Energy dissipation mechanism and ballistic characteristic optimization in foam sandwich panels against spherical projectile impact

This study systematically examines the energy dissipation mechanisms and ballistic characteristics of foam sandwich panels(FSP)under high-velocity impact using the explicit non-linear finite element method.Based on the geometric topology of the FSP system,three FSP configurations with the same areal density are derived,namely multi-layer,gradient core and asymmetric face sheet,and three key structural parameters are identified:core thickness(t_(c)),face sheet thickness(t_(f))and overlap face/core number(n_(o)).The ballistic performance of the FSP system is comprehensively evaluated in terms of the ballistic limit velocity(BLV),deformation modes,energy dissipation mechanism,and specific penetration energy(SPE).The results show that the FSP system exhibits a significant configuration dependence,whose ballistic performance ranking is:asymmetric face sheet>gradient core>multi-layer.The mass distribution of the top and bottom face sheets plays a critical role in the ballistic resistance of the FSP system.Both BLV and SPE increase with tf,while the raising tcor noleads to an increase in BLV but a decrease in SPE.Further,a face-core synchronous enhancement mechanism is discovered by the energy dissipation analysis,based on which the ballistic optimization procedure is also conducted and a design chart is established.This study shed light on the anti-penetration mechanism of the FSP system and might provide a theoretical basis for its engineering application.

A Modified Principal Component Analysis Method for Honeycomb Sandwich Panel Debonding Recognition Based on Distributed Optical Fiber Sensing Signals

The safety and integrity requirements of aerospace composite structures necessitate real-time health monitoring throughout their service life.To this end,distributed optical fiber sensors utilizing back Rayleigh scattering have been extensively deployed in structural health monitoring due to their advantages,such as lightweight and ease of embedding.However,identifying the precise location of damage from the optical fiber signals remains a critical challenge.In this paper,a novel approach which namely Modified Sliding Window Principal Component Analysis(MSWPCA)was proposed to facilitate automatic damage identification and localization via distributed optical fiber sensors.The proposed method is able to extract signal characteristics interfered by measurement noise to improve the accuracy of damage detection.Specifically,we applied the MSWPCA method to monitor and analyze the debonding propagation process in honeycomb sandwich panel structures.Our findings demonstrate that the training model exhibits high precision in detecting the location and size of honeycomb debonding,thereby facilitating reliable and efficient online assessment of the structural health state.

Fabrication and Testing of Carbon Fiber Reinforced Truss Core Sandwich Panels

Truss core sandwich panels reinforced by carbon fibers were assembled with bonded laminate facesheets and carbon fiber reinforced truss cores. The top and bottom facesheets were interconnected with truss cores. Both ends of the truss cores were embedded into four layers of top and bottom facesheets. The mechanical properties of truss core sandwich panels were then investigated under out-of-plane and in-plane compression loadings to reveal the failure mechanisms of sandwich panels. Experimental results indicated that the mechanical behavior of sandwich structure under in-plane loading is dominated by the buckling and debonding of facesheets.

Study on the Fire Behavior of Sandwich Wall Panels with GFRP Skins and a Wood-Web Core

To investigate the temperature field and residual bearing capacity of the sandwich wall panels with GFRP skins and a wood-web core under a fire,three sandwich walls were tested.One of them was used for static load test and the other two for the one-side fire tests.Besides,temperature probe points were set on the sandwich walls to obtain the temperature distribution.Meanwhile,the model of the sandwich wall was established in the finite element software by the method of core material stiffness equivalent.The temperature distribution and performance reduction of materials were also considered.The residual bearing capacity of specimens after fire exposure were simulated considering the effects of web spacing,wall panel thickness and fire exposure time.Because the sandwich wall panels were stressed by eccentric compression after a fire,the residual compressive strength of the wall panel after the fire can be calculated through the eccentric loading analysis.Compared with the numerical results,it can be concluded that the effectiveness of calculation method of residual bearing capacity after fire exposure was proved.

Analysis on Dynamic Response of Hard-Soft-Hard Sandwich Panel Under Blast Loading

Surface contact explosion experiments have been performed for the study of dynamic response of the hard-soft-hard sandwich panel under blast loading. Experimental results have shown that there are four damage modes, including explosion cratering, scabbing of the backside, radial cracking induced failure and circumferential cracking induced failure. It also illustrates that the foam material sandwiched in the multi-layered media has an important effect on damage patterns. The phenomena encountered have been analyzed by the calculation with ALE method. Meanwhile, the optimal analysis of foam material thickness and position in the sandwich panel were performed in terms of experimental and numerical analysis. The proper thickness proportion of the soft layer is about 2.0% to the thickness of sandwich panel and the thickness of the upper hard layer and lower hard layer is in the ratio of ？ to 3 under the condition in this paper when the total thickness of soft layer remains constant.

Stress and buckling analysis of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets

In this paper,the stresses and buckling behaviors of a thick-walled mi-cro sandwich panel with a flexible foam core and carbon nanotube reinforced composite(CNTRC)face sheets are considered based on the high-order shear deformation theory(HSDT)and the modified couple stress theory(MCST).The governing equations of equi-librium are obtained based on the total potential energy principle.The effects of various parameters such as the aspect ratio,elastic foundation,temperature changes,and volume fraction of the canbon nanotubes(CNTs)on the critical buckling loads,normal stress,shear stress,and deflection of the thick-walled micro cylindrical sandwich panel consider-ing different distributions of CNTs are examined.The results are compared and validated with other studies,and showing an excellent compatibility.CNTs have become very use-ful and common candidates in sandwich structures,and they have been extensively used in many applications including nanotechnology,aerospace,and micro-structures.This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

Bending analysis of five-layer curved functionally graded sandwich panel in magnetic field:closed-form solution

In this paper,an exact closed-form solution for a curved sandwich panel with two piezoelectric layers as actuator and sensor that are inserted in the top and bottom facings is presented.The core is made from functionally graded(FG)material that has heterogeneous power-law distribution through the radial coordinate.It is assumed that the core is subjected to a magnetic field whereas the core is covered by two insulated composite layers.To determine the exact solution,first characteristic equations are derived for different material types in a polar coordinate system,namely,magneto-elastic,elastic,and electro-elastic for the FG,orthotropic,and piezoelectric materials,respectively.The displacement-based method is used instead of the stress-based method to derive a set of closed-form real-valued solutions for both real and complex roots.Based on the elasticity theory,exact solutions for the governing equations are determined layer-by-layer that are considerably more accurate than typical simplified theories.The accuracy of the presented method is compared and validated with the available literature and the finite element simulation.The effects of geometrical and material parameters such as FG index,angular span along with external conditions such as magnetic field,mechanical pressure,and electrical difference are investigated in detail through numerical examples.

Bonding strength in carbon steel sandwich panels under condition of diffusion-rolling with small reduction

One of the key problems by diffusion-rolling bonding with small reduction for carbon steel plates is the bonding assistant coat. Abonding assitant coat used below 850℃ was developed. It contained copper as basic element and zinc as main alloy element. Other small elements and rear metals were added to decrease the melting point and to obtain a better clouding and bigh plasticity. Based on the theory of brazing and transient liquid diffusion welding, two carbon steel plates were rolled with small reduction by using self-made bonding assistant coat. Temperature, pressure and holding time are the main technology parameters for controlling the process of diffusion-rolling. The results show that the bonding strength is the greatest when the bonding temperature is 830℃, holding time is 3 min and the reduction rate is 9%.

Theoretical Calculation and Analysis of Slip and Deformation for Concrete Sandwich Panels

Slip and deformation of concrete sandwich panels under uniformly distributed loads is concerned. The effect of slip on the deformation of concrete sandwich panels are studied,and the analytical expressions of slip and deformation for concrete sandwich panels is obtained. These formulae can describe the slip distribution and account for its effect on deformation. In order to restrict the bound of formula, the formula of crack moment is obtained. The results of theoretical calculation are compared with those of tests and finite element methods. The comparison shows that the results of theoretical calculation are in accord with those of tests and finite element methods. So the theoretical calculation can be used to calculate slip and deformation of concrete sandwich panels in practical projects.

Development of Composite Cellular Cores for Sandwich Panels Based on Folded Polar Quadra-Structures

An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented. Polar folded quadra structures are regarded as a geometric basis for these cores whose standard frag ment has lhe fourlh degree of axial symmelry. The classification of the polar strucluresaredeseribedanda method of various quadra slrueture synthesis is developed. A possibilily to provide high strength of lhe structure due m preservation of faces reinforcement pattern is presented. Arrangemen! of the plane core on a bi curvature surface is also introduced. Besides, provision of isotropyof the core in two or three directions are described. Finally, exam ples of cellular folded cores manufaclured from basalt reinforced plaslic are demonslrated.

Dynamic Response of the U-Typed Sandwich Panel Under Explosion Load Based on the SDOF Method

Sandwich panel is commonly used in ship and marine engineering equipment,such as side structure and superstructure deck of a ship,which is of good anti-explosion performance.This paper addresses a study on the dynamic response of the U-typed sandwich panel under explosion load through the numerical simulation and theoretical methods.Based on the orthotropic plate theory,the U-typed sandwich panel is simplified and transformed into a single degree of freedom(SDOF)spring system,the equivalent motion equation of the SDOF system and the expression of triangular explosion load function are established based on the SDOF theory,and the maximum response spectrum of the SDOF system is obtained.Then,the response of the equivalent SDOF system of the U-typed sandwich panel under explosion load is analyzed,and the theoretical results match well with the numerical simulation results,which verifies the accuracy of the theoretical method proposed in this paper.The theoretical method proposed in this paper could have good engineering applications for the structural anti-explosion design,and provide a reference for the evaluation of the anti-explosion performance of ship and offshore platform structures.

Nonlinear thermo-structural behavior of sandwich panels with truss cores under through-thickness gradient temperature field

A theoretical analysis is presented to predict the nonlinear thermo-structural response of metallicsandwich panels with truss cores under through-thickness gradient temperature field, which is acommon service condition for metallic thermal protection system （TPS）. The in-planetemperature distribution is assumed to be uniform, and through-thickness temperature field isdetermined by heat conduction. Two typical conditions are analyzed： nonlinear thermal bendingin fixed inside surface temperature, and thermal post-buckling in fixed temperature differencebetween two surfaces. Temperature-dependent mechanical properties are considered, andgradient shear stiffness and bending stiffness due to non-uniform temperature is included. Resultsindicate that the temperature-dependent material properties obviously affect bending resistance;however, the effect is negligible on post-buckling behavior. Influences of geometric parameters onthe thermo-structural behavior of the sandwich panel according to the present theoretical modelare discussed.

NONLINEAR STABILITY ANALYSIS OF A SANDWICH SHALLOW CYLINDRICAL PANEL WITH ORTHOTROPIC SURFACES

In this paper, the large deflection theory is adopted to analyse the geometrical nonlinear stability of a sandwich shallow cylindrical panel with orthoiropic surfaces. The critical point is determined and the postbitckling behaviour of the panel is studied.

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

How to ensure the safety of occupants has become a challenge for protective design of armored vehicles against intensive blast loadings.In this study,for armored vehicles subjected to shallow-buried explosions,an analytical model was established to characterize the dynamic performance of an all-metallic sandwich floorboard attached with a double mass-spring-damping system(mimicking seat and occupant),with the former consisting of a front face,a core and a rear face.For validation,numerical simulations with the method of finite elements(FE)were performed.Good agreement between analytical predictions and numerical results was achieved.The analytical model was then employed to quantify the effects of explosive mass,yield stress of material make,configurational parameters of sandwich panel,spring stiffness,and damping coefficient on dynamic response of the sandwich panel and double mass-spring-damping system.With increasing explosive mass and decreasing yield stress of material make,the peak displacements of rear face,seat and occupant were all found to increase.As core relative density was increased,these peak displacements also increased when the ratio of face thickness to core height was relatively small.Increasing the ratio of face thickness to core height led to increased peak accelerations of seat and occupant.The peak displacement of rear face was insensitive to the increase of either spring stiffness or damping coefficient,while the peak acceleration of occupant increased with increasing spring stiffness.Upon increasing the damping coefficient between the rear face and seat or that between the seat and occupant or both,the peak acceleration of occupant increased.With occupant safety duly considered,the proposed analytical model provides useful guidance for designing high-performance protective structures for armored vehicles subjected to intensive blast loadings.

Structural modeling of sandwich structures with lightweight cellular cores

An effective single layered finite element （FE） computational model is proposed to predict the structural behavior of lightweight sandwich panels having two dimensional （2D） prismatic or three dimensional （3D） truss cores. Three different types of cellular core topology are considered： pyramidal truss core （3D）, Kagome truss core （3D） and corrugated core （2D）, representing three kinds of material anisotropy： orthotropic, monoclinic and general anisotropic. A homogenization technique is developed to obtain the homogenized macroscopic stiffness properties of the cellular core. In comparison with the results obtained by using detailed FE model, the single layered computational model can give acceptable predictions for both the static and dynamic behaviors of orthotropic truss core sandwich panels. However, for non-orthotropic 3D truss cores, the predictions are not so well. For both static and dynamic behaviors of a 2D corrugated core sandwich panel, the predictions derived by the single layered computational model is generally acceptable when the size of the unit cell varies within a certain range, with the predictions for moderately strong or strong corrugated cores more accurate than those for weak cores.

Sound absorption performance of acoustic metamaterials composed of double-layer honeycomb structure

The purpose of the research is to assess the sound absorption performance(SAP)of acoustic metamaterials made of double-layer Nomex honeycomb structures in which a micro-orifice corresponds to a honeycomb unit.For this purpose,the influences of structural parameters on the SAP of acoustic metamaterials were investigated by using experimental testing and a validated theoretical model.In addition,the sandwich structure was optimized by the genetic algorithm.The research shows that the panel thickness and micro-orifice diameter mainly affect the second resonant frequency and second peak sound absorption coefficient(SAC)of the structure.The unit cell size is found to influence the first and second resonant frequencies and two peaks of the SAC.An extremely low side-length of the honeycomb core decreases the SAP of the structure for low-frequency noise signals.Additionally,the sandwich structure presents a better SAP when the diameter of micro-orifices on the front micro-perforated panel(MPP)exceeds that of the back MPP.The sandwich structure shows better noise reduction performance after the optimization aiming at the noise frequency outside trains.

Foldcore Structures with Origami Initiators for Energy-Absorbing Sandwich Panels

Origami foldcore structures can be used in thin-walled sandwich panels to provide unique advantages over traditional honey-comb structures.For instance,their continuously connected space is available for flowing through cooling liquid or compact pipeline placement.However,origami foldcores suffer from relatively low-energy absorption.This paper proposes a new design of energy-absorbing foldcore structures for sandwich panels,including the geometric design,experimental tests,numerical parametric study,and theoretical estimation of energy absorption.Origami initiators are introduced to the Miura foldcores to induce a failure mode with more transverse folds,which is not common for regular foldcore structures.As a result,60%higher energy absorption and tunable load uniformity can be achieved.

Structural performance of a façade precast concrete sandwich panel enabled by a bar-type basalt fiber-reinforced polymer connector

In this study,a novel diagonally inserted bar-type basalt fiber reinforced polymer(BFRP)connector was proposed,aiming to achieve both construction convenience and partially composite behavior in precast concrete sandwich panels(PCSPs).First,pull-out tests were conducted to evaluate the anchoring performance of the connector in concrete after exposure to different temperatures.Thereafter,direct shear tests were conducted to investigate the shear performance of the connector.After the test on the individual performance of the connector,five façade PCSP specimens with the bar-type BFRP connector were fabricated,and the out-of-plane flexural performance was tested under a uniformly distributed load.The investigating parameters included the panel length,opening condition,and boundary condition.The results obtained in this study primarily indicated that 1)the bar-type BFRP connector can achieve a reliable anchorage system in concrete;2)the bar-type BFRP connector can offer sufficient stiffness and capacity to achieve a partially composite PCSP;3)the boundary condition of the panel considerably influenced the out-of-plane flexural performance and composite action of the investigated façade PCSP.

EXPERIMENTAL AND NUMERICAL STUDIES OF THE ANTI-PENETRATION PERFORMANCE OF SANDWICH PANELS WITH ALUMINUM FOAM CORES

Effects of face-sheet thickness and core thickness of sandwich panels, and shape of projectiles on the penetration resistance of sandwich panels were discussed, while typical pen- etration failure modes were presented. It was shown that the anti-penetration performance of sandwich panels was enhanced with the increase of face-sheet or core thickness; The penetration resistance of sandwich panels was shown to be strongest to blunt-shaped projectile impacts, weaker to hemispherical-nose-shaped projectile impacts, and weakest to conical-shaped projectile impacts. The corresponding numerical simulation was carried out using the finite element code LS-DYNA V970. Numerical results showed that the penetration time decreased with the increase of projectile impact velocity.

Dynamic response of ultralight all-metallic sandwich panel with 3D tube cellular core to shallow-buried explosives

The underbody of a vehicle system, either military or civil, is typically made of a relatively thin metallic plate, thus vulnerable to mine blast attacks. To improve the blast resistance, a multitude of protective structures have been proposed as attachments to the thin plate. In the present study, a novel ultralight all-metallic sandwich panel with three-dimensional(3D) tube cellular cores mounted to the vehicle underbody was envisioned as such a protective system. A metallic substrate(mimicking vehicle bottom)was placed above the proposed sandwich panel to construct a sandwich-substrate combinative structure. A series of sandwich panels having 3D tube cellular cores were fabricated via argon protected welding and laser welding. Mechanical responses of the combinative structure subjected to the denotation of 6 kg TNT explosives shallow-buried in dry sand were experimentally measured. Full numerical simulations with the method of finite elements(FE) were subsequently carried out to explore the physical mechanisms underlying the observed dynamic performance and quantify the effects of key geometrical parameters and connection conditions of the protective system. The performance of the proposed sandwich panel under shallow-buried explosives was also compared with competing sandwich constructions having equal mass. Finally, a preliminary optimal design of the 3D tube cellular core was carried out.