Acoustical diagnoses of porous drainage pavements
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Road traffic noise reduction of drainage pavement with small air gaps among grains is well known. However, traffic flow over many years fills those gaps with mud and sand, thereby degrading the noise reduction effect. To regain that effect, cleansing or reconstructing the pavement is necessary after precise assessment of the air gaps. For that purpose, acoustical diagnoses of drainage pavement are proposed and test results are introduced. One method is to check sound absorption of the pavement surface, which normally has high absorption near frequencies of 1 kHz, which is related to the reduction of road traffic noise. The use of a particle velocity sensor together with a microphone greatly simplifies measurements and judgments. Another analysis method is based on sound propagation through air gaps in the pavement. Transmission characteristics clearly indicate pavement conditions. Low-attenuation sound transmissions are shown in a wide frequency range below 1 kHz for sound air gaps, and weak transmissions in a narrow frequency range are shown when air gaps are filled. These acoustic diagnostic methods are effective in investigating porous drainage pavement.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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Normalization
Power function
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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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SiC/Al composites were fabricated by pressureless infiltration technique.The effect of pore-making agent on porosity of porous preforms was studied.The results show that infiltration of liquid Al into porous preforms relies on various obstructions and force of infiltration,especially on the properties of the porous preforms.Composities with 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.
Infiltration (HVAC)
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