An High Order Mixed Interpolation Tensorial Components (Mitc) Shell Element Approach for Modeling the Buckling Behavior of Delaminated Composites

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An High Order Mixed Interpolation Tensorial Components (Mitc) Shell Element Approach for Modeling the Buckling Behavior of Delaminated Composites
Marco Gaiotti a, Cesare M. Rizzo a,⇑, Kim Branner b, Peter Berring b
a b s t r a c t
This paper describes the experimental and numerical studies carried out on delaminated fiberglass epoxy
resin laminates made-up by different fabrication methods, namely by vacuum infusion and prepreg.
While the tested specimens were originally intended for the assessment of buckling behavior of composite laminates of wind turbine blades, results were found valuable for the marine industry as well, because
similar laminates are used for the hull shell and stiffeners. Systematic calculations were carried out to
assess the effects of an embedded delamination on the buckling load, varying the size and through thickness position of the delamination. Different finite element modeling strategies were considered and validated against the experimental results. The one applying the 9 nodes MITC shell elements was found
matching the experimental data despite failure modes were different for the two fabrication methods
Keywords:
Composites
Buckling
Tests
FEM modeling
Delamination
Conclusions
In the present paper a 9-noded MITC9 shell elements modeling
strategy has been presented as an alternative reliable strategy to
reduce computational efforts required by traditional 3 DoF solid
element models, allowing the simulation of a delaminated single
skin laminate panel by appropriately offsetting the contact surfaces of the delamination.
An extensive numerical campaign has been conducted to account for the effects of an embedded delamination on the buckling
load, varying the size and through thickness position of the
delamination.
The results have been compared with the ones obtained by a
traditional 3 DoF solid model, showing interesting differences,
attributed to the bending properties of thin shell surfaces, particularly useful for local buckling problems.
Thereafter, experimental tests conducted by DTU Wind Energy
led to the identification of two distinct failure modes related to
the fabrication method. In particular early delaminations leading
to sudden failure are reported for the prepreg panels, due to an inter-laminar fracture mode not involving fibers bridging.
The proposed shell elements numerical model matches very
well the experimental data, especially for infusion made panels.
It is able not only to represent the correct compressive stiffness
of the panels, but also to predict with noticeable accuracy the critical buckling load and the sudden collapse of the infusion made
panels not affected by the early failure induced by the initiation
and growth of new delaminations.
The sudden collapse observed in the experimental campaign is
well simulated by the shell model in term of both ultimate load
and load-displacements curve, where the experimental specimen
does not suffer of early delaminations growth due to inter-laminar
fracture mechanism.
Fig. 15. Experimental/numerical comparison: normalized in-plane displacement vs. in-plane load.
M. Gaiotti et al. / Composite Structures 108 (2014) 657–666 665The FE model simulating the prepreg panel behaves very similar
to the infusion one. This confirms, as expected, that the delamination size has rather limited influence onto global buckling collapse.
Global buckling is believed to be influenced mainly by the thicker
sub-laminates which, in the considered cases, were similar. The
slightly higher stiffness of the prepregs models is clearly due to
the higher thickness of the plate. In this latter case the experimental/numerical mismatching is therefore attributed to the early delaminations suffered by the prepregs, which obviously cannot be
reproduced by the proposed finite element modeling strategy.
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