고체역학 (Beer) — Stress and Strain—Axial Loading: Problem 2.111

2.111 Two tempered-steel bars, each \(\frac{3}{16}\) in. thick, are bonded to a \(\frac{1}{2}\)-in. mild steel bar. This composite bar is subjected as shown to a centric axial load of magnitude \(P\). Both steels are elastoplastic with \(E = 29 \times 10^6\) psi and with yield strengths equal to 100 ksi and 50 ksi, respectively, for the tempered and mild steel. The load \(P\) is gradually increased from zero until the deformation of the bar reaches a maximum value \(\delta_m = 0.04\) in. and then decreased back to zero. Determine (a) the maximum value of \(P\), (b) the maximum stress in the tempered-steel bars, (c) the permanent set after the load is removed.