Why are displacement and stress results so high when not using a reference point and rigid body constraint for a static simulation

General Questions
1

I am a mechanical engineering student and I am just starting in PrePoMax for the first time. I think it is amazing software and very intuitive but I am struggling to understand this result.

I will first start by explaining the results I was expecting. I created a part that has Fixed constraints and a force for a material that has approximates PLA plastic (E = 4 Gpa and poissons ratio 0.35).

Here is an Image explaining all my findings:

image
image1920×11138 1.31 MB

So my question is why is the simulation result so high (showing an unrealistic displacement and a stress so high it would snap steel) when not using a rigid body constraint tied to a reference point? Should I always use these constraints and reference points when using PrePoMax? Am I doing something horribly wrong in the simulation? Should I use some other method to always ensure my results are not returning strange values? I simply could not find an explanation for why simply applying a force to the faces the way that I did was causing so many issues.

2

It’s good practice to always check reaction and action forces are in balance. If you do it, I think you will find the explanation.

3

For your applied load, use "Surface Traction’ and not ‘Concentrated Force’ since the latter applies the force to each node.

This specific naming convention sometimes leads to confusion. It’s familiar to those who have experience using Abaqus, but is confusing for those that are familiar with Ansys.

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4

If you look at the descriptions of the fields used to specify the magnitude of the concentrated force load, you will see that it’s force per node meaning that each node is subjected to the specified force. This is likely the most common mistake made by new PrePoMax users. I was even thinking about suggesting some changes in load type names but the same nomenclature is used in Abaqus (and there’s even no such surface traction load other than force per unit area in that software).

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5

Previously, at this threads I do mistake also when testing of plate rested on elastic spring foundation.

Perhaps an option to select between forces assign to individual nodes or group of nodes by distributing could be better and useful feature.

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