Manson-Coffin S-N Curve—Neuber rule

A series of 17 smooth specimens of carbon steel type A 106 B, 6.35 mm (0.25 ) diameter and 15.24 mm (0.6 ) length, has been tested in push-and-pull traction (R = —1) at 288 °C under strain controlled conditions. Results are shown in Fig. 6.42. A further testing with notched specimens having k, — 3, root radius p = 0.28 mm and a diameter D — 8 mm with the reduced notch section having the same diameter d — 6.35 mm as smooth specimens, has yielded results listed in Table 6.14. Analyze the results using Manson-Coffin S-N curve and Neuber s rule. 

Tests have been run to derive the cyclic stress-strain curve both at 25 °C and at the operating temperature of 288 °C. Results are shown in Fig. 6.43. It is possible to recognize that at 288 °C the material is undergoing a dynamic strain aging process that makes the steel behave much better than at room temperature. The Ramberg-Osgood Eq. (6.3) of the cyclic curve at 288 °C is 

6 Strain-Based Fatigue Analysis Low Cycle Fatigue 

Also the true stress and true strain at failure, see Eqs. (5.27) and (5.32), have been calculated as = 910 MPa and 8,/ = 0.47. Knowing from Eq. (6.50) the cyclic strain hardening exponent n = 0.0866 it is possible to derive the b and c exponents of Eq. (6.10) that are 

The process volume of the unnotched specimen used to derive the S-N curve of Fig. 6.42 is 

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