Tensile Requirements

[CessnaGuy]

I am forgetting something simple and need some help. I am working on some composite materials and need to build a carbon and/or fiberglass I beam to hold up to a minimum PSI tensile and compression strength. These are only example numbers but if the bending stress is 25,000 PSI and we are using a composite with a strength of 25,000 PSI, do we need a minimum of 1 square inch of material?

Example:

5 plys of fiber totaling 0.18" thick x 6" for 1.08 square inches.