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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]

In this paper, the quasi-static compression behavior of graded metallic auxetic reentrant honeycomb was firstly studied. Using the selective laser melting method, the unidirectionally-graded auxetic honeycomb (UGAH) and bidirectionally-graded auxetic honeycomb (BGAH) with the equal mass were fabricated to conduct the compression tests. The deformation mode, crushing stress and Poisson's ratio distribution of graded auxetic honeycombs were presented. Experiment results showed that the compression behavior of graded auxetic honeycomb was different from that of graded honeycomb with positive Poisson's ratio owing to the horizontal shrinkage deformation and the gradient distribution had effects on the crushing stress and Poisson's ratio. Then, a finite element (FE) model of the graded auxetic honeycomb was established and the calculation results were systematically compared with the experimental results. The effects of gradient distribution on the energy dissipation characteristics of the graded auxetic honeycomb were studied. The results showed that the energy dissipation of the UGAH was lower than that of the BGAH before the graded layer with the maximum cell-wall thickness was densified. [ABSTRACT FROM AUTHOR]

An analytical framework has been developed for predicting the equivalent in-plane elastic moduli (longitudinal and transverse Young’s modulus, shear modulus, Poisson’s ratios) of irregular auxetic honeycombs with spatially random variations in cell angles. Employing a bottom up multi-scale based approach, computationally efficient closed-form expressions have been derived in this article. This study also includes development of a highly generalized finite element code capable of accepting number of cells in two perpendicular directions, random structural geometry and material properties of irregular auxetic honeycomb and thereby obtaining five in-plane elastic moduli of the structure. The elastic moduli obtained for different degree of randomness following the analytical formulae have been compared with the results of direct finite element simulations and they are found to be in good agreement corroborating the validity and accuracy of the proposed approach. The transverse Young’s modulus, shear modulus and Poisson’s ratio for loading in transverse direction (effecting the auxetic property) have been found to be highly influenced by the structural irregularity in auxetic honeycombs. [ABSTRACT FROM AUTHOR]

In order to improve the energy absorption capacity of the honeycomb, a combined auxetic honeycomb is designed in this paper. By using the double-inclined walls replacing the horizontal walls of the star-shaped honeycomb (SSH), and introducing a thin-walled circle contacting with the four concave corners of the SSH, the star-circle honeycomb (SCH) is designed. The in-plane dynamic crushing behaviors was explored based on finite element method (FEM). There are three types of deformation modes observed with different impact velocity, including low-, medium- and high-velocity loading modes and the stress-strain curve exhibits two plateau stress stages. Based on the deformation characteristics of the representative unit, theoretical calculation models were established to estimate the plateau stress of the SCH under low- and high-velocity loading according the conservation of energy and the theoretical calculation was in keep well with the numerical simulation. A deformation modes map was summarized to investigate the effects of the impact velocity and the relative density on the deformation modes and the energy absorption capability and the dynamic Poisson's ratio were studied. The result shows that the SCH presents better energy absorption compared with SSH as well as retaining the negative Poisson's ratio property. The deformation mechanism was revealed form the structural design and plastic hinge dissipation. This work presents a different design strategy for the auxetic honeycomb, expected to guide the design of more novel auxetic with better energy absorption and mechanical property. • A combined auxetic honeycomb is designed through the intracellular common-node contact between the star and the circle. • Two plateau stages for the honeycomb appears under low-velocity loading with enhanced crushing strength and energy absorption. • Two theoretical calculation models are established for the plateau stress under low velocity and high velocity. • The thin-walled circle can dissipate more energy owing to the lateral compression caused by the transverse contraction. [ABSTRACT FROM AUTHOR]