Micro-pins : the next step in composite to composite & metal to composite joining

• Main Author: Σαραντινός, Νικόλαος
• Other Authors: Sarantinos, Nikolaos
• Language: English
• Published: 2021
• Subjects: Micro-pins; Through-thickness reinforcement; Composite materials; Σύνθετα υλικά

This PhD research was focused on the development of a more reliable metal-to-composite and composite-to-composite connection, utilizing the micro-pinning technology. This technology implements small pin-like structures at the micro-scale which penetrate a composite laminate prior to curing, and create a hybrid mechanical-chemical bonding between two connecting structures. The research performed in this study was primarily oriented in a more technical than academic manner, focusing on a specific industrial application scenario rather than general research – following the ESA/NPI programme requirements. In this study, the micro-pinning technology was focused to be implemented in a space structures joining application scenario. The primary guideline was to find an implementation of the micro-pinning technology, without being intrusive to the state-of-the-art design and manufacturing procedures used in industry. In the next step, a feasibility study to redesign and deviate from the current manufacturing procedures was implemented, which combined and utilized advanced numerical optimization tools, AM procedures and a complete redesign of the application scenario’s reference joint case to accommodate the micro-pinning concept from the start. To reach the goals of this research, a three-phase research plan was envisioned and followed, which followed the building blocks approach. Starting from the micro-scale level of a single pin connection, continuing in the meso-scale with a lap-joint pinned configuration, and finishing on the macro-scale in the full-scale implementation of the pinning concept in a bracket-insert-sandwich panel connection. In every phase, three subdivisions of research were performed. Initially, a numerical optimization study was performed, followed by a manufacture and experimental testing of the designed specimens, and concluding with a numerical testing procedure to validate the correlation and ability to predict the mechanical response using numerical non-linear FEM tools. In the final results of this study, it was shown that performing a redesign of a component to adapt the micro-pinning technology would bear a significantly greater mechanical response compared to the reference case. However, even keeping the initial component and applying the micro-pinning technology would have also an increase in the mechanical response. Plus, using modern numerical optimization tools and advanced manufacturing procedures could help further gain a response of greater strength with a notable system mass reduction.