Metal-Composite Joining Using Hybrid Penetrative Reinforcement

Abstract

Hybrid Penetrative Reinforcement (HYPER) is a unique joining technology that can significantly improve the integration of metal-composite structures. Small pins are built on to a metallic substrate/component using additive manufacturing, embedded into an uncured laminate and then co-bonded. The pins provide a mechanical interlock and the epoxy matrix provides adhesion. Unlike mechanical fasteners, pre-drilling is not required and the pins only penetrate partway through the laminate so there is no aerodynamic penalty. This doctoral research project explored the design, analysis methods, manufacture processes, inspection procedures and performance of HYPER joints. Firstly, a range of non-destructive inspection methods were evaluated based on ability to detect HYPER joint defects. An ultrasonic technique was developed and used to characterise failure modes during subsequent mechanical testing. The influence of design variables, such as pin geometry and surface treatments, on the ultimate strength and fatigue life of HYPER joints was identified. HYPER pins were shown to delay the initiation of failure, slow the propagation of damage and increase the ultimate strength by up to 6.5 times compared to an unpinned reference joint. The maximum elongation, energy absorption and fatigue life were also increased substantially. In addition, a previously unreported failure mode was identified during fatigue testing. Despite impressive performance, the joint design was still thought to be sub-optimal. Thus, prior to the optimisation of the pin/joint design for improved mechanical performance, a new finite-element modelling strategy was conceived. This was used to evaluate the interaction between the pins and carbon-fibre. It was found that “conventional” modelling approaches lacked adequate accuracy for this application and that design rules for mechanical fasteners could not be applied. The work within this thesis has led to the increased maturity of HYPER joining technology and, in part, progression to a new Technology Readiness Level.

Date of Award	24 Jun 2015
Original language	English
Awarding Institution	University of Bath
Sponsors	Airbus Group Ltd
Supervisor	Richard Butler (Supervisor)