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A random generation method of periodic mesostructures of soil-rock mixtures based on random polygon is proposed and used in the generation of an RVE model. A code for generating a periodic mesh and periodic boundary is developed for the numerical simulation. Macroscopic elastic parameters of the SRMs are calculated based on the simulation using numerical homogenization. The elastic modulus shows a size effect, namely, the modulus deceases gradually with an increase in the model size. The border effect is related to the model size and is large in small-sized models. Rock aggregates arranged in a certain direction induce property anisotropy.

Because of the complex geological structure, determination of the field mechanical parameters of the columnar jointed rock mass (CJRM) was a challenging task in the design and construction of the Baihetan hydropower plant. To model the mechanical behaviour of the CJRM, uniaxial compression tests were conducted on artificial CJRM specimens with geological structure similar to that found in the actual CJRM. Based on the test results, the anisotropic deformation and strength were mainly analysed. The empirical correlations of evaluating the field mechanical parameters were derived based on the joint factor approach and the modulus reduction factor method. The findings of the physical model tests were then used to estimate the field moduli and unconfined compressive strengths of the Baihetan CJRM. The results predicted by physical model tests were compared with those obtained from the field tests and the RMR classification system. It is concluded that physical model tests were capable of providing valuable estimations on the field mechanical parameters of the CJRM.

In this work, the Al/GO/Si/Al RRAM device was fabricated with solution-processed graphene oxide (GO) thin film at low temperature (50 □). A superior electrical performance and stable operation of the device has been achieved showing typical bipolar resistive switching characteristics with operation voltage lower than 3 V, retention property sustained over 104 s and endurance over 102 cycles. The results suggest that the solution-processed GO thin films exhibit great potential for use in the flexible device.

This study develops a coupled elastoplastic damage model for brittle rocks within the framework of irreversible thermodynamics. In the model, degradations in the deformation and strength of rocks induced by damage are considered in the elastic stiffness matrix and plastic yield criterion. The thermodynamic force associated with damage is expressed as a state function of elastic strain and the internal plastic variable. The damage potential and criterion, as functions of the thermodynamic force, are constructed to describe the damage evolution of rocks, and to determine whether they are damaged, respectively. Constitutive relationships, and their numerical formulations of a return mapping algorithm for finite element method implementation, are deduced under three different loading conditions: damage, plastic and coupled plastic damage. For engineering application, the developed model is implemented in the finite element programme Abaqus as a user-defined material model (UMAT). The coupled model is then used for simulating the re-distributed stress fields, displacement and EDZs of the sidewall rock mass around the underground powerhouse of the Wudongde hydropower plant.

A micromechanics-based plastic damage model including localised failure is proposed in the present work for heterogenous materials which can be treated as a porous matrix reinforced by mineral inclusions. This model explicitly considers the influences of pores and inclusions volume fractions, also the solid phase dilatancy on the overall mechanical performance. The induced damage in solid phase is also considered. Based on this two-scale model, the bifurcation analysis is performed to detect both the onset and orientation of localization band. Numerical simulations are carried out for different cases. It is found that the material’s microstructure affects importantly the onset point of the localization and the post-localization behavior. As an example of validation, the proposed model enhanced with localization analysis is then adopted to predict the overall mechanical response before and post localization of this typical claystone. Comparing with the experimental results, the capacity of this enhanced modelling is clearly demonstrated.

The conformal load-bearing antenna structure is a new multidisciplinary concept of aircraft structure, in which a microstrip antenna is layered into a composite material structure. For the manufact...

In this paper, we present a numerical modeling of chemo-mechanical behaviour of sandstone. An internal variable is introduced in this model for the purpose of describing pH effect on elasto-plastic properties. A new chemo-elasto-plastic model is proposed for sandstone. The proposed model is applied to predict material responses in triaxial compression tests of sandstone after soaking in different pH acidic solutions. We concluded with good agreement between numerical simulations and experimental data.

Spray forming offers attractive possibilities for the production of high speed steels technically and economically. In this paper, 10V high speed steel billets were produced through spray forming using a two-atomiser scanning facility. Its microstructure, phase composition, chemical composition and hardness were examined using a variety of techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Results showed that the as deposited 10V steel billet has a density over 99·6% of theoretical value. The microstructure is composed of the equiaxed grains with a mean size of less than 20 μm and Vanadium rich MC type carbides. The steel obtained by spray forming has a uniform carbide distribution. No measurable macrosegregation is found. This can be explained by rapid solidification of spray forming for microstructure refining. The hardness of the as deposited 10V steel reaches 42 HRC. Post-thermomechanical processing is r...

The effects of hot extrusion on microstructural evolution in spray formed GH738 were investigated using X-ray diffraction, scanning electron microscopy and electron backscatter diffraction. After hot extrusion, the refined and uniform microstructures showed entirely dynamic recrystallisation (DRX) characteristics that the mean grain size was lower than 10 μm. Decreasing the extrusion temperature can achieve smaller DRX microstructures as a result of the γ′ phase, which can effectively inhibit the recrystallisation and grain growth during deformation. The carbides precipitating in the slow cooling rate after hot isostatically pressing (HIP) could be broken and distributed along the extrusion axis as a typical flow line during the extrusion. HIP can make the γ′ phase grow, while extrusion can refine it into a nearly spherical state.

With complex mechanics character and under the action of compression and tension in tri-direction, rock will show coupled plastic-damage mechanism as its basic character. Phenomenological coupled elastic-plastic-damage constitutive model with internal variable is proposed based on thermal mechanics theory, elastic law and macro damage mechanics. Numerical experiments on this model and analyze the model character. The result shows that the coupling model could realize rocks softening behavior brought about by damage and strength enlargement caused by confining pressure increasing.

Many experiments conducted under the three-dimensional stress condition reveal that damage of brittle rocks shows obvious deformational and time-dependent effect. Based on triaxial rheological test results, the creep behaviours and creep rupture characteristics of metamorphic volcanic fine conglomerate were investigated. It is found that the test results agree well with numerical curve, and the relationship between creep damage variable and loading time can be fitted by an exponential function. By analysing the tertiary creep, a new nonlinear viscoplasticity model on the basis of creep damage was proposed, and then, the three-dimensional nonlinear creep damage constitutive equations were deduced and validated by tests. Comparisons between numerical predication and test data show that this nonlinear creep damage model is valid and reasonable. Therefore, it can better describe the complete creep phases of the metamorphic volcanic fine conglomerate, which include primary creep, secondary creep and tertiary c...

The fluidities of commercial AZ91D and newly developed Mg–3Nd–0·2Zn–Zr (wt-%) (NZ30K) magnesium alloys were investigated at the same superheat temperature (Tpouring−Tliquidus) and temperature difference between solidus line and mould temperature (TDSM) (Tsolidus−Tmould) conditions. The results indicate that in the range of superheat 60–150°C and TDSM 400–100°C, the increases in both pouring temperature and mould temperature can effectively improve the fluidities of both AZ91D and NZ30K alloys. The flow lengths of AZ91D and NZ30K alloys could be estimated approximately by and (ΔT: superheat; T: pouring temperature; T0: mould temperature). In order to achieve better fluidity in permanent mould casting, the ranges of pouring and mould temperatures are suggested to be 718–748 and ≧268°C for AZ91D alloy, and 760–790 and ≧350°C for NZ30K alloy respectively.

International audience; This paper presents a unified micromechanics-based damage model for instantaneous and time-dependent inelastic behaviors of brittle rocks subjected to compressive stresses. The constitutive model is formulated in a combined homogenization/thermodynamics framework. The inelastic deformation is induced by frictional sliding along closed cracks, and strongly coupled with damage evolution by crack growth. Material degradation is described by a scalar-valued internal damage variable that is decomposed into two parts: an instantaneous part induced by applied stresses and a time-dependent part by subcritical cracking due to stress corrosion. Based on the system free energy determined with the Mori–Tanaka homogenization scheme, we propose a Coulomb-type friction criterion, which serves simultaneously as the yielding function and plastic potential, implying the use of an associated flow rule. An instantaneous damage criterion based on the conjugated force associated with the damage variable and a time-dependent damage criterion in terms of progressive evolution of microstructure are introduced. For the latter, an efficient computational algorithm is explored to solve numerically the strain history-dependent integration. As the first phase of validation, the proposed model is finally applied to simulate two typical brittle rocks, Dagangshan diabase and Xiangjiaba sandstone.

Bio-oils were produced from pyrolysis of sewage sludge in a horizontal tubular furnace under the anoxic or anaerobic conditions, by varying operating parameters and moisture content (MC) of the feedstock. Physicochemical properties of the obtained bio-oil (such as density, acid value, kinematical viscosity, high heating value and flash point) were analysed and compared with Chinese fuel standards. Tend, RT and β were found critical to control the yield and physico-chemical properties of bio-oil products. The relative importance of various parameters such as Tend, RT, β and MC was determined and the optimum values for the lowest kinematic viscosity and acid value and the highest yield of the bio-oil were achieved using the orthogonal matrix method. The parameters 550°C, 45 min, 5°C min(-1) and MC of 10% were found effective in producing the bio-oils with most of the desirable physico-chemical properties and yield. Benefit analysis was conducted to further optimize the operating parameters, considering pyrolysis treatment, comprehensive utilization of the pyrolysis products and final disposal of sewage sludge; the results showed the best economy of the pyrolysis parameters 450°C, 75 min, 3°C min(-1) and MC of 10%. The char obtained under this condition may serve as a microporous liquid adsorbent, while the bio-oil may serve as a low grade fuel oil after upgrading it with conventional fuel oil and deacidification. Pyrolysis products may become economically competitive in addition to being environment friendly.

International audience; A discrete viscoplastic damage model is proposed for the description of time-dependent behaviour of quasi-brittle rocks. This model is inspired by micromechanical considerations. Rocks are considered as quasi-brittle materials containing a spatial distribution of microcracks. Viscoplastic strains of rocks are generated by the time-dependent frictional sliding of microcracks surfaces while the damage of rocks is related to the growth of microcracks. The two inelastic mechanisms are coupled. The model is formulated in the framework of discrete thermodynamics of irreversible processes. The local strains and stresses applied to microcracks are related to the macroscopic counterparts through appropriate kinematic and static conditions. Specific viscoplastic flow rule as well as damage evolution law is defined for each family of microcracks. The validity of proposed model is verified through comparisons between numerical results and experimental data in triaxial compression tests and creep tests for sandstone.