Learning Forum

[BINGBING]

I am trying to simulating the fragmentation field of aluminium alloys internal explosion。

with the JC model and Ale-lagrange coupling , but there is a sever mass loss problem.

while i do some search, i found others also seem to have this problem,

[BINGBING]

@tslavik
Could you please help me with this problem´╝ƒthank you very much

[peteroznewman]

you have to have the @ symbol as part of the link or it doesn't notify the user

[tslavik]

An element will be eroded if its erosion criteria is exceeded - whether it's part of a "fragment", or not. Under *MAT_015, the manual states: "Fracture occurs when the damage parameter reaches the value of 1. D is stored as extra history variable 4 in shell elements and extra history variable 6 in solid elements." Erosion can also be due to *MAT_ADD_EROSION, if that keyword is applied to the *MAT_015 part.

[BINGBING]

i mean, if it has become a part of a fragment ,Shouldn't it fly like a rigid body driven by the shock wave? why it wolud still experience a sever deformation and even satisfy the erosion criteria´╝ƒ

[tslavik]

Watch the stresses in an element which is deleted from a fragment If the stress state is changing, it must be under the action of other forces (pressure, contact, ALE coupling, internal forces, inertia forces, etc.) which indicates it is not flying like a rigid body. As well, its damage value is probably increasing; when that reaches unity the element will be deleted.

[BINGBING]

I can understan what you say,I just don't understand , if a element A has become a part of a fragment B , i think there would be no constraint for the fragment B from the nearby structure´╝î there is only two forces acting on the fragment B´╝îthe shock wave pressure and the ALE coupling forces from airÒÇéwhy the fragment B wolud still experience so sever deformation and even all the element of fragment B would be deleted´╝ƒ

is there any better way ´╝êexcept the lagrange-ALE and SPH-ALE´╝ë to simulate the internal explosion fragment field of metal shell´╝ƒI tried SPH-ALE´╝îi feel the result is kind of untrueÒÇéÒÇéÒÇéÒÇéÒÇéÒÇéÒÇé

Thank you very much for replying meÒÇé

[BINGBING]

thank you

[tslavik]

You must determine why the element is eroded. Does it occur when D reaches a value of 1? If so, double check this by studying the time-histories of effective plastic strain and effective stress in that element. Then, you should be able to determine the reason for the change in stress state (external pressure load, contact, ALE coupling, etc.) Otherwise, erosion could be due to ERODE=1 in *CONTROL_TIMESTEP or *MAT_ADD_EROSION / *MAT_ADD_DAMAGE. Please identify the agent which triggers erosion.

[BINGBING]

I didnÔÇÿt use the erosion control parameter in the *Control_TIMESTEP or *MAT_ADD_erosion, the history variable 6 of the deleted element all reach 1.
is it possible that there is something went wrong with my ALE coupling parameters?
I used CTYPE=5 and Direc=2 while others remain default

[tslavik]

Please set END=80 in *CONSTRAINED_LAGRANGE_IN_SOLID to deactivate the FSI at 80 musec. Does this change the erosion?