Improving the delamination bridging behaviour of z-pins through material solutions

点击翻译按钮获取中文摘要

Z-pinning is the most effective method for embedding through-thickness reinforcement in prepeg laminates. Composite Z-pins have been traditionally manufactured employing carbon fibres combined with a bismaleimide (BMI) resin. These materials allow achieving a substantial enhancement of the mode I interlaminar fracture toughness of Z-pinned laminates. Nonetheless, the toughness improvements in mode II are much more modest, due to the inherent brittleness of fibrous carbon/BMI when transversely loaded.Through-thickness reinforcement elements such as Z-pins act as micro-fasteners, restraining the opening and sliding displacements of delaminations and hence inhibiting interlaminar crack growth. As such, ensuring a balanced mode I and mode II performance will reduce the chance of catastrophic failure of damaged composite structures. Mode II delamination toughness is especially crucial in reducing the damage and crack propagation in impacted composite laminates. This includes applications such as gas turbine blades.The aim of this PhD project is to address the poor performance of composite Z-pins under mode II delamination conditions. This will be carried out by means of materials solutions, with the objective of understanding the inherent properties that affect the pin's performance. Ultimately, single-type Z-pins that provide a balanced mode I and mode II delamination toughness will be identified.The key objectives to be completed throughout the length of the project are:- Identify potential reinforcement/matrix materials to be used in Z-pins to achieve a balanced bridging performance in mode I and mode II regimes.- Develop, as necessary, resin blends and fibre architectures that increase the mechanical performance of the pins under mode II loading.- Successfully manufacture candidate Z-pins using the selected materials and architectures, optimising the process to obtain a high-quality output.- Experimentally characterise the meso-mechanics of the candidate Z-pins for the full range of mode mixity and compare with the performance of commercially available Z-pins.Most published work on Z-pinning has concentrated on understanding the performance of only the commercially available carbon/BMI Z-pins. These materials have remained almost unchanged for over a decade. Throughout the project, novel resin blends and fibre architectures will be developed to specifically satisfy the requirements of Z-pins and Z-pinned laminates. Additionally, the study will help to better understand the relationship between the mechanical properties of the pins and their ability to supress mode II delamination.