Buckling due to External Pressure of Tubes Measured by Rayleigh Optical Backscatter Reflectometry.

Abstract

This master s thesis should focus on measuring the buckling suffered by tubes from external pressure. The technique to be studied, is Rayleigh optical backscatter reflectometry (OBR), which through swept wavelength interferometry, measures backscatter as a function of length with high resolution optical fibers. It offers continuous monitoring of strain and temperature along these fibers. Used in Structural Health Monitoring (SHM) as a regular early measurement analysis for possible accidents and dangerous states, this technique have been improved for the last 30 years, getting the same accuracy as current devices working in the same field. The main structure of the thesis will be divided into three blocks, with different objectives.

The first one, analytical and numerical study, explains through simulations in Abaqus CAE Software, the behavior of different tubes exposed to external pressure, giving non-critical values and other information that is quite important for future studies. FEA analysis is the main focus of this part. Therefore, non-critical values are quite high, allowing us to test different situations without not much restrictive limitations.

The second one, experimental study, is responsible of obtaining signals, strain profiles and values regarding deformation due to pressure applied on experimental tubes in the laboratory of the department in which the thesis is being developed. In order to do that, information obtained in previous block will be helpful, and Luna OBR Software is the program which will give us every needed data for a conclusion. Trial and error is the best method used in this part because of the several amount of ideas and possibilities that appear at doing these experiments. Lots of problems and factors that quite significant have been found and should be studied in future developments.

The last one should be an analysis of the results obtained in both last parts, the methods used to get those results, and an analysis of sensibility. Thoughts and statement here will be the basis of the conclusions that must have this thesis about the Rayleigh OBR technique regarding case results, methods and future studies recommendations. Therefore, by this simple study, it can be said that this technique has so much potential not only for SHM, but for other areas too, being a really good focus for future studies.