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This study presents new Nano-enhanced Phase Change Materials, NePCMs, formulated as dispersions of functionalized graphene nanoplatelets in a poly(ethylene glycol) with a mass-average molecular mass of 400 g·mol−1 for possible use in Thermal Energy Storage. Morphology, functionalization, purity, molecular mass and thermal stability of the graphene nanomaterial and/or the poly(ethylene glycol) were characterized. Design parameters of NePCMs were defined on the basis of a temporal stability study of nanoplatelet dispersions using dynamic light scattering. Influence of graphene loading on solid-liquid phase change transition temperature, latent heat of fusion, isobaric heat capacity, thermal conductivity, density, isobaric thermal expansivity, thermal diffusivity and dynamic viscosity were also investigated for designed dispersions. Graphene nanoplatelet loading leads to thermal conductivity enhancements up to 23% while the crystallization temperature reduces up to in 4 K. Finally, the heat storage capacities of base fluid and new designed NePCMs were examined by means of the thermophysical properties through Stefan and Rayleigh numbers. Functionalized graphene nanoplatelets leads to a slight increase in the Stefan number.

Mechanical thrombectomy can be significantly affected by the mechanical properties of the occluding thrombus. In this study, we provide the first characterisation of the volumetric behaviour of blood clots. We propose a new hyperelastic model for the volumetric and isochoric deformation of clot. We demonstrate that the proposed model provides significant improvements over established models in terms of accurate prediction of nonlinear stress–strain and volumetric behaviours of clots with low and high red blood cell compositions. We perform a rigorous investigation of the factors that govern clot occlusion of a tapered vessel. The motivation for such an analysis is twofold: (i) the role of clot composition on the in vivo occlusion location is an open clinical question that has significant implications for thrombectomy procedures; (ii) in vitro measurement of occlusion location in an engineered tapered tube can be used as a quick and simple methodology to assess the mechanical properties/compositions of clots. Simulations demonstrate that both isochoric and volumetric behaviours of clots are key determinants of clot lodgement location, in addition to clot-vessel friction. The proposed formulation is shown to provide accurate predictions of in vitro measurement of clot occlusion location in a silicone tapered vessel, in addition to accurately predicting the deformed shape of the clot.

This research aims at studying the stability and thermophysical properties of nanofluids designed as dispersions of sulfonic acid-functionalized graphene nanoplatelets in an (ethylene glycol + water) mixture at (10:90)% mass ratio. Nanofluid preparation conditions were defined through a stability analysis based on zeta potential and dynamic light scattering (DLS) measurements. Thermal conductivity, dynamic viscosity, and density were experimentally measured in the temperature range from 283.15 to 343.15 K and nanoparticle mass concentrations of up to 0.50% by using a transient plate source, a rotational rheometer, and a vibrating-tube technique, respectively. Thermal conductivity enhancements reach up to 5% without a clear effect of temperature while rheological tests evidence a Newtonian behavior of the studied nanofluids. Different equations such as the Nan, Vogel-Fulcher-Tamman (VFT), or Maron-Pierce (MP) models were utilized to describe the temperature or nanoparticle concentration dependences of thermal conductivity and viscosity. Finally, different figures of merit based on the experimental values of thermophysical properties were also used to compare the heat transfer capability and pumping power between nanofluids and base fluid.

In this paper, the volumetric collapse of an unsaturated soil, upon soaking to saturation under a certain stress level, is referred to as soaking collapse. The soaking collapse for a soil under virgin condition is assumed equal to the difference between the soil’s virgin compression line (VCL) and its normal consolidation line (NCL) at saturated condition based on results of oedometric constant water content compression and soaking tests performed on a compacted Nanyang expansive clay. A one-parameter model is proposed to describe the variation of the soaking collapse with the pre-soaking degree of saturation under virgin condition once (1) a soil’s yielding point can be clearly defined and (2) the degree of saturation during virgin compression is known. This model can be used to predict the VCL from the NCL. Data of the Nanyang expansive clay, along with published data of nine soils that were derived from constant water content or constant suction compression tests (including oedometric and triaxial compression), were used to calibrate and validate the model. It is shown that the model, when combined with a degree of saturation-volume model and the information of yielding and NCL, can predict reasonable VCLs for all examined soils and suitably capture several characteristics of the VCL including the nonlinearity and pressurised saturation. A constant model parameter of 1.5 is found suitable for all examined soils. The model is also used to predict the VCLs of two compacted soils from the constant degree of saturation compression, which is a recently developed testing technique to evaluate the compression behaviour of unsaturated soils, with reasonable agreement achieved.

Assessing soil deformation leading to collapse is often conducted through a suction-controlled method, which can be time-intensive. In this study, the collapse deformation of compacted clay was investigated by conducting time-saving and convenient water content-controlled tests. The compacted clay specimens, each with a unique initial void ratio, were subjected to water retention experiments. The water content-controlled oedometer apparatus performed tests involving compression, wetting, and subsequent recompression. Observed experimental results indicate that water content has an inverse relationship with suction, with suction increasing as water content decreases, suggesting an inverse relationship between the two variables. In compression tests performed at a constant water content, water saturation increases and suction decreases as the void ratio decreases. Wetting leads to a decrease in void ratio as the saturation level rises, gradually declining along the wetting path until it aligns with the compression line of fully saturated soil. The compression lines at varying suction levels are established through theoretical analysis of water retention and water content-controlled compression test results. In addition, the collapse deformation is well predicted with a concise formula related to pore gas saturation. In this way, this study provides a quick and effective method for evaluating the hydro-mechanical properties of unsaturated soils.

An experimental study was carried out to investigate the effects of the mean net stress and suction history on the initial shear stiffness, G 0 , of a compacted clayey silt. Isotropic tests were performed using two suction-controlled devices, a triaxial cell and a resonant column torsional shear (RCTS) cell, so as to investigate the volumetric behaviour of this material. As for saturated soils, one can expect to find a strong correlation among stress history, volumetric state, and G 0 . Initial shear stiffness was measured almost continuously along various isotropic stress paths, including compressions and drying-wetting single stages or cycles, by using the RCTS cell. The collected data demonstrate a strong dependency of G 0 on mean net stress (p - u a ) and suction (u a - u w ). Cycles of suction, in particular increasing suction beyond the past maximum value, induce significant accumulation of irreversible strains and increase of stiffness, confirming that G 0 is not univocally related to the stress state (p - u a , u a - u w ).Key words: unsaturated, compacted, small strain, stiffness, volumetric behaviour, stress history.

Multi-scale approaches of constitutive modeling require an intermediate scale linking the variables in macroscopic scale (incremental stress and strain) to variables in microscopic scale (contact force and contact displacement). In this paper, we introduce a mesoscopic scale, in which the granular material is tessellated into small loops by contact network. Then numerical biaxial tests from different initial states by DEM modeling, is performed to investigate how the meso-structure (mesoscopic loops) evolves along the drained biaxial loading path. Results suggest that the procedure of the biaxial test is accompanied with the exchange between small, dense structures and big, loose structures. The macroscopic dilatancy primarily originates from this exchange. In dense and intermediate specimens the meso-structure evolution is found not to be consistent with the evolution of the macroscopic volumetric strain during contractancy phases. This inconsistency has led to interpret the elastic and the plastic parts of the volumetric strain from a meso-scale viewpoint. It is shown that the initial contractancy in dense and intermediate specimens is largely an elastic process, which is highly dependent on elastic parameters of the material.

We explore the formulation of nearly incompressible behaviors at finite strain in the context of a hybrid or a mixed energy. Such an energy is a function of both an isochoric deformation and a pressure-like quantity that can be considered as an internal variable. From thermodynamical and physical considerations, new energy functions are developed to correctly describe both nearly incompressible elasticity and thermoelastic behaviors. We discuss the advantages of such a formulation; in particular, we show that this approach makes it possible to unify the variational and the thermodynamical formulations in the nearly incompressible context without using Lagrange multipliers or other specific variational principles.

This article presents the results of experimental work carried out both in situ (coring; pressuremeter test) and in the laboratory (drying-wetting and oedometric tests) to describe the volumetric behavior on drying-wetting path of a swelling clayey soil of eastern Algeria. In order to perform drying-wetting tests the osmotic technique and saturated salts solutions were used. These suction-imposed methods have gained widespread acceptance as reliable methods for imposing suction on soil specimens. They allowed to sweep a wide range of suctions between 0 and 500 MPa. The ability to impose suction on soil specimens allows for drying and wetting stress paths to be applied to evaluate resulting changes in state parameters (void ratio, degree of saturation and water content). These paths were carried out on specimens with different initial states. Slurries of soil were used to characterize the reference behavior, while the undisturbed soil samples allow to describe the behavior of material under in situ conditions. In the last part of this article and to specify the behavior observed in the saturated domain, a comparison between the resulting deformations of the drying-wetting test and those resulting from the oedometric test was made.

This is the follow-up paper to Vassallo et al. (2007), which discussed the experimentally observed small-strain behaviour of an unsaturated compacted silt. The influence that suction and, more in general, mean net stress - suction history has on the initial shear stiffness was analysed and ascribed to the accumulation of irreversible volumetric strains. In this study, a model able to predict the observed behaviour is proposed, based on classical unsaturated soil volumetric hardening elastoplastic formulations. Starting from the interpretation of the results relative to simple stress paths, such as preliminary equalization and loading-unloading compression, the results of \"complex\" stress paths, such as those including drying-wetting cycles, have subsequently been modelled by introducing some additional parameters.Key words: unsaturated, compacted, small strain, stiffness, volumetric behaviour, stress history.