F1c

The longitudinal compression strength of unidirectional composites F1c, also called Xc, is very difficul to test for, so often you don't have the value for the particular material (fiber, matrix, volume fraction) that you wish to use. Further, just having data does not tell you what paramaters really influence its value--it is not the compressive strength of the fiber, I can assure you. So, there is a simple formula that you can use to predict its value and also to understand what are the parameters that really affect the compression strength of the composite.