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Abstract- A 3-D finite element model is presented to study the thermo-mechanical response of thick plate weldments under different multi-pass welding sequences. The Anand’s Viscoplastic Model is applied to simulate the mechanical response of weldments. The thermal modelling of welding zone is also carried by applying the isothermal melting pool approach. In this research the temperature dependency of thermal and mechanical properties of material is considered and the welding parameters such as arc movement, welding speed and welding lag between each sequence are simulated. Finally, in the FE model the addition of filler material into the welded zone is modeled using the Element Rebirth Technique (ERT). The accumulated results show that, on specific point as the number of layers of weld increases, a noticeable change occurs in the magnitude of maximum temperature and its time of reach. For the points near to the weld line, this change affects the amount of distortion, and the through thickness stress components but it has no significant effect on the residual stress components which may arise in the plane of plates.

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Active structural acoustic radiation control of a piezolaminated arbitrary thick rectangular plate with a mixed-norm H_2/H_∞ robust controller is developed. The structure is made of a transversely isotropic host layer with a distributed piezoelectric sensor layer as well as a matched piezoelectric actuator layer, facing high frequency uncertainties and random external disturbances. The elasto-acoustic formulation, based on the exact linear 3D piezo-elasticity theory, is developed for problem of fully coupled structure and acoustic mediums. Identification of the fluid/structure interaction system with subspace algorithm is implemented on actuator/sensor data sets. A multi-objective controller with regional pole placement, formulated in LMI framework, is synthesized while unmodeled dynamics are treated as multiplicative uncertainties. Numerical simulations confirm effectiveness of the implemented multi-objective robust active control scheme for reduction of radiated acoustic power from a piezocomposite plate, without stimulating any instability. Also, better tracking performance and disturbance rejection of mixed-norm controller is observed in comparison to that of H_2 and H_∞ controllers. Finally, validity of the elasto-acoustic model is proved by results obtained from a finite element software, as well as with the data available in the literature.

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A finite element formulation for bending analysis of isotropic and orthotropic plates based on two-variable refined plate theory is developed in this paper. The two-variable refined plate theory which can be used for both thin and thick plates predicts parabolic variation of transverse shear stresses across the plate thickness and therefore, it does not need shear correction factor in the formulation and the zero stress conditions are satisfied on free surfaces. The von-Karman nonlinear terms are considered in strain-displacement equations and governing equations are derived using the Hamilton's principle. After constructing weak form equations, a new 4-node rectangular plate element with six degrees of freedom at each node is used for discretization of the domain. The non-linear coupled governing equations are solved by Newton–Raphson method. The finite element code is written in MATLAB which can be used for analysis of thin and thick, isotropic and orthotropic plates with various boundary conditions. Some benchmark problems are solved by the developed code and the obtained displacements and stresses are compared with the existing results in the literature which show the accuracy and efficiency of presented finite element formulation.