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When using MAT/LAW1 or MAT/LAW6, an initial density is set. How is the density change over time calculated in these cases?
Hi Yuki, that's quite a vast question.
Obviously, the density is changing with the compression or expansion of the material, which can be directly linked to the element deformation in case of lagrangian formulation. So it is linked to strain / node displacement, which of course depends on forces and material bulk stiffness.
Then the question could be how does the density change with X variable. If X is the pressure, then I can tell that :
where E is the Young's modulus, nu is the Poisson's ratio and
I hope it helps.
Adrien
For example in OpenRadioss this is done in ./engine/.source/elements/solide/srho3.F for /BRICK elements.
After that Pressure is defined with
What mentionned Adrien for /MAT/LAW1 is correct : for information P=E/3/(1-2nu)*mu is deduced from P=-1/3 trace(sigma) where sigma is calculated using Hooke's law. Resulting EoS is depedent on strain tensor (large strain, small strain, etc…)