Dependence of the limit endurance of specimens with notches from the depth of hardened surface layer

It is shown that, growth of the layer with compressive residual stresses at advanced surface plastic deformation of smooth samples leads to an increase in the endurance limit of the notched specimens due to an increase in the compressive residual stresses in their dangerous section. The study was conducted on the specimens with outer diameter D equal to 10 and 25 mm and on a 25 mm specimen with inner diameter d = 15 mm which were subjected to air shot blasting and roll-in. Residual stresses in smooth specimens were determined by the mechanical method. Circular incisions (R = 0.3 and 0.5 mm) were applied on hardened smooth samples with a shaped cutter. Residual stresses in notched specimens were determined by a numerical method calculating the redistribution of the residual stresses upon the incision. As the diameter of the samples increases with the same strengthening surface treatment,

the depth of the layer with the compressive residual stresses increases due to an increase in the rigidity of the samples. The effect of surface hardening on the endurance limit of notched specimens was evaluated according to the criterion of the average integral residual stresses, which takes into account both the magnitude and completeness of the residual stresses. This criterion was calculated from the depth of the non-propagating fatigue crack that occurs in the surface layer in the dangerous section of the specimen during the fatigue test at the limit endurance. Fatigue tests are carried out in symmetrical cycle, the test base being 3 × 10⁶ cycles of loading. Estimation of the increment of the limit endurance of surface-hardened cylindrical specimens with semicircular notches gave the results acceptable for practice. The use of the proposed method can significantly reduce long-term and expensive fatigue tests.

1. Ivanov S. I., Pavlov V. F. Residual stresses and peening influence on the fatigue strength / Probl. Prochn. 1976. N 5. P. 25 – 27 [in Russian].

2. Pavlov V. F., Prokhorov A. A. The connection between residual stresses and endurance limit under the torsion in stresses concentration conditions / Probl. Prochn. 1991. N 5. P. 43 – 46 [in Russian].

3. Radchenko V. P., Kirpichev V. A., Lunin V. V. Shotblasting influence on the endurance limit of specimens made of alloys V95 and D16T with notches / Vestn. SamGTU. Ser. Fiz.-Mat. Nauki. 2011. N 3(24). P. 181 – 184 [in Russian].

4. Pavlov V. F., Vakulyuk V. S., Chirkov A. V., Sazanov V. P. Surface hardened parts endurance limit prediction in stresses concentration conditions / Vestn. UGATU. 2011. Vol. 15. N 4(44). P. 111 – 115 [in Russian].

5. Pavlov V. F., Kirpichev V. A., Vakulyuk V. S. Residual stresses and fatigue resistance of surface hardened parts with stress concentrators. — Samara: Izd. SNTs RAN, 2012. — 125 p. [in Russian].

6. Kirpichev V. A., Saushkin M. N., Sazanov V. P., Semenova O. Yu. Residual stresses and fatigue resistance of specimens with V-form cuts made of VNS40 steel / Vestn. SGAU. 2012. N 5(36). Part 1. P. 95 – 99 [in Russian].

7. Radchenko V. P., Kirpichev V. A., Lunin V. V. Rolling influence on residual stresses and fatigue resistance of specimens made of steel 40KhN / Vestn. SamGTU. Ser. Tekhn. Nauki. 2013. N 1(37). P. 142 – 150 [in Russian].

8. Vakulyuk V. S., Kirpichev V. A., Pavlov V. F., Sazanov V. P. Surface hardened specimens with stress concentrators endurance limit prediction / Vestn. UGATU. 2013. Vol. 17. N 1(54). P. 45 – 49 [in Russian].

9. Ivanov S. I., Grigor’eva I. V. On residual stresses determining in a cylinder by removing part of the surface / Problems of aircraft constructions elements strength. Issue 48. — Kuibyshev: KuAI, 1971. P. 179 – 183 [in Russian].

10. Ivanov S. I. On residual stresses determining in a cylinder by rings-and-stripes method / Residual stresses. Issue 53. — Kuibyshev: KuAI, 1971. P. 32 – 42 [in Russian].

11. Pavlov V. F., Kirpichev V. A., Ivanov V. B., Semenova O. Yu., Deniskina E. A. The regularities of residual stresses distribution in cylindrical parts with holes of various diameters / Proc. of the fourth All-Russian scientific conference with international participation. Part 1. Mathematical modeling and boundary-value problems. — Samara: SamGTU, 2007. P. 171 – 174 [in Russian].

12. Pavlov V. F., Kirpichev V. A., Semenova O. Yu., Ivanov V. B. The peculiarities of residual stresses distribution in hardened cylindrical parts after shot-blasting / Proc. of the fifth All-Russian scientific conference with international participation. Part 1. Mathematical modeling and boundary-value problems. — Samara: SamGTU, 2008. P. 229 – 232 [in Russian].

13. Ivanov S. I., Shatunov M. P., Pavlov V. F. The influence of residual stresses on the endurance of notched specimens / Problems of aircraft constructions elements strength. Issue 1. — Kuibyshev: KuAI, 1974. P. 88 – 95 [in Russian].

14. Filatov É. Ya., Pavlovskii V. É. Universal machine complex for fatigue tests of materials and structures. — Kiev: Naukova dumka, 1985. — 92 p. [in Russian].

15. Pavlov V. F. On the connection between residual stresses and endurance limit under bending in stresses concentration conditions / Izv. Vuzov. Mashinostr. 1986. N 8. P. 29 – 32 [in Russian].

16. Kirpichev V. A., Filatov A. P., Karanaeva O. V., Chirkov A. V., Semenova O. Yu. Surface hardened parts endurance limit prediction under stresses concentration various degree. Proceedings of the International Scientific Technical Conference «Materials and constructions elements strength». — Kiev: IPP im. G. S. Pisarenko NAN Ukrainy, 2011. P. 678 – 685 [in Russian].