Stud Lengths, Washers and Bolted Joints

The hardened machined washer are always preferred choice when the fasteners are assembled. It avoids scoring damage on the nut/ fastener face- component joint face and also (thereby) helps in having a proper stress distribution and maintaining the pre-load.

The spring washers are basically used to avoid vibration loosening of the fasteners. However as per a number of literatures these are only cosmetic (does not serve the purpose) above 1" (or M24) thread sizes- the spring tension is not enough to prevent the loosening.

Another purpose of the washer is to improve the pressurecone (on the joint face) when one is constrained with thin flanges.

One also uses washer (especially heavyduty ones) when the bolt hole size is on the larger limit or for some reason is deliberately kept large - or the hole is oval shaped for adjustment purposes etc, where the contact area is low there by increaing the hertzian stress to too high level.

There may be other specific reasons too.

Thanks for the information.

Is there any theoritical calculation which triggers out that whether washer is required to be give? Whenenevr the bearing stress against the joint face is coming higher than the prestressing it is required to increase contact area for which we give washer. Is it true?

I want to have detail of how to calculate bearing stress & required prestress?