Figure P12.7 shows a stepped steel bar ABC, axially loaded until it elongates 10 mm, and...

Figure P12.7 shows a stepped steel bar ABC, axially loaded until it elongates 10 mm, and then unloaded. Determine (a) the largest value of P; (b) the plastic axial deformation of segments AB and BC. Given: d₁ = 60 mm, d₂ = 50 mm, E = 210 GPa, and = 240 MPa.