The use of simulation technologies such as FEA to optimise component life both during design and to rectify problems is well established. Whether the analyst is an external consultant or direct hire, however implementing an effective analysis approach that truly drives business results remains a challenge for a lot of NZ companies.
Reduce the risk of your part cracking by a factor of 10 with sensible analysis
1. Reduce the risk of cracking by a
factor of 10 A Better by Analysis™ approach
Leon Daly
Analysis & Operations Manager
Motovated Design & Analysis Ltd
Copyright 2018
2.
3. Minimum Viable Simulation (MVS)™
• Minimize batch size
• Timebox work
• Prioritize validated learning
• Use Moore’s law
• Train designers in analytical methods
• Systematise psychological safety
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4. Fatigue
Material fatigue is a phenomenon where structures fail when
subjected to a cyclic load. This type of structural damage
occurs even when the experienced stress range is far below
the static material strength. Fatigue is the most common
source behind failures of mechanical structures.
https://www.comsol.com/multiphysics/material-fatigue
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5. Fatigue
• Why fatigue matters
• Fatigue evaluation methods
• Fatigue concepts – stress life
• What’s really important (design killers)
• Increasing part life by a factor of ~14000; an example
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10. Effect of surface treatments
1. Shot peening (Steel and Aluminium) +50%
2. Nitriding (Steel): +50%
3. Weld toe grinding (Steel): +30%
4. Induction/flame hardening (Steel): +30%
Note: 50% increase in fatigue strength:
≈ 3.5 fold increase in part life (if welded)
≈ 15 fold increase in part life (typical machined part)
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11. Effect of surface treatments - continued
1. Zinc plating (Steel): No change
2. Hot dip galvanising (Steel): -40%
3. Chrome, Nickel, and Cadmium plating (Steel): -50%
4. Corrosion (Steel): -50%
5. Anodising (Al alloys): -62%
Note: 50% increase in fatigue strength:
≈ 3.5 fold increase in part life (if welded)
≈ 15 fold increase in part life (typical machined part)
12. What's really important
1. Surface finish
2. Surface treatment
3. Preload (bolts)
Email Leon@motovated.co.nz for slides
13. What's really important
1. Surface finish
2. Surface treatment
3. Preload (bolts)
4. Maximising the difference between component stress and
material strength.
Email Leon@motovated.co.nz for slides
17. A worked example
Original stress = 71.8 MPa
Optimised stress = 42.9 MPa
Reduction factor = 0.6
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18. A worked example
Original stress = 71.8 MPa
1. Initial life: 56 hours (50% nominal probability of failure)
2. Increase reliability to ~99%: 5 times life decrease = 11 hours
3. Reduce stress as per example above: 58 times life increase
4. Change material from medium tensile AISI 1040 to PH 17-4
stainless steel: a further 247 times life increase
5. Final life estimate: 158000 hours/6470 days
Email Leon@motovated.co.nz for slides
19. • 38 bogies built
• Several have hit the
1.1 million km mark!
Case study – KiwiRail passenger bogies
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20. Summary
1. Lean/Agile methods can make a big difference in Simulation
2. Be aware of good fatigue design practice
3. Be careful with component surface treatments
4. Bolt preload is your friend
5. Use good materials and minimise stress
Email Leon@motovated.co.nz for slides
Mihi
Simulation Management
Fatigue
KR Bogie
Sim mgmt. Finite, CFD - 10X
Fatigue 90% Awareness
Conferences
Value is obvious
When, how much, what to focus on?
Engineers
Lost in the weeds
Want to be sure – more they look
Rigid definition of quality – believe there is only one appropriate scope
Communication burden between designers and analysts
Overconservative – don’t like to be wrong
80:20
Batch - increasing in scope progressively. Get a feel for risk around what's not analysed.
Timebox – separate analysis timebox from documentation timebox
Learning – Tradeoffs, A3’s, system behaviour, design hardpoint identification
Moores – Computer pwr doubling. Too much simplification for the time taken.
Train – Wasted movement. Absolute results difficult; optimisation and comparative analysis easy to teach
Psychological safety – the secret sauce. Build in. e.g. fatigue
Disclaimer
When a bolt fails – often fatigue
Cam belt brakes
Cracked heels
Mountain bike weld cracks
Cell phone charger port electronics
The living hinge on a plastic lunch box dies - fatigue
Fatigue is responsible for 90% of mechanical failures - important!
key insights into fatigue that I hope will allow you to make better decisions and better designs.
Fatigue is complex. The numbers I give in this presentation are real and well researched. However, nothing is black and white and there are caveats – cases where what I am saying is more or less of a factor. I’m not going to spend my 30 mins getting into the fine detail as I fear the basic points will be lost. So please don’t take these numbers directly and apply them to your circumstance without some research.
Kieland Norweigian 123 Killed
The little things
I’m in a privileged position to learn from the success and failures of the best companies in NZ. The reason I’m doing this presentation is that I see on a monthly basis how important good fatigue design is. The difference between a robust design and a constant warranty headache are often small, seemingly insignificant design choices. I believe that a little rigour in our engineering makes the difference between that bad side of No 8 wire and the good, innovative aspect. So I’d like to kick things off by introducing a few clients https://en.wikipedia.org/wiki/Alexander_L._Kielland_(platform)
Whiteboard
Sample
Normal distribution
Endurance limit
Modifiers
Non linear
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Normal distribution
Endurance limit
Modifiers
Non linear
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Normal distribution
Endurance limit
Modifiers
Non linear
(6470, 24hr days at 1% nominal probability of failure)
The designers were the analysts
Rapid evaluation and multiple analysis rounds with ever increasing level of detail were undertaken.
These methods have proven incredibly powerful; even in the highly regulated aerospace and rail industries.
PRV valve
27 times around the earth
Whiteboard
Sample
Normal distribution
Endurance limit
Modifiers
Non linear
