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Thermoplastic Sandwich Panels with Integrated Skins and Core of Cellular Composite

Tuesday (28.04.2020)
12:40 - 13:00 Room 2

Sandwich-structured composites are important lightweight components. As sandwich cores mainly honeycomb structures or cell-structured foams are used. Honeycomb structures have a low density, however can not be made curved and require an adhesive bond between the core and the skins. With a core of cellular material curved sandwich structures can be produced and the adhesive layer is not mandatory. However, the pores in the core are usually different in size. Thus, the design as a structural component is often hampered by a heterogeneous pore size distribution in the core or a premature failure of the skin-core interface. Therefore, the manufacturing of thermoplastic sandwich panels with core of cellular composite and integrated fiber-reinforced skins on a pilot plant scale is researched.

The function of the sandwich core is to keep the skins at distance to increase the bending stiffness of the sandwich element. To reduce the weight, low-density core material is used. Particularly suitable are syntactic foams, which can be produced by casting around placeholders. Compared to a weight-equivalent foam, the mechanical properties with encapsulated cellular placeholders could be improved. In this study, glass foam granule is used as placeholders.

Integrated fiber-reinforced layers are used as skins, which are manufactured in one operation with the sandwich core. Thus, additional steps such as surface pretreatment and adhesive bonding can be economized. A further advantage of sandwich panels with integrated instead of glued skins is the greater flexural strength, since neither the adhesive layer nor its interface fail prematurely.

The thermoplastic matrix of the sandwich panels consists of cast polyamide. The viscosity of the starting materials in the anionic polymerization of ε-Caprolactam to cast polyamide (5 mPa∙s) is significantly lower compared to conventional thermoplastic melts. Thus, the infiltration of the glass fiber fabric and the glass foam granule is facilitated.

The influence of the process parameters on the properties of the composite material is investigated. The results of Soxhlet extractions are used to determine the residual monomer and oligomer content. With the thermal analysis methods the crystallinity and the fiber volume ratio are analyzed. Porosity and cross-sectional composition are examined with SEM and CT. The mechanical properties of the sandwich panels are determined by 3-point bending tests on machined sandwich beams.

Alexander Fischer
University of Applied Sciences Landshut
Additional Authors:
  • Prof. Dr. Hubert Klaus
    University of Applied Sciences Landshut
  • Prof. Dr. Nicola Hüsing
    Paris Lodron University Salzburg