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An improved finite element modeling method is developed for isotropic curvilinearly stiffened plates under a thermal environment. The existing modeling method for curvilinearly stiffened plates avoids the difficulty of node overlap, which is suitable for plates with different thicknesses. By introducing the influence of temperature on material parameters and thermal stress on additional stiffness, the existing method is improved and extended to the study of thermodynamics. The proposed method is verified by modal test at normal temperature and commercial finite element software at the thermal environment. The variation of dynamic characteristics with temperature under different boundary conditions was studied. Results show that when the boundary conditions are asymmetric, the influence of temperature on the thermal mode shape is more significant than the case of symmetrical. [ABSTRACT FROM AUTHOR]

The out-of-plane crushing resistance of fractal-like honeycombs with self-similar hierarchy are investigated numerically and analytically. The hierarchical honeycombs are developed via replacing each three-edge vertex of a regular hexagonal honeycomb by a smaller hexagon. Hierarchical honeycombs with higher orders are constructed by repeating this process. Theoretical solutions are derived based on the Super Folding Element (SFE) theory to predict the mean crushing forces (MCFs) of the hierarchical honeycombs. Numerical simulations are also conducted in conjunction with the theoretical solutions. Crushing resistances of three groups of hierarchical honeycombs with different relative densities are explored subsequently. Good agreement between results obtained using theoretical and numerical methods indicates that the theoretical predictions are reliable. The results show that hierarchy can significantly improve the crushing resistance of honeycombs. It is found that the MCFs of first to fourth order hierarchical honeycombs are improved by 71%, 114%, 201% and 309% compared with the regular honeycomb under the same relative density, respectively. It reveals that the amplification of the MCF from one generation to the next approaches a constant (ξ n  ≈ 1.26) when the hierarchical order is sufficiently large. The potential maximum achievable amplifications of the MCF for hierarchical honeycombs of different relative densities are also discussed. [ABSTRACT FROM AUTHOR]

The mechanical behavior of honeycomb sandwich structures under low-velocity impact is of great significance. An experimental and numerical investigation on surface deformation and energy absorption subjected to low-velocity impact is undertaken. A high-speed camera system is employed to record the acceleration attenuation process of the impactor, a projection profile system is introduced to measure the surface profiles of the panel and the depth of the ultimate indentation is obtained. A three-dimensional finite element model is constructed and validated by the experimental results. Indentation characteristics and energy absorption are analyzed and in good agreement with experimental data. Effect of adhesive layers on energy absorption is discussed and the contribution of the facesheets and the honeycomb core to the energy absorption process is analyzed separately. Results shown that the effect of adhesive layers on energy absorption is non-ignorable and the honeycomb core plays a dominant role in energy absorption. Most of the energy absorbed by the honeycomb sandwich panel is expended as plastic dissipation, and the rest is transformed into strain energy. [ABSTRACT FROM AUTHOR]

The honeycomb sandwich composite material has been widely applied in engineering due to its excellent mechanical performance. The elastic properties of honeycomb core is of crucial importance in efficient mechanical analysis. An approach on determining the equivalent elastic modulus of honeycomb core using experimental modal data is proposed in this paper. Based on analytically predicted elastic constants of the pure core, the initial finite element model of a honeycomb panel is constructed using a three-layer sandwich theory; according to errors that exist in analytically estimated equivalent parameters and the sensitivity analysis of modal frequencies with respect to system parameters, the out-of-plane shear moduli G cxz and G cyz are selected to be determined. Consequently, the two parameters are determined by minimizing an objective function which is formulated with vibration test and numerical modal data. Comparative investigations are conducted to illustrate that the initial values of the parameters with physical significance play an important role in the identification procedure. The presented method can provide accurate and reliable predictions of material constitutive parameters of honeycomb core. [ABSTRACT FROM AUTHOR]

A dense γ-Y 2 Si 2 O 7 /B 2 O 3 -Al 2 O 3 -SiO 2 glass coating was fabricated by slurry spraying method on porous Si 3 N 4 ceramic for water resistance. Thermal shock failure was recognized as one of the key failure modes for porous Si 3 N 4 radome materials. In this paper, thermal shock resistance of the coated porous Si 3 N 4 ceramics were investigated through rapid quenching thermal shock experiments and transient finite element analysis. Thermal shock resistance of the coating was tested at 700 °C, 800 °C, 900 °C and 1000 °C. Results showed that the cracks initiated within the coating after thermal shock from 800 °C to room temperature, thus leading to the reduction of the water resistance. Based on the finite element simulation results, thermal shock failure tended to occur in the coating layer with increasing temperature gradient, and the critical thermal shock failure temperature was measured as 872.24 °C. The results obtained from finite element analysis agree well with that from the thermal shock tests, indicating accuracy and feasibility of this numerical simulation method. Effects of thermo-physical properties for the coating material on its thermal shock resistance were also discussed. Thermal expansion coefficient of the coating material played a more decisive role in decreasing the tangent tensile stress. [ABSTRACT FROM AUTHOR]

• Fibrous network materials are found to be insensitive to the crack when the crack length is less than a critical length. • The critical length of crack is three times as much as the average length of fiber segments. • Fiber re-orientation contributes to the enhancement of the crack resistance of the fibrous network materials. A 3D numerical model is established to characterize the fibrous network materials and the fracture behavior is investigated through the finite element method (FEM) analysis. The numerical results show that fibrous network material is insensitive to the crack when the crack length is less than a critical value, which is three times as much as the average length of fiber segments in the fibrous network. In addition, the toughening mechanism of the fibrous network material is revealed based on the FEM simulations. Due to the damage accumulation of bonds near the crack tip, the fibers around the crack tip are reoriented and become perpendicular to the crack path, which can further inhibit the crack propagation, and the deformation mode changes from bending-dominated deformation to tensile-dominated deformation, with the loading capacity of the fibrous network materials enhanced. The results in this paper demonstrate that the fibrous network materials show damage-tolerance to the small crack under the critical crack length, and the fibrous network formed by brittle fibers can exhibit ductile behaviors by controlling the microstructure and relative density, which is useful for the design and optimization of fibrous network materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• A modeling method of curvilinearly stiffened plates suitable for both thin and thick plates is established and verified by experimental and existing numerical results. • Similar accuracy can be obtained when fewer mesh is used than finite element software. • The stiffeners can be arranged on the plate in any form without changing the mesh of the plate. Curvilinearly stiffened plates can have superior mechanical properties than traditional straight-line stiffened plates. To avoid the shear locking problem in the modeling of stiffened thick plates by Reissner-Mindlin theory when the thickness of plate decrease, discrete shear triangle element was introduced by employing the discrete shear constraints on each side. The discrete shear triangle element is employed for the plate and the Timoshenko beam theory is employed for the curvilinearly stiffeners, respectively. The FE equations are established through displacement interpolation function of plate and the displacement compatibility conditions at the plate-stiffened interfaces. The plate and stiffener are modeled separately in the present method, which allows the nodes of stiffener element not coincide with nodes of the plate's shell-element. Based on the newly proposed modeling technique, the statics, vibration and buckling behavior of curvilinearly stiffened plates are investigated. Numerical and experimental investigations are conducted to verify the mechanical properties of proposed model for stiffened plates. Results from the proposed method show good agreements with the numerical and experimental results. The present method can conduct static and dynamic analysis for both stiffened thick and thin plates and guarantee the accuracy of calculation with less number of elements. Image, graphical abstract [ABSTRACT FROM AUTHOR]