This procedure can be used to calculate the density and porosity of alloys and composite materials. For this particular article, I concentrate on metal matrix composite that uses fly ash ceramic particles as reinforcement phase and aluminium alloy A356 as a matrix phase.
The density of raw fly ash used in fabricating the composites was determined. First, a measuring cylinder was filled with distilled water to within 0.5 cm of the 100 ml line. It was placed in a bell jar and evacuated to a pressure of between -86 kPa to -96 kPa until the water stopped bubbling. This removes any entrapped voids. The flask was then removed and filled to the 100 ml mark with distilled water.
The weight of the water filled flask was then recorded as WT2.
15-30 g of fly ash (WT1) was weighed into a flask.
The sample was washed down in the flask with distilled water ensuring that the entire sample is under the water. The flask was filled to within 1-2 cm of the 100 ml line. The setup was then placed under a bell jar and evacuated to a pressure of -86 kPa to -96 kPa until the sample stopped bubbling. It was removed and filled to the 100 ml mark with distilled water.
The weight of the flask with sample and distilled water was then recorded as (WT3).
The density of the fly ash particles was then calculated from equation below. The same procedure was used in determining the bulk density of SiC particles.
The weight of the water filled flask was then recorded as WT2.
15-30 g of fly ash (WT1) was weighed into a flask.
The sample was washed down in the flask with distilled water ensuring that the entire sample is under the water. The flask was filled to within 1-2 cm of the 100 ml line. The setup was then placed under a bell jar and evacuated to a pressure of -86 kPa to -96 kPa until the sample stopped bubbling. It was removed and filled to the 100 ml mark with distilled water.
The weight of the flask with sample and distilled water was then recorded as (WT3).
The density of the fly ash particles was then calculated from equation below. The same procedure was used in determining the bulk density of SiC particles.
The densities of the composites were determined by means of Archimedes’ principle. Archimedes’ principle states that when a body is immersed in a fluid, there is buoyant force acting upward on the body equal to the weight of the displaced fluid. The weight of the displaced fluid equals its volume when water is used (density of water = 1 g/cm3). The volume of water displaced is equal to the volume of the body immersed. All weights were obtained by means of an Ohaus ScoutTM Pro Balance SP2001 equipped with a spring balance. The as-cast material was suspended in air on the spring by means of a thin thread and its weight determined as W1. It was then completely submerged in a beaker of water and the new weight recorded as W2. Its density was then calculated from equation below.
Theoretical calculations, according to the rule of mixtures, were also used to determine the densities of the composites. This was obtained from rule of mixture equation as shown below [1].
where Vr is the weight ratio of fly ash, Pc the density of the composite, Pr is the density of fly ash and Pm the density of the unreinforced A356 alloy.The porosity of the test materials were also calculated from equation shown below [2].
References;
1. Smith, W.F., Hashemi. J. 2006. Foundations of Materials Science and Engineering.4th Ed. McGraw-Hill. New York
2. Indiana University. http://www.geology.iupui.edu/research/SoilsLab/procedures/bulk/Index.htm. Online on March 20, 2007.
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