## General Mechanical

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#### Modelling laminate defects (delaminations) with Shell elements + layer offset

• Robert Mehlig
Subscriber

Hi,

I am simulation ultrasonic waves in a CFRP plate. I am comparing (trying to replicate) the simulation results to a dataset by Open Guided Waves [1]. To reduce computing resources I have been using Shell elements and defining layered sections to discretize the laminate layers. This has been producing great results so far, though I have only tried the undamaged scenarios.

Now to my fist question: in an article [2] I read that:

"The concept of delamination modelling is the same as in [31]. The
flat shell is divided into three regions: (I) undelaminated, (II) above
delamination interface, and (III) below delamination interface. These
regions are denoted in the cross–section through delamination shown
in figure 2. In the flat shell, all spectral elements are located at the
neutral plane. There are two layers of elements at the delamination
region with zero gap between them. In other words, at the delamination
are two shell elements on top of each other that have the
same nodal positions but the nodes are not merged. On the boundary
of the delamination, the nodes of all shell elements are then
again merged." [2]

Any idea how to achieve this? Would it be possible to define two layered sections on the same surface element, splitting the layers into two sections? I tried this but I am having issues with the layered section offset.

In a handbook for realease 18.2 layered sections (for the quadratic shell element 281) are discussed and it states:

"Value that locates the node with respect to the default origin (midplane) of the section. Valid only when `Location` = USER. The offset alters only the reference surface of the shell elements (that is, where the nodes are located). It does not change the physical dimensions of the shell itself; the volume and mass remain constant when an offset is specified." [3]

i.e. the offset defines the out of plane displacement of the middle of the section...? This doesn't seem to be the case in v231. Since I always have had the offset set to "top" in the hope that the excitation is at the surface I'd like to apply the defects in a similar manner.

For reference, above is the  Open Guided Waves SHM-plate in ansys.

The second question is regarding to the offset, how does it work?

As an example I added one layer of aluminum on top of the defect D22. For all cases the rest of the plate has the offset "top" and the defect has offset "user defined" at:

0 mm

+2mm

-2mm

I am probably confusing myself, but I cannot figure out what to do to get the top 2mm aluminum layer of the defect to sit on top of the plate, exactly like the 0mm image. These images also show the mesh, I don't know if this is by scale / the proportions fit.

By my logic, "top" should be the same as "-1mm" but it seems to be inverted...

Thanks in advance, I hope I was clear enough.

1. Moll, J.; Kathol, J.; Fritzen, C.-P.; Moix-Bonet, M.; Rennoch, M.; Koerdt, M.; Herrmann, A.; Sause, M.; Bach, M.: Open Guided Waves – Online Platform for Ultrasonic Guided Wave Measurements, Structural Health Monitoring, 2019, vol. 18(5–6), 1903–1914, DOI: 10.1177/1475921718817169

2. P Kudela et al 2020 Smart Mater. Struct. 29 095010
3. Ansys handbook SECOFFSET
• Robert Mehlig
Subscriber
I didn't specify the geometry: The CFRP plate is 500mm x 500mm x 2mm (xyz). The aluminum disc has radius 10mm and depth 2mm.
• Robert Mehlig
Subscriber

Additionally: since I am defining the defect area twice, once in the LS for the whole plate and the second in the LS for the defect area, does this cause a problem? If I define the defect area to include only the aluminum, not the original plate layers, does this cause an contact issue between the CFRP plate and the aluminum disc?

• Robert Mehlig
Subscriber

Does anyone have any experience regarding the above?

• jimawa2986 jimawa2986
Subscriber

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