Variable Stiffness Particles using GRANULAR package

Hi all!

I am hoping to simulate variable stiffness particles using the GRANULAR package. For example, I am simulating 5 grains, each of which should have a different stiffness. I am using a Hookean pair_style. I understand that I can define a spring stiffness and damping prefactor for each pairwise interaction between 2 grains. However, I am unsure of how the pairwise spring stiffness defined for the interaction of particle types X and Y relates to the stiffness of particle X and Y.

Thanks for any help you can provide. Apologies if this question has an obvious answer, I am a beginner!

Perhaps @jtclemm can help you with this.

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Hi owala, if you define a stiffness for type 1-1 interactions, say k11, and for type 2-2 interactions, say k22, by default the 1-2 stiffness will be a geometric mean k12 = sqrt(k11*k22). Alternatively, you can always define k12 manually and not rely on mixing.

Hi @jtclemm, thanks for your reply! Just to make sure I understand, if I had 5 grain types, I could define k11, k22, k33, k44, and k55 to be the stiffnesses for grains 1-5, respectively. Is this correct? Thanks again!

Yes, you can specify just k11, k22, … k55 and LAMMPS will automatically compute kxy = sqrt(kxx * kyy).