Determine strength ratio for unidirectional lamina

Question

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 MPa, σ₆ = 60.0 MPa

σ₂ = -60 MPa, σ₆ = 80.255 MPa

σ₂ = -60 MPa, σ₆ = 90.0 MPa

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