(a) Compare the fatigue limits for PMMA (Figure 15.11) and the 1045 steel alloy for which...

(a) Compare the fatigue limits for PMMA (Figure 15.11) and the 1045 steel alloy for which fatigue data are given in Figure 8.20.

(b) Compare the fatigue strengths at 106 cycles for nylon 6 (Figure 15.11) and 2014-T6 aluminum (Figure 8.20).

Figure 15.11 Fatigue curves (stress amplitude versus the number of cycles to failure) for poly(ethylene terephthalate) (PET), nylon, polystyrene (PS), poly(methyl methacrylate) (PMMA), polypropylene (PP), polyethylene (PE), and polytetrafluoroethylene (PTFE). The testing frequency was 30 Hz.

(From M. N. Riddell, “A Guide to Better Testing of Plastics,” Plastics Engineering, Vol. 30, No. 4, p. 1974. © Society of Plastics Engineers.)

Figure 8.20 Maximum stress (S) versus logarithm of the number of cycles to fatigue failure (N) for seven metal alloys. Curves were generated using rotating–bending and reversed-cycle tests.

(Data taken from the following sources and reproduced with permission of ASM International, Materials Park, OH, 44073: ASM Handbook, Vol. I, Properties and Selection: Irons, Steels, and High-Performance Alloys, 1990; ASM Handbook, Vol. 2, Properties and Selection; Nonferrous Alloys and Special- Purpose Materials, 1990; G. M. Sinclair and W. J. Craig, “Influence of Grain Size on Work Hardening and Fatigue Characteristics of Alpha Brass,” Transactions of ASM, Vol. 44, 1952.)