Swelling Strain Research Articles

Multidimensional multiphysics modeling of TRISO particle fuel with SiC/ZrC coating using modified fission gas release model

TRISO particle is adopted in the design of various types of reactors and accident tolerant fuel (ATF) due to its excellent accident tolerant performance under high temperature and other severe conditions. This study presents a multidimensional thermomechanical analysis of TRISO particle fuel with SiC/ZrC coating under typical operation conditions in reactor. Key fuel performance phenomena were considered including thermal performance (heat generation, conduction, irradiation gap heat transfer, etc.), mechanics (thermal expansion, elastic strain, densification, fission product swelling strain, contact, and thermal, irradiation creep, etc.), also irradiation behaviors (burnup, fission gas production and release, gap/plenum pressure with plenum volume, etc.). All these models have been integrated and solved via finite-element method. As for results, several complicated models were implemented and proved to successfully predict the thermomechanical behaviors of TRISO coated fuel compared with the existing experimental or numerical results. An enhanced fission gas behavior model considering grain boundary diffusion was established, which could complete detailed calculation on fission gas release at both grain size and fuel particle pellet scales. Based on the preliminary thermomechanical analysis, in terms of structural strength and heat transfer efficiency, ZrC appears to be a candidate material of SiC. Moreover, failure mechanisms and effective thermal conductivity have been analyzed using the current modified analysis technique.

Quantifying Strain via Buckling Instabilities in Surface-Modified Polymer Brushes

A compressive strain applied to bilayer films (e.g. thin film adhered to a thick substrate) can lead to buckled or wrinkled morphologies, which has many important applications in stretchable electronics, anti-counterfeit technology, and high-precision micro and nano-metrology. A number of buckling-based metrology methods have been developed to quantify the residual stress and viscoelastic properties of polymer thin films. However, in some systems (e.g. solvent-induced swelling or thermal strain), the compressive strain is unknown or difficult to measure. We present a quantitative method of measuring the compressive strain of wrinkled polymer films and coatings with knowledge of the "skin" thickness, wrinkle wavelength, and wrinkle amplitude. The derived analytical expression is validated with a well-studied model system, e.g., stiff, thin film (PS) bonded to a thick, compliant substrate (PDMS). After validation, we use our expression to quantify the applied swelling strain of previously reported wrinkled poly(styrene-alt-maleic anhydride) brush surfaces. Finally, the applied strain is used to rationalize the observed persistence length of aligned wrinkles created during atomic force microscopy (AFM) lithography and subsequent solvent exposure.

Stress-dependent temperature effect on the swelling behavior of compacted GMZ bentonite

A series of temperature-controlled swelling pressure and swelling strain tests were performed on Gaomiaozi (GMZ) bentonite to study the temperature effects on the swelling behavior. The influence of sample dry densities (for swelling pressure tests) and applied various vertical stresses (for swelling strain tests) were taken into account. Emphasis was put on the stress-dependent properties of temperature effects. Results show that at a certain temperature, there is a unique relationship between the stress level and the void ratio of saturated bentonite specimens for either the swelling pressure or swelling strain tests. This relationship could be defined as “swelling stable line” (SSL), which was bilinear shaped and reflects a stress-dependent swelling behavior of compacted bentonite. This stress-dependent swelling behavior is attributed to the different hydration mechanisms under lower and higher stresses. A comparison of SSLs at different temperatures shows an obvious stress-dependent behavior of temperature effects on swelling properties. These stress-dependent temperature effects on swelling behavior of GMZ bentonite are further confirmed by data collected from literatures on various types (i.e., Ca- or Na-bentonite) of bentonites: regardless of the predominant cations, the elevation of temperature increased the swelling potential in the lower stresses part of SSL, whereas it reduced the swelling potential in the higher stresses part. This phenomenon is related to the influences of temperature on the swelling processes (i.e., hydration, diffuse double-layer repulsion, and separation of elementary layers) under different stress levels.

Complete coal permeability models from initial to ultimate equilibrium

Coal permeability is a crucial property for coal seam gas production. In previous studies, it was assumed that both matrix blocks and coal bridges share an average equalized gas pressure. This assumption results in an equalized swelling strain within the REV (representative elementary volume). As a result of this assumption, no change in fracture aperture is induced by gas sorption. However, this assumption may contradict the conceptual model under stress-controlled conditions. We hypothesize that this contradiction is due to the inability of current permeability models to consider the impact of non-uniform swelling on the evolution of permeability from initial to ultimate equilibrium. In this study, the aperture change is represented by an averaging method after obtaining the distribution of matrix swelling within the REV. The approach shows the matrix swelling initially reduces the fracture aperture, and the aperture recovers from initial to ultimate equilibrium. This approach has led to a new set of non-equilibrium permeability models under different distributions of matrix deformation. The model results clearly demonstrate that coal permeability evolves even under both constant confining pressures and constant effective stresses. Equilibrium permeability models represent the bounds of permeability change while new non-equilibrium models can fill the gap from the initial equilibrium state (pre-gas injection/extraction) to the ultimate equilibrium state (post-gas injection/extraction) to generate a map of permeability change. Therefore, our non-equilibrium permeability models represent complete evolutions of coal permeability.

Cyclic swell–shrink behaviour of an expansive soil treated with a sulfonated oil

The effects of a sulfonated oil (SO) stabiliser on the swell–shrink properties of an expansive soil were investigated through cyclic wetting–drying tests. The cyclic wetting–drying action led to the reconstruction of the soil microstructure by inducing clay particle aggregation. Accordingly, the greater the number of applied cycles, the lower the swell–shrink potential up to the fourth cycle, beyond which the swelling and shrinkage strains attained elastic equilibrium. At any given cycle, the tendency for swell–shrink reduction was in favour of the SO concentration up to 0·75%, beyond which the excess SO molecules self-associated in the form of aggregates, thereby acting as a ‘lubricant’ rather than a clay-stabilising agent. As a result of SO treatment, the accumulated axial strain progressively transitioned towards a desirable, ‘neutral’ state, with 0·75% SO exhibiting the highest resistance against cyclic wetting–drying. For any given SO concentration, the equalised void ratio–moisture content curves for wetting and drying followed the same S-shaped path, further corroborating that the swelling and shrinkage processes, on achieving elastic equilibrium, become reversible. The shrinkage and liquid limits indicated a progressive transition towards a desirable, aggregated fabric, with 0·75% SO identified as the optimum concentration.

On the Correctness of the Well-Known Mathematical Model of Irradiation-Induced Swelling with the Influence of Stresses in the Problems of Elastic-Plastic Deformation Mechanics

The paper provides results of the study of correctness of the mathematical model that includes the influence of stresses on irradiation-induced swelling of metal in the problems of elastic-plastic deformation mechanics. The present-day approaches to modeling irradiation-induced swelling, which take into account a damaging dose, irradiation temperature, and the effect of the stress state on the swelling deformation, are discussed. The constitutive equations that describe the elasticplastic deformation processes allowing for the influence of a stress mode on the irradiation-induced swelling in metal are put forward. Analysis of these equations has made it possible to find the conditions that ensure correctness of the plasticity equations considered and to make a lower-bound estimate of the maximum permissible value of free swelling and irradiation dose. A priori estimates of the maximum permissible value of free swelling and damaging dose are given for 08Kh18N10T steel under various irradiation temperatures. In the practice of strength design such estimates are needed at the stage of problem formulation in order to analyze adequacy of input data, for they enable one to assess a prior the possibility of solving the problem for a given temperature and irradiation dose. The boundary-value problem that describes non-isothermal processes of elasticplastic deformation including swelling strains has been defined in the form of a nonlinear operator equation. Based on the findings regarding the correctness of the constitutive equations, we have established the existence and uniqueness of the generalized solution and its continuous dependence on applied loads, thermal strains and swelling strains. The convergence of the method of elasticity solutions and the method of variable elasticity parameters has been studied as applied to a thermoplasticity problem including irradiation-induced swelling strains.

Experimental Study on Factors Influencing the Expansive Properties of Disturbed Swelling Rock

In this study the vertical swelling pressure in disturbed expansive soil was evaluated under constant-volume hydration swelling tests. The volume change during inundation was observed under two conditions: constant vertical stress at inundation and constant volume. A swelling stress-strain relationship model of compacted expansive soil is established under a one-dimensional axial load, which is related to the properties of the soil and can be used to predict the swelling stress of compacted soil with high density or strain under a specific axial load. This study can help to predict the swelling stress and strain of compacted expansive rock.

CO2 adsorption and swelling of coal under constrained conditions and their stage-change relationship

The adsorption of CO2 into coal will cause the volumetric swelling of coal body, which is a highly concerned issue for the CO2 enhanced coalbed methane recovery (CO2-ECBM). However, the research of adsorption and swelling of coal is not all-inclusive and their relationship is ambiguous. This paper conducted the experiments regarding the CO2 adsorption and corresponding swelling of coal influenced by multiple factors using the self-designed device. Results show that the adsorption capacity is promoted by the injection pressure and is restrained by confining pressure, temperature and water content, but the thermal-induced swelling strain and moisture-induced swelling strain can offset the swelling loss to some extent for the wet coal at a high temperature. There has a stage-change relationship between swelling strain and adsorption capacity of coal, and the adsorption swelling can be divided into three parts: the slow swelling stage, the rapid swelling stage and the stable swelling stage. Under the action of the external stress, the adsorption swelling develops towards to the interior of coal body first and then develops towards to the external when the swelling stress exceeds the external stress. Different extended directions of adsorption swelling are the main causes of the stage adsorption swelling. The study contributes to the deep understanding for the gas adsorption swelling mechanism and the attenuation-rebound of the coal reservoir permeability during the CO2-ECBM.

Effects of matrix-fracture interaction and creep deformation on permeability evolution of deep coal

A new model considering effects of matrix-fracture interaction and creep deformation on permeability of deep coal is established under the condition of triaxial stress state. An internal swelling coefficient is defined to characterize the degree of matrix-fracture interaction. The internal swelling coefficient, reflecting contribution of matrix swelling deformation by gas adsorption to the change of bulk volume and fracture volume, is introduced to a classical stress-strain constitutive equation. Moreover, the proposed permeability model is validated by experimental data-based permeability estimated by the fractional derivative transient pulse method and the nonlinear least square method is used to determine the model parameters. It is indicated that the permeability decreases gradually in the primary and secondary creep stage, consistent with the physical process in which the initial fracture and pores are gradually compacted during the creep process. In addition, it is found that with the decrease of pore pressure, the proposed permeability model appears to be better than the existed various classical models in term of description of the evolution trend of permeability. The effects of creep deformation and internal swelling coefficient on the permeability model are discussed, indicating that under the condition of constant effective volumetric strain, a small volume of the internal swelling coefficient makes a leading role of the effective volumetric strain in permeability evolution, and a large volume of the internal swelling coefficient leads to a domination role of the adsorption swelling strain increment in permeability evolution of deep coal.

Scalable Manufacturing of Bending-Induced Surface Wrinkles.

The wide range of textures that can be generated via wrinkling can imbue surfaces with functionalities useful for a variety of applications including tunable optics, stretchable electronics, and coatings with controlled wettability and adhesion. Conventional methods of wrinkle fabrication rely on batch processes in piece-by-piece fashion, not amenable for scale-up to enable commercialization of surface wrinkle-related technologies. In this work, a scalable manufacturing method for surface wrinkles is demonstrated on a cylindrical support using bending-induced strains. A bending strain is introduced to a thin layer of ultraviolet-curable poly(dimethylsiloxane) (UV-PDMS) coated on top of a soft PDMS substrate by wrapping the bilayer around a cylindrical roller. After curing the UV-PDMS and subsequently releasing the bending strain, one-dimensional or checkerboard surface wrinkles are produced. Based on experimental and computational analyses, we show that these patterns form as a result of the interplay between swelling and bending strains. The feasibility of continuous manufacturing of surface wrinkles is demonstrated by using a two-roller roll-to-roll prototype, which paves the way for scalable roll-to-roll processing. To demonstrate the utility of these textures, we show that surface wrinkles produced in this manner enhance the light harvesting and thus efficiency of a solar cell at oblique angles of illumination due to their strong light scattering properties.

Constitutive Model of Swelling Gypsum Rock

Swelling of soft rock, such as gypsum rock, is one of the major threats in tunnel engineering, causing structure damages such as floor heave and inward movement of sidewalls during construction and operation. It is of practical significance to study the swelling mechanical behavior of such rocks by tests. Swelling strain tests and swelling stress tests were performed by swelling test apparatus to study the variation of swelling strain with time and the swelling stress‐strain relationship for gypsum rock samples, respectively. Three stages of the swelling strain on the time‐strain curve of gypsum rock samples were noticed, which are defined as rapid swelling stage, slow swelling stage, and steady stage. And it was further found that the swelling strain caused in the slow swelling stage is of 76% of the total swelling strain. A constitutive model is proposed to describe the stress‐strain relationship in swelling considering the swelling deformation and swelling pressure. The proposed model was verified using test data, which shows good agreements in describing the relationship between swelling strain and swelling stress, also in the conditions of maximum swelling strain and maximum swelling stress under lateral restraint situations.

Effect of external hydraulic head on swelling of unsaturated clay

Laboratory testing of the one-dimensional swell of soil (usually unsaturated clay) is generally performed according to ASTM standard D4546. The standard procedure requires that “the specimen is inundated with test water and the one-dimensional wetting-induced swell or collapse strain is measured”. This procedure undoubtedly provides an upper limit to the swell which may be expected under field conditions, and may be relevant to cases in which low lying areas are expected to be inundated as a result of a wetting episode. However, in other cases, wetting of the soil may result from less extreme conditions - for example absorption of water from underlying, wetted layers, or soaking of the lower portion of a swelling layer and resultant upward wetting due to suction forces. The present paper describes a laboratory investigation of the effect of external hydraulic head on swell. The results demonstrate the importance of applying test conditions consistent with those expected in the field situation.

Effects of calcium carbonate on hydro-mechanical properties of bentonite

To simulate characteristic changes of the bentonite mixing with CaCO3 crystals that precipitate from groundwater around the high-level radioactive waste repositories, different amounts of CaCO3 powders were mixed in the bentonite. In this study, four series of bentonite/CaCO3 mixtures were prepared with different contents of CaCO3 powders. A series of swelling, compression and direct shear tests were conducted on the bentonite/CaCO3 samples using deionized water. Terzaghi consolidation theory was adopted to compute the hydraulic conductivity of bentonite/CaCO3 mixtures. The results demonstrated that the final swelling strain decreased with increasing vertical stress and the content of CaCO3 powders. The compression index decreased slightly with increasing CaCO3 content. It was found that as the CaCO3 content increased, the hydraulic conductivity of bentonite/CaCO3 mixtures decreased. There was a peak point in the shear strength of unsaturated samples with the differences of the CaCO3 content. The cohesion of unsaturated samples increased first and then decreased, but saturated samples presented the opposite character. It could be seen from the scanning electron micrograph that the existence of CaCO3 powders filled pores of bentonite/CaCO3 mixtures and made the structure denser.

The mechanical significance of the zonally differentiated collagen network of articular cartilage in relation to tissue swelling

BackgroundWe hypothesise that the Benninghoff arcade fibril structure motif of cartilage is able to predict the swelling response of cartilage. MethodsA total of ten healthy adult bovine patellae were used for this study, yielding 20 paired full depth cartilage samples (half with surface layer intact and half with surface layer removed). Following excision from the bone, samples were allowed to equilibrate first in physiological saline for 2 h, and then in distilled water for another 2 h to maximise the swelling response. Images were captured using a stereomicroscope to measure strain and the fully-swollen samples were fixed in 10% formalin to retain shape for microscopic and ultrastructural imaging. FindingsWe expected all swelling samples with an intact ‘strain-limiting’ surface layer to curl upwards, instead only 70% of them did. For samples without a surface layer, we expected the swelling to be evenly distributed and to remain relatively uncurled; but in 40% of the samples there was a downward curvature (i.e. opposite to that of the previous group). Micro-to-ultrastructural imaging, to determine fibrillar structure and organisation, revealed the deep zone cartilage was an additional counter layer limiting swelling strain, and was the likely cause of the unexpected swelling responses. InterpretationOur expectations that the surface layer alone will influence the swelling response, was based on the assumptions of the Benninghoff arcade model. This study highlights the additional importance of sub-micron scale fibrillar interconnectivity and the role of the deep zone.

Full-field moisture-induced strains of the different tissues of tamarack and red oak woods assessed by 3D digital image correlation

The full-field moisture-induced strains (in-plane) and Z-displacements (out-of-plane) of the different tissues of tamarack and red oak woods were assessed by three-dimensional digital image correlation (3D-DIC). Swelling strains in tangential (Ɛxx) and radial (Ɛyy) directions and Z-displacements in axial direction were measured on the cross section of wood samples from dried condition below P2O5 to moisture adsorption condition at 20 °C and 90% RH. Global swelling coefficients (α) were calculated and compared with 3D-DIC strains. Ɛxx, Ɛyy, and Z-displacement data were extracted from earlywood (EW) and latewood (LW) of tamarack, and from three tissue zones of red oak: large vessel zone of the earlywood (EW-v), fiber-dominated (LW-Fiber) and axial parenchyma-dominated (LW-Pa) zones of the latewood. The localized full-field strains were matched with density data obtained by X-ray densitometry. Tamarack wood had a homogeneous Ɛxx, while different Ɛyys were observed for EW and LW. Red oak wood had a more complex mapping of full-field strains, in which the effects of the broad rays on Ɛxx and differences between tissues on Ɛyy appear. A discussion about the radial density profile data and the full-field strains at the tissue level as well as the anisotropic behavior of different tissues is presented for both species. An opposite behavior was found for the EW and LW of tamarack in the longitudinal direction (Z-displacement), showing that EW swells and LW shrinks after moisture adsorption. For red oak, EW-v also swelled and LW-Fiber shrank in the longitudinal direction. LW-Pa zone also shrank after adsorption but to a lower degree.

Experimental study on the 1-D free swelling of compacted bentonite

This paper presents a new designed 1-D free swelling test of compacted bentonite in glass tubes to simulate the process by which the bentonite cushion in the nuclear waste disposal reservoir swells and squeezes into the crack after absorbing the fissure water from surrounding rock. Deionized water and NaCl, Na2SO4, CaCl2 solutions with different concentrations were used as soaking solutions, and the change of the specimen height with time was recorded until the swelling completed. The effects of initial dry density, initial water content, and soaking solution concentration and type on the swelling deformation of bentonite were analyzed. Results show that the maximum swelling strain, almost independent from initial water content, increases with the initial dry density. The increase in the concentration of the salt solution reduces the free swelling deformation, and the degree of inhibition is related to the type of the salt solution. The effect of the concentration and type of the salt solution on swelling property can be uniformly reflected by the osmotic suction that acts as an additional stress applied on bentonite and is quantified as osmotic pressure item of the total effective stress proposed previously that controls the swelling strain of compacted bentonite. Then, the maximum swelling strains of the compacted bentonite under different soaking solutions in 1-D free swelling test can be predicted by a uniform power-law relationship with the total effective stress.

LABORATORY BASED PARAMETRIC STUDY ON THE SWELL RESPONSES IN EXPANSIVE VERTOSOLS

Expansive grey Vertosols are predominant in Australia, especially in Queensland. These soils induce a significant amount of swell strain on the lightweight structures founded on/in these soils when soil moisture changes due to climatic influence. According to AS2870: Residential slab and footing design code (AS2870, 2011) and available literature, active zone depth which contributes to the climate induced-soil displacement in Queensland can be up to 5m. To design lightweight structures founded within the active zone depth, it is imperative to understand swelling behavior of expansive grey Vertosols. The resultant swell strain of these expansive soils is primarily a function of initial water content or initial soil suction and overburden pressure (surcharge). However, there is an extremely limited amount of data available for unsaturated swelling characteristics of expansive soils in Queensland. In this study, a series of conventional oedometer tests were conducted to investigate the effect of the initial water content, initial soil suction and the surcharge on the swelling behavior of expansive grey Vertosol that is predominant in South-East Queensland. The swell strain of expansive grey Vertosol displayed greater sensitivity to surcharge when compared to initial water content or suction. Developed relationship between swell strain per unit change in volumetric water content and surcharge depicted statistically strong (R2 = 0.89) agreement. The application of the knowledge gathered from this study will benefit the decision making in semi-arid regions when building lightweight structures on grey Vertosol.

Hygroscopic swelling of moso bamboo cells

Bamboo is a natural cellulosic material which is strongly reactive to water. Its hygroscopic behavior affects almost all other physical and mechanical properties of bamboo. This study investigated the hygroscopic swelling of moso bamboo (Phyllostachys edulis) cells in response to changes in environmental humidity using a confocal laser scanning microscope. The swelling strains of fiber, vessel and parenchyma cells were obtained and compared. The interactions between adjacent cells were also analyzed. The results demonstrated that the swelling strain of the cell walls increased with relative humidity, and was independent of its location and orientation, but dependent on the cell type. The absolute swelling of fiber cells was highest among all cells because of dominantly high fiber wall thickness. In contrast, the relative swelling of fiber cells was lowest due to constraint of adjacent fibers. Fiber cells governed the deformation and movement of other cell lumens. The difference between tangential and radial swelling of bamboo was insignificant compared to that of wood, possibly due to the similar microfibril angle in both directions, the circular cell shape and the random embedment of vascular bundles.

Coupled effects of saline solutions and temperature on the swelling deformation property of GMZ bentonite-sand mixtures

Based on the results of one-dimensional free swelling tests, the coupled effects of NaCl-Na2SO4 solutions and temperature on the swelling deformation property of compacted GMZ bentonite-sand mixtures were analyzed. The concentrations of the NaCl-Na2SO4 solutions were 0, 0.008, 0.04, 0.08 and 0.16 mol/L, the temperatures were 20 °C, 40 °C, 60 °C, 80 °C and 90 °C and the sand contents were 0, 30 and 50%. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were also performed to find the influences of the temperature, solution concentration and sand content on the mineral composition and microstructure. The results showed that the maximum swelling strain of the specimens increased with an elevated temperature, while it decreased with increases in the solution concentration and sand content. The swelling process was accelerated by the rising temperature. The XRD tests indicated that the combined effect of a high temperature and a high solution concentration may have caused more Na+ from the saline solutions to enter the interlayer, partly displacing the divalent cations. The MIP tests demonstrated that adding sand to the bentonite could reduce the amount of inter-granular pores and increase the intra-aggregate pores. These findings are advantageous to the transfer of heat and pour fluid in the specimens; and thus, the swelling deformation capacity of the bentonite-sand mixtures was higher than that of pure bentonite under the same conditions.

Effect of wetting–drying–freezing–thawing cycles on the swelling behaviour of the Yanji mudstone

One of the most important characteristics of mudstones is their susceptibility to swelling upon absorption of water, which is influenced by climatic processes. This study investigated the swelling pressure and strain of the Yanji mudstone subjected to wetting–drying (W–D), freezing–thawing (F–T) and wetting–drying–freezing–thawing (W–D–F–T) cycles. The swelling curves were analysed using a simulation of the logistic function, and the coefficient of initial swelling (Cis), coefficient of primary swelling (Cps), coefficient of secondary swelling (Css), and ultimate swell were derived from the mathematical simulation. The results show that the cyclic treatments can significantly influence the swelling kinetics and ultimate swell. As the number of treatment cycles increases, Cis increases and then decreases due to the competition between the increasing permeability and the decreasing swelling potential induced by the propagation of cracks and large voids, while Cps and Css decrease because of the compaction and contraction of the aggregates after cyclic treatments. The ultimate swelling pressure and ultimate swelling strain decrease with increasing treatment cycles and the relationships among these parameters were also established, allowing the ultimate swelling pressure and strain of the Yanji mudstone under the full range of seasonal variation to be predicted.