Crack propagation using I-deas

[jazzyg]

Dear all,
I am using I-deas 8 to run some crack propagation tests on various laminate layups (for example uni-directional, quasi-isotropic layups etc.) on a double cantillever beam (DCB) specimen.

The problem is how do i realisticly model a crack using I-deas. I thought that i could create a partition and mesh the whole specimen. After this i thought i could create some contraints on the individual nodes that lie on the partition and get them to split (redefined into 2 nodes) after a certain value has been exceeded (i.e the discrete crack method. Or instead of a partition do i have to create a very small gap in the DCB specimen to represent the crack.
Does anyone know how to enforce these contraints on the node or alternatively does anyone know any method to model crack propagation using I-deas 8. I would appreciated any ideas (no pun intended).

Thank You
jazzyg

 

[feadude]

how about modeling the crack itself as a partition and not meshing it or deleting its elements after meshing?

 

[jazzyg]

Thanks for returning my post, though if i was to do as you stated, the partition wouldn't split into two after a force is applied. I am looking to obtain the strain energy release rate and in order to obtain that i need the elements to split into two.

 

[Drej]

Unfortunately, in order to model a crack correctly you will need to use elements designed for that purpose and/or the correct material model. In fracture mechanics the elements are known as Singularity elements. Any way you try to model this crack (other than with these elements and/or with an appropriate cracking model for quasi-brittle or brittle material i.e. cracking based on total strain or others) will give you meaningless stresses. The further you refine your mesh around the crack face/front, the higher the stress magnitudes will be ad inifinitum.

-- drej --