# When is shear stress concentration factor used?

Q.  Which factor is used to consider the effects of direct shear stress and torsional shear stress when curvature effect stress is not considered?
- Published on 14 Sep 15

a. Shear stress concentration factor
b. Wahl shear stress concentration factor
c. Both a. and b.
d. None of the above

#### Discussion

• Pankaj   -Posted on 06 Nov 15
Shear stress concentration factor: This factor accounts both direct shear stress and torsional shear stress. This factor is used only in case of static loading.

- The formula to calculate shear stress concentration factor is : Ks = [1 + (0.5/C)]

- Shear stress (τ) in spring wire is given by: τ = Ks [8 FC / π d2]

Wahl shear stress concentration factor (Kw): This factor accounts both direct shear stress and torsional shear stress along with the curvature effect stress.

- Shear stress on inner surface of spring increases as curvature of wire increases and decreases on the outer surface. This factor is used only in case of fatigue loading.

- The formula to calculate this factor is: Kw = [(4C - 1) / (4C - 4)] + [0.615 / C]

- As spring index decreases, Wahl factor increases.

- Shear stress (τ) in spring wire is given by: τ = Kw [8 FC / π d2]

here, F = shear force, wire diameter.

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