Considerations with Regards to Fatigue for Extension Springs

Figure 3 shows the fatigue strength diagram of shear stress (JIS B2704).

When considering the permanent deformation (deterioration), it is recommended to set it to 0.45 or less. Figure 4 shows a fatigue strength diagram of tensile stress (JIS B2709).

When considering the permanent deformation (deterioration) , it is recommended to set it to 0.7 or less. For the spring stress, an appropriate value must be selected in consideration of the relationship between the lower limit stress and the upper limit stress when the spring is used, the number of repetitions, the surface condition of the material, and various factors that affect fatigue strength.

Permissible Stress of Extension Springs

Figure 5 shows the permissible shear stress (JIS B2704). The maximum shear stress when the spring is used should be 80% or less of the value shown in Figure 5. Figure 6 shows the permissible tensile stress (JIS B2709).