Does Abaqus software calculate stiffness matrix and mass matrix again and again in per step when a nonlinear dynamic analysis be performed. If the answer is yes, then the software must exclude the elements reached yield point. So, ultimately the stiffness matrix must become singular and subsequently the analysis must stop. However, when i implement a nonlinear analysis in Abaqus, the software doesn't stop any time. What should i do do yo think?
Thanks in advance.
The stiffness matrix should change due to the material or geometrical non-linearity and the mass matrix will additionally be updated in dynamic analysis.
you run your model in Abaqus Explicit or Standard/Implicit ?
Hi,
stiffness is generally not zero if material yields. However, the elastoplastic stiffness is generally smaller than in the elastic range.
In FEM codes similar to Abaqus (e.g. Ansys), users can choose the frequency with which the stiffness matrix is updated. This is usually an option of the Newton-Raphson procedure. A full Newton-Raphson scheme updates stiffness in each iteration, but you may also use the initial stiffness or the stiffness after iteration has converged.
The mass matrix is usually not updated in Lagrangian FEM because mass is conserved.
Regards
Thanks Dear Fares and Aubram;
I tried implicit and explicit solution method, too. Moreover, i use full Newton choice in Abaqus. But i couldn't solve this problem.
"So, ultimately the stiffness matrix must become singular and subsequently the analysis must stop."
That is not correct. If you solve a dynamic problem you do not inverte the stiffnessmaterix. You have to inverte a mixure of stiffness and mass matrix (page 13 K hat). Therefore, a reduction in stiffness does not lead to a problem. Only if you have a static problem it is true, because your mass matrix is zero.
http://ocw.mit.edu/resources/res-2-002-finite-element-procedures-for-solids-and-structures-spring-2010/linear/lecture-10/MITRES2_002S10_lec10.pdf
- Badges
- Science topic
- Similar topics
- Engineering
- Civil Engineering