Machine Design
When an open coiled helical compression spring is subjected to an axial compressive load, the maximum shear stress induced in the wire is (where D = Mean diameter of the spring coil, d = Diameter of the spring wire, K = Wahl's stress factor, and W = Axial compressive load on the spring)

(WD/ πd3) × K
(8WD/ πd3) × K
(2WD/ πd3) × K
(4WD/ πd3) × K

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Machine Design
Plastic flow in ductile materials

Lessens the seriousness of static loading stress concentration
Depends on other considerations
Has no effect on it
Increases the seriousness of static loading stress concentration

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Machine Design
Jam nut is a locking device in which

A hard fibre or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip
A slot is cut partly in middle of nut and then slot reduced by tightening a screw
One smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
Through slots are made at top and a cotter pin is passed through these and a hole in the bolt, and cotter spitted and bent in reverse direction at other end

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