Page 59 - Zmist-n2-2015

cracks reach a critical dimension and the sample is not able to sustain any additional
strain (the fracture takes place, forming the cross-section crack) (Fig. 7b–d).
CONCLUSION
Analyzing the results of fatigue tests of sintered 316L stainless steel samples with
various density (porosity from 26 to 41%) it is possible to draw important conclusions
to predict the damage state as well as the cracking processes in the material. In the pro-
cess of fatigue damage development modelling in the samples made of sintered porous
316L stainless steel two stages can be distinguished. The first one concerns the damage
accumulation in the bridges between the pores, taking place on the microscale. It is cru-
cial to take into account the stress concentration and plastic strain in bridges (on the me-
soscale). The second stage is connected with binding of pores (cracking of subsequent
bridges between them), which has to be considered on the mesoscale. This gives a similar
effect of increasing the susceptibility of the material (decrease of Young’s modulus and
the maximum values of the stress in the load cycle) for the case of evenly spaced cracks
growth in the material, which is attributed to fatigue loading of constant amplitude.
РЕЗЮМЕ. Наведено результати втомних випробовувань зразків аустенітної сталі 316L
з рівнями пористості 26, 33 і 41%. Проаналізовано параметри, отримані із петлі гістерези-
су в циклі навантаження – зміну модуля Юнґа, максимальних і мінімальних напружень.
Використовуючи залежність Mенсона–Коффіна, визначили втомну міцність пористих ма-
теріалів з різним ступенем загущення.
РЕЗЮМЕ. Представлены результаты усталостных испытаний образцов аустенитной
стали 316L с уровнями пористости 26, 33 и 41%. Проанализированы параметры, получен-
ные из петли гистерезиса в цикле нагрузки – изменения модуля Юнга, максимальных и
минимальных напряжений. Используя зависимость Mенсона–Коффина, определили уста-
лостную прочность пористых материалов с различным уровнем плотности.

This paper was supported by the Bialystok University of Technology under the re-
search project № MB/WM/6/2013.
1. Chawla N. and Deng X. Microstructure and mechanical behavior of porous sintered steel
// Mat. Sci. Eng. – 2005. – A390. – P. 98–112.
2. Fatigue of sintered steels (Fe–1.5Mo–3Mn–0.7C) / H. Khorsand, S. M. Habibi, K. Janghor-
ban et al. // Mater. and Struct. – 2004. – 37. – P. 335–341.
3. Sudhakar K. V. Fatigue behavior of a high density powder metallurgy steel // Int. J. Fatigue.
– 2000. – 22. – P. 729–734.
4. Dewidar M. M., Khalil K. A., and Lim J. K. Processing and mechanical properties of porous
316L stainless steel for biomedical applications // Transactions of Nonferrous Metals Society
of China. – 2007. – 17. – P. 468–473.
5. Grądzka-Dahlke M., Dąbrowski J. R., and Dąbrowski B. Characteristic of the porous 316 stain-
less steel for the friction element of prosthetic joint // Wear. – 2007. – 263. – P. 1023–1029.
6. Kurgan N. and Varol R. Mechanical properties of P/M 316L stainless steel materials // Pow-
der Technology. – 2010. – 201. – P. 242–247.
7. Ryan G., Pandit A., and Apatsidis D. P. Fabrication methods of porous metals for use in
orthopeadic applications // Biomaterials. – 2006. – 27. – P. 2651–2670.
8. Fatigue crack growth characterization and simulation of porous steel / C. Verdu, S. Cara-
bajar, G. Lormand, R. Fougères // Mat. Sci. Eng. – 2001. – A319–321. – P. 544–549.
9. Teoh S. H. Fatigue of biomaterials: a review // Int. J. Fatigue. – 2000. – 22. – P. 825–837.
10. Dobrzański L. A. Leksykon materiałoznawstwa. Praktyczne zestawienie norm polskich,
zagranicznych i międzynarodowych. – Warszawa: Verlag Dashofer, 2012.
11. ASTM E606-80/ E 606M-12 Standard Test Method for Strain-Controlled Fatigue Testing.
12. Coffin L. R. A study of the effects of cyclic thermal stresses on ductile metal // Trans. ASME.
– 1954. – 76. – P. 931–950.
13. Manson S. S. Behavior of Materials under Conditions of Thermal Stress. – NACA TN-2933, 1953.
14. Morrow J. D. Cyclic plastic stain energy and fatigue of metals // Internal Friction Damping
and Cyclic Plasticity. – ASTM, 1965. – STP378. – P. 45–84.
Received 24.07.2014
58