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• Effects of heating and cooling thermal shock on thermally induced vibration (TIV) are explored. • Influence of geometric nonlinearity under heating/cooling thermal shock forms is revealed. • The TIV characteristics of sandwich beams with auxetic honeycomb cores are discussed and compared with traditional honeycomb. • The instability conditions of the clamped beam with immovable ends under heating thermal shock are given. The nonlinear thermally induced vibration (TIV) characteristics of sandwich beams with auxetic honeycomb cores under general boundary conditions are studied. Based on first-order shear deformation theory, the dynamic governing equations are obtained through Hamilton principle, in which geometric nonlinearity and temperature dependence are considered. The temperature field along the thickness is calculated by finite element method and nonlinear TIV responses are solved via Newton-Raphson-Newmark method. The effects of temperature dependency, thermal shock forms, geometric nonlinearity, thicknesses of beam and face-sheet, boundaries and honeycomb geometrical parameters are studied. Results show that the reduction of the absolute inclined angle of the auxetic honeycomb can weaken the TIV responses. The influence of geometric nonlinearity on quasi-static and dynamic responses depends on the thermal shock form. Thermal buckling is the necessary condition for the occurrence of the TIV in clamped beams with immovable ends. Moreover, the research provides some design references to suppress the TIV responses of the sandwich beam with auxetic honeycomb core. [ABSTRACT FROM AUTHOR]

A review of the literature reveals a dearth of works on functionally graded material sandwich shells having an auxetic core layer. This study contributes an analytical approach for the free vibration analysis of doubly curved stiffened sandwich shells with the face sheets of functionally graded materials and the core layer of the auxetic honeycomb material. The theoretical formulation is established based on first-order shear deformation theory associated with the smeared stiffener method. The free vibration solution of simply supported shallow shells with the rectangular platform is derived using Navier's form. The proposed methodology is general and can be applied to examine the natural frequencies of various shell types, including flat, cylindrical, spherical, and hyperbolic paraboloidal panels. Numerical results indicate that the fundamental frequency is largely influenced by the relative proportion of the constituent materials of the face layers, the geometrical parameters of the auxetic honeycomb core layer, as well as the stiffeners. Additionally, a simple optimization technique based on Rao algorithms is introduced to obtain the maximum fundamental frequency of the shell. It is shown that the shell parameters, particularly the thickness of the auxetic core and the number of stiffeners, can be tailored to maximize the natural frequency. Moreover, the optimal solutions are fully dependent on the material proportion of the functionally graded material, the geometry of the shell, and the geometrical parameters of the auxetic honeycomb core. • Free vibration of doubly curved stiffened sandwich shells with FGM faces and auxetic core is freshly addressed • Simple optimization technique based on Rao algorithms is introduced to obtain the maximum fundamental frequency of the shell • New parametric studies on the frequencies of doubly curved stiffened auxetic sandwich FGM shells are examined [ABSTRACT FROM AUTHOR]

Sandwich panels/sacrificial cladding systems composed of an auxetic core sandwiched between two faceplates can be considered an effective protective measure for reinforced concrete structures from blast loads. In this study, the effectiveness of re-entrant honeycomb core sandwich (RHS) protective panel systems, which exhibit a negative Poisson's ratio, to protect one-way simply supported reinforced concrete (RC) slabs subjected to a close-range detonation from high explosive charges was experimentally evaluated. Three large-scale field blast trials were carried out, namely an RC slab without protection as the reference test and two RC slabs with RHS protective systems under similar blast loading conditions. The RC slabs with RHS protective systems experienced catastrophic failure, unlike the unprotected reference slab that experienced only localised concrete damage. LS-DYNA numerical models were validated and agreed well with the experimental results. It was demonstrated that the transferred blast impulse to the main structure can be magnified by a factor of 1.6 by using an RHS protective system compared to an unprotected structure. Furthermore, the effect of the mass of the protective system was numerically studied. The numerical results showed that the blast protection level of the main structure is governed by the inertial resistance of the protective system rather than through energy absorption of the auxetic honeycomb core structure. • Response of RC panels protected by auxetic sandwich panels to close-in explosion is investigated experimentally and numerically. • The damage magnification effect of the auxetic sandwich panels is captured experimentally which has not been reported so far. • The impulse transferred to the main structure could be magnified by a factor of 1.6 compared to the unprotected structure. • The duality of energy absorption and inertial resistance of auxetic protective systems need to be considered at close standoff distances. [ABSTRACT FROM AUTHOR]