Mean Stress and Vibrations in Torsion-Bar Helical Spring

3 Mean Stress and Vibrations in Torsion-Bar Helical Spring 

A helical spring of Fig. 5.54 with diameter D — 50 mm and circular section diameter d — 16 mm is made of high strength steel heat treated to 1,400 MPa ultimate strength and fatigue limit oy = 700 MPa. It is subjected to a cyclic load F variable from 500 to 6,000 N. Verify whether it can sustain at least 10 cycles. The generic section is subjected to a torque M, and a transverse component of force F the result in a maximum and minimum shear stress given by 

The American engineer A. M. Wahl has shown that the combined effect of curvature of the wire and transverse force results in a transverse shear stress that is not exactly given by the second term of the above equations. The complete equation for the maximum stress in a coil spring may be calculated as 

The torsional fatigue limit with the mean stress x is given by (5.50) 

5 Stress-Based Fatigue Analysis High Cycle Fatigue 

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