The Journal of Strain Analysis for Engineering Design

The emergence of reliable material characterization techniques in automotive and aeronautical industries, in particular sheet metal forming, promises to underpin a novel advance in materials research. In this regard, 5xxx series aluminium alloys deliver the largest formability range and can be deformed at room temperature. This study aims at determining the mechanical properties of the AA5352 aluminium alloy, using digital image correlation. Thus, tensile sheet specimens manufactured from the corresponding alloy are mechanically tested under a uniaxial condition and deformation fields are monitored. Considering the force/displacement response and stress/strain curves, the material Poisson’s ratio, Young’s modulus and anisotropy coefficient in the transverse direction are characterized by the experimental digital image correlation data. It intends to obtain accurate and reliable mechanical properties to be considered in the future processing analyses. Numerically, adopting the experimentally obtained material properties, the Gurson–Tvergaard–Needleman damage model is implemented using finite element method formulation to forecast the ductile fracture performance of the tested AA5352 sheet. The predicted results are then compared with the experimental digital image correlation solution verifying good agreement with the force/displacement response and the deformation fields. Overall, the acquired numerical results imply that the Gurson–Tvergaard–Needleman damage criterion is capable to render an accurate prediction upon a high stress triaxiality state.

The hardening curve for cylindrical specimens determined by conventional uniaxial tension tests generally corresponds to a relatively narrow strain range due to the occurrence of necking. To achieve the hardening curve within a large strain range, in this study, the multi-specimen tension tests with pre-torsion are developed through extrapolating the hardening curve from the stress–strain data of cylindrical specimens with various magnitudes of pre-torsion strains. The calculation of pre-strain of twisted specimen needs to be addressed for the multi-specimen tension tests. The three calculation methods on the multi-specimen tension tests are proposed, leading to their individual hardening curves for Q345 specimens. An optimal strategy for the multi-specimen tests with pre-torsion is presented by comparison with the inverse method for a single specimen tension test. The results for Q345 specimen show the strain range (0–0.6) of the hardening curve determined by the multi-specimen tension tests is significantly larger than one (0–0.04) from conventional tension test, with reasonable accuracy. Compared with the current multi-specimen tests with pre-extrusion/drawing, the proposed multi-specimen tests with pre-torsion is possessed of stronger applicability and generality, lower cost, and higher efficiency.

In this work, a numerical analysis of the dynamic frequency responses of sandwich plates with micro-lattice core is presented. The finite element analysis is implemented in the commercial software Abaqus/Standard, calculating the natural frequencies and eigenmodes of sandwich plates containing defects on the micro-lattice structure. In order to include the presence of defects, an aleatory algorithm is developed in MATLAB. The effect of the damage percentage, cell type, cell size and material on the frequency and modal responses of the sandwich plates is highlighted. Results show that the dynamic frequency response may be useful for analysing practical issues related to non-destructive damage identification of imperfections in the micro-lattice core of sandwich structures.

This article proposes a new method for the analysis of free vibration of a cracked isotropic plate with various boundary conditions based on Kirchhoff’s theory. The isotropic plate is assumed to have a part-through surface or internal crack. The crack is considered parallel to one of the plate edges. Existence of the crack modified the governing differential equations which were formulated based on the line-spring model. Generalized differential quadrature method discretizes the obtained governing differential equations and converts them into an algebraic system of equations. Then, an eigenvalue analysis was used to determine the natural frequencies of the cracked plates. Some numerical results are given to demonstrate the accuracy and convergence of the obtained results. To demonstrate the efficiency of the method, the results were compared with finite element solutions and available literature. Also, effects of the crack depth, its location along the thickness, the length of the crack and different boundary conditions on the natural frequencies were investigated.

Investigation of flexoelectric effect on nonlinear forced vibration of piezoelectric/functionally graded porous nanocomposite is the objective of this study. The nanocomposite is exposed to electric voltage and external parametric excitation. First, a functionally graded porous core nanoplate is modeled and then two piezoelectric layers are glued with core. It is also rested on a visco-Pasternak foundation. Second, to derive governing equation of motion, two theories including Mindlin and Kirchhoff plate theories and Hamilton’s principle are utilized. In the next step, to obtain and solve ordinary differential equation, Galerkin technique and multiple time scales method are used, respectively. At the end, modulation equation of piezoelectric/functionally graded porous nanocomposite for both primary and secondary resonances is obtained and discussed. Emphasizing the effect of piezoelectric and flexoelectric, von Karman nonlinear deformation and parametric external excitation are simultaneously taken into account. It is found that electric voltage has no effect on the performance of piezoelectricity and flexoelectricity of the material on vibration behavior. The results of this study can be useful as benchmark for the next investigations in field of energy harvesting systems and piezoelectric structures.