• Announcements

    • Rahul Ponginan

      Please click here for a short but important announcement   03/26/17

      Dear Users Our Commercial and Academic users around the world can use these same forums here as before i.e. the Altair Support Forum , Commercial users from India with solver queries can go to the Solver Forum for India Commercial Users , Academic Users from India and AOC India Participants are requested to go to the Forum for India Academic Users and AOC India Participants , We will be tending to all queries in all the forums promptly as before, thank you for your understanding. 
  • 0
Sign in to follow this  
Followers 0
Tiago

Crash test using HyperCrash

Question

Hello,

 

I am making a setup of a simple bumper structure colliding with a rigid wall on HyperCrash. I am using the Johnson-Cook model for the material.

 

The structure is made of a beam with 2 crash boxes attached with spot welds. In the beginning of the test the structure is already vibrating (Capture2) and seems that the boxes are colliding with the beam instead of being attached.

 

Can anyone help me to solve this vibration problem? can it be from the type of connection that I am using? Should I use other? see the print screens and tell me what you think. There are stress concentration close to the spot welds because they are completely rigid elements (Capture3)

 

Another big problem is that the material is not having the desirable behavior. It is aluminum and should bend on crash but is not bending, its fracturing (Capture4)

Capture1.PNG

Capture2.PNG

Capture3.PNG

Capture4.PNG

Share this post


Link to post
Share on other sites

3 answers to this question

  • 0

Hi Tiago,

From the engine out file find what is causing for the time step drop.

It can be an element, a node or an interface.

•For an element, check the related material (especially its Young modulus and density in case of an elastic-plastic material; and its viscosity in case of a visco-elastic material). There must not be an error in the units system that this data is given in.

Check the size of the element, since elemental length is proportional to time step.

•For a node, check the characteristics of connected elements. If the node is on the master side or the slave side of an interface, this interface must be verified.

•For an interface, the gap of the interface must be verified if some failure happens on the master or the slave side of the interface.

 

Once this is cleared you can run the simulation without time step being dropped.

Share this post


Link to post
Share on other sites
  • 0

Hi Tiago,

Check the model and ensure the connectivity between the elements for the boxes. And also recheck the boundary condition applied in the model and ensure it is correctly defined in the master node of the rigid body.

For modelling please follow the steps explained in the tutorial here : http://www.altairuniversity.com/wp-content/uploads/2013/09/Bumper_Crash_final.pdf

Share this post


Link to post
Share on other sites
  • 0

The connectivity is ok and the rigid body too. I followed that tutorial and I am making a new simulation now but it takes 10 times more time than the old one to run. 

 

I am trying to use the exact same material and connections to see if the problem has another source. 

 

For that kind of steel and an element characteristic length of 5mm i am using an inicial timestep of 5 as they recommend. But in my calculations it should be closer to 1 if I am not mistaken.

 

It will take an hour to run. I let you know if its working. 

 

 

 

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0