PSI - Issue 17

D.G. Papageorgiou et al. / Procedia Structural Integrity 17 (2019) 532–538 D.G. Papageorgiou, H. Bravos, C. Medrea/ Structural Integrity Procedia 00 (2019) 000 – 000

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The microstructure of the third support comprised mainly of austenite grains (Fig. 9a). Twins are formed inside the grains during the annealing of the material. Due to extensive plastic deformation caused by thread rolling some martensite is formed (Fig. 9a). Inside the austenite grains, slip lines due plastic deformation are also visible (Fig. 9b). Inclusions are visible inside the grain boundaries also. The microstructure of the stainless steel is uneven mainly due to excessive plastic deformation, martensitic transformation and the presence of inclusions impairing the fatigue strength of the holder.

Fig. 9. (a) The microstructure of the third piece, (b) Deformed grains on threads top area.

4. Conclusions

The previous results of the fan blade supporting system have shown that: • All pieces have totally broken; in all cases the crack initiated from a circumferential point and propagated to the inner area on a fatigue mode. • According to the chemical analysis the holders were manufactured from different materials; indication of lack of technical specifications. • The first two holders were manufactured from low alloy steel in the hardened and tempered condition. The material is suitable for specific application. The hardness measurements indicated the expected values. Metallographic examination revealed high density of inclusions on the grain boundaries rending the material prone to fatigue. Cracks were detected on the tip of the thread probably induced during manufacturing process. • The third holder was manufactured from an austenitic stainless steel; the material is inappropriate material for the specific application. The hardness is lower than the expected and the piece is harder on the surface probably due work hardening. Metallographic examination revealed non uniform microstructure mainly comprised of austenite grains; slip lines and some martensite were formed during piece manufacturing. • The failure is mainly attributed to poor design. Closer examination of fracture surface using electron microscope (SEM) will be carried out in order to confirm the first conclusions and to suggest remedial solutions. Balat M., 2010.Greenhouse gas emissions and reduction strategies of the European Union. Energy Sources, Part B: Economics, Planning and Policy, 5(2), 165 – 177. Bravos H., Papageorgiou D.G., Medrea C., 2018. Preliminary examination of a fan blade supporting system premature fractured.13 th eRA Conference, Athens, Greece. Halford G.R., Gallagher J.P., 2000. Fracture and Fracture Mechanics , 31,. ASTM STP 1389, Pennsylvania, USA. Huda Z., Zaharinie T., Al-Ansary H., 2014. Enhancing power output and profitability through energy-efficiency techniques and advanced materials in today’s industrial gas turbines . International Journal of Mechanical and Materials Engineering 9 (1),1-12. Huda, Z., 2009. Metallurgical failure analysis for a blade failed in a gas-turbine engine of a power plant. Materials and Design, 30, 3121 – 3125. Neves F.O., Oliviera T.L.L,, Braga D.U., Chaves da Silva A..S., 2014. Influence of Heat Treatment on Residual Stress in Cold-Forged Parts. Advances in Materials Science and Engineering, 1-7. Stein K., Makris P., 1993. Mechanical Damages Analysis . (Ed.) Papasotiriou, Athens, Greece. References