Spring Design
Design information for engineers, such as spring calculation formulas,
which are the basis of spring design, can be found here.
- Tokai Spring HOME
- Spring Design
- Extension Springs: How To Calculate Spring Stress
Extension
Springs
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).
