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Maximum allowable Load at specific Factor of Safety

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Old   April 2, 2023, 18:39
Default Maximum allowable Load at specific Factor of Safety
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Atif Ismail
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Dear All,

I am new to ANSYS with Petroleum Engineering background. Sorry if you find this question too basic.

I am trying to find the maximum allowable load of a A36 steel model at FOS 2.
If you help me to understand workflow to do that.

Thanks,
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Old   April 3, 2023, 04:47
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Hello,
what you need to do is to import your model in a "Static Structural" toolbox in ANSYS Workbench. You can find such a toolbox in the dropdown menu on the right when you open Workbench.

The toolbox suggests you the workflow:
geometry --> mesh --> setup --> solution --> results
Moreover before "geometry" you should have another step called "engineering data", where you can set the material properties (in this case of steel A36).

After that you double click on mesh, you mesh an then you go to setup and set your boundary conditions + applied loads.
Then you can simply solve and in solution you can right click on "solution" (dropdown menu on the left of your "setup" page), and select the contours you would like to see (maximum deformation, equivalent stress, etc).

If you want a FOS>2, you can calculate the safety factor in the node with the higher equivalent von Mises stress, which will be your minimum safety factor:
FOS_min = Yield strength of A36 Steel / Maximum von Mises stress > 2
i.e. you check whether your FOS_min is higher than 2.

The maximum allowable load depends on how are the loads distributed in your structure (if you have distributed or point load, pressure load,...), and it is related to the maximum allowable stress, which is given by:
Maximum allowable stress = Yield strength A36 Steel / FOS you set (in your case 2)
To go from maximum allowable stress to maximum allowable load some more information on the load application is needed.
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Old   April 4, 2023, 12:09
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Erik
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The previous recommendation will have problems if there are any stress concentrations, as stress at a sharp corners will be nonconvergent, and mesh dependent. You will also be calculating peak stresses. Most structural codes are written for classical calculations which calculate average membrane stress or classical bending stress through the entire applicable cross section.

Elastic Plastic material properties using LRDF methods are more suitable for most cases than linear elastic stress analysis, which can give you overly conservative results if not interpreted correctly.
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Old   April 4, 2023, 14:56
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Fully agree with you Erik.
I just didn't go into so much detail as we don't have much info on the geometry, as you say "stress singularities" might be a further issue to take into account, together with refining you material model
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