Difference between force and force per area of FEMAP

[SP9109]

What exactly is the difference between a force and force per area on FEMAP?

 

[SP9109]

If you apply a load on femap by selecting "on surface", how is it different if you select "force" or "force per area"?

 

[Twoballcane]

What is your application? In most FEM there is force at a point (which is basically a vector) or force on a surface (which is pressure). If you have a load on the end of a cantilever beam, it is force at a point. If you have a plate with pressure exerted against it, it is force on a surface.

Tobalcane
"If you avoid failure, you also avoid success."
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[SP9109]

Part of the model is applying a load of 50lb in a 12" X 12" steel plate. I'm confused whether I should apply the load as a "force" or "force per area". I ran two analysis with the two different methods and the stress values are significantly different.

 

[IRstuff]

Over what area are you "applying" the force? If the areas used for force and pressure are different, then the stress ought to be different. Generally, forces tend to be applied to points, so if that's the case, then the stress would be expected to be different.

TTFN
faq731-376

 

[BlasMolero]

Hello!,
In FEMAP there are 35 loads available for loads on surfaces. Many of the load types, such as force, force per area, and force at node are just different input methods for the same nodal load type (Force). These different input methods enable FEMAP to distribute loads along the surface.

There are three basic types of load input values: Total, Per Area, and Per Node. The total loads include force, moment, and heat flux. Input the total load value, and FEMAP will automatically distribute it over the surface. The distribution will be based upon the total area associated with each node. Total loads must be input as constant. They cannot be variable.

Loads input as "per area" loads (force per area, moment per area, and heat flux per area) are very similar to "total" loads. The load is distributed identically to a "total" load, except the values are then multiplied by the area associated with each node. The sum of all these loads is simply the input value multiplied by the total area of the elements. These types of loads must also be input as constant.

Please note that TOTAL FORCE option is only available for Force, Bearing Force, Moment, and Torque load types applied to surfaces. Allows you to enter the "Total" Force, Bearing Force, Moment, or Torque to be applied over all selected surfaces, not applied to each surface. Uses surface area to spread the load out proportionally. Total Load is the default for these load types when more than one surface has been selected. When used, "Total" will appear in the default Load Definition title.

Hope it helps!!.
Best regards,
Blas.

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Blas Molero Hidalgo
Ingeniero Industrial
Director

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[rb1957]

if you apply 50 lbs to a surface, FeMap will distribute that force over the area.

if you apply 50 lbs/unit area to a surface, FeMap will apply that pressure over the surface to determine the applied load.

no?

 

[SP9109]

Thanks all for replying!! Blas what you say makes a lot of sense, thanks a lot for you adivce

 

[trainguy]

Keep in mind it's good practice to check the sum of the forces you have applied using, Tools / Check / Sum Forces before your analysis. Then check your reactions after the analysis using List / Output/ Query and select your support nodes, or create a free body diagram. The reason these are both checked is that Body Loads won't be included in the first (pre-analysis) check.

Only then should you start looking at other results (deflection, stress).

tg