Learning Forum

[kikuji.yuki.r3]

I am performing an ultra-high speed impact analysis using Autodyn's SPH.
The impact speed of the projectile is 7 km/s, and normally the impacting object will liquefy upon impact, becoming a group of fragments called a debris cloud.
When I checked the state of the material during this analysis, I found that there were no particles that corresponded to "Void, Hydro", and liquefaction had not occurred.
Regarding this error, I first thought that the EOS Thermal settings (reference temperature, specific heat) were involved, but I cited appropriate literature values ​​from Shock EOS, so I think there is probably no problem.
Could you please tell me why liquefaction did not occur in the analysis?
Also, could you please tell me what state "Bulk Fail", which accounts for the majority of the particles in the figure, indicates?

[Chris Quan]

Void is used in the Autodyn Multi-Material Eulerian domain to represent the empty space where Eulerian materials can flow into. 

Hydro represents a material that its Strength Model is set to "None". It indicates that this material doesn't have any material strength. Usually fluid materials are in this category.

"Elastic", "Plastic", and "Bulk Fail" are usually applied to a solid material to indicate its material state. 

"Bulk Fail" means that the failure is not directional. For example, a material fails when effective plastic strain or its negative pressure exceeds a specified value.

For composite materials, material failure is directional. For example, the failure could be in fiber direction (material direction 11) or perpendicular to the fiber direction (material directions 12 or 13). This kind of failure is not "Bulk Fail". 

In your simulation, "Bulk Fail" in material status plot indicates that the material has already failed. When a solid material fails, it cannot take any tensile loading but it may still take a certain amount of compressive loading. It bahaves like a fluid material. Thus you can say that the material in bulk failure is in the state of "liquefaction".