Anja Winkler

Fibre-reinforced composite structures based on thermoplastic matrices with embedded piezoceramic modules

The paper presents recent developments for the integration of piezoceramic modules into fibre-reinforced composite structures based on thermoplastic matrices. An adapted hot pressing technology is conceptualized that allows for material homogeneous integration of the active modules. The main focus of this contribution is on the development of a robust and continuous manufacturing process of such novel active composites as well as on the operational testing of the produced samples. Therefore, selected specimens are manufactured as bending beams and investigated by means of electrical impedance measurements, modal analysis and structural excitation tests. In particular, the functionality of representative specimens is characterized based on frequency as well as spatially resolved deflection measurements. Moreover, the mentioned samples are compared to non-integrated piezoceramic modules and to equivalent passive reinforced composite structures.

Online Poling of Thermoplastic-Compatible Piezoceramic Modules during the Manufacturing Process of Active Fiber-Reinforced Composites

Due to high specific properties and the ability for the realisation of short cycle times within the production process, the use of fiber-reinforced thermoplastic composites offers a high potential for high volume applications. Furthermore, the layered built-up and the according manufacturing processes of these materials give the possibility to integrate functional elements, like electronic components or piezoelectric sensor/actuator modules. Within the collaborative research center CRC/TRR 39 “Production Technologies for light metal and fiber-reinforced composite-based components with integrated piezoceramic Sensors and Actuators”, the integration of piezoceramic modules into lightweight structures ready for series production is investigated. This paper presents the manufacturing process of active fiber-reinforced thermoplastic composites. Here, the focus is on experimental investigations covering the process-integrated poling of novel piezoceramic modules during the manufacturing of active fiber-reinforced thermoplastic components. Therefore, laboratory and process-oriented tests are performed for the determination of appropriate parameters for the pressing and poling process. The functionality of the embedded and poled TPM is validated by the excitation of an active component structure and the optical measurement of the vibration behaviour using a laser scanning vibrometer.

Combined joining technique for thermoplastic composites with embedded sensor networks

Lightweight components suitable for high-volume production are realizable by utilizing textile-reinforced thermoplastics. These composite structures can be equipped with additional functionalities by embedding sensor networks. With regard to assembly processes, material- and function-adapted joining techniques are required to connect such components efficiently. Therefore, the joint should enable both the transmission of mechanical loads and electrical signals. In order to fulfill these requirements, a combined joining technique based on blind riveting is analyzed in this article. Specimen plates made of glass-fiber-reinforced polypropylene were fabricated by compression molding. They contained adapted conductors embedded between the glass-fiber-reinforced polypropylene layers. In a next step, specimens were joined by blind riveting. The experimental analysis of several joint configurations revealed differences in interface quality and electrical performance. Finally, the reliability of the selected joining concept was verified by the experimental investigation of single-lap specimens under thermal and tensile loading.

Dynamic Behavior of Active Lightweight Compliant Mechanisms with Integrated Piezoceramic Actuators by Under- and Overcritical Periodic Excitation

Integration of active elements as thermoplastic-compatible piezoceramic modules in lightweight compliant mechanisms offers the possibility to actively control its structural behavior by static, dynamic or vibro-acoustic loads. New active lightweight structures with material-integrated structural monitoring, energy-harvesting, or active vibration damping functionalities become possible. Previously, a demonstrator mechanism was designed and built, and its behavior under quasi-static excitation was simulated as a multi-body system, using two-layer cells with torsion and traction springs for compliance and linear motors for excitation. The mechanism was later tested to confirm the simulation results. This paper presents a study of the dynamic behavior of active compliant mechanisms obtained by integration of piezoceramic actuators into fiber-reinforced composite structures. The results of the dynamic mechanical simulation procedure were compared with experimental results for a given demonstrator mechanism. The comparison concluded that the simulation procedure describes fairly accurate the real behavior of the lightweight compliant mechanism, thus it can be used in the development of new active structures.

Experimental Investigations on Integrated Conductor Paths in Fiber-Reinforced Thermoplastic Composite Structures

By the benefit of functional integration the advantages of fiber reinforced plastics (FRP) as construction material can be increased due to the possibilities of integrating sensors and actuators. In Regard to the layer-by-layer definition of the wall thickness, this class of material offers a high potential for the integration of additional smart elements within the stacking and forming process. In addition to the actual integration methods of sensors or actuators, the electrical signal transmission and contacting is of great importance for smart structures. Various approaches can be followed. On the one hand, the conductor path can be defined by means of a wire and, on the other hand, the definition of conductor paths can be accomplished by functionalized films (by means of printing technology). Within this paper, experimental investigations are intended to demonstrate the suitability of screen-printed conductor paths for the press-technical transformation of FRP structures. In addition to the variation of the screen printing material and the film material, for a material-homogeneous integration, an evaluation of a corresponding selection of materials takes place with respect to the stresses derived from the deformation-technical boundary conditions.

Simulation and experimental investigation of active lightweight compliant mechanisms with integrated piezoceramic actuators

Compliant mechanisms with integrated actuators can enable new function-integrative structures through the elastic deformation of elements without the use of classical links and joints. For such designs, the mechanical behaviour of the mechanism has to be well known, because external loads, the utilised materials and the geometry of the structural parts influence the deformation performance significantly. In order to speed up the development process of such mechanisms, a tool for the dynamic analysis of compliant movements is necessary before any further FEM simulation and manufacturing. Therefore, the paper presents a simulating procedure for active compliant mechanisms obtained through the integration of piezoceramic actuators into fibre-reinforced composite structures using a double layer model. A new mechanism was designed, simulated, constructed and tested. The comparison between simulation and experimental results confirm the effectiveness of the presented procedure in regard to the design phase of new active compliant structures.

Multiscale characterization and testing of function-integrative fiber-reinforced composites

Abstract Smart fiber-reinforced composites, such as long fiber or textile-reinforced polymers are often functionalized by integration of piezoelectric transducers to realize sensory and actuatory tasks like condition and structural heath monitoring, energy harvesting or active vibration damping. Each of these tasks is connected with specific requirements with regard to the electromechanical behavior of the composite structure. In this chapter, several qualitative and quantitative methods including nondestructive, optical, electrical, and mechanical testing for the characterization of smart fiber-reinforced composites are described. Beyond their functionality and electromechanical performance, structural integrity and quality assurance are focused. By example of case studies, characterization of long fiber-reinforced thermoset and textile-reinforced thermoplastic polymers with specific test setup and results are shown. Novel developments in the field of sensor and actuator development and manufacture as well as integration of these functional elements into fiber-reinforced composites are presented.

Combined Detachable Joints for Textile Reinforced Thermoplastic Composites with Embedded Sensor Networks

In regard to the realization of innovative lightweight constructions, textile reinforced composites show outstanding mechanical properties, e. g. adjustable high specific stiffness and strengths. Furthermore, these materials enable a process immanent integration of functional elements (f. e. conductors, sensors, actuators or electronic components) directly into the composite structure due to their layered built up. Currently, no joining technologies for such function integrative composite parts exists, which enable a simultaneous mechanical and electrical load transfer from part to part by only one joining element type. Therefore, the paper focuses on detachable functional interfaces, which enable the mechanical connection of two join partners and the transfer of electrical signals by contacting the composite embedded conductors. Investigations in regard to the selection of suitable joining elements and their behavior under mechanical and thermal loads are performed. The investigations show that the electrical resistances are low and not affected significantly by rising tensile loads or repetitive joining operations. Tensile tests using both single lap shear and double lap shear specimens show that the electrical contact almost exists until the mechanical failure of the joints occurs.

Linear Two-Port Model of an Active Thermoplastic Composite Structure

This paper describes new active composite structures based on thermoplastic matrices which contain material homogeneous embedded piezoceramic modules. Starting point is the development of novel thermoplastic compatible piezoceramic modules, so called TPMs. By the utilization of the same matrix material for the composite structure and for the TPM carrier films, these modules afford an opportunity to become directly embedded into the component during its manufacturing process. In this context, the manufacturing technology of the TPMs and of the active composite structure is presented. Furthermore, selected test samples are investigated concerning their modal behavior. Based on the determined characteristics a linear two-port model is used for the reproduction of the experimental results.Copyright