Zero plastic strain for SOLID 186 elements

[icetears]

Hello together,

I'm a little bit confused about a Static Structural analysis in ANSYS Workbench 12.1 which involves an assembly (bracket and ball stud).
I used SOLID 186 elements (Hexa Dominant) for both parts and Yield Strength of the material is exceeded for both. Plastic strain arises for bracket but for stud there is no plastic strain (though yield limit is exceeded with 108 MPa).
In areas where plasticity is expected,elements are small enough to capture stres gradients( two quadratic hexahedron elements were used on small radius).
I've made another analysis with SOLID 187 elements (quadratic tetrahedrons) and this time the results are more realistic (maximum plastic strain in a node is 0,77%).
My question is: why the results are different? What's happening with Hexa elements that they don't deform plastically even yield strength is over exceeded?
If someone could give me an explanation, I would appreciate this.

Many thanks

Best regards,

Marius

 

[icetears]

Does anybody know the reason for the problem described above?

Many thanks