multiple drop test in 1 analysis 2

[matthat]

i am modeling a helmet that needs to undergo 3 drop tests in one analysis
it needs to drop at a velocity 3m/s where i request the deceleration data, it then needs to drop 5.9m/s and then a third drop of 5.9m/s, how do i do this as i cant add a step after the 1st drop that will allow me to change the velocity of the helmet
any help?

 

[rstupplebeen]

Why do you need all 3 in 1 analysis? You will have to decelerate and accelerate to get to each drop velocity and direction. Why not just do 3 drops?

Rob Stupplebeen

 

[matthat]

i am attemting to model a helmet for an american polo standard where the helmet is dropped 3 times onto the same spot, after the 1st impact the eps liner deforms and the the protection to the head decreases, the next drop is faster at 5ms and yet again more deformation and less proetection. the head in the helmet needs the deceleration to be under a certain level for the helmet to be accredited with the standards. therefore 3 drops in one analysis
is there some way of stringing 3 tests together and keep the deformed helmet for each one or do the 3 drops in one tests to replicate this?

 

[rstupplebeen]

You could do a restart analysis which could include the deformations and damages of the first model.

Rob Stupplebeen

 

[Elabbasi]

You can also do multiple steps without restarts. Just apply velocity boundary condition in a new step after each impact to prepare the helmet for the next impact, then remove the velocity boundary condition (in another step). You mentioned that you can't add a step where you change the velocity of the helmet. However, this kind of BC change is allowed in Abaqus.

It may get a little tricky if the helmet is allowed to rotate during impact. In that case preparing for the next impact will be a little harder but doable.

Nagi Elabbasi
Veryst Engineering

 

[matthat]

elabbasi, i have done as you have suggestedbut now i have anew problem, after the helmet has impact once it goes back for the next impact but noe the helmet judt goes straight throught the impact surface as though its not there, or as though my general contact interaction no longer works, but it says it s still propagated through each impact

 

[Elabbasi]

That's strange. Did you remove the velocity boundary condition before the second impact? Basically, you should apply the velocity BC, then remove it, and do both before the second impact occurs. Otherwise, the helmet will keep moving with the prescribed velocity (it's a boundary condition not an initial condition).

Nagi Elabbasi
Veryst Engineering

 

[matthat]

is there any chance you could explain it step by step

 

[rstupplebeen]

Step, action
1, initial velocity
2, free fall on to surface 1
3, initial velocity turn off surface 1
4, free fall onto surface 2
5, initial velocity turn off surface 2
6, free fall onto surface 3
You may need to add an additional relocation step to orient and position the helmet reliably. I hope this helps.

Rob Stupplebeen

 

[Elabbasi]

Here's another description probably the same as Rob's:

Initial Step: Initial velocity of 3 m/s
Step 1: First impact with surface
Step 2: Velocity BC of 5.9 m/s to prepare helmet for second impact
Step 3: Remove velocity BC, impact second surface
Step 4: Velocity BC of 5.9 m/s to prepare helmet for third impact
Step 5: Remove velocity BC, impact third surface

 

[matthat]

Why is there 3 surfaces . I have only one surface. Do I need 3

 

[Elabbasi]

No you don't need 3. One surface is fine.

 

[rstupplebeen]

It depends on if you want to move the helmet or create a new surface where you need it or to move the surface.

Rob Stupplebeen

 

[matthat]

Thanks I will try this when I get to work in the morning

 

[matthat]

this works, thanks guys
exactly as you said
1 initial 3.42ms
2 drop 1
3 velocity 5.42
4 turn off v5.42 - impact
5 velocity 5.42
6 off v5.42 then impact