 
POROSITY
What is porosity? and How can porosity help you?
Porosity is a measurement of the voids in a solid.
However it is not a complete description of the performance delivered by a part.
The applications section notes how porosity is used
in some products.
Apparent porosity is generally the ratio of total void volume to solid
volume. 10% apparent porosity indicates that pores occupy 1/10 of the
total volume of the part. This also includes surface porosity.
Open porosity are void volumes that are interconnected and allow fluid
flow into or through the solid.
Closed porosity are void volumes that are trapped within the solid
with no manner in which to exchange the void contents.
Surface porosity is related to the surface finish. On a
microscopic level the surfaces are not smooth but represent the profile from the
finishing process.
Porosity, properly controlled in part design and fabrication, is the key
parameter in providing certain product performance levels.
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