Dynamic Response Of Sandwich Structures Research Articles

Resistance of all-metallic honeycomb sandwich structures to underwater explosion shock

All-metallic honeycomb sandwich structure is a new kind of ship protection structure, which has a broad application prospect in the field of ship protection. However, there is not enough research on the dynamic response of honeycomb sandwich structures under the actual underwater explosion load. The dynamic behavior and protective performance of honeycomb sandwich structures subjected to underwater explosion load were investigated, both experimentally and numerically in this paper. A backplane stiffened honeycomb sandwich structure and the corresponding buoyant box were designed and fabricated for the subsequent experimental study in a large open water pool. The structural response was numerically simulated using the coupled acoustic-structural approach (integrated in commercial FE code ABAQUS/Explicit). The numerical simulation results are in good agreement with the experimental measurements. Then, the deformation process and energy absorption characteristics of the honeycomb sandwich structure subjected to underwater explosion load were investigated. The effects of the load parameter (impact factor) and two geometric parameters (i.e., facesheet thickness ratio and core relative density) on the dynamic response of the sandwich structure were analyzed. Finally, the Pareto optimal designs with minimize value of non-dimensional areal density and minimize value of non-dimensional maximum deformation of the central point on back facesheet were obtained using the NSGA-Ⅱ algorithm. The results show that with the increase of impact factor, the overall deformation of the structure increases significantly. The honeycomb core is the main energy absorbing substructure during this process, and its energy absorption ratio gradually decreases. With the increase of either face sheet thickness ratio or core relative density, the deformation of the structure first decreases and then increases, accompanied by changes in deformation modes. The influence of core relative density is more significant. The optimized structures obtained from multi-objective optimal design effectively reduce the areal density and the maximum deformation, which can be used as a reference for the future design of honeycomb sandwich structures.

An advanced five-unknown higher-order theory for free vibration of composite and sandwich plates

Accurate prediction of dynamic characteristics is quite critical to understand the strength of layered structures. Nevertheless, the existing five-unknown higher-order theories encounter difficulties to forecast accurately the dynamic response of sandwich structures. Therefore, a new five-unknown higher-order theory is developed for free vibration analysis of composite and sandwich plates, which possesses the same degree of freedom as those of other five-unknown higher-order theories. The developed model can meet beforehand interlaminar continuity conditions and the free-surface conditions of transverse shear stresses. To assess capability of the proposed model, analytical solution for such composite structures with simply-supported conditions has been presented by employing Hamilton’s principle, which is utilized for analysis of mechanical behaviors of composite and sandwich plates. Compared with the three-dimensional (3D) elasticity solutions, 3D finite element results and the results obtained from the chosen five-unknown higher-order models, the proposed model can yield accurately natural frequencies of composite and sandwich plates. Even for the thick plates, the higher-order frequencies calculated from the proposed model are in good agreement with the 3D finite element results. By studying effect of the thickness/length ratios on natural frequencies, it is found that the proposed model is adaptable to predicting natural frequencies of the sandwich plates with the thickness/length ratios between 1/4 and 1/100. In addition, some factors influencing accuracy of five-unknown higher-order models have been investigated in detail. Finally, by means of numerical analysis and discussion, some conclusions have been drawn as well, which can serve as a reference for other investigators.

Sandwich Panels with Polymeric Foam Cores Exposed to Blast Loading: An Experimental and Numerical Investigation

Sandwich panels have proven to be excellent energy absorbents. Such panels may be used as a protective structure in, for example, façades subjected to explosions. In this study, the dynamic response of sandwich structures subjected to blast loading has been investigated both experimentally and numerically, utilizing a shock tube facility. Sandwich panels made of aluminium skins and a core of extruded polystyrene (XPS) with different densities were subjected to various blast load intensities. Low-velocity impact tests on XPS samples were also conducted for validation and calibration of a viscoplastic extension of the Deshpande-Fleck crushable foam model. The experimental results revealed a significant increase in blast load mitigation for sandwich panels compared to skins without a foam core, and that the back-skin deformation and the core compression correlated with the foam density. Numerical models of the shock tube tests were created using LS-DYNA, incorporating the new viscoplastic formulation of the foam material. The numerical models were able to capture the trends observed in the experimental tests, and good quantitative agreement between the experimental and predicted responses was in general obtained. One aim of this study is to provide high-precision experimental data, combined with a validated numerical modelling strategy, that can be used in simulation-based optimisation of sandwich panels exposed to blast loading.

The Dynamic Response of Sandwich Structures with Cellular Metallic Core under Blast Loading

The dynamic responses of sandwich structures with MHS(metal hollow sphere)and closed cell aluminum foams under blast loading were simulated numerically by employing the finite element software ANSYS/LS-DYNA. Both sandwich panels and sandwich spheres were modeled. Some factors that determine the blast resistance of the sandwich structures were investigated. According to the parametric studies, the sandwich structures with thin inner face sheet and thick outer face sheet have stronger blast resistance than others. Also the results show that sandwich structures with interlaced hollow spheres have a better performance than those with paratactic hollow spheres. Moreover, it's inferred that the density graded core with the biggest density as the first impact layer and the least density as the last layer has more benefits in energy absorption. The comparison between sandwich structures with metal hollow spheres and those with aluminum foams was studied experimentally and numerically and the results demonstrate that structures with aluminum foam have advantage in energy absorption but structures with MHS are stronger and can undertake more TNT.

Dynamic failure of a sandwich structure subjected to an in-plane axial impact

Dynamic response of sandwich structures subjected to in-plane axial impact loading is investigated experimentally and numerically. A comprehensive set of impact test results on sandwich panels with various configurations is presented. Experimental observation is made using high-speed cameras to closely examine the detailed temporal responses of the sandwich columns before the collapse of the entire structures. It is found that the failure mode is significantly affected by the core thickness. Finite-element based simulation is also performed to have a better understanding of the failure mechanism. Discrete cohesive zone model (DCZM) is utilized to model delamination failure at the interface between the skins and core. The interfacial failure is driven by dynamic buckling of the skin, competing against the bonding strength at the interface.

Dynamic response of sandwich structures with graded auxetic honeycomb cores under blast loading

Abstract An innovative sandwich structure with auxetic re-entrant cell honeycomb cores was proposed in this paper, and the dynamic responses and blast resistance of the honeycomb sandwich structures under blast loading were investigated numerically by employing the LS-DYNA. The honeycomb structures with thicker walls have a higher plateau force and specific energy absorption (SEA) under the compression loading. Deformation modes and deflections distribution along the axis direction caused by plastic stretching and bending were investigated in detail to have a better understanding of the deformation mechanism. Results show that the sandwich structures have a higher ability of resisting deformation along the longitudinal(Y)-direction than the transverse(X)-direction. In addition, the dynamic responses of honeycomb sandwich structures with different stand-off distances, graded cores and arranged orientations were studied. Results show that both the graded honeycomb cores and cross-arranged honeycomb cores can significantly improve the resistance ability of the sandwich structures under blast loading, compared with the ungraded honeycomb cores and regular-arranged cores. Comprehensively, the cross-arranged graded honeycomb cores with higher density of the upper layer performs the best under the blast loading compared with the other configurations, taking the effects of graded cores and arranged orientations into consideration. This work provides a reliable basis to design the sandwich structures with auxetic re-entrant cell honeycomb cores under compression and blast loading.

Multi-physics modeling of the fabrication and dynamic performance of all-metal auxetic-hexagonal sandwich-structures

In the present paper, various computational methods and tools are used to investigate the effect of the prior processing and the resulting microstructure on the performance of all-metal sandwich-structures with an auxetic-hexagonal core. Specific fabrication processes analyzed in the present work include: (a) sheet-metal fabrication using cold flat rolling; (b) a simple stamping process used to impart the desired corrugation to the as-cold rolled sheet-metal blanks; and (c) laser welding used to join the corrugated and stacked adjacent blanks over their areas of contact. The computational analyses employed yielded the results which clearly revealed how each of the three fabrication processes affects the grain microstructure of the sheet-metal blanks, the presence of residual stresses within the sandwich-structure as well as the presence of distortions. In the last portion of the present work, a series of transient nonlinear dynamics finite-element computational analyses is carried out in order to demonstrate how the prior fabrication processes and the material microstructure, residual stresses and distortions yielded by them affects the dynamic performance of the all-metal auxetic sandwich-structures subjected to blast loading. The results obtained clearly showed that the effect of prior processing must be taken into account in order to obtain accurate insight into the dynamic response of sandwich structures when subjected to blast loading.

Some theoretical considerations on the dynamic response of sandwich structures under impulsive loading

A theoretical solution is obtained to predict the dynamic response of peripherally clamped square metallic sandwich panels with either honeycomb core or aluminium foam core under blast loading. In the theoretical analysis, the deformation of sandwich structures is separated into three phases, corresponding to the transfer of impulse to the front face velocity, core crushing and overall structural bending/stretching, respectively. The cellular core is assumed to have a progressive crushing deformation mode in the out-of-plane direction, with a dynamically enhanced plateau stress (for honeycombs). The in-plane strength of the cellular core is assumed unaffected by the out-of-plane compression. By adopting an energy dissipation rate balance approach developed by earlier researchers for monolithic square plates, but incorporating a newly developed yield condition for the sandwich panels in terms of bending moment and membrane force, “upper” and “lower” bounds are obtained for the maximum permanent deflections and response time. Finally, comparative studies are carried out to investigate: (1) influence of the change in the in-plane strength of the core after the out-of-plane compression; (2) performances of a square monolith panel and a square sandwich panel with the same mass per unit area; and (3) analytical models of sandwich beams and circular and square sandwich plates.

Implication of Nonclassical Effects on Dynamic Response of Sandwich Structures Exposed to Underwater and In-Air Explosions

A study devoted to the dynamic response of sandwich panels to underwater and in-air explosions is presented. The study is carried out in the context of a geometrically nonlinear model of sandwich structures featuring anisotropic laminated face sheets and a transversely compressible orthotropic core. The unsteady pressure generated by the explosion and acting on the face of the sandwich panel includes the effect of the pressure wave transmission through the core. Its implications on the structural time-histories as corresponding to the underwater and in-air explosions are put into evidence. The effects of the transverse core compressibility on dynamic response are highlighted. In this sense, one of its major implications is the possibility to capture interactively the global and local (wrinkling) dynamic response of the panel. It is shown that implementation of the structural tailoring technique in the face sheets can constitute an important mechanism for enhancing the dynamic load-carrying capacity of sandwich panels when exposed to blast pulses. Effects of the core, the composite architecture of face sheets, orthotropy of the material of the core, geometrical non-linearities, initial geometric imperfection, and the damping ratio are investigated, and their implications for the dynamic response are highlighted. The comprehensive structural model considered in conjunction with the time-dependent loads generated by the underwater and in-air explosions, and the results obtained in this context, are expected to contribute to a better understanding of the response behavior and to be instrumental toward a better design of these structures.

Recent results on the effect of the transverse core compressibility on the static and dynamic response of sandwich structures

This paper is devoted to a study of the effects played by transverse core compressibility of sandwich plates and shells on their static and dynamic behavior. The analysis is based on a higher-order structural model using the standard Kirchhoff–Love assumption for the face sheets and a higher order displacement representation for the core layer. The model accounts for the geometrical nonlinearities that are considered in the von Kármán sense and for initial geometric imperfections. Transverse shear effects are included in the soft-core layer. Consistent equations of motion and boundary conditions are derived via the application of Hamilton’s principle. In the cases that are analyzed and presented in this paper, it was revealed that the static and dynamic buckling/response and postbuckling of flat and curved sandwich structures, are strongly affected by transverse compressibility of the core. It is also shown that in the context of this structural model, the wrinkling instability and response are captured directly from the derived governing equations, and not, as customarily, via a post-processing analysis.

Dynamic response of anisotropic sandwich flat panels to underwater and in-air explosions

The problem of the dynamic response of flat rectangular sandwich panels subjected to underwater and in-air explosions is analyzed. The study is carried out in the framework of a geometrically non-linear model of sandwich structures featuring anisotropic laminated face sheets and an orthotropic core, in conjunction with the unsteady pressure generated by an explosion. Effects of the core and of the orthotropy of its material, as well as those related to the ply-thickness, directional material property and stacking sequence of face sheets, geometrical non-linearities and of the structural damping ratio are investigated, and their implications upon the dynamic response are highlighted. To the best of the authors’ knowledge, the specialized literature addressing the dynamic response of sandwich structures to underwater and in-air explosions is rather scanty. This work is likely to fill a gap in the specialized literature on this topic.