Response to the following problem:
Using the Mohr-Coulomb failure criterion, calculate the strength ratio R for a unidirectional lamina of glass-epoxy LY556 subjected to:
σ2 = -60 MPα, σ6 = 60.0 MPα
σ2 = -60 MPα, σ6 = 80.255 MPα
σ2 = -60 MPα, σ6 = 90.0 MPα