Definition of process parameters for manufacturing of thermoplastic composite sandwiches - Part B: Model verification

Thermoplastic composite (TPC) sandwich structures offer great potential to meet the demands of lightweight structures for aeronautical applications. In this study, compression moulding of sandwich components, consisting of carbon fibre-reinforced polyetheretherketone (CF/PEEK) skins and polyetherimide (PEI) cores, is studied with the aim of verifying a previously proposed model. This model predicts the influence of processing conditions on the properties of the sandwich structure, particularly the skin to core bond. Sandwich specimens are manufactured according to the parameters resulting from the model, in particular to verify skin and core pre-heat temperatures. The resulting bond quality is characterized by flatwise plane tensile testing and compared to the predicted values. This comparison shows a reasonable good agreement between predicted and experimentally obtained tensile strengths, which mainly depend on the skin pre-heat temperature. In addition, the specimens mostly fail as predicted by the model. While the model predicts that pre-heating the core leads to an improvement of the bond strength, the experiments show that core pre-heating leads often to core collapsing, which was not considered in the model. Therefore, it is proposed to complement the modelling approach with an analysis of the heat flow into core.