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Prediction of the mechanical properties of porous materials is crucial for their industrial applications. There are various types of porous materials: natural (bones, wood, coral) or man made (porous ceramics, aluminium foam); porous compacts (low or intermediate porosity) or foams (porosity up to 1). This article deals with the porous solids prepared as follows: At the beginning there is certain green density or tap density at which the consolidation of powders starts. Then, the physical bonds begin to create in the regions where powder particles touch each other. When certain number of such bonds is created and the material is able to carry its weight the powder compact starts to exist. This undergoes usually at smaller porosity as was porosity prior densification. Such porosity is called critical porosity or percolation threshold. [1] Further, the interconnected pores close down and disappear as porosity is going to zero.Due to random structure porous materials properties cannot be predicted analytically. On the other hand, prediction by numerical computations requires the knowledge of exact porous materials microstructure. The only practical ways to obtain it are microscopy, X-ray microtomography or models of the structure. However the costs and/or computational time of used method are very high and/or the accuracy of the method is very bad. Especially the models are able to create microstructure only at low porosity. [2] Another problem is 2D modeling of porous material: Garboczi et al. [3] stated that to reproduce 3-D experimental results it is crucial to use 3-D models. Moreover they pointed out that as the percolation threshold is approached during computer modeling, the statistical fluctuation and finite size effect errors grow quickly. The problem is also the variation of porous materials microstructure from sample to sample at constant porosity. Randomness is the result of the preparation method and type of used powders. Using future computers it will be possible to predict the properties more precisely and cheaper. Until that numerical models containing some errors or models that predict effective properties of porous materials on empirical or semi-empirical basis (this is a subject of this article) can be used. TheoreticalTo obtain the exact prediction of Young's modulus for a porous material at given porosity, various models, such as linear dependence, exponential dependence or quadratic equation, have been extensively used during the past years. [4] Main disadvantage of these models is that they can be used either for low or high porosity range, but not for entire porosity range. It seems that some requirements ought to be fulfilled by good model for whole porosity range: It must be as simple as possible, must possess the smallest number of fitting parameters as possible and it is necessary to incorporate the critical porosity (percolation threshold) into the model. For this reason Knudsen and Spriggs exponential model is not suitable as no percolation threshold is taken into account. Moreover, i...
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