Strain softening behavior

hi my friends, i am new in abaqus, i want to use Mohr-Couloumb plasticity to simulate the uniaxial compression of a coal sample, the behavior of coal is stain softening, i want to know how many data points should i use in the hardening menu of Mohr-coloumb plasticity (cohesion yeild stress & Absolute plastic strain ).

you know that the strain sofening bhavior has yield point and peak and then post peak (softening).

when i make the simulation i used 3 data points

although i put the initial, maximum  increment time are small, i got the following error message,

the plasticity/creep/connector algorithm did not converge at 8 points. what should i do to overcome this problem.

please help me

thanks alot.

Gamal