## 2 Manufacturing of Hybrid Laminates with Sensor Functionality  
For manufacturing of hybrid laminates with sensor functionality [21], a large-scale process chain was developed. This innovative process chain combines the polymer processing technologies of compounding and foil extrusion with the rolling and forming of metal parts. In the first subprocess (Figure 1, label 1), the starting materials are blended into a piezoceramic thermoplastic compound and extruded as a thin foil, which forms the active component of the hybrid laminate. Therefore, the polypropylene homopolymer Moplen HP501H (Lyondell-Basell, Rotterdam, the Netherlands) is functionalized with piezoceramic lead zirconate titanate (PZT) powder NCE 55 (Noliac A/S, Kvistgaard, Denmark) and carbon nanotubes (CNTs) NC7000 (Nanocyl S.A., Sambreville, Belgium). The optimal material composition and processing properties were determined in previous investigations. Hence, the piezoceramic foil consisted of 70 wt % PZT and 0.5 wt % CNTs [22; 23]. A foil thickness of 250 \(\upmu\)m provides the optimal conditions for joining (Figure 1, label 2) the piezoceramic foil with aluminum sheets. The surface of the aluminum metal sheet (EN AW-6082 T4 with a thickness of 0.5 mm) was treated before joining. Grinding and additional etching with sodium hydroxide has proven to be a reliable method (acceptable adhesion when close to a large-scale reaction). After joining the piezoceramic foil and the copper sheets, cutting was carried out by water jet. A special tool concept was developed for the forming process, in which the composite is heated, formed, and cooled in the tool (Figure 1, label 3). For continuous joining, the first tests were carried out on a pilot rolling mill [24]. After successful completion, a system was developed which allows a sample size with a width of up to 300 mm and a theoretically infinite length. The concept is shown in Figure 2. The system consists of a sheet metal inlet, which is also used for heating, and a sheet metal outlet, in which the finished composite cools down slowly. The actual joining process takes place directly after heating by infrared radiation (Figure 2, right A). After feeding the piezoceramic foil and (optionally) the copper strips, the composite is joined by the pressure of the rubber rollers. The thermoplastic melts in the contact area and forms a strong bond by adhesion. The process is monitored by thermocouples under the infrared radiators, and the temperature is measured by a pyrometer just before the rolls. The first tests showed that the parameters are not completely transferable from the pilot rolling mill. Due to the larger width of the sheets, the infrared emitters were arranged differently, thus causing better coupling and heating in the sheet. After a short parameter variation, it was possible to find the appropriate setting and produce hybrid laminates with sensor functionality. The forming of the hybrid laminates was investigated in preliminary tests by V-bending and deep-drawing. The forming temperature, at which the brittle plastic does not tear or flow out, was particularly important. All the described preliminary work was carried out with a tool heated by heating cartridges and samples preheated in the furnace. The V-bending experiments showed that if the temperature is too low, the piezoceramic compound cracks. This is due to the fact that it is rather brittle due to the high proportion of ceramics. Only from a forming temperature of 100 \({}^{\circ}\)C did the piezoceramic compound not fail. With a further increase in temperature to 180 \({}^{\circ}\)C, the plastic flowed due to the reduction in viscosity. This was particularly evident at 180 \({}^{\circ}\)C, at which the piezoceramic compound was strongly thinned out and flowed laterally out of the sample (a more exact description is published in [24; 25]).