Adhesion characterisation of bonded steel/composite cleavage joints

Shahid, Muhammad (2000) Adhesion characterisation of bonded steel/composite cleavage joints. PhD thesis, University of Glasgow.

Abstract

There are an increasing number of applications for adhesive bonding in structural design with thick adherends. These include hybrid metal/composite materials, particularly in the marine, construction, and automotive industries. Failure of such connections normally arises from cleavage stresses. This study is largely experimental with theoretical aspects. The overall aims and objectives are: to improve the understanding of local cleavage strength and failure of bonded steel and composite adhesive joints, to develop a suitable experimental technique for evaluating the mechanical adhesion mechanism between steel and composite and to establish simplified theoretical models to assess critical stresses in cleavage joints, with reference to bonding parameters. The experimental programme to evaluate cleavage specimens was based on the method described in BS 5350: Part Cl:19861. Mild steel and glass-fibre reinforced epoxy composite (GRE) adherends and a two-part toughened epoxy adhesive were used. The composite laminates were produced in-house by hot press moulding, from prepregs. The standard cleavage specimen was modified by inserting a GRE laminate between the steel adherends to allow testing of the cleavage joint between steel and composite, to prevent delamination failure. The specimens were tested to destruction on a universal tensile testing machine to examine the effect of adherend pre-treatments and surface conditions such as roughness and fibre orientation (in composites). Elastic finite element analyses (FEA) were performed to assess cleavage stresses in the adhesive at various conditions. A partial FEA modelling technique based on idealised butt joints was also used to study surface roughness and composite geometric and material details. Visual and light microscopic examination of the failure surfaces was used to verify the analyses. Mathematical relations based on classic mechanics and FEA results were developed to calculate the cleavage strength of standard joints. The work shows that: (i) the modified cleavage specimen is a good specimen for testing composite/metal joints, (ii) grit-blasting of steel produces better and more consistent strengths than polishing, (iii) polished epoxy composite produces a joint strength consistently higher than that of both grit-blasted and polished steel, (iv) cleavage strength increases with the roughness level and profile area of adherends' surfaces and, (v) partial modelling of cleavage joints into elements of butt joints provides a useful evaluation technique.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Civil engineering.
• Colleges/Schools: College of Science and Engineering
• Supervisor's Name: Hashim, Dr. Safa A.
• Date of Award: 2000
• Depositing User: Enlighten Team
• Unique ID: glathesis:2000-73239
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 12 Nov 2021 11:32
• URI: https://theses.gla.ac.uk/id/eprint/73239