Influence of different consolidation processes on the mechanical properties of AS4/PEEK manufactured with Automated Fiber Placement (Masterarbeit)

Abstract

Fiber composite materials are becoming increasingly popular in many areas of industry. The combination of high specific strength and stiffness combined with low density makes this material combination an excellent candidate for all possible applications. However, there are still many unexplored influences, especially in the field of automated production, which can reduce the production quality or drive up manufacturing costs. To make further progress in these areas, DLR is currently researching the use of thermoplastic matrices in combination with Automated Fiber Placement and In-Situ consolidation. This combination of manufacturing process and material is still used relatively little for industrial production due to costly manufacturing of good starting materials for structural components, but has high protential in terms of manufacturing costs and component geometry. Currently, postconsolidation, e.g. by means of a hot press, is used to increase the material quality after In-Situ consolidation in order to remove as many defects as possible from the layered structure. The following research work deals with the influences of different consolidation processes on the material state of the carbon fiber/plastic combination AS4/PEEK, produced by means of Automated Fiber Placement, and with the effects of defects in the ply structure on the mechanical and fracture properties. For this purpose, panels with different consolidation processes were manufactured at the Institute of Structures and Design: One variant with the In-Situ consolidation and one with In-Situ consolidation followed by hot pressing. In order to determine the differences between the two methods on the material state, various non-mechanical investigations were carried out. The samples are examined step by step from the outside to the inside in order to determine the discrepancies in all areas and to specify their origin: Thickness measurements, microsectioning, ultrasonic and CT examinations and the determination of the degree of crystallization, to name but a few of the investigations. The defects were then quantified to predict the expected differences in mechanical properties. Subsequently, various tests were carried out to determine the material behaviour under different loading conditions. These tests were divided into two groups: For the mechanical properties, tests with unidirectional layup were conducted, such as tensile or in-plane shear tests. For the investigation of the fracture mechanics, special material tests for the quasi-isotropic ply structure were used. Those tests were further developed at the UBC in Vancouver to collect more information about the hevabiour after damage initiation. Finally, the expected and real test results were compared in order to make a statement about the effects of the defects and the usability of different consolidation processes. This research work is a cooperative project between the DLR Institute for Manufacturing Methods and Structural Technologies and the Composite Research Network of the University of British Columbia in Vancouver, Canada