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Title: Identification of damage in composite materials using thermoelastic stress analysis
Author: Emery, Trystan Ross
ISNI:       0000 0001 3447 4667
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2007
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A quantitative damage assessment methodology for composite materials has been achieved using Thermoelastic Stress Analysis (TSA). The TSA technique provides fullfield data which is collected in a non-contacting and real time manner. The damage assessment methodology proposed requires a means of calibrating and temperature correcting the thermoelastic signal; these are developed and presented in this thesis. The thermoelastic theory for calibrating thermoelastic data from orthotropic bodies has traditionally been based on a stress formulation. There are difficulties in calibrating orthotropic materials in this manner and an alternative calibration routine has been devised and validated. The calibration routine provides the thermoelastic theory as a function of strain and permits a simplified calibration route as the laminate strains are the basis and can be measured in a straightforward manner. During damage propagation in laminated structures the specimen heats. The increase in temperature has a significant effect on the thermoelastic data and necessitates that the thermoelastic data be corrected to remove the effect of temperature from the data. A routine is developed that enables the correction of the thermoelastic data in a point-bypoint manner. By combining the strain calibration and temperature correction procedures a damage assessment methodology has been devised. The application of the methodology is demonstrated on glass / epoxy laminate specimens that are fatigue damaged and the damage state assessed using this method; the extent and type of damage is verified qualitatively using visual inspection methods. The work described is applicable to any orthotropic material. The effect of fatigue damage is assessed by periodically collecting thermoelastic data during the specimen life. This data is analysed using damage metrics based on the calibrated strain obtained from the TSA. The wider application of the TSA damage assessment methodology is considered by assessing the ability to locate subsurface damage. A complementary IR technique is used in conjunction with TSA known as Pulse Phase Thermography (PPT). Initial studies demonstrate the ability to resolve the spatial extents of subsurface damage. The purpose of this step is to guide TSA to areas of concern that can subsequently be assessed using the damage metrics to characterise the effect of damage on the residual life of the component. The strain calibration and temperature correction methods that enable TSA to be applied quantitatively to damaged composite materials have not been accomplished prior to this work. They provide novel methods by which TSA data can be assessed, and their application is not restricted to damage studies alone. The ability to temperature correct TSA data has been shown to be of vital importance if thermoelastic data is to be compared in a quantitative fashion. The strain calibration procedure presented will enable thermoelastic studies to be reported quantitatively and expand the application of TSA particularly in validation studies. The damage assessment methodology presented represents a step forward in the application of TSA to the damage assessment of composite materials.
Supervisor: Barton, Janice Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)