Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 74 (2014) 392 – 396
XVII International Colloquium on Mechanical Fatigue of Metals (ICMFM17)
Rolling contact fatigue life assessment of induction hardened raceway Peter Göncza*, Sreþko Glodežb a,b
University of Maribor, Faculty of Mechanical Engineering, SI-2000 Maribor, Slovenia
Abstract In this paper the assessment of the rolling contact fatigue life of an induction hardened raceway is presented. For determination of the equivalent subsurface stress distribution field in the raceway, 3D numerical model of the contact between the through hardened roller made of 100Cr6 steel and the surface hardened raceway made of 42CrMo4 was employed. The calculation of the contact fatigue life of the raceway was then carried out in the stress-life regime. Additionally, alternative HCF parameters for the 42CrMo4 steel in compression were experimentally determined with pulsating compression tests. For the experimental validation of computationally determined fatigue life of the induction hardened raceways, test specimens for RCF bench were manufactured and their testing has started.
© Elsevier Ltd. Published Open access CC BY-NC-ND license. © 2014 2014 The Authors. byunder Elsevier Ltd. Selection and peer-review peer-reviewunder underresponsibility responsibilityofofthethe Politecnico Milano, Dipartimento di Meccanica Selection and Politecnico di di Milano, Dipartimento di Meccanica. Keywords: roller slewing bearings, rolling contact fatigue, 42CrMo4 steel.
1. Introduction Slewing bearings are mechanical components used to connect large structures, while allowing relative rotation and transmission of external loads between them. Although there are standardized calculation procedures for conventional rolling element bearings [1, 2], they are not directly suitable for slewing bearings [3, 4]. One of the reasons for that is the use of different steels and heat treatments in case of slewing bearings. Thus, rings of slewing bearings are machined from high grade steels, such as 42CrMo4 [5] and are case hardened. By this, higher load capacity and wear resistance of the raceways is achieved. This also results in with depth changing mechanical
* Corresponding author. Tel.: +386-2-220-7671 E-mail address:
[email protected]
1877-7058 © 2014 Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and peer-review under responsibility of the Politecnico di Milano, Dipartimento di Meccanica doi:10.1016/j.proeng.2014.06.286
Peter Göncz and Srečko Glodež / Procedia Engineering 74 (2014) 392 – 396
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properties of these rings. Because of this, different numerical computational approaches are usually used for both static and dynamic load capacity determination of slewing bearing raceways. In this paper, a computational procedure for determination of fatigue life of a roller slewing bearing’s raceway is presented. First, a quasi-static numerical simulation of the roller – raceway contact was used to determine the subsurface equivalent amplitude stress in the raceway. Then the stress-life or high cycle fatigue (HCF) approach was used to assess the raceway’s service life. Additionally, alternative high cycle parameters for steel 42CrMo4 were experimentally determined to directly take the effect of compression mean stress for contact fatigue into account. Finally, the experimental setup for fatigue life on a rolling contact fatigue bench in presented. Nomenclature b c E N Q R Ȟ ıa ıeq ı f’ ım ıu
[/] [/] [GPa] [/] [kN] [/] [/] [MPa] [MPa] [MPa] [MPa] [MPa]
fatigue strength exponent; fully reversed cyclic loading (R = 1) subscript for pulsating compression cyclic loading (R = ) Young's modulus number of loading cycles contact force load ratio; Qmin/Qmax Poisson's ratio alternating stress equivalent stress fatigue strength coefficient; fully reversed cyclic loading (R = 1) mean stress ultimate tensile strength
2. Fatigue life assessment 2.1. Numerical model of the contact problem The first step in the fatigue life assessment was the determination of the subsurface equivalent amplitude stress (ıeq,a) distribution in the raceway at given contact force (Q) (Fig. 1a). A numerical model of the contact between the roller and raceway was used for this. A 3D solid 1/4th symmetry model of the roller and raceway segment was prepared in FEA software ABAQUS [6]. In the contact simulation a partially-crowned roller (type ZB [7]) with a nominal length and diameter of 25 mm and profile curvature of 475 mm was used. For both parts in contact a linearelastic material model (Ȟ = 0.3, Eroll = 201 GPa and Erace = 207 GPa) was defined, while a hexahedral mesh was applied on them. A normal contact without friction was defined between them (Fig. 1b).
Fig. 1. (a) 3D numerical model of the roller –raceway contact; (b) resulting equivalent amplitude stress (ıeq,a) field.
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2.2. Fatigue life calculation In this paper the stress-life approach was used to calculate the service life of the slewing bearing’s raceway. In this approach the Basquin’s equation (Eq. 1) is usually used to describe the relation between the alternating stress (ıa) and the number of loading cycles (N) until failure [8]. As the fatigue parameters ıf’ and b are experimentally determined at fully reversed cyclic loading (R = 1) [9], the effect of non-zero mean stress must be considered, e.g. with Goodman’s relation (Eq. 2) [8]. Mises’ equivalent stress theory was used to consider the multiaxial stress field.
ıa(c) = ıf(c) ' (2 N )b( c ) ıa =
(1)
ı eq,a ı u
(2)
ı u − ı eq,m
2.3. Experimental determination of HCF parameters in compression There are different ways for the equivalent mean stress (ıeq,m) consideration (Eq. 2). Thus, it can be calculated as the equivalent Mises stress (ıeq,m) [8], as the equivalent Mises stress with a negative sign (−ıeq,m) [10], etc. To directly include the mean stress effect in fatigue parameters for steel 42CrMo4 at contact fatigue (ıfc’, bc), special specimens (Fig. 2a) were subjected to pulsating compression loading (Fig. 2b) on a servohydraulic fatigue test machine (Fig. 2c). The results of experiments for different hardnesses are presented in Fig. 3, together with fatigue curves calculated on the basis of standard fatigue parameters (ıf’, b) [10] and two equivalent mean stress considerations.
ıfc' = 1162 Nmm-2 bc = −0.0077 ıac = ıfc'(2N) r² = 0.414
800 600
Nizi1 failure no brezfailure porušitve + N ı(+ Mises) eq,m оı N (-eq,m Mises)
400
200
102
103 104 105 Load cycles- N [/]
a)
106
bc
1600 1400 1200 1000
ıfc' = 929 Nmm-2 bc = −0.0116 ıac = ıfc'(2N) r² = 0.742
Alternating stress - σa [MPa]
1600 1400 1200 1000
Alternating stress - σa [MPa]
Alternating stress - σa [MPa]
Fig. 2. (a) Specimen dimensions; (b) fully reversed (R = 1) and pulsating compression (R = F\FOLFORDGLQJ F experimental setup.
bc
800 600 400
200
failure porušitev no failure brez porušitve +Nı(+ Mises) eq,m оı N (Mises) eq,m 102
103 104 105 Load cycles- N [/]
b)
1600 1400 1200 1000 800 600
ıac = ıfc'(2N) r² = 0.602
bc
400 ıfc' = 685 Nmm-2 bc = −0,0374
200 106
failure porušitev brez porušitve no failure + N ı(+ Mises) eq,m оı N (-eq,m Mises)
102
103 104 105 Load cycles- N [/]
c)
106
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Peter Göncz and Srečko Glodež / Procedia Engineering 74 (2014) 392 – 396 Fig. 3. Experimental ı N diagrams for steel 42CrMo4 in pulsating compression loading at (a) 56 HRC, (b) 45 HRC and (c) 28 HRC.
2.4. Computational results The raceway’s fatigue life can be calculated on the basis of subsurface equivalent amplitude stress (ıeq,a) profiles at different critical positions (y) along the roller – raceway contact line. This method also allows to consider the influence with depth (z) changing material properties of the case hardened raceways on the fatigue life. Fig. 4 shows the influence of two different depths of case hardened layers on fatigue life at contact force Q = 92 kN. For the smaller case depth the shortest fatigue life is at the transition between the case and the basic material (Fig. 4a), whereas for the larger case depth the position of the minimal fatigue life is expected in the case hardened region (Fig. 4b). 0,0
0,0 center R=-1 (ı (S+) f', b; +ıeq,m)
-0,5 -1,5
rob
transition
center R=-1 (ı (S-) f', b; ıeq,m)
-2,0
center
-2,5
edge R=-1(ı(S-) robeq,m) f', b; ı
-3,0 -3,5
center (ıfc', bc) R=-8 center
-4,0
R=-8(ırob edge fc', bc)
-4,5 103
104
105
106
107
108
Load cycles - N ͬ
a)
109
edge R=-1(ı(S+) f', b; +ıeq,m)
case
-1,5
rob center (ıf', b; ıeq,m) R=-1 (S-)
-2,0
center
-2,5
transition
edge R=-1(ı(S-) ıeq,m) f', b; rob
-3,0 -3,5
R=-8 center center (ıfc', bc)
-4,0
basic mat. 102
center
-1,0
edge R=-1(ı(S+) f', b; +ıeq,m)
Depth - z [mm]
Depth - z [mm]
-1,0
center (ıf', b; +ıeq,m) R=-1 (S+)
-0,5
center
case
basic mat. R=-8(ırob edge fc', bc)
-4,5 102
103
104
105
106
107
108
109
Load cycles - N ͬ
b)
Fig. 4. Fatigue life profiles N(z) of the case hardened raceway at Q = 92 kN: (a) dcase = 1.5 mm and (b) dcase = 2.5 mm.
3. Conclusion In the presented paper a service life assessment method of an induction hardened raceway of a large roller slewing bearing is demonstrated. Alternative fatigue parameters (ıfc’, bc) for steel 42CrMo4 in pulsating compression loading (R = ) were experimentally determined and used for computational determination of fatigue life. Additionally, two ways of equivalent mean stress considerations (ıeq,m ,−ıeq,m) were used in combination with standard fatigue parameters (ıf’, b). Case hardened rolling contact fatigue (RCF) specimens from steel 42CrMo4 were manufactured and their experimental testing on a RCF bench is currently being carried out to validate the herein presented service life assessment method. References [1] ISO 76. Rolling bearings - Static load ratings. International Organization for Standardization, Geneva, Switzerland, 2006. [2] ISO 281. Rolling bearings - dynamic load ratings and rating life. International Organization for Standardization, Geneva, Switzerland, 2007. [3] P. Göncz, M. Drobne, S. Glodež, Computational model for determination of dynamic load capacity of large three-row roller slewing bearings. Engineering Failure Analysis (2013), vol. 32, pp. 44-53. [4] P. Göncz, R. Potoþnik, S. Glodež, Computational model for determination of static load capacity of three-row roller slewing bearings with arbitrary clearances and predefined raceway deformations. International Journal of Mechanical Sciences (2013), vol. 73, pp. 82-92. [5] Catalog 390. Slewing rings/turntable bearings. Kaydon Corporation, 2010. [6] Abaqus/CAE User's Manual (ver. 6.12), 2012, Dassault Systèmes. [7] Zylinderrollen / Technische Information, 2013, TIS Wälzkörpertechnologie GmbH. [8] R. I. Stephens, A. Fatemi, R. R. Stephens, H. O. Fuchs, Metal Fatigue in Engineering, 2nd Edition: John Wiley & Sons, Inc., 2001. [9] DIN 50113. Testing of metals; Rotating bar bending fatigue test. Deutsches Institut für Normung e.V., Berlin, 1982.
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Peter Göncz and Srečko Glodež / Procedia Engineering 74 (2014) 392 – 396 [10] S. Glodež, R. Potoþnik, J. Flašker, Computational model for calculation of static capacity and lifetime of large slewing bearing's raceway. Mechanism and Machine Theory (2012), vol. 47, pp. 16-30.
