And the resulting curves have the same general shape
| 9.10 The S–N Curve | ● | 259 |
|---|
for some specified number of cycles (e.g., 107cycles). The determination of fatigue strength is also demonstrated in Figure 9.25b.
The fatigue behaviors represented in Figures 9.25a and 9.25b may be classified into two domains. One is associated with relatively high loads that produce not only elastic strain but also some plastic strain during each cycle. Consequently, fatigue lives are relatively short; this domain is termed low-cycle fatigue and occurs at less than about 104to 105cycles. For lower stress levels wherein deformations are totally elastic, longer lives result. This is called high-cycle fatigue inasmuch as relatively large numbers of cycles are required to produce
|
Stress, S (MPa) | 108 | 109 | 70 | Stress (103psi) | ||||
|---|---|---|---|---|---|---|---|---|---|
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60 | ||||||||
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|||||||||
| P = 0.90 | 50 | ||||||||
| 40 | |||||||||
| and T. J. Dolan, Trans., |
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107 | ||||||
| 30 | |||||||||
| P = 0.10 | |||||||||
| 20 | |||||||||
| permission of the | |||||||||
| 105 | 106 | ||||||||
| 10 | |||||||||
| Mechanical Engineers.) | |||||||||
| 104 | |||||||||
| 260 | ● |
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|---|
9.12a CRACK INITIATION AND PROPAGATION [DETAILED VERSION (CD-ROM)]
9.12b CRACK INITIATION AND PROPAGATION (CONCISE VERSION)
| Stress amplitude (MPa) | 25 | PP | PMMA | PET |
|
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3 | Stress amplitude (ksi) | ||
|---|---|---|---|---|---|---|---|---|---|---|
| 20 | ||||||||||
| polyethylene | ||||||||||
| 15 | 2 | |||||||||
| polymethyl | ||||||||||
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10 | |||||||||
| 1 | ||||||||||
| 5 | PE | |||||||||
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PTFE | |||||||||
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||||||||||
| 0 | 103 | 104 | 105 | 107 | 0 | |||||
| Plast. Eng., Vol. 30, No. | ||||||||||
| 4, p. 78, 1974.) | ||||||||||
| Number of cycles to failure |
