PPT Slide
With the ASTM method, the grain size is specified by the number n in the expression N = 2 n-1, where N is the number of grains per square inch (in an area of 1 in2), when the sample is examined at 100 power micrograph.
In a grain size measurement of an aluminum sample, it was found that there were 56 full grains in the area, and 48 grains were cut by the circumference of the circle of area 1 in2. Calculate ASTM grain size number n for this sample.