Nondestrucitve Detection Approach For Delamination Patches In FRP

With the development of science and technology, fiber reinforced plastic (FRP) laminate composite materials are widely used in a variety of applications of practical engineering. However, the internal delamination or debonding with other material have seriously hampered the development of such structures and ingredients. Therefore, a new delamination and debonding detection technique based on fiber optic interferometry is proposed 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. The results of deformation for damaged specimens are higher than undamaged specimens. By comparing with the two results, the location and extent of delamination can be deduced.This purpose of this research is to prove the feasibility of this method and verify the correctness of the theory research through experimental study. The testing equipment of this experiment is mach-zehnder fiber interferometer. By applying load on FRP beam with the method of point-to-point so as to form phase difference between Induction arm and reference arm. After pass through 3×3 couplers ,we can get the displacement output of marked points on the beam by using software demodulation, and then processing and analyzing data to determine the location and extent of delamination. By comparing the results of experiment and theory, we can provide reference basis for future practical engineering application.The contents of this experiment have two parts including simple support beam and continuous support beam. The fiber position including paste in beam surface and buried in beam neutral layer, offsets for classification combination experimental displacement output curve change rule, confirmed This experiment is divided into simple support beam and continuous support beam is divided into two parts, fiber position paste in beam surface and buried in beam neutral layer, offsets for classification combination experimental displacement output curve change rule, confirmed the feasibility of this method for nondestructive testing of FRP experiment. The research content and research results mainly include following parts:1) For the continuous supported beam, the fiber is buried in the neutral layer. The output displacement of two edges of the beam is the most small and the curvature of the displacement output curves has sudden slop change at the two ends of the delamination. Increase the length of layer will improve the layered detection and determine the location and extent of delamination. The farther away from stratification fiber, its testability abate. Change load line position, load line in layered above the best effect, output which not is not on layer is almost zero. By comparing displacement output curve and strain curve theory of integral, both overall trend is basically the same theoretical research, and verifies the correct.2) For the simple supported beam, the fiber is buried in the neutral layer. Comparing with the continuous supported beam, its overall output displacement increase. Because of the whole deformation is so sharp that the influence of layer for the output of interferometer is not obvious. But the overall tendency of displacement output curve is the same as the integral strain curve. In the same condition,Increase the length of layer will improve the layered detection. If the layer is very small ,the results of detection are not perfect. Changing the load line on the beam from the layer to the edge of layer, and then not above the layer, three phenomenon is appeared including the value of displacement output reverse, the sudden slop change points increase and no sudden slop change points. The best position of load line is the line which above the layer.3) For the continuous supported beam, the fiber is paste on the surface of beam. The displacement output at both edges of the beam is the most largeste, the length of layer get from displacement output curve is a little shorter than actual length of layer. The whole tendency of displacement output that the fiber is paste on the surface of beam is the same of the fiber which is buried in the neutral layer. In the same conditions, the effect of detection is a little worse than the situation when the fiber is buried in the neutral layer, but it still can determine the location of the layer. It also can provide reference basis for future practical engineering application.