Hi FEA expert...I need advice on how to choose the suitable hourglass type in Abaqus. As we know, in Abaqus, there are options of (default/enhanced/relax stiffness/stiffness/viscous/combined) hourglass control. In this regard, how to decide which hourglass control is suitable for our FEA problem. Any guideline?.. Further, I found the following statement in Abaqus manual help.
"Using values larger than the default values for hourglass control can produce an excessively stiff response and sometimes can even lead to instability if the values are too large. Hourglassing that occurs with the default hourglass control parameters is usually an indication that the mesh is too coarse. Therefore, it is generally better to refine the mesh than to add stronger hourglass control."
Regarding the above statement, how to set the hourglass value since there is no space to key in any value in Abaqus. By referring to the attached file, we just allow selecting a different type of hourglass control. Only space for combined type (stiffness-viscous weight factor) is available to set the dominant between stiffness & viscous hourglass which 0.5 for a default value.
Thanks in advance.
Hello Ashaari,
my first question is "Are you sure you need to change hourglass control parameters?".
Does your model show severe hourglass problem?
From my experience the default values of hourglass control parameters work perfect with fine enough mesh.
Sincerely,
Pavlo
Hi Pavlo..Yes, my FEM model undergone hourglass problem where unexpected drop of load happened. I hve tried change it to stiffness control and its look well and the result preety good to the theoritical. Yet, the FEM curve show a bit higher/stiff when it come to inelastic part. FYI, I'm using dynamic explicit since my FEM model dealing with critical contact problem which doesn't work well (susceptible to convergence problem)in implicit scheme.
Hi Ashaari,
If you need for the model to generates more resistance to hourglass forces (to avoid hourglass modes or element distortion) you can increase the displacement hourglass scaling factor at the end of the picture. as mentioned here:
https://abaqus-docs.mit.edu/2017/English/SIMACAEELMRefMap/simaelm-c-sectioncontrol.htm
Setting the hourglass control to stiffness with a scale factor of 1 or 2 may be good choice.
However be aware that increasing the hourglass scaling factor may lead to more artificial energy (ALLAE in Abaqus history outputs) in the results that should be checked for all the simulations with reduced integration elements. the rule of thumb is that this energy should be less than 10% of the total energy of the system, if it is more than that the results cannot be trusted.
Best,
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