(a) Compare the fatigue limits for polystyrene (Figure) and the cast iron for which fatigue data are given in Problem 8.20.

(b) Compare the fatigue strengths at 106 cycles for poly(ethylene terephthalate) (PET, Figure) and red brass(Figure).

25 PET PS 20 15 PMMA 10 PP Nylon (dry) PE PTFE 107 103 104 105 106 Number of cycles to failure 80 500 70 60 400 50 1045 steel 300 40 2014-T6 aluminum alloy 30 200 20 100 10 Red brass 103 104 105 10 107 10 10 1010 Cycles to failure, N Stress amplitude (MPa) Stress amplitude, S (MPa) Stress amplitude (10 psi) Stress amplitude (ksi)