Papers by Author: S. Quinn

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Authors: S. Quinn, S.S.J. Moy, Keith Piggott
Abstract: The combination of simulation and physical testing is powerful. In this case study Finite Element Analysis (FEA) and a 96 tonne load test were used to prove that the lifting points for a new semi-rigid inflatable rescue craft met their statutory requirements before full manufacture. The FEA was used to optimise the detailed design of the lifting points, without the need to test each different configuration, and the load test was used to prove the final design in practice, before full manufacture. The FEA showed that the bearing stresses in the Glass Reinforced Polymer (GRP) hull of the initial design were unacceptable and appropriate design changes were made from further analysis. However, to suitably risk manage the project a full load test was required to demonstrate that the revised lifting point details met their statutory requirements, before full manufacture of the new craft.
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Authors: Janice M. Dulieu-Barton, S. Quinn, C. Eyre, P.R. Cunningham
Abstract: A means of calibrating the effect of temperature on the thermoelastic signal obtained from the Deltatherm system is described. A design of a suitable calibration device is covered and sample results presented and discussed.
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Authors: Crispin Doyle, S. Quinn, Janice M. Dulieu-Barton
Abstract: Fibre-optic sensors have advantages over existing electrical sensors in many strain and stress monitoring applications. However, bare optical fibres are fragile and packaging techniques must be developed before these sensors can be used more widely. One such method is the Smart Patch, in which the fibre Bragg grating is encapsulated between plies of glass-reinforced epoxy where rugged cables are anchored. This forms a flat flexible patch in which the fibre is protected from mechanical and environmental damage. However, it is important that the mechanical strength of the patch is not achieved at the expense of good strain transfer characteristics. To confirm this, fibre Bragg gratings with acrylate and polyimide coatings were embedded in a glass-epoxy patch that was bonded to an aluminium tensile specimen. An electrical strain gauge was also bonded to the specimen to provide a strain reference. Tests were carried out at different loading rates and at temperatures from -30°C to +80°C. There was good agreement between the fibre-optic sensors and the electrical strain gauge demonstrating that the patch performed in a practically identical manner to the conventional gauges. A second experiment on a representative part of ship structure demonstrated the versatility of the patch.
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Authors: R.K. Frühmann, S. Sambasivam, Janice M. Dulieu-Barton, S. Quinn
Abstract: The sensitivity of the thermoelastic response to variations in the fibre volume fraction, resin material and manufacturing route is assessed. To quantify any effects a comprehensive materials testing programme has been conducted to obtain coefficients of thermal expansion, specific heat, density and the elastic properties, which is described in detail in the paper. The work is focused on attempting to ascertain if the source of the response is from the isotropic resin rich layer or from the orthotropic substrate. It is also demonstrated that small variations in material properties can have a significant effect on the calculated thermoelastic response.
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Authors: S.J. Lin, S. Quinn, B.R. Boyce, R.E. Rowlands
Abstract: Thermoelastic stress analysis and grey-field photoelasticity are combined with the Laplace and Beltrami-Michell equations to non-destructively evaluate the individual internal components of stress in a loaded 3-D aluminium member. Experimental results agree with those predicted numerically by the finite element and finite difference techniques.
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Authors: R.C. Waugh, Janice M. Dulieu-Barton, S. Quinn
Abstract: The feasibility of using pulse phase thermography (PPT) to identify defects in adhesively bonded joints is assessed. Artificial defects created in solid materials are successfully identified using the phase images produced by PPT. Contaminants typical of those found in the manufacturing environment have been used to recreate kissing defects in joints in polymer composite materials constructed using a single shot process and by using secondary bonding. It is shown that PPT has the potential to identify kissing defects.
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Authors: S. Quinn, Janice M. Dulieu-Barton
Abstract: A review of the Stress Concentration Factors (SCFs) obtained from normal and oblique holes in thick flat plates loaded in uniaxial tension has been conducted. The review focuses on values from the plate surface and discusses the ramifications of making a plane stress assumption.
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Authors: R.K. Fruehmann, W Wang, Janice M. Dulieu-Barton, S. Quinn
Abstract: The work described in the paper investigates the stresses in the vicinity of a debond between the face sheet and core in a foam core / composite sandwich beam. Experiments were conducted in which the damaged side of the beam was loaded in compression in a four point bend test. Thermoelastic stress analysis (TSA) was used to obtain a measure of the stress field in the central part of the beam to evaluate its potential for damage detection and assessment. It is shown that TSA is capable of both identifying the damage and assessing its severity in terms of the remnant load carrying capacity of the beam. Fatigue tests were also performed, which showed that the cyclic load applied as a necessity for TSA did not cause the damage to grow, thereby demonstrating the potential of TSA as a non-destructive method for inspecting sandwich structures.
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Authors: A. F. Robinson, Janice M. Dulieu-Barton, S. Quinn, R. L. Burguete
Abstract: In some metals it has been shown that the introduction of plastic deformation or strain modifies the thermoelastic constant, K. If it was possible to define the magnitude of the change in thermoelastic constant over a range of plastic strain, then the plastic strain that a material has experienced could be established based on a measured change in the thermoelastic constant. This variation of the thermoelastic constant and the ability to estimate the plastic strain that has been experienced, has potential to form the basis of a novel non-destructive, non-contact, full-field technique for residual stress assessment using thermoelastic stress analysis (TSA). Recent research has suggested that the change in thermoelastic constant is related to the material dislocation that occurs during strain hardening, and thus the change in K for a material that does not strain harden would be significantly less than for a material that does. In the work described in this paper, the change in thermoelastic constant for three materials (316L stainless steel, AA2024 and AA7085) with different strain hardening characteristics is investigated. As the change in thermoelastic response due to plastic strain is small, and metallic specimens require a paint coating for TSA, the effects of the paint coating and other test factors on the thermoelastic response have been considered.
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Authors: R.K. Fruehmann, Janice M. Dulieu-Barton, S. Quinn
Abstract: The thermoelastic response obtained from an infra-red (IR) detector contains two components: the magnitude of the small stress induced temperature change caused by the thermoelastic effect and the phase angle of the temperature change relative to a reference signal generated by an application of a stress change. The phase angle is related to nonlinearity in the thermoelastic response and departures from the simple linear relationship that underpins thermoelastic stress analysis (TSA). The phase data could be used to make an assessment of temperature evolutions caused by viscoelastic behaviour resulting from damage and provide a basis for its evaluation. In the current paper the physics of other infra-red techniques used for non-destructive evaluation is used to better understand the nature of the thermoelastic response. The objective is to provide better exploitation of TSA by alternative processing of the IR measurements. Three case studies are presented that demonstrate the potential of the alternative processing for evaluating damage.
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