Event Simulation - Impact Force

[HoRnZz]

Hi all,

I'm looking for set-up advice on the Event Simulation FEA I need to run for a Uni project. 

I have a hanging bracket fixed by screws at two points. I want to simulate a mass dropping on the brackets hooks, for worse case scenarios. I know the: -

• Weight, 32.5 kg (static force of ~319 N)
• Time to fall = 0.04 seconds
• Velocity = 0.369 m/s
• Height of the drop is 8 mm. 

I am unsure how to set up the "Multiplier Curve". I've had a bash at it but I'm seeing very different results from my hand calcs. 

The picture attached is what I'm working with. The rectangular section with the eyelet cut out is representing the mass.

Any help will be muchly appreciated.

Thanks.

Regards.

[John_Holtz]

Hi @HoRnZz 

It has been awhile since I did an Event Simulation, so I do not know what "multiplier curve" are you referring to?

Normally, a "magnitude curve" is used for things like forces which might change over time. In your analysis, I assume that you are applying an initial velocity and have no other loads, so there would not need to be any multiplier/magnitude curves (in theory).

What results are you comparing between your hand calculations and the simulation results? Keep in mind that the stress results can be very dependent on the size of the mesh.

[HoRnZz]

Hi John,

First off, thanks for the reply.

The multiplier curve I am referring to is in the "Prescribed Translations" settings. I am setting the displacement as the drop height (8 mm), then the multiplier curve,

1. Time: 0, Magnitude: 0,
2. Time: 0.04 (time it takes to drop), Magnitude: 0.8 (drop height)

The Von Mises stress results I'm seeing are next to nothing, which is a clear indication that my set up is wrong.

Basically, I need assistances setting up a drop test.

Thanks.

Phil. 

[Anonymous]

Hi @HoRnZz ,

This link might clear your doubt on defining a multiplier curve : https://knowledge.autodesk.com/search-result/caas/CloudHelp/cloudhelp/2014/ENU/SimMech/files/GUID-C5...

[John_Holtz]

Thanks for the link @Anonymous . That documentation is for different software (Simulation Mechanical), so the commands are different than Fusion 360. But the concepts for a prescribed translation are the same.

Controlling the displacement as a function of time means that you are setting the velocity to a known value. That would not be appropriate for a drop test because you do not know how the velocity changes after the impact. The proper way is to assign an initial velocity to the dropped part, define gravity (if significant) and a constant multiplier curve for the gravity load, and separation contact between the parts. The Event Simulation analysis will calculate the velocity of everything after time 0, the impact loads, and so on.