7.7-13 An element in plane stress is subjected to stresses 7.5 MPa, and Txy -12 MPa = 58 MPa, o, = 7.5 MPa, (see figure). The material is aluminum with modulus of elasticity E = 69 GPa and Poisson's ratio v = 0.33. Determine the following quantities: (a) the strains for an element oriented at an angle 0 = 30, (b) the principal strains, and (c) the maximum shear strains. Show the results on sketches of properly oriented elements. T PROBS 7.7-13 and 7.7-14 S