asperities and surface initiated rolling contact fatigue bo alfredsson solid mechanics at kth...
TRANSCRIPT
![Page 1: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/1.jpg)
Asperities and surface initiated rolling contact fatigueBo Alfredsson Solid Mechanics at KTH2015-10-07 – Tribodays Nynäshamn
![Page 2: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/2.jpg)
Rolling contact fatigue
Rolling contact fatigue has been considered the default failure mode of Hertzian rolling contact elements:
If all other failure modes could be avoided, then rolling contact fatigue would eventually limit the component life.
![Page 3: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/3.jpg)
Rolling Contact Fatigue – gears and bearings
![Page 4: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/4.jpg)
Two types of Rolling Contact Fatigue
w
v ≈ w · r Rollingcontact
Sub-surface initiation
3 mm
Tallian 1992
Surface initiation
![Page 5: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/5.jpg)
Surface initiated spalling
0.2 mm
0.1 mm
b
= 20 – 24º
![Page 6: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/6.jpg)
General conditions for fatigue initiation and fatigue crack growth
Initiation Sufficiently large shear stress amplitude Tensile maximum stress
Fatigue crack growth Sufficiently large DKI ( > Kth, which is R dependent)
Open crack tip: KI,max – DKI > KI,cl
Crack with mode II or mode III fatigue load will arrest or kink to mode I Crack will follow direction of maximum DKI
![Page 7: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/7.jpg)
Whole contact: 2D line contact
Þ Always pressure!Þ Stress free surface
r
Pr
cos2 (J 2.15)
sr
rq
Line load – 2D
P
![Page 8: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/8.jpg)
The spall is local,asperity is local – local point contact
Tensile radial stress!
3
21max,
or
p
z
r
sr
Sphere
![Page 9: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/9.jpg)
Asperity mechanism for surface initiated spalling
Inside – compression
Together
Line
Cmpressive stressesStress free
Entry – compression and tension
Asperity point contact
Tensile surface stress
![Page 10: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/10.jpg)
Gear surface roughness profile
• Asperity size from roughness measurements• Radius of curvature at roll circle – R = 13.6 mm• Nominal contact pressures: 2.10 – 2.27 Gpa• Model asperities
d h /mm
200 2100 150 2
Yes, asperities exist! How can they be responsible for spalling?
![Page 11: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/11.jpg)
Stress in front of rolling contact entering asperity
d = 200 mm h = 2 mm
d = 100 mm h = 2 mm
d = 100 mm h = 1 mm
d = 50 mm h = 2 mm
![Page 12: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/12.jpg)
Influence of asperity size: lasp = hasp/rasp
![Page 13: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/13.jpg)
Influence of contact friction: m
![Page 14: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/14.jpg)
Influence of residual surface stress: sR / MPa
![Page 15: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/15.jpg)
Asperity mechanism for surface RCF: Questions to be answered
Can a point contact give fatigue? Do the conditions exist in applications?
Asperities?Stress levels?
Is the crack behaviour predicted? Crack profile of spalls Spalling life
Is the parameter influence predicted? Residual surface stress Surface roughness
Lubrication film thickness and EHD influenceo Well, more to followo On-going research
Mechanism explains why and how • Design guidelines
![Page 16: Asperities and surface initiated rolling contact fatigue Bo Alfredsson Solid Mechanics at KTH 2015-10-07 – Tribodays Nynäshamn](https://reader035.vdocuments.net/reader035/viewer/2022062519/5697bff11a28abf838cbb6d8/html5/thumbnails/16.jpg)
Asperities and surface initiated rolling contact fatigue
Bo Alfredsson