| In recent years, pultruded section fiber-reinforced plastic (FRP) structures has been widely studied and used in many applications, due to its excellent performance and ease of production. However, the material's heterogeneity and anisotropy is very easy to make the interface relative to failure, and resulting structure destruction.The traditional non-destructive technologies have many shortcomings because the material's multi-interface and high damping characteristics, and them they are difficult to meet the engineering requirements in terms of rapidness, efficiency and simplicity. Therefore, developing a highly reliable layered detection technology has become the key to promote the application of such materials.In this issue a novel technique for detecting delamination in I beam is proposed. In this method a PZT transmitter was employed to create the stress waves in the beam, and an optical fiber interferometric sensor was attached to the surface of the beam to detect the stress wave propagation in the beam. By analyzing the propagation characteristics of ultrasound and the wavelet time-frequency spectrum of the signal, the delamination location can be identified.This thesis using ABAQUS finite element software simulates the simply supported I-shape FRP beams with delamination. Based on the theoretical analysis and simulation results, the feasibility of delamination detection with the proposed technique is demonstrated. The main research contents and results are as follows:(1) By using the theory of plane body wave, we calculated out the velocity of three model body wave in experimental I-shaped beam and the time required of the wave transmit to the location of the optical fiber. Finally we determine using quasi-longitudinal wave as the main object of study.(2) We tested the finite element model by extracting stress conditions on a specific path of different moments, and determined a reasonable signal extraction duration by combined with the stress wave attenuation characteristics. In practice, we should calculate the stress wave velocity and dissemination of circumstances accurately, to prevent them from interfering with each other for effective signal.(3) Through simulation the experimental model beams, under the premise of non-contact we extraction the integral strain-time curve under various incentive points, and use Morlet wavelet time-frequency analysis the signal before 11×10-5s, them obtained the time t of the qP-wave reach to the location of the optical fiber for the second time corresponds to the second peak.Then according to the relationship of displacement and time we can calculate the distance between the neutral fiber and reflector under the various incentives point. Through the comparative with the theoretical results we have proposed a preliminary determination of the feasibility of this detection method.(4) Through simulation the beam with different hierarchical levels delamination we know that, the length of affected zone have relation with the length of the stratified area, while the sub-level width and their tiered zone has little effect. With the area of delamination become smaller the volatility of the detection curve become larger, and detection error under stratified area increased, but the boundary of layer still can be detect easily and able to determine the location and size of the delamination zone.(5) Comper the simulation result of ipsilateral, middle and different side stratified we know that, fiber and the different forms of hierarchical arrangement has little effect on the test results, in practical application the optical fiber can be stick on the beam flexibly or embedded into the beam.(6) Through simulation the beam with different size sections and different delamination locations we know that when the cross-section size becomes smaller then the signal components more complicate and the detection of errors become larger. In practical applications we should pay attention to the impact of the reflecter from the end of the beam.
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