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A computational inverse technique is presented for characterizing the material property of functionally graded material (FGM) plates, using the dynamic displacement response on the surface of the plate as input data. A modified hybrid numerical method is used as the forward solver to calculate the dynamic displacement response on the surface of the plate for given material property varying continuously in the thickness direction. A uniform crossover micro-genetic algorithm (uniform [micro]GA) is employed as the inverse operator to determine the distribution of the material property in the thickness direction of the FGM plate. Examples are presented to demonstrate this inverse technique for material characterization of FGM plates. The sensitivity and stability to noise contamination in the input displacement response data are also investigated in detail. It is found that the present inverse procedure is very robust for determining the material property distribution in the thickness direction of FGM plates.

A method of damage detection for composite plates using Lamb waves and a projection genetic algorithm is investigated in this study. This method first formulates the damage detection as an optimization problem of minimizing the error between the measured and calculated surface displacement response derived from Lamb waves. The calculated response is obtained by using the strip element method with the trial crack parameters (location, size). Then a projection genetic algorithm is used to solve the optimization problem and thus identify the actual crack parameters. The projection genetic algorithm is developed from the hybridization of the modified micro-genetic algorithm with a projection operator. It has an excellent convergence performance, taking only 9.9 ~ 14.2% of the number of function evaluations required by the conventional micro-genetic algorithm to obtain the global optima for six benchmark functions. Numerical examples are presented to verify the proposed method for detection of cracks inside composite plates. The maximal error of detected crack parameters is -4.3% for four simulated cases, which is achieved by running only 60 generations of projection genetic algorithm.

An analytical model for the characterization of delamination in beams using flexural wave scattering analysis is presented. In the beam model of wave propagation, the beam is divided into four regions; to each of them the beam theory of wave propagation is applied to obtain the wave fields excited by a harmonic load on the beam surface. The solution for the entire beam is obtained in terms of the solution for the respective regions using continuity conditions at the junctions. Numerical results on beam displacement for various delamination sizes, materials and excitation frequencies are presented. Experiments using a scanning laser vibrometer on specimens containing simulated delamination are also conducted. The results are then verified by comparing with those obtained by the Strip Element Method (SEM) and experiment. Good agreement is observed between the present model with SEM and experiment. [DOI: 10.1115/1.1387023] Keywords: Delamination, Flexural Wave, Strip Element Method, NDE, Dynamic Analysis

A strip element method is presented for analyzing wave scattering by a crack in a composite laminate submerged in a fluid. In this method, the fluid and laminated plate are modeled using two-nodal-line and three-nodal-line strip elements, respectively. A system of governing equations of the fluid and solid strip elements in frequency domain are derived using a variational method and the Hamilton principle, which are converted as a set of characteristic equations in wave number domain by applying Fourier transform techniques. A particular solution to the equations is obtained using a modal analysis method in conjunction with inverse Fourier transform techniques. A complementary solution to the equations is found employing horizontal boundary conditions on cross sections at the crack tips. The addition of the particular and complementary solutions yields a general solution. Numerical examples are presented for immersed steel and composite plates with either a horizontal or a vertical crack. Computed results indicate that the fluid has considerable influence on the wave fields scattered by a crack in a composite laminate.

A simple procedure is proposed in this paper to estimate the global failure probabilities of a submarine oil pipeline subjected to underwater explosion shock wave. The deterministic response of a pipeline subjected to an underwater shock loading is first given by solving a simplified fluid-structure interaction problem. Compared with an FEM/BEM coupling model, the present method gives good results at much lower computational efforts. Then, the Monte Carlo method is used to find the global failure probabilities of the pipeline. Finally, a practical example is given.