This study develops the governing equations and characterizes the mechanical properties of a new orthotropic accordion morphing honeycomb structure containing periodic arrays of U-type beams reinforced with glass fibers. Castigliano's second theorem is modified to develop the analytical equations to predict the deformation behavior of a single orthotropic ply under a combined axial, bending and shear loadings. Accordingly, the elastic properties of the orthotropic structure including elastic stiffness, shear stiffness and in-plane Poisson’s ratios are calculated by the developed equations. The honeycomb structure is manufactured by 3D printing, and the samples are subjected to tensile tests to experimentally validate the analytical solutions. Multiple finite element simulations are also used to validate the results. A good agreement is observed between the analytical solution, the experiments, and simulations, confirming the robustness of the analytical solution to predict the full elastic properties of the composite cellular. The results show that the periodic arrays of U-type and vertical beams can generate low in-plane stiffness in the morphing direction and high in-plane stiffness in the transverse direction, respectively. A zero Poisson’s ratio feature is achieved by employing straight beams which result in a high stiffness in the perpendicular direction. The proposed accordion cellular honeycomb structure exhibits the flexible response along the accordion shape direction, with a significant stiffness in its transverse direction. Moreover, the new orthotropic structure has considerably greater strain to failure in the morphing direction compared with a conventional isotropic configuration. These features prove that this type of structure can be applied for the aerospace morphing structures such as wings.
Phenomenological constitutive modeling of Ti-6Al-4V at temperatures between 923 and 1023 K under 0.0005–0.05 s−1 quasi-static rates is studied based on a phenomenological approach. For this purpose, the Johnson–Cook constitutive model is revisited. At low temperature conditions under moderate to high strain rates, the material’s stress–strain curves are the most similar to power-law function. Contrary to this, at high temperature conditions under low to moderate strain rates, the saturation-type function well describes the stress–strain curves. On the other hand, it is illustrated that the Johnson–Cook constitutive model is feeble to predict the material’s behavior correctly. Accordingly, in this study, a viscoplastic temperature-dependent constitutive model is developed. The strain rate hardening as well as thermal softening of the developed model is the same as the Johnson–Cook model. But a temperature-dependent strain hardening function is proposed in which both the saturation-type and power-law hardening behaviors of the material are implemented. In comparison with the Johnson–Cook model, the new constitutive model’s fidelity in capturing the titanium behavior is depicted. At last, by considering an Arrhenius-type phenomenological constitutive model, it is noted that the developed constitutive model has the best correctness in predicting the Ti-6Al-4V stress–strain behavior at high temperature conditions under quasi-static rates.
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