Thursday, April 20, 2017

Bolts and Nuts - Design - Chapter Knol Collection

It is necessary to determine the stresses in screw fastening due to both static and dynamic loading in order to determine their dimensions based on the strength of material being used. In order to design bolts for static loading both initial tightening and external loadings need be known.

Initial tightening load

When a nut is tightened over a screw following stresses are induced:

(a) Tensile stresses due to stretching of the bolt
(b) Torsional shear stress due to frictional resistance at the threads.
(c) Shear stress across threads
(d) Compressive or crushing stress on the threads
(e) Bending stress if the surfaces under the bolt head or nut are not perfectly normal to the bolt axis.

(a) Tensile stress

Bolts are usually designed on the basis of direct tensile stress with a large factor of safety. The initial tension in the bolt is estimated by an empirical relation P1 =284 d kN, where the nominal bolt diameterd is given in mm. The relation is used for steam tight joints. If such leakproofing is not required half of the  above estimated load may be used (142 d kN).

23 April 2017

NPTEL Material on Design of Bolted Joints

30 March 2012

Design of Fasteners and Power Screws

Original knol - 3609

Updated  23 April 2017, 30 March 2012

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