FEA Results interpretation for these 3 simulations

[Smushiehippo]

Homework Statement

Explain where the first point of failure is likely to originate, and why.

An analysis of the studies, do you think that they will be an accurate representation of what will happen in practice?

Relevant Equations

none

Hi

Im slightly stuck not sure what i put is ok.

FEA was used to carry out analysis on 3 structures and diagram results obtain (no data)
Explain where the first point of failure is likely to originate, and why.
An analysis of the studies, do you think that they will be an accurate representation of what will happen in practice?

Red indicates high stress and blue indicates low stress

For the (i) there is high stress at both ends and low stress in center. I believe 1st point of failure would be at centre (blue area) and not indicated on diagram of high stress (red). Trusses support the bridge and take the majority of the load and stresses. Blue section centre of the bridge and where load and stress will be most concentrated. contentrated stresses and loading will likely fatigue in beam.

For the (ii) there is high stress at each blade and low stress at the base. I believe 1st point of failure would be at blade (red). Impeller blade are the thinest point on the structure. strength in this area is lowest compared to base. excess high vibration could lead to fatigue and first point of failure.

For the (iii) there is high close to the small end and low stress in big end. I believe 1st point of failure would be at small end (red). connecting rod under goes compression and tension in operation. high speed causing high rpm lead to stretching of the rod leading to failure.

Im stuck on comparing accurcy. I believe (i) is inaccurate but (ii and iii) are accurate. how do i compare accuracy with only pics and no data. im not 100% what each pic is showing, eg compression, tension, deformation.

 

[berkeman]

Since you haven't gotten any replies yet, I'll chime in with a couple thoughts/questions:

i) You say that you think the center of the truss bridge would be prone to fail first, but the FEA simulation shows blue in the middle and red at the supporting ends of the bridge. How do you reconcile that? Also, the red horizonal members at the two supporting ends look wrong to me, depending on how the ends are supported by the banks/ground. I can see why the vertical members at the end would be red, since they are supporting all of the weight of the bridge where it attaches to the ground, but I don't see a source of stress for the horizontal members on the ground at the ends.

ii) I don't know much about pump impellers, but it seems like a more typical failure would be for most of a vane to break off mid-way, not just at the tip. But I could be wrong about that.

ii) That looks like a reasonable stress distribution for the piston connecting rod. Can you say why the red area is where it is, and not at the top? What about a piston connecting rod might cause more stress in that area versus the opposite side of the piston pin?

 

[erobz]

So, is this assignment about sanity checking FEA results?

 

[Smushiehippo]

So, is this assignment about sanity checking FEA results?

pretty much checking.

Im doing online, so on my own working through this.

only given pic and with the question is do you think that they will be an accurate representation of what will happen in practice?

no data or notes, or info to read on it.

looking through a source i saw that ti said FEA red means high stress and blue low. other than that vary hard to find truss bridges FEA results with stress.

was guessing max bending motion would be in center so max stress would be as well and that lowest stress would be on the ends. there would more stresses on top than bottom of the beams. so diagram is not accurate. persumption that is evenly loaded across the bridge.

 

[erobz]

looking through a source i saw that ti said FEA red means high stress and blue low. other than that vary hard to find truss bridges FEA results with stress.

ok

was guessing max bending motion would be in center so max stress would be as well and that lowest stress would be on the ends. there would more stresses on top than bottom of the beams. so diagram is not accurate. persumption that is evenly loaded across the bridge.

If it was evenly distributed load, we should see symmetric stress distributions across the mid planes?

 

[erobz]

Maybe @FEAnalyst would chime in?

 

[Smushiehippo]

ok

If it was evenly distributed load, we should see symmetric stress distributions across the mid planes?

Looking at past examples of failure in truss bridges, high has been recorded at ends of bridges where failure happened in chord of truss.

With out info of loading or anything. I just don't know on the diagram.

 

[erobz]

Looking at past examples of failure in truss bridges, high has been recorded at ends of bridges where failure happened in chord of truss.

With out info of loading or anything. I just don't know on the diagram.

What I'm saying is that the loading seems to be asymmetric. Going across the bridge, as you would traverse it stresses appear symmetric, but the dark blue stress zone isn't mirrored in the opposite truss.

I'm probably out of my depth of understanding.

 

[FEAnalyst]

Interpretation of FEA results based only on colorful images is not the way to go. You should know at least the boundary conditions and loads plus, of course, actual values of output variables and properly scaled deformed shape. Otherwise, you may conclude that red is always bad and blue is always fine which is not true. Results should be always compared with allowable values. Apart from that, the first part of this task comes down to saying where red areas are located on each model which is obvious. The second one requires guessing how a component can be loaded and constrained. Instead of trying to interpret those images lacking any context, I would strongly suggest you download geometries like this from GrabCAD and run your own analyses in any FEA software, even open-source if you don't have a license for a commercial solution. You will learn so much more this way.