Modeling the cracking process of porous media due to moisture evaporation
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Shrinkage cracking is a common phenomenon in soils and cementiously stabilized soils that often leads to water infiltration and eventually causes serious pavement distress. Drying shrinkage during evaporation of moisture is one of the main reasons for shrinkage cracking. This study proposes a methodology to investigate the cracking process during drying shrinkage using finite element analysis. The migration of moisture is analogized to heat transfer process and utilizing the similarity between the sets of differential equations and boundary conditions, the heat module in Abaqus finite element software is used to analyze the initiation and propagation of cracking during drying shrinkage. It is found that shrinkage cracking initiates due to moisture gradient from evaporation. Minor cracks also occurred and expanded during the drying process.The reason of porosity formation,effect of pressure on porosity and linking of pores in metallic porous material were studied.Several groups of samples were made on moulding press and geometrical model of porosity formation was established to explain the mechanism.The porosity of sintered samples was observed on microscope,calculated and measured.The linking of pores was proved by measured permeability.The results showed that the samples prepared have high porosity and the pores are linked with each other quite frequently.
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The SiC preform was prepared by compression molding.The porosity of porous SiC preform was determined by Archimedes method,mass-volume method and mercury intrusion method,the measured results were compared.The results showed that the porosity measured by Archimedes method was small because the open porosity was large,the test results of mass-volume method and mercury intrusion method were near,then Al alloy volu-me fraction in AlSiC composite and porosities measured by the above three methods were also compared.The results proved that the porosity measured by mass-volume method has an excellent agreement with Al alloy volume fraction in AlSiC composite.Therefore the mass volume method is a simple and practical method of porosity measuring.Then the effects of the pore-forming agents content on the porosity of SiC porous preform were investigated.The results showed that the porosity rose unobviously with the content of pore-forming agents when content of pore-forming agents was less than5%;and that the porosity rose linearly in general when content of pore-forming agents was more than 5%.And the porosity tended to 40% when the pore-making agents content was 14%,which can fully meets subsequent Al infiltration requirements.
Volume fraction
Mass fraction
Compression molding
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Shrinkage
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Since Porosity is a basic parameter for the calculation of gas reservoir reserves,determining the porosity under the reservoir condition is the only way to enhance the precision of the calculation.Based on the measurement of the porosity changes with effective stress and the irreversibility of porosity changes with stress,this paper proposes a conceptual model of porosity change history with the confining pressure.Through the study,two methods to calculate the in-situ porosity value are set up.According to the experimental data of core samples from Jia-2 gas reservoir of Moxi Gasfield,the ratio of conventional confining porosity φ_f to core analysis porosity φ_0 is 0.846(average).The error of confining porosity φ_f with in-situ porosity φ_0 is 5.7%.The error of conventional porosity φ_0 with in-situ porosity can reach 11.5%.It is suggested that it is necessary to modify the porosity and connect it with the logging porosity to make interpretation charts for the reservoir reserve calculation.
Effective porosity
Overburden pressure
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TiC/Ni3Al conmposites with high content of TiC were fabricated by pressureless infiltration method.The effect of content of TiC on porosity of porous preforms was studied.The results show that infiltration of liquid Ni3Al into porouspreforms depended on various factors and infiltration force,especially on the properties of porous preforms.Composities of low porosity and high properties can be obtained by adjusting porosity and pore structures.Practice shows that the higher the porosity of porous preform and the larger diameter of pore in porous preforms,the lower the porosity of composites was.
Infiltration (HVAC)
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Abstract Excessive cracking due to restraint of thermal and shrinkage strains is a widespread problem in the concrete construction industry. In design, restraint induced cracking is managed by the provision of reinforcement intended to distribute internal strains in such a way as to control the cracking pattern and limit crack widths. The area of secondary (horizontal) reinforcement required in members such as retaining walls and water tanks is often governed by the need to control early age thermal cracking. This paper presents results from four edge restrained walls tested at Imperial College London and the University of Leeds as part of an Engineering and Physical Sciences Research Council funded project into restraint induced cracking. The paper describes the development of volumetric strain and cracking in the tested walls. The cracking performance is assessed by comparing the restrained strain with the tensile strain capacity of concrete.
Shrinkage
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Normalization
Power function
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Shrinkage
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Experimental design technique was used in this investigation to illustrate the relationship between the porosity degree as well as its morphology on the mechanical properties and the wear resistance of iron metal compacts. Two different porous iron compacts of porosities 21 and 46% were chosen for the present investigation as metal compacts of moderate porosity (10–70%). The results indicated that the 2N factorial design technique could be used in evaluating the wear resistance of the iron compacts dependent on the percentage of porosity. It has been indicated that the increase in porosity is largely affected the wear behaviour of such porous metals. However, the stress–strain relationship of these metals is largely dependent on the degree of porosity. Since the compacts poses lower porosity (21%) provides distinct stages of elastic plastic behaviour, the compacts having higher porosity (46%) exhibit identified ultimate strength point.
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Porosity generation situation was observed from surface to center in a DC slab of Al–4.4%Mg alloy. The quantities and area fractions of the porosity were measured quantitatively by using an image analysis apparatus (LUZEX). An explanation of this kind of the porosity generation mechanisms and distribution of the porosity was attempted by using a local equivalent pressure in dendritic solidification. The next conclusion was obtained, (1) The quantities of the porosity increase with decreasing the local equivalent pressure. (2) Distributions of the quantities of porosity correspond to the distribution of the area fractions in the slab, both increase to 180 mm, after that they decrease until the center (203 mm). (3) In the surface layer from surface to 60 mm, the porosity sizes are very small and almost exist between secondary dendrite arm. In the middle layer from 80 mm to 140 mm, the porosity sizes become large and the quantities of the porosity become much too. The most of the porosity exist between secondary dendrite arm and a part distributes along grain boundaries. In the center layer from 160 mm to 203 mm, the porosity sizes become more large and they exist not only between the dendrite arm but also the grain boundaries. The shapes of porosity are irregular and a typical shrinkage porosity.
Dendrite (mathematics)
Slab
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