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)

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

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Machine Design
The ends of the leaves of a semi-elliptical leaf spring are made triangular in order to

Have variable bending moment (M) in each leaf
Permit each leaf to act as an overhanging beam
Obtain variable moment of inertia (I) in each leaf
Make M/I constant throughout the length of the leaf

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