I always wander what stretched force would be in a thread if it is tightened between two impossible to move briks and the thread, by any means becomes shorter just in one mm? Is there any solution?

Pre-tension section might be what you are looking for. You can apply displacement boundary condition to the reference node and obtain force as a result.

Happy 2023!

Thank you, do you know a formula that pre-tension section was based on?

k_rod = section_area * elastic_modulus / length

F = k_rod * x

k_rod is stiffness

x is stretch or compression

Happy New Year (it just began in my country)!

Internally, pre-tension section is realized by multiple point constraint (MPC). The rest belongs to FEM.

Well, well then,

Absolute longitudinal deformation

∆l = l1 - l

where:

l1 - length of the thread after deformation

l - length before deformations

Relative longitudinal deformation

epsilon = ∆l / l

Tensile stress

sigma = E * epsilon

where:

E - modulus of elasticity

And that is all.

What political position do you occupy?

I live in Poland.

There’s also a formula that can be used to calculate pre-tension force based on applied torque.

I would do a simple test in your FEA software to check if that’s all.

I will some day., I will.