## Theoretical Faliure torque Calculation !!

## Theoretical Faliure torque Calculation !!

(OP)

Hello Friends,

I need your expert opinion on below case.

I have failure in my part at 30 Nm torque, so I need to calculate theoretical failure torque so that I can know the safety factor of this sealing thread joint.

Torque Spec : 15-20 Nm

Thread size - M10x1.0

Thread on nut part - 7.5±0.5

Material - En1A

Pic - http://files.engineering.com/getfile.aspx?folder=7...

Material - Aluminium

Pic - http://files.engineering.com/getfile.aspx?folder=0...

I need your expert opinion on below case.

I have failure in my part at 30 Nm torque, so I need to calculate theoretical failure torque so that I can know the safety factor of this sealing thread joint.

Torque Spec : 15-20 Nm

Thread size - M10x1.0

Thread on nut part - 7.5±0.5

__Bolt:__Material - En1A

Pic - http://files.engineering.com/getfile.aspx?folder=7...

__Nut:__Material - Aluminium

Pic - http://files.engineering.com/getfile.aspx?folder=0...

## RE: Theoretical Faliure torque Calculation !!

To calculate on a torque basis, you need to provide the inner and outer contact radii for the bolt and any surface treatments to determine friction coefficient.

## RE: Theoretical Faliure torque Calculation !!

## RE: Theoretical Faliure torque Calculation !!

## RE: Theoretical Faliure torque Calculation !!

## RE: Theoretical Faliure torque Calculation !!

But I need to prove this on paper (means what is pratically happening should be match with the theoretical calculation).

Can anybody help me with some formulas...Actually this application is automotive braking, where we are connecting bundy tube with wheel cylinder.

## RE: Theoretical Faliure torque Calculation !!

Some equations to develop a basic understanding of torque and forces are shown here: FAQ725-536: How do I calculate an assembly torque? and here: thread725-35222: Tensile capacity/minimum engagement

## RE: Theoretical Faliure torque Calculation !!

There are numerous technical references that will give you an analytical approach for calculating axial force vs applied torque from a screw thread. But as Screwman1 pointed out, due to the wide variations in the calculated results from factors like friction, to obtain an accurate result you would need to test a statistically relevant number of samples. Unfortunately, a statistically relevant number of test samples in your case may likely number in the hundreds.

## RE: Theoretical Faliure torque Calculation !!

https://www.faa.gov/regulations_policies/handbooks...

## RE: Theoretical Faliure torque Calculation !!

It is important to add the variation bolt tensile strength allowed by the bolt spec. Testing one batch will not indicate a safe design unless the break tensile strength of the tested bolt is known and documented in the manufacturer C.O.T. Then the result should be normalized to the minimum allowed bolt tensile strength. The tested bolt may be in the maximum bolt strength allowed by the spec and will pass the torque test but, a minimum properties bolt may not. The variations in the bolt tensile strength can vary up to 20% according to military specs.