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978-3-8439-1994-4, Reihe Ingenieurwissenschaften
Ana Carolina Nogueira da Silva
Investigation of a Damage Tolerant Joining Technology for Lightweight Structures (Band 8)
187 Seiten, Dissertation Technische Universität München (2014), Softcover, A5
With the increasing demand in the aerospace industry for lightweight structures, due to economic and ecological reasons, the application of carbon fiber reinforced plastics (CFRP) has been growing in the last decades. The current design approach for CFRP joining includes the weight penalty of thousands of bolts and fasteners. To address this issue and further a higher lightweight potential, an innovative joining technology integrating metallic pins into composite structures was investigated in the present work. The main objective was to develop a high-performance lightweight joint that combined damage tolerance with efficient load transfer.
In the first instance, the development of special manufacturing techniques for the metallic pinned inserts and the reinforced joints was presented and discussed. The experimental research work was focused on three distinct levels of increasing structural complexity. Foremost, the in-plane properties of laminates containing different reinforcement configurations were verified through adapted filled-hole testing. Very low knockdown factors (reaching a maximum of only 0.88) were established. Subsequently, joint performance and crack-arresting mechanisms were analyzed with static and fatigue testing of reinforced single-lap shear joints. In static, the performance improvement reached up to 25% in ultimate joint strength. During fatigue investigations, fatigue life was extended by up to one order of magnitude in comparison to the reference samples due to the successful decrease of crack propagation rates. The testing program was then extended to a T-joint element for integral tank structures, in order to further examine the energy absorption capability and potential applications in the aircraft industry. The novel reinforcement concept furthered a significant increase in residual force and damage tolerance. In addition, optimization studies were carried out with numerical methods, permitting a thorough understanding of the important parameters in joint design.
With the obtained results, an examination of this innovative joining technology, considering its manufacturing concept, its energy absorption capability and crack arresting features, was performed. The extensive experimental and numerical characterization promoted the establishment of important design guidelines for joints and structures reinforced with metallic pinned inserts.