Internal Thread Yield Strength Calculation

[tyler_graham]

Hi all,

I have an M12x1.75 CL 12.9 socket head cap screw, that is threaded into a 303 stainless steel insert (picture attached for reference). The company that provided the system that uses these inserts did not design them to have a comfortable amount of thread engagement, so I'm trying to see how strong the internal threads of this insert are with the amount of thread engagement I can get out of the insert.

I have a calculation sheet that I made that finds the shear area of the thread and multiplies it by the ultimate tensile strength of the material. I believe this gives me the force at which the bolt threads are stripped, but I'd like to find how much it would take to just make the internal threads yield and not completely fail.

Am I able to just substitute the ultimate tensile strength of the material with the yield strength of the material to find the yield strength of the bolt threads? If so, what is the reasoning behind this?

I've been having a lot of trouble finding any actual decent sources to provide me with an in depth explanation of how these thread strength calculations work and the reasoning behind them, so if anyone could point me to a source or sources that will help explain this in better detail than just telling me the answer, that would be absolutely fantastic.

Thank you for the help and your time!

[Kelly_Bramble]

Ultimately, to determine the yield strength of those inserts you may need to conduct testing. I'm sure you could estimate yield strength base on similar engineering materials and then compare that to a reasonable factor of safety and decide from there.

I do think that if you're not comfortable with the amount of thread engagement provided you may want to explore other options that do.

[langnerfrancesco]

To calculate the yield strength of an internal thread, you need to determine the material type, cross-sectional area, and the thread geometry. The yield strength is a measure of the maximum stress that the material can withstand before it starts to deform permanently.
The formula for yield strength is:


Yield Strength = Stress / Strain


Where stress is the force applied per unit area and strain is the change in length per unit length. To calculate stress, you can use the following formula:


Stress = Force / Cross-Sectional Area


To calculate the cross-sectional area of the internal thread, you can use the formula:


Cross-Sectional Area = π/4 x (Major Diameter - (0.9382 x Pitch))^2


Where π is the mathematical constant pi, the Major Diameter is the outer diameter of the thread, and the Pitch is the distance between the threads.
Once you have calculated the stress and cross-sectional area, you can use these values to calculate the yield strength of the internal thread using the first formula mentioned. Keep in mind that the yield strength may vary depending on the specific material properties and thread geometry being used.