Structures made of carbon fiber reinforced plastic (CFRP) offer enormous potential for lightweight construction due to their high specific strength. In recent years, the trend has moved from thermoset to thermoplastic materials in order to exploit the advantages of recyclability and the ability to join two components by melting the matrix locally. A particularly good ratio of mechanical properties to weight is achieved with sandwich structures. However, the production of thermoplastic sandwich structures using conventional processes is currently limited to flat components. Isolated approaches to the production of three-dimensional structures require highly complex tools and multi-step production processes and are also limited to a single defined shape.
Thermoplastic Automated Fiber Placement (TAFP), on the other hand, offers a flexible fiber composite production process. A comprehensive understanding of the process already exists for processes in which similar semi-finished products are used. However, there is a lack of knowledge about the mechanisms and the characteristics of the optical-thermomechanical interactions in the placement of anisotropic tapes on isotropic foam structures. Preliminary investigations have shown that the formation of a cohesive bond between the deposited tapes and the foam core is possible in principle under TAFP process conditions. However, the choice of unsuitable process parameters leads to local collapse of the foam structure or insufficient cohesive bonding of the two joining partners.
The aim of the TheSaLab project is therefore to develop a fundamental understanding of the relationships between the optical-thermomechanical interactions in the heating and joining zone during the deposition of thermoplastic carbon fiber-reinforced tapes on thermoplastic foam cores using laser-based TAFP. In a first step, the optical interaction of the laser radiation with the foam material and the prepreg tapes is investigated. Subsequently, the power distribution in the heating zone resulting from the reflection, absorption and transmission characteristics of the two joining partners is determined based on a model as a function of the laser settings. Furthermore, the foam and consolidation roll behaviour under process parameters are mechanically characterized and transferred to material models. The results of the investigations are then combined and validated in a thermomechanical process model. By coupling the thermomechanical process model with a bond strength model, the influence of the process parameters on the bonding quality between the deposited tape layers and the foam core is investigated.
Contact:
For further information, please contact Dr.-Ing. Carsten Schmidt, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, on +49 4141 77638 11 or by e-mail (schmidt_c@ifw.uni-hannover.de).
