Need some help performing an impact test

[Ateyx]

Hello everybody,

So I'm trying to perform a basic crash test in SolidWorks of a model I have created. But first, I'm trying to figure out how to exactly perform a crash test! From what I've read online, impact tests are normally done in nonlinear dynamic studies. My long term goal is to extrapolate what I learn here to a larger, more complex model for impact testing. Here is what I have so far:

http://i.imgur.com/M58O6cH.jpg

Right now, I'm more concerned with just getting the basics of crash simulation down, so I've chosen a very simplistic model to learn from. The large wall is fixed, and there is an initial condition of 20m/s set on the smaller cube in the direction of the wall. There is a no penetration contact set between the wall and the cubes front faces, and a global contact between the two parts (I've tried running it with Global contact off, didn't seem to make a difference). Currently when I try to run the simulation, I get some pretty weird results, indicating to me I've obviously done something horribly wrong. I've also tried looking up YouTube videos and help guides on impact simulations, but unfortunately it doesn't look like there is a whole lot to learn from. This is the best example of what I'm trying to do I have found so far:

https://www.youtube.com/watch?v=JnO3wfnQXLs

From his simulation, I know its possible to perform an impact test, I just can't figure out for the life of me what I am doing wrong!! Anyways, If anybody is willing to give me any information they have on performing an impact test using nonlinear dynamic simulation, I would love to hear it. Also, for anybody who wants to take a look at the assembly:

https://www.dropbox.com/s/v4fd90nal7vs1an/Impact%2...

Thank you!

 

[academix]

Hello:

You are trying to simulate a Non-linear dynamic event that can very well be done in SolidWorks Simulation Premium. Before going into the details of your simulation, let us say, for the moment, that you are trying to capture this event in the physical world.

Then you would have a camera that would capture the event in terms of frames per second, right? More the number of frames per second, the better the resolution of the time steps to capture the event more 'smoothly,' right? Here in lies the answer. You choose the time duration of the event, extract the results and then post-process the same. There are two types of integration schemes, namely, explicit and implicit. From the picture you have shared, I am inferring that you can try and estimate the time of impact using Newton's laws of motion. Up until contact happens, you can use explicit integration for faster computation. Just before the impact, say, 10 milli seconds before impact, you can stop the analysis and restart with implicit integration scheme and extract results, say every 1 milli-second or lesser (yes, lesser. Some times it happens to be in micro seconds). If you monitor the reaction at the wall, you will see a delayed reaction increase, indicating shock wave propagation.

Remember, the stability and accuracy of the result depends on the edge length of the element (translating into wavelength of the wave) and instabilities in solution can occur with wrong choice of element, integration and contact schemes. This is a close-to-natural-phenomena simulation and you need to be careful about it. Also keep in mind that contact, if defined without friction (first try it without friction and then introduce friction) would be simulating impact between two polished surfaces. Damping is also an important criteria to get proper results. Good luck on your simulations,

Let me know if there issues that remain unresolved,

Regards
Nat

Natarajan Ramamoorthy
Design Engineering Consultant

http://www.egsindia.com