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Crash test using HyperCrash

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)

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Altair Forum User

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

Altair Forum User

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.

Altair Forum User

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.