Outer Fiber Strain Factor
For rectangular specimens in a 4-point bend test:
Outer fiber strain factor = (support span2 * (3 - (1 - load span/support span)2))/(thickness * 12)
For rectangular specimens in a 3-point bend test:
Outer fiber strain factor = support span2/(thickness * 6)
For cylindrical specimens in a 4-point bend test:
Outer fiber strain factor = (support span2 * (3 - (1 - load span/support span)2))/(diameter * 12)
For cylindrical specimens in a 3-point bend test:
Outer fiber strain factor = support span2/(diameter * 6)
