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Analysis of static and fatigue damage in aluminium/GFRP hybrid composites

Al-Azzawi, Ahmad ORCID: 2017. Analysis of static and fatigue damage in aluminium/GFRP hybrid composites. PhD Thesis, Cardiff University.
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This study has focused on investigating the initiation, propagation and effects of damage in fibre-metal laminates (FMLs) specifically Glare® 4B under buckling, postbuckling and high cycle fatigue through the use of novel numerical and experimental techniques. In terms of numerical analysis, a 3D user-defined cohesive zone model (CZM) has been generated to simulate delamination initiation and growth in specimens under static compressive stresses, using the software Abaqus. The generated models have been validated using a comprehensive literature review in order to gather reliable mechanical properties for the Glare® material constituents. Following this, a modified cohesive zone model (CZM) based on a trapezoidal traction-separation law has been developed by the author to simulate damage evolution under high cycle fatigue loading. This model was implemented through a user-written VUMAT subroutine working through the interface of Abaqus/Explicit software. This model is able to simulate elastic-plastic interfacial damage behaviour and as such is suitable for ductile adhesives including toughened epoxy unlike bilinear cohesive zone models which can only accurately simulate damage in brittle adhesives. This makes it suitable for modelling any material interface which incorporates ductile adhesives. The numerical buckling results were validated using a series of experimental tests conducted on Glare® 4B specimens containing splice and doubler features in addition to flat specimens containing artificial circular delamination manufactured by Airbus Germany, demonstrating the ability of the models developed to predict the onset and propagation of damage. Experimental fatigue tests were then implemented on Glare® 4B specimens containing splice and doubler features manufactured in-house, to Abstract iii obtain fatigue life for these types of joints, with fatigue parameters extracted from literature on similar grades of Glare® used to validate the trapezoidal traction-separation law based cohesive zone model. Static tests were monitored using Digital Image Correlation (DIC) to provide full-field displacement data and Acoustic Emission (AE) for the detection and location of the damage using traditional AE analysis and novel Delta-T techniques respectively, with Acoustic Emission (AE) using traditional AE analysis technique being used for damage detection under fatigue loading. Finite element models were also generated to model the buckling and postbuckling behaviour of Glare specimens containing splice and doubler joints and showed good agreement with experiments in terms of in-plane and out-of-plane displacements. In experiments, artificial delaminations representative of those which could potentially be generated during manufacturing had a negligible effect on the compressive strength of specimens. Acoustic Emission (AE) was successfully used to detect and locate damage initiation and propagation under buckling loads. Of particular importance in this body of work are the implementation of a trapezoidal traction separation model to predict the initiation and propagation of damage in elastic-plastic materials such as the resin used in the Fibre Metal Laminate Glare under high cycle fatigue and the detection and location of this damage using a bespoke mapping algorithm for the interpretation of Acoustic Emission data.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: FML; Glare; Fatigue; Buckling; Damage Modelling; Delamination.
Date of First Compliant Deposit: 21 November 2017
Last Modified: 03 Nov 2022 10:02

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