Bolt Preload Calculator

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Bolt Preload Calculator:

Enter the values of constant, c, cross-sectional area, A(mm2)and yield strength, S(MPa)to determine the value of Bolt preload, F(N).

Enter Constant : V
Enter Cross-Sectional Area: mm2
Enter Yield Strenght: MPa
   
Result – Bolt Preload : N

Bolt Preload:

Bolt preload refers to the initial force or tension applied to a bolt during tightening. It is the force that stretches the bolt slightly, clamping the connected parts together firmly. Preload is essential to prevent joint separation, fatigue failure, or loosening due to external loads or vibrations.

A properly preloaded bolt ensures that the external forces acting on the joint are distributed uniformly, enhancing structural integrity.The preload depends on factors like bolt size, material strength, tightening method, and the coefficient of friction. Achieving the correct preload is critical in applications such as machinery assembly, automotive parts, bridges, and aerospace structures.

Bolt preload is directly related to the bolt’s cross-sectional area, the material’s yield strength, and a constant that accounts for tightening conditions. A higher preload improves fatigue resistance but over-tightening can cause bolt failure.

Torque wrenches, tensioners, and other precision tools are often used to control the applied preload accurately. Regular inspection of preload is necessary in critical joints exposed to dynamic or cyclic loads.

Bolt preload, F(N)in Newtons is calculated by multiplying a constant, c by the cross-sectional area, A(mm2)in millimetres and the yield strength, S(MPa)in mega Pascals of the bolt material.

Bolt preload, F(N)= c * A(mm2)* S(MPa)

F(N)= bolt preload in Newtons, N.

c = constant.

A(mm2)= cross-sectional area in millimetres, mm2.

S(MPa) = yield strenght in mega Pascals, MPa.

Bolt Preload Calculation:

  1. A bolt has a constant (c) of 0.75, a cross-sectional area (A) of 100 mm2, and a yield strength (S) of 400 MPa. Calculate the bolt preload.

Given: c = 0.75, A(mm2)= 100 mm2, S(MPa) = 400 MPa.

Bolt preload, F(N)= c * A(mm2)* S(MPa)

F(N)= 0.75 * 100 * 400

F(N)= 30000N.

  1. A bolt has a preload (F) of 25,000 N, a cross-sectional area (A) of 80 mm2, and a constant (c) of 0.8. Find the yield strength (S).

Given: c = 0.8, A(mm2)= 80 mm2, F(N)= 25000N.

Bolt preload, F(N)= c * A(mm2)* S(MPa)

S(MPa) = F(N)/ c * A(mm2)

S(MPa) = 25000 / 0.8 * 80

S(MPa) = 25000 / 64

S(MPa) = 390.625MPa.

 

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