Novel interfaces in hybrid composite-metal struts

Abstract

This research aims to propose and examine a novel composite-metal joining solution, for applications to hybrid, tubular struts. The joint is initiated via the filament winding of carbon-fibre tows around features (pins) that are structured onto the surface of the metal.The interlocking between the fibre-tows and metal pins provides a joining mechanism that both, exploits the high tensile stiffness and strength of the fibre reinforcement, and results directly from composite manufacture.
Design parameters of the hybrid composite-metal joint and strut are considered. Unique winding patterns are required for joint and strut fabrication, without inducing manufacturing defects such as tow puncturing. The resulting tow trajectories contribute to non-uniform fibre volume content on the structure. The effect on the strut’s elastic properties is assessed using
numerical methods, in which the tow’s volumetric contribution is considered at discrete sections of the strut. Joint efficiency is dependent upon design considerations, including the pin distribution, the tow path through the pin array and the manner in which the tow’s direction is reversed around the pins, during a process referred to as "pull-back". A simple analytical framework is developed to study these effects, in which the interaction between the filament wound fibre-tows and the pins, is described using a belt-and-pulley analogy. These analyses allow for a preliminary performance ranking of joint and strut configurations.
A multi-scale modelling framework is developed to determine the mechanical properties of the hybrid strut, using a meso-scale approach. Firstly, the Single-Filament (SF) method is used to predict the as-manufactured path of the tows on the structure. The virtual tows are represented as a chain of truss elements, which allows for their kinematic behaviour to be simulated. The virtual tows are then meshed using 3D continuum (solid) elements for their cross-sections, prior to mechanical analyses using quasi-static virtual tests. Matrix material is included and linked with the virtual tows using a constraint-based coupling mechanism, so that strut properties can be assessed in its final, consolidated, operating form.
A higher fidelity modelling approach is then used to predict joint properties in further detail. The virtual tows are modelled using the Multi-Filament (MF) method, in which the tows are described as bundle of virtual fibres. Deformations induced in the fibre-tows, due to their interactions with the metallic pins during the filament winding process, are simulated. Information regarding the tows’ non-uniform geometric shape and internal architecture, is then used to assess the joint’s mechanical performance with improved realism.
Following assessment of the joint’s theoretical capabilities, manufacturability is considered via the fabrication of a conceptual, prototype hybrid strut. Modifications are made to a commercial 4-axis filament winding machine to improve tow placement around the pins; with winding patterns constructed using the numerical programming language G-code. X-ray computed tomography scans are conducted to provide high resolution images for the joint, in order to visually appraise the novel interface initiated between the tows and the pins during the filament winding process.

Date of Award	28 Nov 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Stephen R Hallett (Supervisor), Luiz F Kawashita (Supervisor) & Byung Chul (Eric) Kim (Supervisor)