The tensile and compressive yield stresses of polystyrene are 73 and 92 MPa, respectively. Crazing occurs at 47 MPa in uniaxial tension and 45 MPa in equal biaxial tension. Poisson's ratio is 1/3. Use Equations (20.10) and (20.13) to pre- dict the stress state, σ 1, σ 2, with σ 3 = 0 at which yielding and crazing occur simultaneously.