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CRC/TR 39: Production technologies for light metal and fiber reinforced composite based components with integrated piezoceramic sensors and actuators


A1 – Manufacturing Technologies for Piezoelectric Fibers and Laminates for Integration into Lightweight Structures

Aim of the sub project A1 is the development of piezoceramic modules based on piezoceramic fibers and plates. These modules will be tailored according to geometry and electrical termination to be integrated into structural components. Therefore large-scale production methods for piezoceramic fibers and modules have to be engineered and introduced. Two module types will be considered in special: 1) geometrically defined piezofiber/polymer composites for integration into polymer fiber composites as well as thin walled sheet metal plates and 2) LTCC/PZT Sensor-Actuator-Modules (LTCC = low temperature cofired ceramics) for integration into die casted metal structures.

A2 – Microstructuring and Integration Technology for Piezo Fibers in Metallic Carrier Materials (sheet metal)

Object of research are preproduction compliant mechanisms and technologies for high-volume manufacturing of piezo metal modules by direct integration of piezo elements into micro structured aluminum based material with renunciation of elastic interlayers. The research activities include investigations of forming processes for micro structuring, production technologies for high precision integration, and joining of piezo elements in aluminum carriers. In further steps the complete process chain for a high-volume production of piezo metal modules will be focused.

A3 – Thin film technologies for metal-based piezoelectric modules

For the lightmetal-based piezo modules it is necessary to secure electrical insulation against high voltages and to transfer the generally small strain values formed by the piezo elements into the lightmetal as completely as possible. Moreover, both the dielectric and electrode films must maintain their functionality through all technological steps including assembling, contacting, joining and forming. In order to increase the efficiency of the technological chain as a whole, laterally structured thin films shall be deposited. The main task of the project is to investigate the plasma-enhanced thin film deposition in order to gain the necessary knowledge for realisation of the desired film parameters also in case of the piezo fibre/epoxy resin composite substrates.

A4 – Laser based electrical and mechanical contacting of composite materials with integrated active elements

Within this project new concepts for the realisation of contacts useable in different process chains for the manufacturing of active functional work pieces will be developed. In the first period the joining technologies laser welding, laser soldering, laser brazing and laser droplet joining will be investigated with the aim to reach long-time stable contacts. It can be seen that especially Laser Droplet Welding has a potential for electrical and mechanical contacting. Challenges are to keep the droplet energy in a defined window as well as to get 100% crack-free contacts. The result at the end of the second period will be a method which will lead to a series-production technology for a reproducible contacting of piezo-ceramic modules.

A5 – Development of thermoplastic-compatible piezoceramic modules (TPM) and corresponding production processes

Aim of the subproject is the systematic development of novel thermoplastic-compatible piezoceramic modules (TPM), whose thermoplastic carrier film is adapted to the thermoplastic matrix of the composite structure. Furthermore associated high volume manufacture technologies will be developed. By a defined melting of the thermoplastic components of TPM and composite structure, a material homogeneous embedding of TPM in composite structures can be realised during the subsequent processing of the TPM with a novel direct technique. Thus, conventional additional adhesive bonding steps and corresponding inhomogeneities and compatibility problems can be avoided.

The thermoplastic-compatible piezoceramic modules are manufactured by means of a new quasi-continuous manufacturing process. Beside the technology and material adapted layout special attention is put on the functional extension of the module design. Additionally, the specially designed unique module manufacturing device is to be complemented by the process steps electrode application and piezo placement with the aim of a complete manufacturing process chain. Thereby the individual subprocesses have to be attuned by accompanying process simulations regarding the technical-technological interdependency.

A6 – Manufacturing technology for Piezo-moduls with integrated ceramic-fibre-composites and functional polymers for the 
         integration in active metallic devices

Purpose of the subproject is research and development of a novel production technology suitable for series production of piezo transducer modules with a high contour freedom for use primarily in active metallic components. Based on the large series two-component (2K) injection molding technology piezo-ceramic elements are electrically conducted and connected by electrically conductive thermoplastics. Afterwards, the isolation, the packaging and the close-contoured finish of the piezo-ceramic elements take place in an injection molding in-situ process.

B1 – Shaping of Piezo-Metal Composites

Objective of research is the integration of piezoceramics within sheet structures in a way that allows a moderate forming. The functionality of the brittle ceramic fibres is to be sustained during forming. Therefore an integration method was investigated, which allows the fabrication of a semi-finished part and is able for the processing to a structural part by forming. The time- and cost-intensive subsequent application of sensors and actors on shaped sheet metals consequently can be avoided.

B2 – Numerical study of the influence of forming operation on function of piezo-metal-compounds

Within the subproject B2 the evaluation of functionality of piezo-metal-compounds after forming takes place with numerical simulation by means of finite element methods. The piezo-modules are encapsulated by sheet metals. During forming of this compound combined bending-, torsion- and tension-loads act on the modules. The piezo-fibers in the modules are characterized by brittle material behaviour. Hence the deformations during forming have to be reduced. With a fluid bearing (‘swimming bed’) of the piezo-module between the sheet metals, reached due to embedding in low-viscous adhesive, tension loads can be drastically reduced. After forming the adhesive cures and provides a stiff connection between module and sheets, which is a requirement for the functionality of the compound.
Module loading in the forming operation can cause damage of the piezo-patches, which leads to a reduction of the functionality of the formed final part. For the description of module-functionality-degradation, experimental and numerical investigations under different load combinations are used to determine the load limits and beyond that the residual functionality. Thus by means of numerical simulation, performance reduction and sensitivity of module-position tolerance are analyzed.

B3 – Integration of piezoceramic modules into metallic components by casting - Technolgy and numerical simulation

The objective of this project is the integration of piezoceramic modules into metallic components within high pressure die casting. The main challenge is the control of the thermo-mechanical loads during mould filling and cooling. A new technology for a robust integration process suitable for mass production is explored. The experimental approach is always supported by the numerical simulation of the integration process.

B4 – Robust manufacturing technologies for active thermoplastic composite structures with integrated piezoceramic modules

The main target of the subproject is the development of high-volume-compatible manufacturing technologies for active polyamide (PA) and polyetheretherketone (PEEK) composite structures with material homogeneous embedded thermoplastic-compatible piezoceramic modules (TPM). Due to their excellent mechanical, thermal and biophysical properties, these novel active PA and PEEK composite components exhibit an innovation leading technology with wide influence on numerous fields of application.

After the successfull development of technological fundamentals for the highly productive manufacturing of thermoplastic fibre-reinforced composites with integrated piezoceramic modules (TPM) elaboration of robust production technologies based on the hot-pressing technique for singly curved structures with embedded conductive paths and TPM capable for serial production is aimed at. Especially the linkage of the individual process steps is realized by adapted handling systems and adaptable multi-contour tools as well as a comprehensive process analysis for the description and feedback of manufacturing-effective influences on the characteristics of the structural part is accomplished.

B6 – High-volume production technolgies for glass fibre-reinforced polyurethane composite structures with integrated
         piezoceramic sensor elements and adapted electronics

Aim of the project is the development of the technological basics for the high volume production of active structures using glass fibre polyurethane composites (GPV) with integrated piezoceramic sensors and adapted electronic systems. The advantages of the established Long-Fibre-Injection (LFI) process are used for the development of a novel Multi-Fibre-Injection (MFI) spray coat method, in order to merge the so far separated production steps sensor manufacturing and part manufacturing into an efficient serial process. 

C3 – Study of poling technology as part of series fabrication of smart structures

The polarisation as a process step to the activation of the electromechanical coupling of piezoceramic materials is considered and designed as step of the manufacturing chains of the SFB/Transregio. In particular, the conditions to form appropriate actuation and sensing functions of the integrated piezoelectric ceramics in composite structures are investigated. The long-term, general aim of the program is focused on the development of the experimental and theoretical
methods for adjusting of the polarisation technology for the up-scaled production of adaptive structural components.

C6 – Material Characterization an Numerical simulation of Adaptive Composites

The development of adaptive composite materials (piezoceramic-plastics- and piezoceramic-metal-composite) requires their characterization by means of the material tensors (elastic, dielectric and piezoelectric tensor). Therefore, an Inverse Method is arranged which allows the identification of the material parameters for all involved composite materials. The method is used for the determination of both, the statistical error band as well as the temperature dependency of the material parameters. Moreover, the non-linear behavior of the piezoceramic actuators should be investigated. The efficient simulation based description of composite materials is a further main topic of the project. In particular, the research is concentrated on higher order finite elements and homogenized transducer models.

C7 – Simulation of adhesives curing and shrinking processes within piezo-metal-composites

The sub-project C7 offers scope for further improvements of novel piezo-metal composites that can be processed by forming. The main goal is to provide a possibility of taking the special operating conditions of piezoelectric elements (as sensors or actors) into account. That task can be accomplished by the numerical simulation of cure shrinkage in the glue bedding of piezoelectric elements after the forming of the overall composite. Basing on these FEM simulation results, the undesirable subsequent deformations of the composite, the remaining stresses due to forming and curing, as well as the resulting loads on the piezo elements can be predicted.

C8 – Polarization Determination of Integrated Piezoceramics as Part of Process Control and Non-destructive Device Evaluation

The investigation is aimed at the creation of a non-destructive and in-situ method allowing for the determination of the polarisation distribution in piezoceramic elements integrated in composite structures. The approach uses thermal waves with different penetration depths defined by the modulation frequency. The spectrum of generated pyroelectric current and the phase shift between thermal wave and pyroelectric current as well as the time dependence of the pyroelectric current will be measured and used for the reconstruction of the depth profile of polarisation by a mathematical procedure. Additionally, the method enables the analysis of structural defects like parasitic layers and delaminations at the interface to the piezoceramic.

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