Learning Forum

[Kelan Barreto]

Hello,

I want to set up an Explicit Dynamis simulation, where I'm trying to study the energy absorption and other crash absorption metrics of a 80x80x100mm Gyroid specimen. The idea is that I want to compare this numerical study to some data I have for a crashbox that was experimentally validated using a drop test experiment with the following conditions:

4m Drop Tower Test
Impactor Mass: 108.35 kg
Impactor Velocity : 7.03m/s

In terms of modelling the geometry, I've modelled two platens that are in contact with the gyroid specimen on both faces in the Z direction.



I'm using solid elements and i'm new to Ansys as well, so I wanted some guidance as to how to set up the boundary conditions for this test.

At the moment what I have done is utilised the AlSi10Mg (additively manufactured) material from the Ansys Database itself, but overwritten its default bilinear plasticity model with a Johnson Cook strain rate model and damage model.

To achieve the mass of the impactor, I've created another material and set a density value of 1,504,861 kg/m3 assigning it to the top platen, as the dimensions I have set for both the platens are 120x120x5mm. I've assigned structural steel to the bottom platen. 
Additionally I've set the Behaviour for both Platens to be Rigid, and i'm given to understand that this causes the solver to ignore their other material properties like Stiffness and Poisson's ratio.

How do I set up the boundary conditions for the movement of the top platen? Do I use a standard Displacement object or a Remote displacement object (for the top platen) to constrain its degrees of freedom and why?

Do I apply a velocity matching the test set up to the top platen? and for this velocity object is it correct to set the X and Y components to zero instead of Free?

How do I define contacts for this test? Do I define frictional contacts between the top platen and the bottom platen? And additionally also define a self contact through a 'Body Contact ' object? Do I scope it only to the gyroid speicmen?


I would appreciate if anyone would provide some details and advice on how to set this up

[cxquan]

You can right-click Initial Conditions > Initial Velocity to assign the impact velocity to the top platen. Please set the vertical velocity to 7.03 m/s and the other two directions to 0. Please also double-check that the mass of the top platen is correct, since an incorrect mass value can lead to inaccurate results.

For contact definition, you can use Body Interactions > Body Interaction and scope it to All Bodies (default) so that any possible contacts in the model are included, including the gyroid specimen. This is important because the gyroid structure may experience self-contact under impact loading. You can define the interaction as Frictional by specifying the coefficient of friction. If different coefficients of friction are needed for different bodies, you can add additional Body Interaction objects and assign them accordingly.