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Mohr-Coloumb plasticity model

i am simulating a uniaxial test for coal specimen using Mohr-Coloumb plasticity, there is a friction between the coal sample and the platens, the coal behavior is stain sotening.

i want to know how many points should i use in the hardening table of the mohr-coloumb plasticiy to get a good reults?

 i used 3 points:- the first one is the yield stress and the associated plastic stain, the second one the peak stress and the associated plastic strain the third one is the post peak stress and the assoiacted plastic strain. is that right?

i assume that the friction angle=the dilation angle =30 degree.

i apply the load through moving the upper plate, when the displacement is small the model converge, but when the displacement is large i got the following error message "plasticity/creep/connector friction algorithm did not convergeat 8 points.

what should i do to overcome this problem.

thank you.



Regards, Gamal

Regards, Gamal

i forgot to tell you that i am using Abaqus program in such simulation.

(1) I think, those kind of things is obtained from Lab test, you can select one point for C value and abs strain take zero (??)

(2) The calculation does not converge because you know the ABAQUS program uses the newton method for calculation (repeat), if ABAQUS tries many times on calculation and can not get the final result, then it should be some errors which coressponding to critical yield surface.

Regards, Gamal thanks Ichhung, you mean that i should use only one cohesion yield stress and its Abs strain which is zero, i think that, if i used only one point that means elastic perfect plastic behavior, but you know that the material that i use has strain softening behavior, i am not sure what i should do.

also you did not tell me what should i do to overcome the other error message "the plasticity/ creep/friction algorithem did not converge at 8 points, please help me.

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