Material properties of thermoplastic matrix carbon fiber reinforced high performance composites using automated fiber placement

Abstract

Technological developments lead a way through change on material performance requirements. Material science has been one of the oldest areas of interest of humankind since ancient history, even historical milestones has been identified according to the materials used during the time interval. Throughout the years, material science has been evolved and improved such that, nowadays people are able to tailor the material to get desired property of final product. Material engineers deals with finding solutions to make desired final property products [28,31]. Aerospace is one of the engineering fields that requires strong, lightweight, resistant and flexible materials. This is a must since all aircrafts must be lightweight relatively to the other transportation machines. To answer high performance requirements studies on composite materials have significantly increased during the last decades. Composite materials consist of two or more distinguished material having individual properties, to be able to create a composite material an interface between individual components must take place. Composite materials should have improved final properties than the individual components. Composite materials can be divided into sub classes according to the reinforcement and the matrix phase. Matrix phase holds the reinforcement together and protects the reinforcements from external damages, which can be physical, mechanical or environmental conditions. Matrix materials can be polymer, metal, ceramic, reinforcement on the other hand, can be fibers, structures or particles. One of the most commonly used materials for the engineering applications is carbon fiber reinforced polymer matrix composites on critical parts of design for. For the matrix phase, thermoplastic or thermoset matrix are suitable options for such applications. Thermoplastic matrix has several advantages over thermoset matrix for being recyclable, lighter, durable and easier to storage with respect to thermoset matrix. In this study, unidirectional carbon fiber reinforced thermoplastic matrix composite panels consisting of 11 plies are laid down with automated fiber placement (AFP) robot with [[0°/90°]20°]/90°]s orientation to address a typical design approach. AFP is an additive manufacturing method of producing high quality, near absent flaw final product. It requires less time to manufacture parts with AFP than conventional methods. Impregnation means to wet fibers with matrix, prepreg is shortened name for pre-impregnated. To be able to manufacture a composite part, prepregs are laid down on to each other. Conventional way of manufacturing a composite material is hand lay-up of prepregs. If the reinforcement phase is a continuous fiber, then the stacking of prepregs can be named after orientation of fiber. There are two different options of matrix used for this study, one having relatively higher melting temperature than the other. Different matrix material is used to address, whether melting temperature change causes any difference in thermo-mechanical properties or not. In this study 8 panels are manufactured, they are laid down with different lay-up speeds with average of 100 mm/sec and 400 mm/sec. Change of lay-up speed gives an idea of how fast the production rate can be, in order not to lose thermo-mechanical strength and crystallinity of the material. For the thermoplastic materials, consolidation takes place under certain circumstances. Consolidation is a process of solidification of the polymer. In this study, half of the identical panels are post consolidated in the autoclave. By doing so, the effect of the post consolidation is investigated by post consolidating one of two set of the identical panels in autoclave, others left as in situ. The objective is to investigate the trend of approaching post consolidated performance level without any further need of post consolidation by changing the process parameters. In order to be able to evaluate the outcomes of parameter, material and process change, differential scanning calorimetry (DSC), microscope, gas pycnometer and dynamic mechanical analysis (DMA) tests are conducted. Various results are investigated with respect to crystallinity, defect formation, void content, and mechanical performance of the panels. Results has shown that there is no significant effect of lay-up speed and melting temperature of the matrix on crystallinity, whereas post consolidation has a strong influence on both degree of crystallinity and thermo-mechanical properties. Post consolidated panels have 25000 MPa of storage modulus while in situ panels have 15000 MPa. The results are also elaborated with the void content which is relatively decreases with the post consolidation treatment.