Fatigue Failure Analysis

[haniie]

this is why i dont go to class anymore. a long-winded 1 hour lecture can never beat a well-explained 6 minute video

[henzehe]

Bending a wire back and forth to break it struck me as a strange choice of example of fatigue failure. It is an example of repeatedly exceeding yield stress and repeated permanent deformation in a ductile material. When making a structure or device out of ductile/malleable materials the designer should almost always keep cyclic stresses lower than the yield stress (and usually non cyclic stresses too for that matter). Breaking this design rule usually results in a uselessly short lifespan. The value of fatigue failure analysis lies in its ability to predict if/when parts that seem to be working fine initially will crack. This isn't the case with the bent wire. A little research revealed a better analytical tool for the wire bending example exists; the Coffin-Manson relation uses strain rather than stress in order to predict failure in ductile materials that are subjected to repeated deformation.

[Vrang]

Wow. That was easier than I thought. Thank you for taking the time to make this!

[jasonr]

The best visualisation and explanation of fatigue i have seen thanks

[VirendraBG]

0:30 it's *Ratcheting* (cyclic load which results stress more than yield stress in every cycle) and I guess not fatigue.
Fatigue is when cyclic load results in stress below yield stress in every cycle, but the system fails because of no. Of cycles. For example pressure vessels.
Here is another explanation of fatigue.

[MegaShriyash]

Fatigue was beautifully explained! Thank you!!

[AS-fmew]

great explanation ....giving a good physical understanding of what fatigue

[nilofarpathan]

Thank you for the simple and effective explaination

[peglor]

Materials such as steel and titanium have a fatigue/endurance limit. Aluminium and most other materials however do not, so it's not possible to design structures in these materials to never fail from fatigue. In this case the number of cycles must be set much higher than the expected number of stress cycles in service.

Also the diagram is misleading in that it showed a crack forming and growing inside the material - in all cases of homogeneous materials without case hardening or similar surface property modifications, fatigue cracks always start at the surface.

[Shaikhshadat]

awesome work

i respect your hard work

:)

plz keep uploading more videos, it is helping a lot

[TheSunshineRequiem]

wow this is very good, you should hire someone to read it out loud though.

[lekhrajdewangan]

Finally after a long time I got its ans

[syedmuhammadtayyeb]

!!
The example of wire you have given isn't fatigue but it's strain hardening
Because we bend the wire permanently that isn't the case in fatigue

[naviddavanikabir]

great video.
I need to do this test on PEEK, a rigid plastic. the standard we follow is ASTM 7791. knowing only the ultimate stress and with limited number of specimen, how should I choose the stress/strain level to find the endurance limit and to waste as little specimen as possible?

[MarkKRogalski]

Not all materials show an endurance limit, for example steel and titanium are the only two metals that have one.

[obadiahmaxwell]

Good day. Please can you explain Double linear Damage (DLD) in contrast to Miner's Rule (Linear Damage)?

[jwais]

This is amazing thank you so much for the effort U put in this :)!!! Really appreciated!!!

[saiteja]

Great video sir like upload videos of mechanical engineering sir

[Medhusalem]

It is wrong, that the material will never fail after reaching the "limit". It is just an assumption because  not a high enough number of cycles have been tested. As seen in wind energy components where cycles are over 10^9 this limit is wrong and components are still being damaged by fatigue loads below their assumed limit!

[kymattok]

So if the stress is under the endurance limit is the material undergoing stresses that would be in its elastic range on a stress strain graph?