Full-field analysis of the dynamic behaviour of thermally stressed panels

This thesis details the research conducted over the course of three years under funding from the European Office of the United States Air Force (EOARD) and the Engineering and Physical Sciences Research Council (EPSRC) as a part of a long-standing effort to collect high-quality experimental data which can be used in the development and validation of predictive computational mechanics models. The focus of this study is on the acquisition of full-field displacement and temperature data when thermally and thermo-mechanically loading aerospace grade material panels as a means to study the effect of non-uniform temperature distributions on their dynamic behaviour at a component level (macroscale). The inclusion of this data in the development of a robust predictive model has also been investigated. To that end, a review of the existing literature is provided which highlights the current knowledge gaps in the modelling and experiments on the thermal and thermo-vibratory loading of panels, as well as the state-of-the-art in full-field data analysis. Initially, a finite element (FE) model was developed and compared to predictive and experimental data available in literature. This allowed for an investigation into the best practices to adopt in the development of a computational mechanics model with temperature-dependent material properties. It was found that a successful representation of experimental conditions strongly depends on the effective depiction of the thermal load and initial shape of the component. Then, a thin plate with free edges and constrained about its centre was heated using quartz lamps arranged in two different configurations and mechanically loaded using a shaker. Experimental modal analysis was used to acquire the resonant frequencies and mode shapes of the plate. Mode shapes were studied by exciting the plate to its first eleven resonant frequencies and acquiring displacement data using a Pulsed Laser Digital Image Correlation method (PL-DIC). Infra-red imaging was used to acquire temperature maps across the specimen. Experimentally-acquired temperature maps and measurements of the plate’s initial shape were included in a temperature-dependent FE model, developed according to the findings in the preliminary study, previously described. For the first time, experimental results showed the resonant response of the plate to strongly depend on the temperature distribution across the structure, correlating well with past predictive work in the literature. This was supported by the results from the finite element model, which were validated against experimental data and found to yield reliable predictions. The influence of temperature distribution in the deformation of panels was further investigated using a 1 mm plate with reinforced edges. The geometry was designed to emulate an aircraft’s skin with the reinforced edges performing the function of stringers and ribs. High temperatures were achieved using quartz lamps arranged in various configurations with controllable power output. PL-DIC was used to measure surface displacements and a commercially-available micro bolometer mapped the temperature distribution across the plate. Deflection results for the reinforced plate showed it to behave as a dynamic system that buckles out-of-plane when heated before relaxing to a steady state. It was demonstrated that the out-of-plane displacement experienced by the plate is strongly influenced by the in-plane spatial distribution of temperature