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17-Peridot

## Fastener "separation stress" measure

Hi all,

I wondered the real significance of that measure that you have when you create a fastener.
In my opinion it is the value of pressure in the little area around each hole, whose diameter you can indicate in the fastener tab.
But in mechanics normally the pressure/tension is positive when there is a traction and negative for the compression.
In my simulation I have a positive value when I expected a negative value because the plate does not lift.
Is there something wrong in my simulation or in my observation?

The first two analysis are made with screws preloaded, where in the Analisi_2 I correct the values of preload with the value of the Analisi_1.

Fn= Nominal Load input in static analysis
Fp= Tensile force reported in static analysis.

Fi = Fn^2/Fp

In the Analisi_3 I've tried without preload.

My goal is to see the load on each screw M12 - 8.8 (640 MPa Sy) where

Fn = 0.8 Ar * Sy

Ar = resistant area

Regards

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3 REPLIES 3
17-Peridot
(To:gfraulini)

nobody can "illumine" me on this argument?...

1-Newbie
(To:gfraulini)

Are you talking about the first run or the run after you have scaled the preload? Because the first run is not really intended to "make sense", but to help you find the appropriate pre-load to ensure the second run provides reasonable results.

17-Peridot
(To:gkoch)

Second run.

The problem is not ensure that each screw has the right preload, but understand why the axial force measure of each screw is what it is and why; because in this example some screws should be unloaded (from external load, so only preload) and some other must be loaded.

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