共查询到11条相似文献,搜索用时 15 毫秒
1.
The process of capillary impregnation of porous materials is studied numerically. A physicomathematical model of liquid diffusion
in a porous sample is proposed. The model involves an analytical presentation of the diffusion coefficient, which describes
available experimental data. A method of solving one-dimensional unsteady problems of impregnation is developed and tested
on a self-similar solution of the corresponding boundary-value problem of impregnation. If the impregnation process is sufficiently
long, the motion of the liquid in the sample is described by a stable self-similar solution. A classification of moisture
diffusion on the basis of the initial humidity on the sample boundary is proposed.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 42–51, January–February, 2009. 相似文献
2.
P. C. Philippi P. Rosendo Yunes C. P. Fernandes F. S. Magnani 《Transport in Porous Media》1994,14(3):219-245
Building materials such as cement mortars and concrets present a very broad distribution of pore sizes, from some tenths of angstroms to several micra. This distribution is very important in establishing their macroscopic properties, e.g., vapor adsorption and desorption and moisture transfer. It is, thus, important to develop procedures to analyze the microstructure of these materials in the full range of pore sizes. In the present work, two complementary methods are used for obtaining the pore sizes distribution of a cement and lime mortar, often used as a building coating material. Electron scanning microscopy is used for pore sizes greater than 1250 å, from a sequence of pictures taken with magnifications from 25x to 12500x, for highly polished surfaces. The heterogeneous spatial distribution of pores is discussed, related to the problem of the geometrical reconstitution of porous structure. For pore sizes smaller than 1250 å, adsorption isotherms obtained at 30 C are used. Molecular physical adsorption is supposed to be the dominant adsorption mechanism in a wide range of relative humidities and modeled using the De Boer and Zwikker theory. This is confirmed by a very high correlation coefficient equal to 0.994 for the present case, for values of RH smaller than 80%. Capillary condensation is supposed to become significant at the point where the adsorption curve deviates from the linear behavior as predicted by the De Boer and Zwikker theory, and the Broekhoff and De Boer theory is used for predicting the pore size distribution from the adsorption isotherm,starting from the deviation point andincreasing RH. The results show the pore size distribution between 200 å and 13m. 相似文献
3.
A lower bound approach to the yield loci of porous materials 总被引:1,自引:0,他引:1
A lower bound approach is proposed for the first time to solve the macroscopic yield loci of porous materials. The results
are then compared with Gurson's upper bound yield loci and those of the experiments. It is shown that the present analysis
is much more in accordance with the experimental results than the Gurson's. 相似文献
4.
《International Journal of Solids and Structures》2014,51(25-26):4316-4326
In this paper, an exponential framework for strain energy density functions of elastomers and soft biological tissues is proposed. Based on this framework and using a self-contained approach that is different from a guesswork or combination viewpoint, a set strain energy density functions in terms of the first and second strain invariants is rebuilt. Among the constructed options for strain energy density, a new exponential and mathematically justified model is examined. This model benefits from the existence of second strain invariant, simplicity, stability of parameters, and the state of being accurate. This model can capture strain softening, strain hardening and is able to differentiate between various deformation-state dependent responses of elastomers and soft tissues undergoing finite deformation. The model has two material parameters and the mathematical formulation is simple to render the possibility of numerical implementations. In order to investigate the appropriateness of the proposed model in comparison to other hyperelastic models, several experimental data for incompressible isotropic materials (elastomers) such as VHB 4905 (polyacrylate rubber), two various silicone rubbers, synthetic rubber neoprene, two different natural rubbers, b186 rubber (a carbon black-filled rubber), Yeoh vulcanizate rubber, and finally porcine liver tissue (a very soft biological tissue) are examined. The results demonstrate that the proposed model provides an acceptable prediction of the behavior of elastomers and soft tissues under large deformation for different applied loading states. 相似文献
5.
Sophie Cariou Franz-Josef Ulm Luc Dormieux 《Journal of the mechanics and physics of solids》2008,56(3):924-952
Recent progress in instrumented nanoindentation makes it possible today to test in situ phase properties and structures of porous materials that cannot be recapitulated ex situ in bulk form. But it requires a rigorous indentation analysis to translate indentation data into meaningful mechanical properties. This paper reports the development and implementation of a multi-scale indentation analysis based on limit analysis, for the assessment of strength properties of cohesive-frictional porous materials from hardness measurements. Based on the separation-of-scale condition, we implement an elliptical strength criterion which results from the nonlinear homogenization of the strength properties of the constituents (cohesion and friction), the porosity and the microstructure, into a computational yield design approach to indentation analysis. We identify the resulting upper bound problem as a second-order conical optimization problem, for which advanced optimization algorithms became recently available. The upper bound yield design solutions are benchmarked against solutions from comprehensive elastoplastic contact mechanics finite element solutions and lower bound solutions. Furthermore, from a detailed parameter study based on intensive computational simulations, we identify characteristic hardness-packing density scaling relations for cohesive-frictional porous materials. These scaling relations which are developed for two pore-morphologies, a matrix-pore morphology and a polycrystal (perfect disordered) morphology, are most suitable for the reverse analysis of the strength parameters of cohesive-frictional solids from indentation hardness measurements. 相似文献
6.
Analytic plastic potential for porous aggregates with matrix exhibiting tension-compression asymmetry 总被引:1,自引:0,他引:1
This paper is devoted to modeling the effects of the tension-compression asymmetry of the matrix on yielding of the void-matrix aggregate. The matrix plastic behavior is described by the Cazacu et al. [2006. Orthotropic yield criterion for hexagonal closed packed metals. Int. J. Plasticity 22, 1171-1194] isotropic yield criterion, which captures strength differential effects. Using an upper-bound approach, a new analytic isotropic plastic potential for a random distribution of spherical voids is obtained. The derived analytic potential is sensitive to the third invariant of the stress deviator and displays tension-compression asymmetry. In the case when the matrix material has the same yield in tension and compression, it reduces to Gurson's [1977. Continuum theory of ductile rupture by void nucleation and growth: Part I: Yield criteria and flow rules for porous ductile media. J. Eng. Mater. Technol. Trans. ASME Ser. H 99, 2-15.] criterion. Furthermore, the proposed criterion predicts the exact solution of a hollow sphere loaded in hydrostatic tension or compression. The accuracy of the proposed analytical criterion is assessed through comparisons with finite-element cell calculations. 相似文献
7.
8.
Development of a portable shear test fixture for low modulus porous (foam) materials 总被引:2,自引:0,他引:2
The shear properties of brittle and highly porous carbon (graphitic) foam cannot be measured reliably with most standard test
methods, such as single rail, double rail, Iosipescu shear, etc. A new testing device has been developed to accurately measure
the shear stiffness and strength of carbon foam or other porous materials. Specimens of cylindrical cross section are used
to reduce the high stress concentration that normally occurs in the vicinity of the grip section. Since strain gages could
not be installed on the specimen surface (due to porosity), the shear strain is determined from the specimen end rotation.
A high resolution in the rotational measurement is achieved by using a stepper motor with multiple gear reduction. In view
of testing low modulus material, the load cell of the fixture was mounted onto an axial roller to relieve the axial constraint
while twisting the specimens. The accuracy of the measurement and calibration of the test fixture has been demonstrated by
measuring the shear modulus of two plastic (polyvinyl chloride (PVC) and urethane). 相似文献
9.
This paper is concerned with the modeling of randomness in multiscale analysis of heterogeneous materials. More specifically, a framework dedicated to the stochastic modeling of random properties is first introduced. A probabilistic model for matrix-valued second-order random fields with symmetry propertries, recently proposed in the literature, is further reviewed. Algorithms adapted to the Monte Carlo simulation of the proposed representation are also provided. The derivations and calibration procedure are finally exemplified through the modeling of the apparent properties associated with an elastic porous microstructure containing stochastic interphases. 相似文献
10.
We present pulse shaping techniques to obtain compressive stress-strain data for elastic-plastic materials with a split Hopkinson
pressure bar. The conventional split Hopkinson pressure bar apparatus is modified by placing a combination of copper and steel
pulse shapers on the impact surface of the incident bar. After impact by the striker bar, the copper-steel pulse shaper deforms
plastically and spreads the pulse in the incident bar so that the sample is nearly in dynamic stress equilibrium and has a
nearly constant strain rate in the plastic response region. We present analytical models and data that show a broad range
of incident strain pulses can be obtained by varying the pulse shaper geometry and striking velocity. For an application,
we present compressive stress-strain data for 4340 Rc 43 steel. 相似文献
11.
Based on Huang's accurate tri-sectional nonlin- ear kinematic equation (1997), a dimensionless simplified mathematical model for nonlinear flow in one-dimensional semi-infinite long porous media with low permeability is presented for the case of a constant flow rate on the inner boundary. This model contains double moving boundaries, including an internal moving boundary and an external mov- ing boundary, which are different from the classical Stefan problem in heat conduction: The velocity of the external moving boundary is proportional to the second derivative of the unknown pressure function with respect to the distance parameter on this boundary. Through a similarity transfor- mation, the nonlinear partial differential equation (PDE) sys- tem is transformed into a linear PDE system. Then an ana- lytical solution is obtained for the dimensionless simplified mathematical model. This solution can be used for strictly checking the validity of numerical methods in solving such nonlinear mathematical models for flows in low-permeable porous media for petroleum engineering applications. Finally, through plotted comparison curves from the exact an- alytical solution, the sensitive effects of three characteristic parameters are discussed. It is concluded that with a decrease in the dimensionless critical pressure gradient, the sensi- tive effects of the dimensionless variable on the dimension- less pressure distribution and dimensionless pressure gradi- ent distribution become more serious; with an increase in the dimensionless pseudo threshold pressure gradient, the sensi- tive effects of the dimensionless variable become more serious; the dimensionless threshold pressure gradient (TPG) has a great effect on the external moving boundary but has little effect on the internal moving boundary. 相似文献