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Title: Development of optical techniques for the experimental analysis of local stress and strain distributions in adhesively bonded composite joints
Author: Crammond, G.
ISNI:       0000 0004 2743 4706
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2013
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This research seeks to evaluate the local stress and strain distributions formed in adhesively bonded composite joints under quasi static and high strain rate loading. A literature review of current analytical, numerical and experimental studies of adhesively bonded joints is presented and identifies the lack of knowledge in the behaviour of composite bonded joints in the through-thickness direction. Detailed analysis of the stress and strain in the joint, and their impact on the development of damage prior to and during failure have been obtained using Digital Image Correlation (DIC). An experimental methodology is established to perform DIC at the mesoscopic scale using high magnification optics, enabling accurate, high spatial resolution analysis of the strains around the geometric discontinuity between adherends. It is demonstrated that the small through-thickness strains are critical in the development of damage in the joint around the discontinuity between adherends. Errors in the DIC technique are assessed using a robust morphological methodology to evaluate the quality of different speckle patterns based upon the properties of the speckles in the pattern. The strain data is manipulated to evaluate the principal stresses in the joint, which govern failure in the brittle epoxy matrix of the composite, providing a concise evaluation of the transfer of load between the adherends and damage initiation within the joint. The DIC results and methodology are validated against independent infra-red measurements using Thermoelastic Stress Analysis (TSA). Limitations in the TSA analysis approach are identified around joint discontinuity due to the varying principal stress direction. A new TSA analysis methodology is presented to overcome this. The results of the experimental analysis are used to validate a representative 2D finite element model modelling approach for adhesively bonded joints, showing good agreement to the experimental data. Finally the full-field DIC methodology is applied to analyse the response of a single lap joint during high strain rate loading, providing unprecedented full-field measurement of the strain fields up to failure.
Supervisor: Boyd, Stephen Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)