Improving the mechanical properties of aerospace carbon fibre-epoxy joints by z-pinning

Koh, T 2012, Improving the mechanical properties of aerospace carbon fibre-epoxy joints by z-pinning, Doctor of Philosophy (PhD), Aerospace, Mechanical and Manufacturing Engineering, RMIT University.

Document type: Thesis
Collection: Theses

Attached Files
Name Description MIMEType Size
Koh.pdf Koh.pdf application/pdf 7.45MB
Title Improving the mechanical properties of aerospace carbon fibre-epoxy joints by z-pinning
Author(s) Koh, T
Year 2012
Abstract The use of carbon fibre/epoxy laminates and other types of composites in aircraft and helicopters has increased greatly over the past decade. These applications include structural bonded joints and stiffener-skin bonded panels such as ribs, spars and stringers. A long-standing problem with bonded composite structural joints is the low strength and toughness of their bond-line, which makes them susceptible to bond-line cracking under the application of normal (through-thickness) tensile, in-plane secondary bending or impact loads. One promising through-thickness reinforcement method is z-pinning. Z-pins are thin metallic or fibrous rods inserted through the bonded region of a composite joint, and they act as fine nails which hold the adherends together by bridging tractions after the bond-line has fractured.

The general aim of this PhD study is to investigate the structural properties and damage tolerance of z-pinned composite bonded joints. This PhD investigates two types of bonded carbon fibre/epoxy joints commonly used in aircraft (and other engineering) structural composites: T-shaped joints and single lap joints. Specifically, the PhD examines the influences of various parameters on the mechanical performance of bonded T-joints to optimise the z-pinning conditions. The parameters studied include the volume content, diameter and embedded length of the z-pins; the location of the z-pins in the joint; and the direction of the applied load. The PhD also investigates the mechanical performance of z-pinned lap joints, and in particular their creep and stress rupture properties as well as the creep toughening mechanisms.

This thesis presents an experimental investigation into the efficacy of z-pins to improve the structural properties of bonded T-joints under an applied tensile (pull-off) load. This study is the first comprehensive assessment of the effect of z-pin content on the strengthening and toughening of T-joints, and provides important analytical information and experimental data to optimise the z-pinning conditions for maximum structural performance. The study found that z-pinning significantly improves the mechanical performance of T-joints under different pull-off load angles, and when a pre-existing crack is present in the joint. Also, effects of z-pin reinforcement location and z-pin embedded length (i.e. joint thickness) were investigated experimentally and analytically. Lastly, this thesis presents a study into the creep properties, stress rupture and creep mechanisms of single lap joints reinforced with z-pins. The PhD thesis concludes with a summary of the major research findings, a discussion of future research directions into z-pinned composite joints, and the remaining challenges in the certification of z-pinned joints for use in primary aircraft structures.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Aerospace, Mechanical and Manufacturing Engineering
Keyword(s) Composites
Version Filter Type
Access Statistics: 420 Abstract Views, 924 File Downloads  -  Detailed Statistics
Created: Fri, 21 Sep 2012, 11:19:44 EST by Kelly Duong
© 2014 RMIT Research Repository • Powered by Fez SoftwareContact us