Dynamic Response Of Sandwich Panels Research Articles

Application of Auxetic Core to Improve Dynamic Response of Sandwich Panels Under Low-Velocity Impact

Application of Auxetic Core to Improve Dynamic Response of Sandwich Panels Under Low-Velocity Impact

Dynamic response of sandwich panel attached with a double mass-spring-damping system to shallow-buried explosion: analytical modeling

Dynamic response of sandwich panel attached with a double mass-spring-damping system to shallow-buried explosion: analytical modeling

Analytical modeling and optimal design of clamped sandwich beams with cellular cores subjected to shock loading

PurposeSandwich structures with well-designed cellular cores exhibit superior shock resistance compared to monolithic structures of equal mass. This study aims to develop a comprehensive analytical model for predicting the dynamic response of cellular-core sandwich structures subjected to shock loading and investigate their application in protective design.Design/methodology/approachFirst, an analytical model of a clamped sandwich beam for over-span shock loading was developed. In this model, the incident shock-wave reflection was considered, the clamped face sheets were simplified using two single-degree-of-freedom (SDOF) systems, the core was idealized using the rigid-perfectly-plastic-locking (RPPL) model in the thickness direction and simplified as an SDOF system in the span direction. The model was then evaluated using existing analytical models before being employed to design the sandwich-beam configurations for two typical engineering applications.FindingsThe model effectively predicted the dynamic response of sandwich panels, especially when the shock-loading pulse shape was considered. The optimal compressive cellular-core strength increased with increasing peak pressure and shock-loading impulse. Neglecting the core tensile strength could result in an overestimation of the optimal compressive cellular-core strength.Originality/valueA new model was proposed and employed to optimally design clamped cellular-core sandwich-beam configurations subjected to shock loading.

Determination of the effect of adhesive fillets and viscous damping on the dynamic response of aluminum honeycomb sandwich panels

The dynamic characteristics of an aluminum honeycomb sandwich panel are experimentally determined under free boundary conditions and the computational model is updated according to the experimental results. The study confirms that the adhesives used to bond the core and face sheets affect the dynamic response of the sandwich panel through the adhesive fillets formed between the face sheets and the core during the bonding process. The viscous damping of the structure is also determined by experimental modal analysis. It is observed that the results of the experimental and computational results agree well when the effects of adhesive fillets and viscous damping are considered. Furthermore, a dynamic response analysis under random vibration is conducted to reveal the differences between the results of the initial and the updated models.

Scaling behaviour of corrugated sandwich panels under impact load

The majority of the experimental studies investigating the dynamic response of sandwich panels are conducted using small-scale models that cannot be applied directly in the marine industry. In this study, a velocity–stress–mass (VSG) method based on the Johnson–Cook equation (VSG–JC) is derived to determine the relationship between a full-size structure (prototype) and its scaled-down model. The developed methodology is verified using theoretical and numerical solutions for an impact-loaded beam and plate, respectively. Theoretically, the model response can explicitly predict the behavior of a full-size structure using the VSG–JC method, whereas the strain rate cannot be obtained precisely via numerical simulation; hence, the corrected results for the model deviate slightly from the prototype results. Additionally, this method is compared with the VSG method based on the Cowper–Symonds equation (VSG–CS) in the numerical simulation of sandwich panels. The comparison results indicates that the VSG–JC method is more accurate than the VSG–CS method. The dynamic response of the scaled models predicted using the VSG–JC method coincides with that of the prototype, thus demonstrating that the VSG–JC method is valid for evaluating the scaling behavior of sandwich structures subjected to impact loads.

Experimental investigations into the dynamic response of sandwich panels with multi-layered corrugated cores subjected to underwater impulsive load

Sandwich panels with multi-layered core have attractive performance due to the excellent designability and tailorable mechanical properties. In present study, the dynamic responses of the sandwich panels with multi-layered corrugated core were investigated experimentally under underwater impulsive loads. In order to exploit the potential for performance improvement, some attempts have been made by designing core configuration from several aspects including stack orientation, layer number, core gradation and core topology. Experimental results indicate that the core in the cross-stacked would deteriorate back face deflection. The core with three layers performed best in constraint back face deflection because of the well balance between energy absorption and residual flexural stiffness. The core gradation in wall thickness would reduce back face deflection, while the one in corrugation angle would increase back face deflection. The core topology designed into reentrant trapezoidal corrugation behaved effectively in inhabiting back face deformation due to the periodic progressive collapse mechanism of core webs.

Dynamic response of the hybrid honeycomb sandwich panel with zero Poisson’s ratio under low-speed impact

The dynamic response of the hybrid honeycomb sandwich panel under low-speed impact is studied. According to Hamilton’s principle and first-order shear deformation theory, the motion equation of the hybrid honeycomb sandwich panel is deduced. Then the Navier method and Duhamel’s integral are used to solve the vibration displacement of panels. Besides, the mass-spring (MS) model is used to calculate the contact force between the honeycomb sandwich panel and the impactor. The results of this model are compared with those of Abaqus and published studies, which verifies the feasibility of the theoretical model in this paper. Based on the developed theoretical model, the influences of the unit cell angle, cell wall length, cell wall thickness, core layer height and impact speed on the dynamic response of sandwich panels have been studied. The results show that under the same low-speed impact, the maximum lateral displacement of hybrid sandwich panels was 11.65% smaller than that of conventional sandwich panels when honeycomb parameter θ = 60°, and was 15.45% when honeycomb parameter The energy absorption character of the hybrid honeycomb sandwich panel are better than those of the traditional hexagonal honeycomb sandwich panel and the concave hexagonal honeycomb sandwich panel.

Low- and high-fidelity modeling of sandwich-structured composite response to bird strike, as tools for a digital-twin-assisted damage diagnosis

The constant requirement of aerospace industry to enhance the structural efficiency has driven to the usage of high-performance composite materials, either monolithic or sandwich. However, aerospace composite structures are prone to damage due to high-velocity impact events such as bird strike, hail impact, etc. These impact events can result in extensive damage including structure perforation, which will eventually degrade its post-impact residual strength. Therefore, the early detection of damage in composite structure is imperative to avoid catastrophic failure. This paper develops the computational models which predict the dynamic behavior of a helicopter composite sandwich structure undergoing a bird strike. The models are aimed to be used as virtual tools for a future digital-twin-assisted fault detection technique. Firstly, a high-fidelity (HF) FE/SPH model was developed in LS-DYNA, and it was validated against the soft body impact experiments. Afterwards, a computationally efficient low-fidelity (LF) model was developed and correlated with the high-fidelity model. It was concluded that the high-fidelity model can sufficiently accurately predict the strain history experimentally recorded by the FBG sensors, and that size of the predicted delamination area at the front face of the sandwich structure agrees very well with the experimentally observed delamination area. It was also shown that the LF model can rapidly predict the global dynamic response of sandwich panel under the impact loading, through the good agreement between the numerical strain histories with the FBG measurements. Consequently, the LF model can be used as a quick numerical guide for the identification of the loading condition, whereas the HF model can be used as virtual damage detector and estimator of damage extension before the scheduled inspection.

Dynamic Stability of Sandwich Beams/Wide Plates Subjected to Axial Impulsive Loads

Abstract This paper presents an analysis for the dynamic stability of sandwich beams/wide plates subjected to axial impulsive loads. The formulation and solution of the problem is done by use of the extended high-order sandwich panel theory (EHSAPT). With the initial geometric imperfection included, the equations of motion in terms of seven generalized displacements are derived. The dynamic response of sandwich panels subjected to three different types of impulsive loads, namely, step, linear decay, and triangular impulse, is studied. Furthermore, the effects of the oscillation mode number, face/core materials, and geometries are investigated. It is observed that all measurements of the dynamic response, such as the maximum displacements, strains, and stresses, change at the same rate as the change of the impulse load magnitude and duration, for a specific impulse load profile. When the impulse load is lower than the static buckling load, the dynamic response is bounded no matter how long the load is applied. A step impulsive axial load with magnitude lower than the static buckling load can lead a sandwich panel to have a dynamic response as high as twice the static response. When the impulse load is higher than the static critical load, the dynamic response is unbounded with increasing load duration. However, it is possible that the dynamic response can be controlled at a low level if the duration of the impulse load is short enough, and thus, in this case, the load can safely exceed the static critical load.

Dynamic response of sandwich panels with multi-layered aluminum foam/UHMWPE laminate cores under air blast loading

The air blast responses of sandwich panels with multi-layered aluminum foam/UHMWPE laminate cores were analyzed experimentally and numerically. The focus was placed on the effects of foam core gradation and the locations of UHMWPE laminates. Multiple failure modes were exhibited by the panels, including local indentation and global bending deformation of face sheets, crushing and fragmentation of foam core, debonding of adhesive, and delamination and fracture failure of UHMWPE laminate. Experimental results showed that the ascending density foam core was beneficial to decrease the face sheet deformations and to alleviate the shear-induced collapse of foam core. Incorporating the UHMWPE laminates would induce a lower front face deformation and a higher back face deformation. The phenomenon would be more evident with the UHMWPE laminates placed close to the front face. Numerical results demonstrated that deploying the UHMWPE laminate as a first layer core significantly lowered the center velocity of front face. The existence of UHMWPE laminate would change the response modes of the panels. Most of the blast energy was dissipated by the multi-layered cores. The UHMWPE laminates exhibited less efficient in absorbing energy than the aluminum foam. Generally, the findings revealed the undesirable performance of the panels with multi-layered aluminum foam/UHMWPE laminate core under air blast loading.

Dynamic response of sandwich panel with hierarchical honeycomb cores subject to blast loading

This paper introduces a novel hierarchical core structure to sandwich panel for bearing the blast loading, in which each vertex of a regular hexagonal cell was replaced with a smaller hexagonal unit. The finite element (FE) models of such hierarchical honeycomb sandwich panels were established and validated with the experiments under different impulse loads. The hierarchical honeycomb cores were compared with the regular honeycomb counterpart in terms of the peak deflection on the back facesheet, compression and specific energy absorption (SEA) of the core. The results showed that the maximum deflection at the back facesheet of the hierarchical honeycomb sandwich panels were smaller than the regular honeycomb counterpart for a higher level of blast load (specifically, the dimensionless impulse higher than 0.06). It was found that the structural hierarchical parameter γ (i.e. the ratio of the newly-introduced smaller hexagonal edge length (L1) to the regular hexagon edge length (L0)), had limited influence on the maximum deflection of back facesheet of the sandwich panel, but had a significant effect on the SEA of the cores.

Numerical investigations on blast resistance of sandwich panels with multilayered graded hourglass lattice cores

This research focuses on the dynamic response of sandwich panels with multilayered graded hourglass lattice core subjected to blast loading. A three-layer lattice core configuration is proposed to improve the absorption efficient of kinetic energy resulted from blast shock wave. The relative density of each core layer is changed with sectional dimension of core truss members to regulate the energy absorption of each core layer. Three-dimensional numerical simulation analyses of dynamic response are carried out, and the applied impulsive pressure distribution on the surface of the panels is calculated using the CONWEP code. The panels are made of stainless steel AL6XN, which is assumed to follow bilinear strain hardening and strain rate-dependence. Peak back sheet deflection and energy absorption of core layers for four types of hourglass lattice panels are comparatively analyzed and the effects of load intensity on the peak deflection are discussed. Furthermore, the near-optimal configuration under blast loadings is proposed.

Research on the dynamic mechanical properties of polymethacrylimide foam sandwich structure

Polymethacrylimide foam is fully closed-cell isotropic foam which possesses high stiffness and strength to weight ratios. The paper reports the findings of an experimental study developing to investigate the quasi-static and dynamic response of sandwich panels based on polymethacrylimide foam using compression tests and Split Hopkinson Pressure Bar, respectively. The effect of thickness of aluminum face sheet, thickness and density of the polymethacrylimide core on the mechanical properties of the sandwich structures are studied respectively. It is shown that core density has the greatest effect on compressive strength of sandwich structure. The elasticity modulus and compressive strength of sandwich decreased by 40% under quasi-static compressive when the density of the core reduced by 28%. Secondly, dynamic compressive experiment results show that when the density of the core reduced by 28%, at the strain rate of 150 s−1, compressive strength decreased by 45%; strain rate 310 s−1, compressive strength reduced by 42%. When the strain rate increased from 7.6 × 10−4 s−1 to 150 s−1, compressive strength increased by 26%; strain rate increases from 7.6 × 10−4 s−1 to 310 s−1, compressive strength increased by 43%. The dynamic mechanical properties of polymethacrylimide foam sandwich panels accompanied with the increase of strain rate. Finally, dynamic constitutive relation of Cowper-Symonds function is fitted.

Nonlinear dynamic response of sandwich wide panels

This work focuses on the general nonlinear dynamic formulation of sandwich panels based on the Extended High-order Sandwich Panel Theory. The faces and the core are both considered undergoing large deformation with moderate rotation. In the literature, when it comes to nonlinear dynamic response, various simplifying assumptions are adopted in the nonlinear kinematic relations. A critical assessment of these simplifications, as well as a comprehensive investigation of the geometric nonlinearity effects on the dynamic response of sandwich beams/wide panels is presented. The Extended High-order Sandwich Panel Theory (EHSAPT)-based finite element is used to formulate the equations of motion, and the time response is obtained by the central difference method. The transient response of a sandwich panel subjected to a distributed blast loading is studied as a numerical example. By neglecting the nonlinear terms, the nonlinear dynamic analysis is reduced to the linear dynamic small deformation analysis, for which a closed-form elasticity solution exists. This, the linear response is first compared with the closed-form linear dynamic elasticity solution. It is shown that the linear EHSAPT yields an identical response to the dynamic elasticity analysis. Subsequently, the dynamic response is evaluated by considering the geometric nonlinearities. Several simplified nonlinear models with partial nonlinear terms included are considered. These models reflect the assumptions commonly adopted in the literature. Numerical results are presented to investigate the effects of geometric nonlinearities on the displacements and stresses. It is shown that the geometric nonlinearities have a significant effect on the dynamic response of sandwich panels and, in particular, the nonlinear terms in the core kinematic equations are especially important.

Response of aramid honeycomb sandwich panels subjected to intense impulse loading by Mylar flyer

The deformation/failure modes and impact resistance of composite sandwich panels with titanium alloy plates and aramid honeycomb cores subjected to intense impulse loading were investigated experimentally using electric gun technique. A velocity measuring instrument, known as the velocity interferometer system for any reflector (VISAR), measured the velocity history at the mid-point of the back plates. Typical deformation/failure modes were analyzed and classified systematically, and then a comparison of structural deformation resistance between sandwich panels and plates of equivalent mass was studied. It was found that both the deformation/failure modes and the dynamic response of the plates were sensitive to the impact velocity. The impact resistance of sandwich panels could be improved by core crushing and deformation of the front plate. Finally, effects of impact velocity and boundary conditions on the dynamic response of sandwich panels were identified. It was worth noting that the fully clamped boundary reduced the damage extent of the front plate, but increased the local plastic deformation of the back plate.

Damping of Sandwich Panels via Three-Dimensional Manufactured Multimode Metamaterial Core

Acoustic metamaterials offer an approach to reducing the dynamic response of sandwich panels. The key concept underlying this approach is to consider a metamaterial as a highly distributed system of continuous vibration absorbers that introduces multiple stop bands in which the response of the global structure is reduced. Multiple modal frequencies of the absorber system may be tuned to match global resonance frequencies and/or excitation frequencies. Using the assumed modes method, a metamaterial system is designed for integration into the honeycomb core of a representative sandwich panel. The metamaterial system is modeled as an effective distributed complex mass density in the global sandwich-panel model. The cores for two sandwich panels are fabricated using three-dimensional printing technology and then characterized statically and dynamically to determine effective elastic properties and natural frequencies of the cores, as well as loss factors of the vibration absorbers. The sandwich panels, constructed by bonding unidirectional carbon-fiber face sheets to both cores, are tested dynamically for two different boundary conditions: cantilevered and free–free. Experimental results confirm that the metamaterial core reduces the peak dynamic response at the natural frequencies of the sandwich panel with reasonably good agreement with model predictions.

The dynamic response of sandwich panels with cellular metal cores to localized impulsive loading

Abstract The deformation/failure modes and dynamic response of peripherally clamped square monolithic and sandwich panels of localized impulsive loading were investigated experimentally by metallic foam projectile impact. The sandwich panels comprise three different types of cellular metallic cores, i.e., closed-cell aluminum foam core, open-cell aluminum foam core and aluminum honeycomb core. Experimental results show that all the sandwich panels present mainly large global inelastic deformation with obvious local compressive failure in the central area, except for those open-cell foam core sandwich panels. The dynamic response of sandwich panels is sensitive to the applied impulse and their geometrical configurations. Based on the experimental investigation, a theoretical analysis was developed to predict the dynamic response of sandwich panels by employing a comprehensive yield locus and a modified classic monolithic panel theory. A comparison of experimental results and theoretic predictions was made, and a good agreement was then found. These findings are very useful to guide the engineering applications of metallic sandwich structures for the protection purpose.

Experimental study of the medium velocity impact response of sandwich panels with different cores

The impact response of sandwich panels is not only dependent on the facesheet but also on the core material. This paper compares the dynamic response of sandwich panels with different core materials when subjected to medium velocity impacts. The sandwich panels were made of aluminium facesheets with five different cores, viz., low density balsa wood, high density balsa wood, cork, polypropylene honeycomb, and polystyrene foam. All the specimens were impacted by an instrumented projectile with a hemispherical steel head at three impact energies of 43, 85 and 120J. An accelerometer attached to the projectile and a high speed camera were used to collect data and record the impact process. 3D scanning technique was used to measure the deformation of front and back faces after impact. The impact properties of the sandwich panels with the five different cores were compared in terms of contact force, energy absorption, depth of indentation, overall bending deflection, etc. Post-mortem sectioning was conducted to examine the impact induced failures such as facesheet rupture, crush of core material, and debonding between facesheet and core. Finite element modelling was also carried out to elucidate the observed experimental results and further understand the effect of core material.

A parametric study on the stress analysis and transient response of thick-laminated-faced cylindrical sandwich panels with transversely flexible core

In the present work the effects of important parameters such as core thickness, radius of curvature and sector angle on the static and dynamic response of composite cylindrical sandwich panels have been investigated using a higher-order sandwich panel theory (HSAPT). The presented higher-order theory, which applies first-order shear deformation shell theory (FSDT) for the face sheets and the equivalent elasticity theory for the core, is a rigorous approach that includes the higher-order effects incurred by the nonlinearity of the in-plane and transverse displacements of core. Equations of motion along with associated boundary conditions are derived by using Hamilton's principle. For simply-supported panels closed-form solutions can be achieved by Navier techniques. However, for dynamic analysis, the solution is obtained in the time domain by implementing Newmark method. Finally numerical parametric studies are performed to provide some insight into the roles of key variables that influence the static and dynamic response of sandwich panels.

Dynamic response of sandwich panels with auxetic cores

Effective properties and dynamic response of a sandwich panel made of two face sheets and auxetic core are analyzed in this study by computer simulations. The inner composite layer is made of a cellular auxetic structure immersed in a filler material of a given Poisson's ratio (filler material fills the voids in structure). Each cell is composed of an auxetic structure (re‐entrant honeycomb or rotating square), i.e., exhibiting negative Poisson's ratio without any filler. Influence of filler material on the effective properties of the sandwich panel is investigated. The proposed structure shows interesting structural characteristics and dynamic properties. Our results clearly show that it is possible to create auxetic sandwich panels made of two solid materials with positive Poisson's ratio. This is even possible if the filler material is nearly incompressible, but can move in out‐of‐plane direction. Moreover, effective Young's modulus of such sandwich panels becomes very large if the Poisson's ratio of the filler material tends to −1.