Plan for Friday, November 20, 2015
9:00
Review
- For fully reversed ferrous and non-ferrous metals we can estimate the S-N curve for our actual mechanical part.
- The low cycle fatigue boundary can be estimated with f.
- The endurance limit can be estimated by the unmodifed endurance limit (different for ferrous and non-ferrous) and the Marin parameters.
- The high cycle fatigue strength can then be estimated.
- This is an estimate and no factor of safety has been applied.
Goals
- Introduce fatigue stress concentrations and notch sensitivity
- Do some fully reversed examples.
- Introduce fluctuating stress and the modifications needed to relate the S-N curve for fully reversed.
- Do fluctuating examples.
- Discuss tables in the back of the book.
- Discus memos.
- Discuss project struggles: modeling, FEA
9:05
Broken derailleur
9:10
Stress concentrations lecture
9:20
Fully reversed example #1
9:30
Fully reversed example #2
9:40
Discuss tables in the back of the book
9:45
Questions
9:50
Break
10:00
Fluctuating Stress Lecture
10:15
Example
10:30
Memo discussion:
- Memos are small portion of overall grade.
- The goal is to show me the results of your weekly work so that I can give you feedback for your final report to be awesome.
- You have 3-4 people so your memo's should be higher quality that project one drafts.
- Make every word count, don't add things that don't tell your story. Make an outline of the main points you want to express to me and focus on those.
- Things in the memo can be wrong and need improvements. That is fine! You don't have to get it perfect now but you need to show me that you are putting critical thought into it.
Modeling discussion:
- Please come and see me to discuss your specific designs as I can give you tons of little tips that are specific to you design.
- Folks are struggling with the modeling step: taking a real physical thing and seeing the simplified versions of it for stress estimations.
- Break into the smallest components, simplify (ignore welds, ignore stress concentrations), and draw free body diagram.
- Fully detailed designs are not needed for FEA stress estimations. Only draw the essential parts so that you can iterate quickly through the main design descisions: tube diameter and wall thickness, etc
- You will get statically indeterminant designs!
Next is a memo on fatigue:
Short activity. Pair up and make a list of 5 essential things you are going to need to determine for the upcoming memo: