Stress analisys simulation for explosion ...

[Bolthosue]

I'm trying to run a simulation on a part to test it's resistance to explosive forces and pressures. All the tutorials I find on stress analisys seem to be grared toward mechanical parts or tables. Can somone direct me to a tutorial that can show me how to deal with explosive forces?

[JDMather]

Don't you need to simply apply the max expected pressure?

Inventor only analyzes in the elastic range.

Can you attach your files(s) here?

[blair]

You would need both a ramp up to Max positive pressure and then cycle down to Max negative pressure and return to static pressure.

I guess just two sim's, one Max Positive and the other Max Negative for a "quickie"

[Anonymous]

I do not know if heat will be a factor,  as material strengths will change with temperature.

With all the bombings lately,  maybe they should work in balistic and explosive features into FEA.

T.S.

[Bolthosue]

The part I'm designing is a fireworks mortar.

I need to run the simulation to prove a point, that my new design is more efficent at launching a firework than traditional designs. Also, that it will better controll the explosive force in a a catastophic failure when compared to our compeditors design.

While your sugjestions here are valid, I forgot to mention that the explosive force is actually launching a projectile (the fireworks shell). This will dramaticly affect the forces being directed into the walls mortar for a split second as the pressure builds before ejecting the shell.

If I use the max power/min power trick, can I simply include a place holder in the mortar (for the shell) and let the simulation naturally eject it?

Or is the setup for this more complicated?

[Anonymous]

I don't think it will be that easy.

I am not sure if that is something you can start in dynamic simulation and export into FEA.

You may have to create the projectile and bond it to the tube, creating a pressure chamber for the analysis.

not true to world, but it might simulate the max condition per your needs.

T.S.

[Anonymous]

I tried a simple version,  it did not move the projectile.

and pressure on the side walls of the tube is extended across the entire face of the tube,  there is no division where the projectile seals the bore, so the analysis will run right past the projectile, exerting pressure evenly on the whole bore tube.

unless of course you split the faces of the tube, or bond the projectile to create the simulated pressure chamber, then assign pressure force to all faces in the chamber.

T.S.

[Bolthosue]

What is FEA? (I've only been using inventor for a week.)

[Anonymous]

Appoligies.

FEA is Finite Element Analysis AKA (stress analysis)

Inventor Ribbon Tab  under Environments

When I referred to exporting to FEA I was refering to the scenerio below.

In Inventor you can create a dynamic simulation,  adding movement, accelerations, momentum etc..
The dynamic simulator can then export the forces to the stress analysis system at a particular point in the simulation timeline,  giving you all the forces at that exact moment in the system.

T.S.

[LT.Rusty]

FEA = Finite Element Analysis = Inventor's Stress Analysis Environment.

It's also almost certainly the wrong tool to be using for this sort of simulation. I suspect you need to get one of the dedicated simulation packages, at LEAST Simulation Mechanical, but probably Simulation CFD.

Inventor's stress analysis environment doesn't really handle motion or anything. I've tried doing more or less what you're doing, using .22 LR parameters. The results were ... messy.

[Bolthosue]

I'm coming from a background in 3D Studio MAX. If I where to simulate these interactions I would place the "force generator" in a position where the initial lift charge would be, then place the shell into the tube on top of that.

I would tell the program that the shell can't intersect the tube and that the "force generator" should apply force to the tube and the shell.

At that point the physics simulation would have no choice but to "launch" the shell because it's the only moveable part in the simulation.

I would assume that I could do the same in inventor ... does inventor have a setting for "world physics" where it's just generating gravity and physical interactions with all objects in a scene (or assembly)? Or do you need to set mechanical type constraints on everything?

[LT.Rusty]

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@Bolthosue wrote:

I'm coming from a background in 3D Studio MAX. If I where to simulate these interactions I would place the "force generator" in a position where the initial lift charge would be, then place the shell into the tube on top of that.

I would tell the program that the shell can't intersect the tube and that the "force generator" should apply force to the tube and the shell.

At that point the physics simulation would have no choice but to "launch" the shell because it's the only moveable part in the simulation.

I would assume that I could do the same in inventor ... does inventor have a setting for "world physics" where it's just generating gravity and physical interactions with all objects in a scene (or assembly)? Or do you need to set mechanical type constraints on everything?

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Doesn't work the same way.

[Bolthosue]

How does inventor apply force? Do you have to apply it to a spesific point? Or face?

Or can you setup a sort of "omni" force where the force is radiated from a point in space?

[JDMather]

Go to Environments>Dynamic Simulation and a tutorial message should pop up.

This is an advanced topic and deserves (requires?) advanced training.

You might also obtain book by Wasim Younis>

The end question remains, is Inventor really the proper tool.
You can simulate you projectile, but.....

[LT.Rusty]

In general, it's on points or faces. Gravity is the only universal force.

You really need to look into Simulation Mechanical or CFD. Inventor simply will NOT give you an accurate representation of what you're doing.

As a for instance, I did a thing a while back based on .22 LR. I used a couple of different barrels. One was a model I made of a Ruger 10/22 barrel, and the other was a solid bar of I believe .920 diameter, drilled and rifled. Of course the 10/22 factory barrel is completely safe, but because Inventor's stress analysis environment cannot really work with the motion loads, varying pressures, deformation of the lead projectile, decreasing chamber pressure as volume increases, temperature, etc. ... the results were worthless. According to Inventor, the barrel failed catastrophically, and the .224" lead somehow turned into a disc 11" wide and a few thousandths thick.

Inventor is the right tool for creating your models, probably, but it's emphatically the WRONG tool for performing this sort of simulation.

[Anonymous]

Loads apply to faces.

If you need a load in one small spot on a face,  you either need to model the component applying the load, and use that object to apply the load, or you can split the face with a sketch, and apply the load to the split off portion of the face.

I don't think inventor can model the type of load you are after,  you will have to simulate it.

Kinda like simulating light bounces in the old 3d studio before radiocity,  by creating lights that represented the light reflecting off of other surfaces, you could simulate radiocity before it was part of the renderer. So it may be possible to fake, but as stated above, the results will probably be innacurate unless you find a really clever way to do it.

T.S.

maybe you could build a tube in your shop, and explode it.  see where it failed, and try to reproduce it in inventor.

[Bolthosue]

I know what you're saying about 3DS before radiocity.

I have no budget or much time to put into this simulation ... I noticed that Autodesk had a demo for "Robot Structural Analysis Professional" ... would this be capable of running the simulation I'm looking for?

Has anyone used this software before?

If I can't come up with a digital solution, that I will resort to prototyping and destructive testing.

[JDMather]

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@Bolthosue wrote:
If I can't come up with a digital solution, that I will resort to prototyping and destructive testing.

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Even with the right software tool, I don't think it is easy to set up a valid simulation.  You would definately want to verify the digital "solution" with physical testing.  What is the risk of being wrong.... 

[Anonymous]

Can I help with the physical testing....  That sounds like fun! 🙂