I don't understand the Excel file.

On the compression tab, the formula to calculate Stress in column F is

(B9*1000)/(PI()*$L$3^2)

where L3 is the cylinder radius of 35 mm so I understand this is dividing force by area of the cylinder.

On the traction tab, the formula to calculate stress labeled as sigma in column E is

(1000*D10)/$M$3

where M3 is the Total Fiber Area of 35.2 mm^2 which is also force divided by area.

However, this implies a radius of 3.3 mm for a circular cross section.

I don't understand why the area changes by so much between compression and traction (tension).

Is it that the shape of the sample for traction testing is completely different than the compression sample?

Or do you mean that there are two different materials, the concrete that has been tested for compression and the fiber has been tested in a traction or tension test, **without being mixed in with the concrete?**

If you are separately testing two materials that will later be mixed, then to use this mixture in ANSYS, you create two materials and you have a body for the concrete and a line body for each fiber in the concrete. The fiber is called a reinforcement to the concrete. Please review this discussion for more information. Are the fibers arranged in a repeatable pattern or are they in random orientations?