Learning Forum

[mostafam]

Hi

I am trying to do an element test for seeing the behavior of MAT_173 in ls-dyna. I have a solid element (1x1x1m) and I apply 5 cm horizontal displacement to the top nodes. I fix the base nodes. When I check the shear stress diagram in ls-prepost, I do not see the mohr coulomb cap for it. I mean that according to the mohr coulomb shear strength equation, "\tau = \sigma * tan(\phi) + c" where \tau is shear strength, \sigma is normal stress, \phi is friction angle and \c is soil cohesion. According to the hand calculation, when I have such a solid element, the shear strength has to be more than c, since normal stress in compression and phi are positive, but the value I get is less than that.

Does anybody know what am I doing wrong?

Thanks

Mostafa 

[Pedram Samadian]

Hi,

Please check the following thoughts about the possible sources of error:

• Ensure you are outputing a right variable for the shear stress. The "maximum shear stress" needs to be output, not any shear stress components in the stress tensor. 
• Revisit the input material parameters in the material card and verify their values and unit consistency. LS-DYNA Theory Manual and Keyword User's Manual (LSDYNA Manuals) are good resources for the better understanding of this material card and its parameters.
• Make sure that the material passes the yield strength. 
• Use a fully integrated elemen type.
• Run the model with multiple elements to see if you can get what expected.

I hope there are helpful.

Thanks,

Pedram