changes in expansive and normal concrete. These findings suggest the possible improvement in the durability performance of expansive concrete in cases where the loss of its expansive strain can be controlled.

Thermomechanical Analysis and Numerical Simulations of Fused Filament Fabricated Polylactic Acid Parts

This work aimed to investigate the thermal deformation of polylactic acid (PLA) samples 3D-printed by Fused Filament Fabrication. The irreversible thermal strain (ITS) and coefficient of linear thermal expansion (CLTE) of four sets of samples with various sizes and thicknesses of the layer in the three directions of the measurements were investigated. The thermomechanical analysis (TMA) was used for the investigation of thermal deformation. During the study, the dependencies of deformation on temperature were obtained. The samples' CLTE values at various ranges of temperatures were estimated using the obtained dependencies. ITS was observed after heating to 80 ℃ during the first TMA cycle. The values reached 8 – 9 %. The impact of layer thickness and the number of layers in the sample on ITS was noticed. Shrinkage in the X direction and expansion in the Z direction with almost the same values were observed. Finite element code ANSYS was used to simulate the distribution of temperature and accumulation of residual thermal stresses in the printed part. The correlation was obtained between the level of simulated residual thermal stresses for samples with different number of layers and layer thicknesses and measured ITS after annealing.

DEM investigation on flow instability of particulate assemblies under coupling between volumetric and axial strains

AbstractThe discrete element method (DEM) is employed to investigate the impact of coupling between volumetric and axial strains on the flow liquefaction vulnerability of 3D cubic particulate specimens. The virtual testing program conducted here encompasses a wide range of initial states and varying degrees of coupling between volumetric and axial strains. Utilizing data obtained from DEM simulations, the evolution of micro- and macroscale variables, including coordination number, contact fabric anisotropy, redundancy index, strong force networks, invariants of the effective stress tensor, and excess pore-water pressure, is examined. Results from DEM tests indicate that coupling expansive volumetric strain with axial strain leads to a gradual loosening of the load bearing microstructure, a decrease in coordination number, and a faster change in contact anisotropy. DEM simulations demonstrate that the triggering of flow liquefaction instability is followed by a sudden increase in contact fabric anisotropy and abrupt drops in coordination number and redundancy index. Moreover, a detailed analysis of the findings suggests that the stress ratio at the onset of post-peak softening decreases with increasing expansive volumetric strains.

Validated enhancement and temperature modulated absorbance of a WS2 monolayer based on a planar structure.

Transition-metal dichalcogenides (TMDCs), as emerging optoelectronic materials, necessitate the establishment of an experimentally viable system to study their interaction with light. In this study, we propose and analyze a WS2/PMMA/Ag planar Fabry-Perot (F-P) cavity, enabling the direct experimental measurement of WS2 absorbance. By optimizing the structure, the absorbance of A exciton of WS2 up to 0.546 can be experimentally achieved, which matches well with the theoretical calculations. Through temperature and thermal expansion strain induced by temperature, the absorbance of the A exciton can be tuned in situ. Furthermore, temperature-dependent photocurrent measurements confirmed the consistent absorbance of the A exciton under varying temperatures. This WS2/PMMA/Ag planar structure provides a straightforward and practical platform for investigating light interaction in TMDCs, laying a solid foundation for future developments of TMDC-based optoelectronic devices.

Numerical simulation on transport-crystallization-mechanical behavior in concrete structure under external sulfate attack and wetting–drying cycles

External sulfate attack (ESA) coupled with wetting–drying alternation poses a significant threat to the concrete durability, while there are few models to simulate the above ESA behavior. In this paper, a simplified transport-mechanical model is proposed to numerically analyze the deterioration of concrete prism under ESA and dry-wet cycles. Firstly, a transport model of sulfate ion in concrete prism is established by considering the behaviors of ion diffusion, convection and chemical reaction, and numerically solved by the finite difference method. Secondly, the crystallization pressure of sulfate products in porous system is analyzed to calculate the equivalent expansion force. Then, the expansion strain and its-induced damage are calculated, and the criterion of boundary movement is further proposed. On the basis of model validation, a numerical simulation is performed to analyze the transport-mechanical response in concrete prism under ESA and dry-wet cycles. The results show that, there is no clear demarcation between the convection and diffusion zones in the prism. The spatial–temporal evolution of ESA-induced damage is similar to that of ion concentration. The longer the wetting time in one dry-wet cycles, the deeper the spalling of concrete prism caused by ESA.

Investigation into hydrogen induced fracture of cable bolts under deep stress corrosion coupling conditions

The coupling effects of geostress and multi-attribute corrosion environments are the major causes of damage and rupture of prestressed cable bolts in deep underground environments. To determine impacts of different environmental factors on stress corrosion cracking of cable bolts in underground conditions, the accelerated stress corrosion tests and finite element numerical simulations were carried out. By implementing the material diffusion theory and appreciating the hydrogen induced lattice expansion effects, the diffusion and aggregation behavior of hydrogen in cable bolts were simulated. The influences of stress intensity and hydrogen concentration on failure mechanisms of cable bolts were studied by considering the hydrogen induced expansion strain. The failure only occurred in the environments where sufficient hydrogen concentration existed. The hydrogen diffusion flux and distribution were consistent with stress concentration distribution. The prestress accelerated the hydrogen diffusion to stress concentrated position leading to a greater strain in the stressed areas, which consequently induced hydrogen expansion stress and decreased cohesion strength of lattice near crack tip. The fractographic features of failed specimen were analysed and hydrogen assisted fracture was confirmed to be one of the main failure mechanisms leading to stress corrosion failures. The methodologies proposed could be used to study the diffusion and distribution of hydrogen in metals and the obtained results improved the understanding failure mechanism of hydrogen assisted SCC.

A mechanistic model of the degradation of cement-based materials subjected to sulfate attack

The durability of concrete structures is usually threatened by sulfate attack in their service progress. However, there is still no widely accepted model that can accurately predict the process of sulfate attack on concrete. Combined the diffusion-reaction process, constitutive relationship, and fracture criterion, a mechanistic model is proposed by considering the effects of pore filled by products of sulfate attack on the diffusion coefficient and total expansion strain in this study. The establishment assumptions of model can be observed from the macro- and micromorphology of cement-based materials subjected to sulfate attack. The results show that the route of decohesion goes along the interface between the compressed degraded layer and the tensed non- degraded matrix as the triggered by sulfate attack, and the thickness of decohesion is between 50 and 400 μm. The time index used to correct the diffusion coefficient is close to −0.41, while the range of pore filling degree is 3.16–6.29% based on the debonding thickness. Compared with the Atkinson model, the degradation rate calculated from the modified model is the closest to the actual test value with an error less than 10%.

Study on frost heaving force and the propagation of cracks in freezing rocks using the phase field method

In cold regions, the water in rocks expands volumetrically after freezing, leading to the propagation of fractures. In this study, the effective volume expansion coefficient is employed as a substitute for the volume expansion strain after the water in the fracture undergoes freezing and transforms into ice, and the phase field method is used to simulate the propagation of fractures in freezing rocks under various conditions to further explore the law of fracture propagation. The Abaqus software is used to solve the mechanical field control equation and the phase field evolution equation. First, the theoretical calculation of the frost-heaving pressure is compared with that obtained by experimental and numerical calculations. This comparison indicates that the numerical model presented in this study can effectively calculate the frost-heaving pressure during fracture propagation. Subsequently, the propagation of single and double fractures caused by frost heave is simulated based on fracture propagation experiments under frost heave conditions. The simulation results closely resemble the observed morphology of fracture propagation caused by frost heave obtained from the experiments. This confirms the suitability of the proposed model for simulating and predicting the propagation of fractures caused by frost heave. Finally, the influence of volume expansion strain growth path on fracture propagation due to frost heave is discussed. Although the final volume expansion strain value is the same, different growth paths of the volume expansion strain result in different fracture propagation morphologies.