How Max Degradation Value affect my models. 1

[xingling]

Hi every body.
Quote (Abaqus Analysis User's Guide
Maximum degradation and choice of element removal


You have control over how Abaqus treats elements with severe damage. You can specify an upper bound,DMAX , to the overall damage variable, D; and you can choose whether to delete an element once maximum degradation is reached. The latter choice also affects which stiffness components are damaged.

Specifying the value of maximum degradation
The default setting of DMAX depends on whether elements are to be deleted upon reaching maximum degradation (discussed next). For the default case of element deletion and in all cases for cohesive elements,DMAX=1.0 ; otherwise,DMAX=0.99 . The output variable SDEG contains the value of D. No further damage is accumulated at an integration point once D reaches DMAX(except, of course, any remaining stiffness is lost upon element deletion).

Now my main question is this:
I used cohesive elements to predict cast iron crack initiation and propagation. The cohesive elements were inserted globally into my model. Static general steps is used in my model. My model will aborted if I set the maximum degradation of the cohesive element's value to 0.95(see attachment). However, if I set the maximum degradation of the cohesive elements value to 0.4. The crack will be more realistic.
My question is that why does this happen? And how does it affects my model? What should I do to let my crack propagate easily when the maximum degradation value is 0.95?

Best regards,
Xingling

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[xingling]

max degradation 0.95 is attached.

 

[FEA way]

Such a difference can be expected. With D_max=0.4 elements are deleted from the mesh sooner (when their stiffness is less degraded) than with D_max=0.95. It's a common approach to play with damage initiation and evolution settings until the results match the experiment or other reference. To achieve convergence in the case of D_max=0.95 you can try e.g. enabling stabilization.

 

[xingling]

Dear FEA way,
Thank you so much FEA way.
I'll try it.

Best regards,
Xingling

 

[xingling]

By the way, could you please tell me why my crack split into two cracks and not continuous?
It should have only one main crack.

Best regards,
Xingling

 

[FEA way]

Further adjustment of damage criteria may help but there's no way to make Abaqus prevent the formation of multiple cracks in this kind of simulation. The software simply deletes all elements that satisfy the given criterion. It doesn't take into account the location of these elements.