Hi,

I am currently modelling articular cartilage as a simple 2D plane stress rectangle of approximate size 1mm by 8mm. I have collected stress-strain (nominal) data from physical compressin testing, with stress's from 0-(-1.23) MPa and strains from 0-(-0.5), and I am attempting to use this data to fit a hyper-elastic model. I have run the ABAQUS material evaluation and found that the material is stable for Ogden N=3 and N=1 along with Neo-Hookean. However, when I run my analysis the material is not stable and converges with error 'To many attempts for the increment' or 'Time increment required is smaller than the minimum specified'.

I have followed advice of other forums and reduced my time increment to 1E-30 (Which I appreciate is unrealistic), altered the number of increment attempts allowed to 200 (Again, unrealistic), varied my mesh density, the types of elements used, changing the physical data from negative to positive stresses and strains and used the explicit model instead of the standard.

None of this has been successful. Does has one have any experience in fitting physical data to hyper-elastic models? I am modelling compression between 0 and 1.8MPa as a pressure force applied to the top surface.

Thanks

bmellors