An investigation into the surface pre-treatment of CFRPs prior to adhesive bonding
File(s)
Author(s)
Li, Chang
Type
Thesis
Abstract
This thesis aims to develop guidelines for designers to select adherend materials
and surface pre-treatment methods/parameters for adhesive joints in aerospace
applications. Academic issues in the research field of adhesive/adhesion concerning
composite interface, adhesion theory, and failure mechanism are also explored.
Firstly, state-of-art technologies of surface pre-treatment have been reviewed. As
oxygen plasma treatment is environmentally friendly and is an effective pre-treatment
method on composites, it has been the focus of this study. Acetone cleaning and grit
blasting are also employed for comparison.
Secondly, in the experiments conducted, aerospace-grade carbon fibre reinforced
polymer (CFRP) composites were prepared and employed as adherends, i.e., two
thermosetting CFRPs made of similar prepregs but manufactured via different
techniques, and three thermoplastic CFRPs made of different prepregs. An aerospace
epoxy-film adhesive was used to join two pre-treated adherends. Both CFRP/CFRP and
CFRP/aluminium alloy joints were investigated.
Thirdly, interfacial characterisation was studied by the techniques of SEM, EDX,
XPS and contact angle analysis. These results show that plasma treatment is highly
effective on the different CFRPs, due to the removal of surface contamination, the
development of an appropriate surface topography, the activation of the surface
chemistry, and the improved interfacial wetting. Furthermore, thermoplastic matrix
composites usually exhibited slower erosion of the surface by the plasma treatment
than thermosetting ones.
Finally, it is proposed that the dissimilarity of the two adherends in a hybrid joint
can influence the joint performance. For example, a patterned surface created by
autoclave processing can realise a high specific surface area of exposure to plasma,
strengthening the effect of plasma and leading to higher joint strengths; however, the
uneven surface can exacerbate air retention during the preparation of hybrid joints
(when an uneven composite surface is adhesively bonded to a relatively-flat aluminium
alloy surface), reducing the joint strength.
and surface pre-treatment methods/parameters for adhesive joints in aerospace
applications. Academic issues in the research field of adhesive/adhesion concerning
composite interface, adhesion theory, and failure mechanism are also explored.
Firstly, state-of-art technologies of surface pre-treatment have been reviewed. As
oxygen plasma treatment is environmentally friendly and is an effective pre-treatment
method on composites, it has been the focus of this study. Acetone cleaning and grit
blasting are also employed for comparison.
Secondly, in the experiments conducted, aerospace-grade carbon fibre reinforced
polymer (CFRP) composites were prepared and employed as adherends, i.e., two
thermosetting CFRPs made of similar prepregs but manufactured via different
techniques, and three thermoplastic CFRPs made of different prepregs. An aerospace
epoxy-film adhesive was used to join two pre-treated adherends. Both CFRP/CFRP and
CFRP/aluminium alloy joints were investigated.
Thirdly, interfacial characterisation was studied by the techniques of SEM, EDX,
XPS and contact angle analysis. These results show that plasma treatment is highly
effective on the different CFRPs, due to the removal of surface contamination, the
development of an appropriate surface topography, the activation of the surface
chemistry, and the improved interfacial wetting. Furthermore, thermoplastic matrix
composites usually exhibited slower erosion of the surface by the plasma treatment
than thermosetting ones.
Finally, it is proposed that the dissimilarity of the two adherends in a hybrid joint
can influence the joint performance. For example, a patterned surface created by
autoclave processing can realise a high specific surface area of exposure to plasma,
strengthening the effect of plasma and leading to higher joint strengths; however, the
uneven surface can exacerbate air retention during the preparation of hybrid joints
(when an uneven composite surface is adhesively bonded to a relatively-flat aluminium
alloy surface), reducing the joint strength.
Version
Open Access
Date Issued
2023-05-24
Date Awarded
01/09/2023
License URL
Advisor
Blackman, Bamber
Shi, Zhusheng
Lin, Jianguo
Sponsor
Aviation Industry Corporation of China (AVIC) Manufacturing Technology Institute
China Scholarship Council
Grant Number
China Scholarship Council (File No. 202008060076)
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)