Session: 03-05-01 Performance and Reliability of Non-Metallics

Paper Number: 79308

79308 - Load Capacity of Sandwich Panel With Core Foam Evaluated by 3-Point Bending Test 

To classify vessels, classification societies require a structural assessment to confirm the compliance with applicable rules. For composite materials construction, Bureau Veritas applies mechanical sample tests to secure the mechanical characteristics of the hull structure. They include, for sandwich panels three-point bending tests (ISO 14125).

However, for sandwich panels with a low density foam core (like PVC) local phenomena like indentation or wrinkling may occur in the skin of the sandwich panel at the loading punch. The intended load capacity of the sandwich panel, with contributions from the core, will then not be reached.  For such cases, it is proposed to perform complementary shear tests (ASTM C273) to capture the behaviour of the core of the sandwich panel.

In the present paper the load capacity in a 3-point bending test is simulated with emphasis on the influence of the constitutive modelling of the core foam, as calibrated against experimental results for shear tests. Three different models of the core foam are evaluated as a benchmark study (with 3 universities participarting), and the simulated load capacity of the sandwich panel is compared with experiments carried out by Bureau Veritas and with analytical expressions for the ultimate strength for shear failure in the core or local phenomena in the upper skin of the panel. The skins of the sandwich panel consist of some 9 glass fibre plies and are modelled as elastic with a Hashin damage criterion.

The FE-simulations showed that the shear test, though only providing uni-axial loading, can be used to accurately model the load capacity of the core foam. However, the geometry of the 3-point bending specimen with a very high panel length / thickness ratio will result in a large part of the load transfer in bending of the upper (superior) skin, with less involvement of shear in the core. The FE-simulations showed that local failure of the upper face sheet is promoted prior to shear failure of the core, even when the plastic core model from the shear test is employed. At the maximum load, all plies of the upper face sheet have failed (and local plastic deformations below the load punch is seen in the core). One participant checked for delamination between the skins and the core but did not detect any.  The FE-simulated force-displacement curves were in good agreement with analytical formula for local failure in the upper skin, and they were also in fair agreement with the experimentally found load capacity.

Therefore, to fully evaluate the load capacity of sandwich panels with a foam core parallel shear tests need to be carried out.

Presenting Author: Lennart Josefson Chalmers University of Technology

Authors:

Lennart Josefson Chalmers University of Technology
Stephane Paboeuf Bureau Veritas Marine & Offshore
Konstantinos Anyfantis National Technical University of Athens
Albert Zamarin University of Rijeka
Carolyn Oddy Chalmers University of Technology
Benjamin Collier Bureau Veritas Marine & Offshore
Katerina Ntouni National Technical University of Athens
Davor Bolf University of Rijeka