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Mechanical behaviour of composite sandwich panels in bending after impact

Weijermars, Wouter (2016) Mechanical behaviour of composite sandwich panels in bending after impact.

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Abstract:This master thesis is about the mechanical behaviour of composite sandwich panels in bending after impact. The goals were to identify the influence of an impact loading on the residual bending stiffness, to determine the failure modes after impact and during bending, to illustrate the influence of core material type on the mechanical behaviour in bending after impact and to demonstrate the effect of impact energy on the mechanical response in bending after impact. In literature, several articles describe the mechanical behavior in compression after impact, but bending after impact is not yet investigated before. In sandwich composites, four different failure types are described; Core Shearing, Microbuckling, Indentation and Face Wrinkling. In order to answer the research questions, use is made of an experimental analysis and a Finite Element Method analysis. For the sandwich panels use is made of an epoxy/glass facesheet with three different core materials; SAN foam, PET foam and Balsa. A three-point bending test is performed according standard ASTM C393/C393M in order to determine the reference stiffness of the different panels. Then a reference impact test is performed according standard ASTM D7136/D7136M. Finally, an impact test is performed on specimens with the dimensions of the bending test and thereafter a three-point bending test is performed with the same specimens in order to determine the stiffness in bending after impact. The same tests are also performed in the ABAQUS FEM simulation software. It is shown that the impact tests cause a skin-core delamination at the bottom of the Balsa cored panels, while the SAN foam and the PET foam cores do not show signs of this delamination. Furthermore, it is shown that an impact has a significant influence on the bending stiffness of composite sandwich panels, dependent on the core material. The SAN foam cored specimens lose 46.1% stiffness, the PET foam cored specimens lose 25.7% stiffness and the Balsa cored specimens lose 19.1% stiffness after impact compared to bending-only tests. The SAN foam and PET foam cored specimens also show miniature cracks in the bending-after-impact tests, which do not occur in the bending-only tests. The FEM simulations show that the impact energy has an influence on the mechanical behaviour of the composite sandwich panels. The simulations show that the higher the impact energy, the lower the bending stiffness for the PET foam core and the Balsa core, but for the SAN foam there is no significant influence. The impact energy also a significant influence on the shear stress distribution of the Balsa core and on the PEEQ distribution of the PET foam core.
Item Type:Essay
Faculty:ET: Engineering Technology
Subject:50 technical science in general, 51 materials science, 52 mechanical engineering, 58 process technology
Programme:Industrial Design Engineering MSc (66955)
Link to this item:http://purl.utwente.nl/essays/71376
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