A systematic procedure to detect closed delamination in composites is investigated in this thesis. The detection method relies on measuring the integrated strain along a line on the structural member as a function of load position. By comparing the results for damaged and undamaged cases, the location and extent of delamination can be deduced. To measure the small change in integrated strain induced by the delamination, an interferometry-based fiber optic sensor is employed. The research work involves both theoretical and experimental investigations. In the theoretical study, FEM is employed. Both 2D and 3D models have been developed to study the effect of various factors (including support conditions, delamination location, size and shape as well as geometry of the delamination tip) on...[ Read more ]

A systematic procedure to detect closed delamination in composites is investigated in this thesis. The detection method relies on measuring the integrated strain along a line on the structural member as a function of load position. By comparing the results for damaged and undamaged cases, the location and extent of delamination can be deduced. To measure the small change in integrated strain induced by the delamination, an interferometry-based fiber optic sensor is employed. The research work involves both theoretical and experimental investigations. In the theoretical study, FEM is employed. Both 2D and 3D models have been developed to study the effect of various factors (including support conditions, delamination location, size and shape as well as geometry of the delamination tip) on the integrated strain. The results indicate that the delamination size and location in a composite member on elastic foundation can be identified from the two peak points of the integral strain vs load position curve. For a simply supported member, the change in integrated strain is too small compared to the global bending effects, and the curve has to be differentiated for the delamination to be identified. In the experimental study, a testing process with a vibrating load and subsequent filtering has been developed to obtain a signal/noise ratio that is high enough for accurate measurements. Composite members with different delamination locations and sizes have been prepared and tested, and the results are in good agreement with theoretical predictions. The results of the present study have clearly demonstrated the feasibility of the proposed technique for delamination detection in practice.