Pro/Mechanica deformed scaling percentage box

[Nose Bleed]

Can some one help me understand this percentage of deformation scaling box - in the results setup window?



What is its true function?



And why - when I set the value to 1 (in wildfire) - without the percent box checked, it does not show any deformation? Even though I know that this item that I'm testing gets completely destroyed...





...and - why is it's default set to 10 percent?



Thanks -

 

[JHardy]

I use 2001 SE, but I assume Wildfire is similar.



Normal engineering structures and components deform very small amounts in normal practice; too small for the deformations to be seen clearly unless the magnitude is exaggerated. (Structures that are held together by soft springs etc are an exception – but then you would only see the deformation due to the spring settlement, NOT the bending of the individual components.)



You can exaggerate the apparent deformation by applying either a numeric multiplier, or by declaring the desired deflection to be a certain proportion of the model size.



If you choose to use a multiplier (eg 10 or 100 times actual deflection), you may need to experiment to choose a sensible multiplier to get a reasonable looking deflection shape for each load case, but if you use the same multiplier for various load cases, you will be able to see clearly which load case is causing your structure to deform more. If you choose a multiplier of 1.0, you are looking at the actual (unexaggerated) deflection shape, which will often mean you can’t see any apparent deflection at all.



Alternatively, if you choose to plot the maximum amplitude of deformation as being 10% (say) of the model size, you will always be able to sense the shape and nature of the deformation, but you won’t be able to quickly see which load case causes the biggest deflection, because all load cases appear to generate deformations of approximately equal magnitude.



For example, consider a simply supported mild steel pin, 100 mm long, 10 mm diameter, with two load cases. Case 1 is a 1 kN load at mid-span, and Case 2 is a uniform distributed load of 10 kN/m. Both load cases have the same total load (1 kN), but Case 1 will deflect by just 0.21 mm at mid-span, and Load Case 2 will deflect by just 0.13 mm. The peak stresses in the bar is about 254 MPa for Case 1, and 127 MPa for Case 2, so the bar is stressed up to a fair degree as far as design stresses are concerned.



The deformations in both cases are barely visible if you don’t exaggerate the deflection. If we choose a multiplier of 10, say, we get an apparent deflection at mid-span of 2.1 mm for Case 1, and 1.3 mm for Case 2, both of which are just visible, and it is reasonably obvious which load case causes the biggest overall deformation. However, some load cases might give no apparent deflection with a multiplier of just 10.0. (A multiplier of say 20 or 50 might be more appropriate in this case.)



If instead we choose a deflection scale of 10%, this will scale ALL load cases to give an apparent deflection of 10% of 100 = 10 mm, so all load cases now produce obvious apparent deflected shapes, but it is not immediately apparent which case actually causes the biggest deformation.



Hope this helps.