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Improvement of fatigue life of AISI 1045 carbon steel of parts obtained by turning process through feed rate
ScienceDirect ScienceDirect StructuralIntegrity Procedia 00 (2018) 000–000
Available online at www.sciencedirect.com
Available online www.sciencedirect.com Available online at at www.sciencedirect.com StructuralIntegrity Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
Procedia Structural (2018) 243–249 Structural IntegrityIntegrity Procedia900 (2016) 000–000
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
www.elsevier.com/locate/procedia
IGF Workshop “Fracture and Structural Integrity” IGF Workshop “Fracture and Structural Integrity”
Improvement of fatigue life of AISI 1045 carbon steel of parts obtained by turning process through feed steel rate of parts Improvement of fatigue life of AISI 1045 carbon XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paço de Arcos, Portugal obtained by turning process through feed rate Khadija Kimakha*, Abdelkarim Chouafa, Samir Aghzera,b, Amal Saouda, Thermo-mechanical modeling of pressure blade a a a a high a a,b,turbine Khadija Kimakha*,ElAbdelkarim Chouaf , Samir Aghzer Amal Saoud , of an , M’hamd Chergui hassan Malil airplane gas turbine engine a LCCMMS,ENSEM, Hassan II Universitya , 7 km road of el jadida, Casablanca, Morocco a
El hassan Malil , M’hamd Chergui P. Brandão , V. Infante , A.M. Deus *
EST, ENSEM, Hassan II University , 7 km road of el jadida, Casablanca, Morocco a b c a LCCMMS,ENSEM, Hassan II University , 7 km road of el jadida, Casablanca, Morocco b EST, ENSEM, Hassan II University , 7 km road of el jadida, Casablanca, Morocco a Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract c work investigates the effect of cutting conditions on the fatigue performance of the parts generated by turning This CeFEMA, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal process. There are various parameters such as cutting speed, feed rate and tool nose radius that are known for their b
This work investigates thequality effect of conditions on the fatigue performance of rate the parts significant impact on the of cutting machined parts. The relationship between feed as a generated parameter by of turning cutting process. There such cutting speed, feed ratecase and tool radius are known for were their conditions and are the various fatigue parameters performance willas be highlighted. In that threenose batches of that fatigue specimen Abstract impact on the quality of machined parts. The relationship between feed rate as a parameter of cutting significant realized on an Alpha 1530xs CNC lathe, then tested on fatigue with a stress ratio R=0.1. The results are presented conditions and the fatigue performance will beofhighlighted. Inonthat three of fatigue specimen were through S-N curves which illustrate the engine impact the feed rate the case fatigue life batches performance. In operating fact, the feed rate During on their operation, modern aircraft components are subjected to increasingly demanding conditions, realized an Alpha 1530xs CNC lathe, then tested on fatigue with a stress ratio R=0.1. The results are presented affects the fatigue life performance spatially for low values of feed rate. The fatigue lifetime decrease with the especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent through S-N curves which illustrate the impact of the feed rate on the fatigue life performance. In fact, the feed rate increase of feed degradation, onerate. of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict affects the behaviour fatigue life spatially low values of feed rate. The fatigue lifetime with the the creep of performance HPT blades. Flight datafor records (FDR) for a specific aircraft, provided by a decrease commercial aviation increase of feed rate. company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model
© needed 2018 The Authors. Published byaElsevier B.V. the FEM analysis, HPT © 2018 Thefor Authors. Published by Elsevier B.V.blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fedItaliano into theFrattura FEM different simulations were run, first with a simplified 3D Peer-review under responsibility of the Gruppo (IGF)and ExCo. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF)model ExCo. © rectangular 2018 The Authors. Published by to Elsevier block shape, in order better B.V. establish the model, and then with the real 3D mesh obtained from the blade scrap. The Peer-review underprocess; responsibility of theofGruppo Italiano Frattura (IGF)inExCo. overall expected behaviour in conditions; terms displacement was observed, particular at the trailing edge of the blade. Therefore such a Keywords:Turning cutting feed rate; fatigue life; model can be useful in the goal of predicting turbine blade life, given a set of FDR data. Keywords:Turning process; cutting conditions; feed rate; fatigue life;
© 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation.
* Corresponding author. Tel.: +212 67 50 91 55 05. E-mail address:[email protected] * Corresponding author. Tel.: +212 67 50 91 55 05. E-mail address:[email protected] 2452-3216© 2018 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. 2452-3216© 2018 The Authors. Published by Elsevier B.V.
Peer-review underauthor. responsibility the Gruppo Italiano Frattura (IGF) ExCo. * Corresponding Tel.: +351of 218419991. E-mail address: [email protected]
2452-3216 © 2016 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Scientific Committee of PCF 2016. 2452-3216 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. 10.1016/j.prostr.2018.06.039
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija. KIMAKH / StructuralIntegrity Procedia 00 (2018) 000–000
244 2
1. Introduction The lifetime prediction of mechanical structures has become a major subject in many industrial sectors: aeronautics, automotive... Many factors other than the mechanical proprieties of the material affect its ability to resist fatigue phenomenon. Besides these factors, the manufacturing process has a significant role in the fatigue strength. In fact, these methods including the machining are often associated with significant thermo-mechanical stresses that may result in heterogeneous properties in the materials. The impact of these properties, usually generated in surface and subsurface of the machined parts, could significantly affect the behavior of mechanical component subjected to fatigue loads. The fatigue cracks are generally initiated from free surfaces. The surface of a piece has two important aspects that have to be defined and controlled. The first aspect is geometric irregularities on the surface, and secondly the metallurgical alterations of the surface and the subsurface. This second aspect has been termed surface integrity. Several researchers have been interested in investigating the influence of cutting conditions on fatigue life. Ming Zhang (2016) proves that surface roughness has a significant effect on VHCF properties of FV520B-I, and VHCF properties of FV520B-I impeller can be improved by reducing surface roughness. D. Novovic et al. (2004) attest that both surface integrity and surface topography have a significant effect on fatigue performance of machined parts. It has been testified that for low surface roughness the fatigue lifetime depends on surface roughness. But for surface roughness higher than Ra = 2.5 µm, the fatigue performance depends on residual stress. Guoliang Liu et al. (2016) analyzed the modifications generated by cutting operation on surface integrity (residual stress, microstructure and surface roughness). The influence of surface roughness on the fatigue performance could be overshadowed by other surface integrity characteristics. Monchaï Suraratchaï et al. (2005, 2008) investigate the influence of machined surface on the fatigue life of 7010 aluminum alloy. They proposed a model, based on surface topography to predict fatigue lifetime. D P Davies et al. (2014) interested in Critical Helicopter Components. Different manufacturing methods were carried out to enhance the fatigue performance. Our work aims to identify a relationship between turning process parameters and fatigue behavior of the mechanical component. An experimental study is carried out to analyze this relationship. The cylindrical specimen for fatigue testing was released in CNC lathe Alpha 1530XS with 3 different values of feed rate. After specimen’s preparation, fatigue testing is accomplished to determine the fact of feed rate on fatigue lifetime. The results obtained are presented through S-N curves which highlighted the impact of feed rate on the fatigue life of parts. Nomenclature Re0.2% Rm A E R f ɛ σ σmax Nf
Yield strength Tensile strength Elongation Elasticity modulus Stress ratio Feed rate strain Stress Maximum stress Number of cycles failure
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija.KIMAKH / Structural Integrity Procedia 00 (2018) 000–000
245 3
2. Material and experimental set-up 2.1 Material The material used in this study was AISI 1045 steel with 0.42 of Carbone. The chemical compositions of the material have been identified by using spectrometer machine. The chemical composition of this steel is given in Table 1. Table1. Chemical composition of AISI 1045 Steel
Chemical composition (%)
AISI 1045
C
Mn
S
P
Si
0.42
0.72
0.02
0.04
0.19
A tensile test was carried out According to the ASTM E8 Standard, to establish mechanical proprieties of the material used. The mechanical proprieties are shown in table2. Table 2. Mechanical proprieties of AISI 1045. Steel
Mechanical proprieties
AISI 1045
Re0.2%[MPa]
Rm [MPa]
A%
E [GPa]
432
645
23
211
2.2. Fatigue test This study aims to analyze the effect of feed rate on fatigue life of the pieces obtained by turning process. Then three batches of specimens were machined. Fatigue tests were carried out on four levels of stress and for each level the fatigue tests were repeated three times. The test specimens were machined by turning process in wet condition. Turning operation was performed using DNMG 11 04 08 insert. A CNC lathe (Alpha 1530XS) was used for the longitudinal turning of the specimens and the cutting conditions employed for machining are listed in Table 3. Table 3. Cutting conditions Parameters
Description
Feed rate (mm/rev)
0.05, 0.15, 0.25
Cutting speed (rev/min)
2000
Depth of cut (mm)
0.5
Tool nose radius(mm)
0.8
Coolant
Wet
Specimens are conforming to the standard ASTM 466. Figure 1 present dimension of fatigue specimen with the recommended diameter d =6.35mm.
246 4
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija. KIMAKH / StructuralIntegrity Procedia 00 (2018) 000–000
Fig. 1. Fatigue specimen.
After specimens preparation fatigue tests were performed with MTS 810 hydraulic testing machine shown in figure 2 with a maximum capacity 100 kN. The machined specimens were subjected to constant amplitude tension– tension axial fatigue. Tests were conducted in load control with a sinusoidal load waveform and for each batch of specimens four levels of stress load were applied. Table 4 listed the levels of stress. The fatigue tests were carried out with a constant frequency of 40 Hz and a stress ratio R = 0.1 (minimum load/maximum load) was applied throughout the experiment. Once the specimen was broken, the machine stopped automatically.
Fig. 2. Fatigue specimen configuration. Table 4. Levels of the applied load. stress σmax σmin
levels 400 40
450 45
500 50
525 52.5
550 55
3. Result and discussion 3.1 S-N curve Figure 3 presents the S-N curve for the three batches of machined AISI 1045. Based on the experimental data and the observations of fatigue tests for every batch of specimens, the feed rate affects the fatigue life of the AISI1045 steel parts obtained by turning process. The results show that the machined specimens with a low feed rate f3 = 0.05mm/rev have a longer lifetime than specimens machined with high feed rate (f2 = 0.15mm/rev and f1 = 0.25 mm/rev). We also notice that when thefeed rate decrease from f1 = 0.25 mm/rev to f2 = 0.15 mm/rev with a step of 0.1 mm/rev, the number of cycles to faillure increase with a percentage of 17% forσmax = 550MPa and 135% for σmax = 500MPa. But when it decrease from f2 =
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija.KIMAKH / Structural Integrity Procedia 00 (2018) 000–000
247 5
0.15 mm/rev to f3 = 0.05 mm/rev the number of cycles to faillure increase clearly with a percentage of 30% for σmax= 550MPa and 184% for σmax = 500MPa (figure 4). 600
f = 0.25 mm/rev f = 0.15 mm/rev
550
f = 0.05 mm/rev
σmax MPa
500 450 400 350 300 10000
100000
1000000
10000000
Nf cycles Fig. 3. S-N curves of machined AISI1045.
Fig. 4. Evolution rate of change of Nf function of feed rate.
Youngsik Choi (2015) investigated the influence of feed rate on surface integrity and fatigue strength of machined surface. He showed that the feed rate significantly affects fatigue life. The crack initiation lifetime as well as the propagation lifetime decreased with the increase of feed rate. The S-N curves of the machined AISI 1045 prove that the fatigue behavior is influenced by the surface roughness which is conditioned by the cutting conditions (the feed rate in our case). In what follows, surface state observations of fatigue specimen will be examined to see the modifications generated on surface roughness by the feed rate which affect the fatigue lifetime. 3.2. Effect of feed rate on surface state. Figure 5 shows global observations of the generatrix for fatigues specimens taken by optical microscopy.
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Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija. KIMAKH / StructuralIntegrity Procedia 00 (2018) 000–000
Furrow
Streak
Tearing material
(a)
(b)
(c) Fig. 5. Global observations of specimens machined with different feed rate (a) f1=0.25 mm/rev, (b) f2=0.15mm/rev and (c) f3=0.05 mm/rev.
According to the specimen observations, we notice that the feed rate changes the surface state. The specimens machined with a very high feed rate have a rougher surface state compared to those machined with low feed rate. So the surface roughness increases with the increase of feed rate. When the feed rate decreases, the number of streaks decreases and their widths increase. Also, the furrows become deeper with the increase of feed rate. On the other hand, we notice the presence of the tearing material which decreases with the decrease of the feed rate. All these geometrical irregularities represent defects which are
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija.KIMAKH / Structural Integrity Procedia 00 (2018) 000–000
249 7
more and more pronounced with the increase in the feed rate. Consequently, these defects generate stress concentrations or micro cracks, which produce a decrease in fatigue life. Surarachai et al. (2008) analyzed the influence of the surface condition on the fatigue life of the 7010 aluminum alloy tested in 4-point bending. They explained the strong dependence between the surface roughness and the fatigue strength by the stress concentration generated by the roughness streaks.N.A.Alang (2011) studied the effect of surface condition on fatigue behavior. The roughness was varied over three levels (1.77, 2.88, 5.48 μm). He found that for lifetimes less than 105 cycles, no significant difference had been recorded, but beyond 105 cycles, low roughness specimens had a longer lifetime than rough specimens. Finally, we can conclude that the fatigue behavior of the materials is influenced by the surface integrity which is a direct result of the machining process. 4. Conclusion This study presents an experimental approach to highlight a correlation between the feed rate and the fatigue performance of the AISI 1045 steel parts obtained by turning process. Three batches of fatigue specimen were machined with three different values of feed rate ( 0.25 mm/rev, 0.15 mm/rev and 0.05 mm/rev), Then tested on uniaxial fatigue with a stress ratio R=0.1. The S-N curves registered present a marked gab that illustrates the significant effect of feed rate on fatigue lifetime of fatigue specimen. In fact, a variation in the feed rate affects directly the surface roughness of the specimens which generates local stress concentrations. The level of these concentrations governs the damage process. For σmax=550MPa, an increase of feed rate from f = 0.25 mm/rev to f = 0.15 mm/rev leads to 30% of increase of fatigue lifetime and 184% of the increase of feed rate from 0.15 mm/rev to f = 0.05 mm/rev. Also it can be concluded that: The effect of feed rate is very significant for feed rate higher than 0.15mm/rev. The effect of feed rate is more pronounced for low-stress levels. The fatigue lifetime of parts obtained by turning process improves with the decrease of feed rate. References Alang, N.A., Razak, N.A., Miskam, A.K. 2011. Effect of Surface Roughness on Fatigue Life of Notched Carbon Steel. International Journal of Engineering & Technology 11, 160-163. Choi, Y. 2015. Influence of feed rate on surface integrity and fatigue performance of machined surfaces. International Journal of Fatigue 78, 4652. Davies, D. P., Jenkinsa, S. L. Legga, S. J. 2014.The Effect Machining Processes can have on the Fatigue Life and Surface Integrity of Critical Helicopter Components. Procedia CIRP 13, 25-30. Liu, G., Huang, G., Zou, B., Wang, X., Liu, Z., 2016. Surface integrity and fatigue performance of 17-4PH stainless steel after cutting operations. Surface & Coatings Technology 307, 182-189. Novovic, D., Dewes, R.C., Aspinwall, D.K., Voice, W., Bowen, P. 2004. The effect of machined topography and integrity on fatigue life. International Journal of Machine Tools & Manufacture 44, 125-134. Suraratchai, M., Limido, J., Mabru, C., Chieragatti, R. 2008. Modelling the influence of machined surface roughness on the fatigue life of aluminium alloy. International Journal of Fatigue 30, 2119–2126. Suraratchaï, M., Mabru, C., Chieragatti, R., Rezai, F.A. 2005. Influence de gammes d'usinage sur la tenue en fatigue d'un alliage léger aéronautique. 17ème Congrès Français de Mécanique. Troyes, France. Zhang, M., Wang, W., Wang, P., Liu, Y., Li, J., 2016. The fatigue behavior and mechanism of FV520B-I with large surface roughness in a very high cycle regime. Engineering Failure Analysis 66, 432-444.
Available online at www.sciencedirect.com
Available online www.sciencedirect.com Available online at at www.sciencedirect.com StructuralIntegrity Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
Procedia Structural (2018) 243–249 Structural IntegrityIntegrity Procedia900 (2016) 000–000
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
www.elsevier.com/locate/procedia
IGF Workshop “Fracture and Structural Integrity” IGF Workshop “Fracture and Structural Integrity”
Improvement of fatigue life of AISI 1045 carbon steel of parts obtained by turning process through feed steel rate of parts Improvement of fatigue life of AISI 1045 carbon XV Portuguese Conference on Fracture, PCF 2016, 10-12 February 2016, Paço de Arcos, Portugal obtained by turning process through feed rate Khadija Kimakha*, Abdelkarim Chouafa, Samir Aghzera,b, Amal Saouda, Thermo-mechanical modeling of pressure blade a a a a high a a,b,turbine Khadija Kimakha*,ElAbdelkarim Chouaf , Samir Aghzer Amal Saoud , of an , M’hamd Chergui hassan Malil airplane gas turbine engine a LCCMMS,ENSEM, Hassan II Universitya , 7 km road of el jadida, Casablanca, Morocco a
El hassan Malil , M’hamd Chergui P. Brandão , V. Infante , A.M. Deus *
EST, ENSEM, Hassan II University , 7 km road of el jadida, Casablanca, Morocco a b c a LCCMMS,ENSEM, Hassan II University , 7 km road of el jadida, Casablanca, Morocco b EST, ENSEM, Hassan II University , 7 km road of el jadida, Casablanca, Morocco a Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract b IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Abstract c work investigates the effect of cutting conditions on the fatigue performance of the parts generated by turning This CeFEMA, Department of Mechanical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal process. There are various parameters such as cutting speed, feed rate and tool nose radius that are known for their b
This work investigates thequality effect of conditions on the fatigue performance of rate the parts significant impact on the of cutting machined parts. The relationship between feed as a generated parameter by of turning cutting process. There such cutting speed, feed ratecase and tool radius are known for were their conditions and are the various fatigue parameters performance willas be highlighted. In that threenose batches of that fatigue specimen Abstract impact on the quality of machined parts. The relationship between feed rate as a parameter of cutting significant realized on an Alpha 1530xs CNC lathe, then tested on fatigue with a stress ratio R=0.1. The results are presented conditions and the fatigue performance will beofhighlighted. Inonthat three of fatigue specimen were through S-N curves which illustrate the engine impact the feed rate the case fatigue life batches performance. In operating fact, the feed rate During on their operation, modern aircraft components are subjected to increasingly demanding conditions, realized an Alpha 1530xs CNC lathe, then tested on fatigue with a stress ratio R=0.1. The results are presented affects the fatigue life performance spatially for low values of feed rate. The fatigue lifetime decrease with the especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent through S-N curves which illustrate the impact of the feed rate on the fatigue life performance. In fact, the feed rate increase of feed degradation, onerate. of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict affects the behaviour fatigue life spatially low values of feed rate. The fatigue lifetime with the the creep of performance HPT blades. Flight datafor records (FDR) for a specific aircraft, provided by a decrease commercial aviation increase of feed rate. company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model
© needed 2018 The Authors. Published byaElsevier B.V. the FEM analysis, HPT © 2018 Thefor Authors. Published by Elsevier B.V.blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fedItaliano into theFrattura FEM different simulations were run, first with a simplified 3D Peer-review under responsibility of the Gruppo (IGF)and ExCo. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF)model ExCo. © rectangular 2018 The Authors. Published by to Elsevier block shape, in order better B.V. establish the model, and then with the real 3D mesh obtained from the blade scrap. The Peer-review underprocess; responsibility of theofGruppo Italiano Frattura (IGF)inExCo. overall expected behaviour in conditions; terms displacement was observed, particular at the trailing edge of the blade. Therefore such a Keywords:Turning cutting feed rate; fatigue life; model can be useful in the goal of predicting turbine blade life, given a set of FDR data. Keywords:Turning process; cutting conditions; feed rate; fatigue life;
© 2016 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of PCF 2016. Keywords: High Pressure Turbine Blade; Creep; Finite Element Method; 3D Model; Simulation.
* Corresponding author. Tel.: +212 67 50 91 55 05. E-mail address:[email protected] * Corresponding author. Tel.: +212 67 50 91 55 05. E-mail address:[email protected] 2452-3216© 2018 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. 2452-3216© 2018 The Authors. Published by Elsevier B.V.
Peer-review underauthor. responsibility the Gruppo Italiano Frattura (IGF) ExCo. * Corresponding Tel.: +351of 218419991. E-mail address: [email protected]
2452-3216 © 2016 The Authors. Published by Elsevier B.V.
Peer-review under responsibility of the Scientific Committee of PCF 2016. 2452-3216 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Gruppo Italiano Frattura (IGF) ExCo. 10.1016/j.prostr.2018.06.039
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija. KIMAKH / StructuralIntegrity Procedia 00 (2018) 000–000
244 2
1. Introduction The lifetime prediction of mechanical structures has become a major subject in many industrial sectors: aeronautics, automotive... Many factors other than the mechanical proprieties of the material affect its ability to resist fatigue phenomenon. Besides these factors, the manufacturing process has a significant role in the fatigue strength. In fact, these methods including the machining are often associated with significant thermo-mechanical stresses that may result in heterogeneous properties in the materials. The impact of these properties, usually generated in surface and subsurface of the machined parts, could significantly affect the behavior of mechanical component subjected to fatigue loads. The fatigue cracks are generally initiated from free surfaces. The surface of a piece has two important aspects that have to be defined and controlled. The first aspect is geometric irregularities on the surface, and secondly the metallurgical alterations of the surface and the subsurface. This second aspect has been termed surface integrity. Several researchers have been interested in investigating the influence of cutting conditions on fatigue life. Ming Zhang (2016) proves that surface roughness has a significant effect on VHCF properties of FV520B-I, and VHCF properties of FV520B-I impeller can be improved by reducing surface roughness. D. Novovic et al. (2004) attest that both surface integrity and surface topography have a significant effect on fatigue performance of machined parts. It has been testified that for low surface roughness the fatigue lifetime depends on surface roughness. But for surface roughness higher than Ra = 2.5 µm, the fatigue performance depends on residual stress. Guoliang Liu et al. (2016) analyzed the modifications generated by cutting operation on surface integrity (residual stress, microstructure and surface roughness). The influence of surface roughness on the fatigue performance could be overshadowed by other surface integrity characteristics. Monchaï Suraratchaï et al. (2005, 2008) investigate the influence of machined surface on the fatigue life of 7010 aluminum alloy. They proposed a model, based on surface topography to predict fatigue lifetime. D P Davies et al. (2014) interested in Critical Helicopter Components. Different manufacturing methods were carried out to enhance the fatigue performance. Our work aims to identify a relationship between turning process parameters and fatigue behavior of the mechanical component. An experimental study is carried out to analyze this relationship. The cylindrical specimen for fatigue testing was released in CNC lathe Alpha 1530XS with 3 different values of feed rate. After specimen’s preparation, fatigue testing is accomplished to determine the fact of feed rate on fatigue lifetime. The results obtained are presented through S-N curves which highlighted the impact of feed rate on the fatigue life of parts. Nomenclature Re0.2% Rm A E R f ɛ σ σmax Nf
Yield strength Tensile strength Elongation Elasticity modulus Stress ratio Feed rate strain Stress Maximum stress Number of cycles failure
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija.KIMAKH / Structural Integrity Procedia 00 (2018) 000–000
245 3
2. Material and experimental set-up 2.1 Material The material used in this study was AISI 1045 steel with 0.42 of Carbone. The chemical compositions of the material have been identified by using spectrometer machine. The chemical composition of this steel is given in Table 1. Table1. Chemical composition of AISI 1045 Steel
Chemical composition (%)
AISI 1045
C
Mn
S
P
Si
0.42
0.72
0.02
0.04
0.19
A tensile test was carried out According to the ASTM E8 Standard, to establish mechanical proprieties of the material used. The mechanical proprieties are shown in table2. Table 2. Mechanical proprieties of AISI 1045. Steel
Mechanical proprieties
AISI 1045
Re0.2%[MPa]
Rm [MPa]
A%
E [GPa]
432
645
23
211
2.2. Fatigue test This study aims to analyze the effect of feed rate on fatigue life of the pieces obtained by turning process. Then three batches of specimens were machined. Fatigue tests were carried out on four levels of stress and for each level the fatigue tests were repeated three times. The test specimens were machined by turning process in wet condition. Turning operation was performed using DNMG 11 04 08 insert. A CNC lathe (Alpha 1530XS) was used for the longitudinal turning of the specimens and the cutting conditions employed for machining are listed in Table 3. Table 3. Cutting conditions Parameters
Description
Feed rate (mm/rev)
0.05, 0.15, 0.25
Cutting speed (rev/min)
2000
Depth of cut (mm)
0.5
Tool nose radius(mm)
0.8
Coolant
Wet
Specimens are conforming to the standard ASTM 466. Figure 1 present dimension of fatigue specimen with the recommended diameter d =6.35mm.
246 4
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija. KIMAKH / StructuralIntegrity Procedia 00 (2018) 000–000
Fig. 1. Fatigue specimen.
After specimens preparation fatigue tests were performed with MTS 810 hydraulic testing machine shown in figure 2 with a maximum capacity 100 kN. The machined specimens were subjected to constant amplitude tension– tension axial fatigue. Tests were conducted in load control with a sinusoidal load waveform and for each batch of specimens four levels of stress load were applied. Table 4 listed the levels of stress. The fatigue tests were carried out with a constant frequency of 40 Hz and a stress ratio R = 0.1 (minimum load/maximum load) was applied throughout the experiment. Once the specimen was broken, the machine stopped automatically.
Fig. 2. Fatigue specimen configuration. Table 4. Levels of the applied load. stress σmax σmin
levels 400 40
450 45
500 50
525 52.5
550 55
3. Result and discussion 3.1 S-N curve Figure 3 presents the S-N curve for the three batches of machined AISI 1045. Based on the experimental data and the observations of fatigue tests for every batch of specimens, the feed rate affects the fatigue life of the AISI1045 steel parts obtained by turning process. The results show that the machined specimens with a low feed rate f3 = 0.05mm/rev have a longer lifetime than specimens machined with high feed rate (f2 = 0.15mm/rev and f1 = 0.25 mm/rev). We also notice that when thefeed rate decrease from f1 = 0.25 mm/rev to f2 = 0.15 mm/rev with a step of 0.1 mm/rev, the number of cycles to faillure increase with a percentage of 17% forσmax = 550MPa and 135% for σmax = 500MPa. But when it decrease from f2 =
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija.KIMAKH / Structural Integrity Procedia 00 (2018) 000–000
247 5
0.15 mm/rev to f3 = 0.05 mm/rev the number of cycles to faillure increase clearly with a percentage of 30% for σmax= 550MPa and 184% for σmax = 500MPa (figure 4). 600
f = 0.25 mm/rev f = 0.15 mm/rev
550
f = 0.05 mm/rev
σmax MPa
500 450 400 350 300 10000
100000
1000000
10000000
Nf cycles Fig. 3. S-N curves of machined AISI1045.
Fig. 4. Evolution rate of change of Nf function of feed rate.
Youngsik Choi (2015) investigated the influence of feed rate on surface integrity and fatigue strength of machined surface. He showed that the feed rate significantly affects fatigue life. The crack initiation lifetime as well as the propagation lifetime decreased with the increase of feed rate. The S-N curves of the machined AISI 1045 prove that the fatigue behavior is influenced by the surface roughness which is conditioned by the cutting conditions (the feed rate in our case). In what follows, surface state observations of fatigue specimen will be examined to see the modifications generated on surface roughness by the feed rate which affect the fatigue lifetime. 3.2. Effect of feed rate on surface state. Figure 5 shows global observations of the generatrix for fatigues specimens taken by optical microscopy.
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Furrow
Streak
Tearing material
(a)
(b)
(c) Fig. 5. Global observations of specimens machined with different feed rate (a) f1=0.25 mm/rev, (b) f2=0.15mm/rev and (c) f3=0.05 mm/rev.
According to the specimen observations, we notice that the feed rate changes the surface state. The specimens machined with a very high feed rate have a rougher surface state compared to those machined with low feed rate. So the surface roughness increases with the increase of feed rate. When the feed rate decreases, the number of streaks decreases and their widths increase. Also, the furrows become deeper with the increase of feed rate. On the other hand, we notice the presence of the tearing material which decreases with the decrease of the feed rate. All these geometrical irregularities represent defects which are
Khadija Kimakh et al. / Procedia Structural Integrity 9 (2018) 243–249 Khadija.KIMAKH / Structural Integrity Procedia 00 (2018) 000–000
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more and more pronounced with the increase in the feed rate. Consequently, these defects generate stress concentrations or micro cracks, which produce a decrease in fatigue life. Surarachai et al. (2008) analyzed the influence of the surface condition on the fatigue life of the 7010 aluminum alloy tested in 4-point bending. They explained the strong dependence between the surface roughness and the fatigue strength by the stress concentration generated by the roughness streaks.N.A.Alang (2011) studied the effect of surface condition on fatigue behavior. The roughness was varied over three levels (1.77, 2.88, 5.48 μm). He found that for lifetimes less than 105 cycles, no significant difference had been recorded, but beyond 105 cycles, low roughness specimens had a longer lifetime than rough specimens. Finally, we can conclude that the fatigue behavior of the materials is influenced by the surface integrity which is a direct result of the machining process. 4. Conclusion This study presents an experimental approach to highlight a correlation between the feed rate and the fatigue performance of the AISI 1045 steel parts obtained by turning process. Three batches of fatigue specimen were machined with three different values of feed rate ( 0.25 mm/rev, 0.15 mm/rev and 0.05 mm/rev), Then tested on uniaxial fatigue with a stress ratio R=0.1. The S-N curves registered present a marked gab that illustrates the significant effect of feed rate on fatigue lifetime of fatigue specimen. In fact, a variation in the feed rate affects directly the surface roughness of the specimens which generates local stress concentrations. The level of these concentrations governs the damage process. For σmax=550MPa, an increase of feed rate from f = 0.25 mm/rev to f = 0.15 mm/rev leads to 30% of increase of fatigue lifetime and 184% of the increase of feed rate from 0.15 mm/rev to f = 0.05 mm/rev. Also it can be concluded that: The effect of feed rate is very significant for feed rate higher than 0.15mm/rev. The effect of feed rate is more pronounced for low-stress levels. The fatigue lifetime of parts obtained by turning process improves with the decrease of feed rate. References Alang, N.A., Razak, N.A., Miskam, A.K. 2011. Effect of Surface Roughness on Fatigue Life of Notched Carbon Steel. International Journal of Engineering & Technology 11, 160-163. Choi, Y. 2015. Influence of feed rate on surface integrity and fatigue performance of machined surfaces. International Journal of Fatigue 78, 4652. Davies, D. P., Jenkinsa, S. L. Legga, S. J. 2014.The Effect Machining Processes can have on the Fatigue Life and Surface Integrity of Critical Helicopter Components. Procedia CIRP 13, 25-30. Liu, G., Huang, G., Zou, B., Wang, X., Liu, Z., 2016. Surface integrity and fatigue performance of 17-4PH stainless steel after cutting operations. Surface & Coatings Technology 307, 182-189. Novovic, D., Dewes, R.C., Aspinwall, D.K., Voice, W., Bowen, P. 2004. The effect of machined topography and integrity on fatigue life. International Journal of Machine Tools & Manufacture 44, 125-134. Suraratchai, M., Limido, J., Mabru, C., Chieragatti, R. 2008. Modelling the influence of machined surface roughness on the fatigue life of aluminium alloy. International Journal of Fatigue 30, 2119–2126. Suraratchaï, M., Mabru, C., Chieragatti, R., Rezai, F.A. 2005. Influence de gammes d'usinage sur la tenue en fatigue d'un alliage léger aéronautique. 17ème Congrès Français de Mécanique. Troyes, France. Zhang, M., Wang, W., Wang, P., Liu, Y., Li, J., 2016. The fatigue behavior and mechanism of FV520B-I with large surface roughness in a very high cycle regime. Engineering Failure Analysis 66, 432-444.