Extension Spring Calculator to find shear and tensile stresses on
ordinary helical extension springs with full twisted end for static loading case.
Calculations are done with the knowledge of extension spring wire
diameter, spring diameter and maximum working load. Calculation results generated by the calculator are shear and tensile
stress at extension spring end, shear stress at spring body, factor of safety values for
the points where the stress values are calculated.
The points where
maximum stresses occurred on extension spring twisted end are shown in the following figure. At
point A, maximum tensile stress is occurred due to bending moment and axial
force. At point B, maximum torsion stress is occurred. In addition to these
points, high shear stresses are occured at the body of the extension spring.
For the extension springs which works under static loading, first define the design
parameters with the " Dimensional Design of Extension Spring " calculator. Then
use this calculator to check spring against yielding.
Note 1 : ^{x} Material properties are from Ref2 except "User defined" selection.
Note 2 : ^{+} See supplements for reference values.
Note 3 : ^{o} The design factor value that used for all of the points
of interest ( Tensile stress at pointA, shear stress at pointB and shear
stress at spring body).
RESULTS 
Parameter 
Value 
STRESS RELEATED PARAMETERS 
Maximum working load [F_{max}] 



STRESS PARAMETERS AT POINT B 
Shear stress at point B for maximum working load [τ_{B}] 



Allowable torsional strength at point B [S_{all_B}] 


Safety factor at point B [fos_{B}] ^{+} 


 
STRESS PARAMETERS AT POINT A 
Tensile stress at point A for maximum working load [σ_{A}] 



Allowable tensile strength at point A [S_{A}] 


Safety factor at point A [fos_{A}] ^{+} 


 
STRESS PARAMETERS AT SPRING BODY 
Shear stress at spring body for maximum working load [τ_{sb}] 



Allowable torsional strength for spring body [S_{sb}] 


Safety factor at spring body [fos_{sb}] ^{+} 


 
SPRING MATERIAL PARAMETERS 
Ultimate tensile strength of material [S_{ut}] 



Material ASTM No. 


Note 1 : ^{+} Green color means, fos ≥ n_{s}, red color means fos ≤ n_{s}
Extension springs are usually
coiled with an initial tension which keeps the extension spring coils closed. Due to initial tension incorporated into spring, spring can’t be extended theoretically until a force that is greater than initial tension. In practice, extension springs extends slightly with smaller forces than initial tension due to deflection of end loops.
Tension springs are generally used to return back the component to its default position by providing return force.