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This study presents an analytical solution for cross-ply composite laminates integrated with a piezoelectric fiber-reinforced composite (PFRC) actuator subjected to electromechanical loading using the four-variable refined plate theory. This theory predicts parabolic variation of transverse shear stresses and satisfies the zero traction on the plate surfaces without using the shear correction factor. Using the principle of minimum potential energy, the governing equations for simply supported rectangular plates are extracted and the Navier method is adopted for solution of the equations. The comparison of obtained results with other common plate theories and the exact solution indicates that besides the simplicity of the presented formulation, it is very accurate in analysis of laminated composite plates integrated with PFRC. Also the effects of the thickness ratio, aspect ratio, number of layers, staking sequence and amount of electrostatic loading on the displacements and stresses are investigated and the obtained findings are reported.

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A new type of energy absorber called an expansion joint (i.e. a corrugated tube) is examined in this research. Several experiments are performed on three types of thin-walled specimen, namely circular tubes, preformed corrugated tubes and complete corrugated tubes, to investigate the energy absorption of steel specimens under different conditions for quasi-static lateral loading and axial loading. For this purpose, some steel specimens were compressed between two rigid platens in the axial direction, and the other specimens were laterally compressed. The preformed corrugated tubes and the complete corrugated tubes were produced by the hydroforming method. In each geometrical group of specimens, several tubes, which have different wall thicknesses, different inner diameters and different lengths and which are either empty or filled with polyurethane foam, were tested. Experiments show that, for a lateral load, the specific absorbed energies of the complete corrugated tubes are higher than those of the corresponding preformed corrugated tubes and circular tubes with the same characteristics. Tests show that, under lateral loading, a complete corrugated tube with a thicker wall and a smaller diameter is the optimum energy absorber system. Therefore, when a circular tube transforms into the corrugated tube, a better energy absorber system with a higher capability is achieved under lateral loading. Also, experiments show that, under axial loading, simple circular tubes with no forming process have higher specific absorbed energies than corrugated tubes do. Corrugated specimens have more controllable plastic deformation and a more regular deformation mode than simple tubes have. Tests under axial loading illustrate that, when the preformed corrugated tubes are filled with polyurethane foam, the specific absorbed energy increases by up to 74%. A comparison of the results on empty and filled specimens shows that, in some cases, the specific absorbed energies of corrugated tubes under lateral loading are higher than the specific absorbed energies of circular tubes under axial loading. This means that, by shaping the circular tubes into preformed corrugated tubes and complete corrugated tubes via the hydroforming process, a new thin-walled structure with a high specific absorbed energy during the lateral compression process is introduced.

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