Bolt preload definition 1

[pegus]

Good day team,

I would like to know if you can give me an explanation about how to define bolt preload.

I asked some peers about it, and they told me that my preload needs to be the same as the acting force, is this necessary true? because in some point the tension force in the bolt will duplicate.

I research about it and found that it helps the joint to withstand more load, but I did not find anything about how to establish the required preload.

The application will be for a 2 bolted V-clamp.

If you can please provide me any sources in which I can research more, that would be great.

Thanks in advance!

 

[BrianE22]

A common value for the places I've worked is to make sure the external load is less than 60%-70% of the preload. That seemed to work out well for joints loaded in fatigue situations.

 

[CoryPad]

I recommend reviewing some literature. Try the ones in this FAQ, especially NASA RP-1228:

faq725-600

 

[rb1957]

preload is intended to clamp up the joint. If the preload equals the design tension load, then you can be pretty sure that the joint will not gap. The bolt load doesn't duplicate ... with no load applied load in bolt equals preload; at some intermediate load, load in bolt is preload plus some portion of the applied load; eventually the joint gaps and load in bolt equals the applied load.

The 2nd reason for preload is to reduce fatigue effects when you have varying tension loads.

another day in paradise, or is paradise one day closer ?

 

[desertfox]

Hi pegus

See this link

http://portal.ku.edu.tr/~cbasdogan/Courses/MDesign/course_notes/Joint_Stiffness.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Tmoose]

By V clamp do you mean something like this?

http://www.normaamericasds.com/sites/default/files/product_images/R.G. Ray V Clamp Halves.jpg

If so, I think the wedging action and friction and clamp distortion would make figuring the required bolt clamping and thus preload kind of complicated.

X2 on others' comments about preload exceeding all working loads.