Tensile yield strength of fiber reinforced plastic

[drbananas]

Hello! I am in a student-run engineering team that heavily utilizes fiber reinforced plastics, and I am just trying to get a better understanding of FRPs. I am wondering how exactly the fiber reinforces the plastic. Let's say the yield strength of the fiber in the 0 degree tensile direction is 2500 MPa, and the yield strength of the plastic resin is 80 MPa. If a force is applied on the FRP along the 0 degree tensile direction that garners a stress greater than 80 MPa, will the plastic resin yield?

 

[mjc123]

It will yield if the stress in the resin is greater than 80 MPa. In the composite, the stiffer fibres carry more of the load, so the stress in the matrix is less than the nominal applied stress. For unidirectional continuous fibres, it is easy to calculate the applied stress that would give 80 MPa in the matrix. For other configurations, it is more complicated.
In addition, the presence of the fibres physically restricts the ability of the resin to yield plastically. It would probably fail in a brittle manner at higher stress.