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This paper presents an analytical approach for buckling and postbuckling analysis for functionally graded graphene‐reinforced composite (FG‐GRC) toroidal shell segments with the trapezoidal or round corrugated core under the axial tension and compression. The considered shells are placed in a thermal environment and surrounded by an elastic foundation. Based on the von Kármán‐Donnell shell theory with geometrical nonlinearities, Stein and McElman approximation, and a homogenization technique for corrugated shells, the basic equations of shells are established. The previous homogenization technique is improved by adding the thermal forces in the internal force expressions. The shell‐foundation interaction is expressed using the model of the Pasternak assumption. The Ritz energy method is used to obtain the pre‐buckling and postbuckling behaviors of the shells, from which the critical buckling tensions and compressions can be investigated. The influences of FG‐GRC face sheets, corrugated core, and foundation on the buckling behavior of sandwich shells can be shown in the numerical analysis. Highlights: Postbuckling of toroidal shell segments with the corrugated core is analyzed.A homogenization technique is improved for the thermal forces in the core.The shells are made of functionally graded graphene‐reinforced composite.The nonlinear Kármán‐Donnell shell theory and Ritz energy method are applied.Special effects of input parameters on the buckling behavior are investigated. [ABSTRACT FROM AUTHOR]

Sandwich structures are often prone to catastrophic failure due to premature separation between the core and skin layers. Geometric parameters, such as the thickness of the skin and core, along with the materials used in their manufacturing, directly influence the resistance to separation between the skin and core. This study explores how variations in skin thickness affect both failure modes and maximum load capacity in sandwich structures, utilizing both experimental testing and numerical simulations. Specimens were categorized as intact and pre-debonded samples. Each specimen featured four different skin thicknesses (3, 6, 8, and 10 layers of composite laminated skins, with corresponding thicknesses of 0.68, 1.33, 1.73, and 2.1 mm respectively). The specimens incorporated a foam-filled square corrugated core and underwent 3-point bending tests. Results revealed a significant shift in the failure mode: initially observed as upper skin fracture (V-shaped failure), it transitioned to separation between skins and cores with increased skin thickness, particularly in the presence of pre-debonding. Notably, the predominant failure mode did not involve separation between the skin and core in specimens without a pre-existing crack. Furthermore, numerical simulations effectively demonstrated the accurate capture of failure modes and loads using the Hashin and cohesive zone model (CZM). [ABSTRACT FROM AUTHOR]

This paper presents an experimental examination of the compression demeanor of lightweight corrugated core composite (CCC) sandwich panel and corrugated core smart composites (CCSC) sandwich panels subjected to quasi‐static edgewise compression loading. The existence of shape memory alloy (SMA) wires and pre‐strain percentages of SMA are the indicators studied in this article. The fabrication procedure presented and the appraisement of the mechanical properties of the CCC and CCSC sandwich panels are expressed. The core geometry of samples is trapezoid corrugated made of aluminum. The facesheets are four layers of woven glass fiber/ epoxy laminated composite. For evaluation of the efficacy of the presence of SMA wires on mechanical specifications of sandwich panels, three SMA wires with various pre‐strain percentages (0%, 3%, and 6%) are embedded in each composite facesheet. Mechanical properties of all types of CCC and CCSC sandwich panels such as maximum force, critical damage force, specific strength, absorb energy, specific toughness, Young's modulus, and specific stiffness were evaluated. Results showed that the CCC sandwich panel has higher mechanical specifications than the CCSC sandwich panels with 0% and 3% pre‐strain. Also, increasing pre‐strained SMA wires improves all mechanical parameters of CCSC sandwich panels. CCSC sandwich panel with 6% pre‐strain has the highest compression properties than other sandwich panels. Maximum Force, Critical Damage Force, Specific Strength, Absorbed Energy, Specific Toughness, Young's Modulus, and Specific Stiffness of CCSC sandwich panel with 6% pre‐strain are 14.73 kN, 13.6 kN, 9.55 MPa/g, 26.61 kJ, 0.346 MJ/m3g, 4395 MPa and 0.61 kN/mm g, respectively. Highlights: Lightweight CCC sandwich panel and CCSC sandwich panel manufactured.Compression behavior of CCC sandwich panel and CCSC sandwich panel evaluated.Pre‐strained SMA wires improves energy absorption of CCSC sandwich panels.Higher specific toughness was obtained with 6% pre‐strain SMA.Presence of SMA wires with no pre‐strain cannot improve the specific strength. [ABSTRACT FROM AUTHOR]

Outstanding progress in manufacturing technology of fiber-reinforced composite materials, allows designers to go beyond classical design rules. Composites with variable stiffness are an innovative division of composite materials that provide more efficient designs for engineers due to their diverse design parameters. In this study, a straightforward methodology is presented for the design of sandwich panels with corrugated variable stiffness core. Based on the homogenization method, a unit-cell of the sandwich panel is used as a representative volume element for the sandwich panel with corrugated core. Due to multiple design variables, conventional numerical and analytical methods cannot be applied to variable stiffness composites, thus PYTHON/ABAQUS framework is developed to determine the extensional and bending behavior of unit-cells. Details of this framework including PYTHON scripting and ABAQUS finite element solver are given along with their corresponding functions. Furthermore, the elitist genetic algorithm is incorporated into a framework for the optimum design of variable stiffness cores. Two optimization problems, namely composites with variable thickness and variable angle are considered for unit-cells, and associated constraints, boundary conditions, and fitness functions are discussed in detail. In addition to the benefits of the proposed framework, the obtained results reveal notable enhancement in the extensional and bending behavior of unit-cell. Results reveal that corresponding displacements are significantly improved (up to 80%) when using the optimum variable thickness case. For variable angle cases, the improvement of displacements is up to about 28%. [ABSTRACT FROM AUTHOR]

An analytical approach for nonlinear buckling and postbuckling responses of corrugated-core toroidal shell segments with carbon nanotube (CNT) reinforced face sheets in thermal environment subjected to radial pressure is reported in this work. Three distribution laws of functionally graded CNT-reinforced layers and the trapezoidal and round forms of the corrugated core are investigated. An equivalent technique for corrugated panels is improved by adding thermal forces to model the behavior of the corrugated core. The nonlinear equations are formulated by using the geometrically nonlinear Donnell shell theory considering Pasternak's foundation. An algorithm to solve a system of nonlinear equations is established using the Ritz energy method with three shell deflection amplitudes. The postbuckling expressions between the compressive and tensile loads with maximal deflection and the critical compressive and tensile loads are determined. The numerically investigated examples present the significantly beneficial effects of corrugated core and functionally graded CNT-reinforced face sheets on nonlinear buckling responses of structures. [ABSTRACT FROM AUTHOR]

The nonlinear buckling behaviors of sandwich functionally graded graphene reinforced composite (FG-GRC) laminated toroidal shell segments with corrugated core under lateral pressure in thermal environment are reported in this study. Three distributed types of the FG-GRC face sheets and two forms of corrugation including the trapezoidal and round corrugations are considered. By adding the thermal forces into an existing equivalent technique, the behavior of the corrugated core is modelled. The nonlinear formulations can be obtained by using the nonlinear Donnell shell theory taking into account the shell-foundation interaction. The Ritz energy procedure is used for three states of deflection to obtain the postbuckling curve expressions of the load-maximal deflection. The bifurcation buckling type of critical buckling pressure is obtained in the explicit form. The numerical examinations present the significant effects of corrugated core and FG-GRC laminated face sheets on nonlinear buckling behaviors of shells. [ABSTRACT FROM AUTHOR]

• Nonlinear torsional buckling of toroidal shell segments is presented using the Ritz energy method. • The corrugated core sandwich toroidal shell segments with FG-GRC coatings are considered. • The thermal forces are added to improve the homogeneous model for the corrugated core. • Ritz energy method, Donnell shells theory, and Pasternak's foundation model are applied. • Effects of corrugated core, material and geometrical parameters on the buckling behavior of shells are investigated. An investigation on the nonlinear torsional buckling of corrugated core sandwich toroidal shell segments with functionally graded graphene-reinforced composite (FG-GRC) laminated coatings in temperature change is mentioned in this paper using the Ritz energy method. The complex configuration of sandwich toroidal shell segments with double curvatures and the combination of the corrugated core and the FG-GRC coatings create the special behavior of structures. A homogenization model for corrugated structures and the extended Halpin-Tsai model can be applied to estimate the stiffnesses of shells. The effects of uniform temperature change are taken into account by supplementing the thermal forces into the total forces of shells. The Donnell shell theory and Pasternak's foundation model are used to establish the total potential energy of the structures. Ritz energy method is applied, and the closed condition and circumferential stress are taken into account, the postbuckling curve expressions of torsion-deflection and torsion-twist angle are obtained in explicit forms. The numerically obtained examples can show the significantly beneficial effects of FG-GRC laminated coatings and corrugated core on nonlinear buckling responses of structures. [ABSTRACT FROM AUTHOR]

The deflection behavior of square sandwich panels with corrugated core of trapezoidal cross section at different pitch lengths and heights of trapezoidal pattern was investigated using the FEM analysis, where the panel size was fixed at total height of 13.6 mm and panel side length of 600 mm. FEM analysis was performed under the condition that four sides were fixed and uniformly distributed load was applied. With decreasing the pitch length, the panel deflection decreased. At extremely short pitch length, the panel deflection increased with decreasing the pitch length because the conversion of the external load into the shear force became ineffective by small amount of bonding area. On the other hand, with increasing the pattern height, the panel deflection increased. This behavior of deflection could be approximated by Gompertz curve, and the suppressive factor of deflection was considered to be the inclination angle of trapezoidal pattern. The larger the bonding width, the higher the inclination angle and the lower the pattern height of the inflection point. Moreover, with increasing the pattern height, the weight ratio of the panel decreased. This is because the reduction in the weight of the panel due to the thickness reduction is greater than the effect of increased deflection due to the increased pattern height. The product of panel deflection and weight ratio became minimal at a given pattern height. This suggests adaptability to weight reduction needs or stiffness needs by selecting the appropriate pattern height, and the compatibility for both needs can be met at the minimal point.

This study deals with experimental and numerical response of trapezoidal corrugated core sandwich panels made of ST37 subjected to oblique blast loading. Sandwich target plate is 270*270 mm that consist of front/ back plate with 1 mm and trapezoidal corrugated core with 0.7mm thickness. The experimental explosive was done at the end of four different blast tube with angle of 0°, 15°, 30° and 45°respect to sandwich target plate. The mass of explosive (C4) was 10g and the stand-off distance was constant at 300 mm. The results of numerical simulation, obtained using coupled Eulerian–Lagrangian (CEL) model at commercial ABAQUS/Explicit software. The results show good agreement between the numerical and the experimental values. The results show that with increasing angle of tilt from 0° up to 45°, the maximum displacement decreases. At the higher masses of explosive, this reduction in deformation will be greater than the lower masses of explosive. Also, due to directing a large part of the blast wave to out of the blast tube, the amount of plastic dissipation energy at the angle of 45 degrees is significantly reduced compared to other angles.

Corrugated cores with structural hierarchy are one types of advanced cores that inspired from nature. In this work, the bending behavior of a second order, hierarchical corrugated structure has been analyzed. Experimental tests are implied to sandwich panels with both first- and second-order corrugated core by means of three-point bending test. For trapezoidal core, finite element model is provided and numerical results are validated by experimental results. Then, the validated properties are used to model sandwich panel with first- and second-order corrugated cores. To make a correct comparison, out-of-plane shear modulus of mentioned cores is calculated. Further to classical approach of ASTM7250, based on the first-order shear deformation theory (FSDT), a closed-form solution is used to predict the out-of-plane core shear modulus and compared with ASTM procedure. Results reveal that including shear deformation effects, the determined shear modulus based on FSDT is larger than classical standard procedure. Furthermore, shear modulus of second-order corrugated core is smaller than first-order one of the same relative densities. [ABSTRACT FROM AUTHOR]

The present study experimentally evaluates delamination of hybrid corrugated-core sandwich structures in the mode II of failure under flexural loading. Three sandwich structures with different cores, including core with no reinforcement, trapezoidal reinforcement, and triangular reinforcement, were fabricated. The strain energy release rate (G) of each specimen was then measured in the mode II of crack growth. The R-curves of the specimens were also extracted using experimental data, and by photographing the crack growth. Furthermore, the effects of the initial crack length on the R-curve were measured. In the last phase of this study, the specimens were numerically modeled using the finite element method (FEM). The delamination of the core and face sheets was modeled using the cohesive zone method (CZM), and the load–displacement curves of the specimens were extracted and compared to those of experimental data. [ABSTRACT FROM AUTHOR]

The corrugated foam core sandwich construction is used in variety of structural applications. These structures are subjected to flexural, impact, edgewise compression and shear loads. Traditional process for manufacturing of sandwich panel is not suitable for making corrugated core sandwich panel. In this work a novel methodology has been developed for construction of corrugated foam core sandwich panel. The present study focuses on the flexural behaviour of sandwich panel by varying the foam densities and corrugated cell. Two types of densities with one cell and two cells are used. The sandwich employs a Glass Reinforced Polymer (GRP) orthotropic material for both the two outer skins and the inner core web. In particular, the core is designed to have uneven topology to cooperate with GRP skins in membrane and flexural properties by adding a corrugated foam core. At first, a comparison has been performed between different density foams. Initially, 40 kg/m³ with 1 unit cell and 32 kg/m³ with 1 unit cell are compared, and then the same densities are compared with 2 cells. Among all, 40 kg/m³ with two cells shows highest flexural strength compared to the other specimens. Also, the sandwich panel with an empty core has been tested to understand the strength of the face sheet and corrugated core. [ABSTRACT FROM AUTHOR]

This paper reports the relationship between the length of panel side and the deflection of the sandwich panels with corrugated core. The deflections of the sandwich panels having the lengths of panel side from 100 to 1300 mm and the height of the panel of 13.6 mm were determined by finite element method, where the four sides of the panel were rigidly fixed and a uniformly distributed load was applied to the top surface of the panel. The maximum deflection at the center of the panel increases with increasing the length of panel side, confirming that a power law is established between the length of panel side and the deflection. The scaling exponent of the sandwich panel was about 3.3 and this value was smaller than that of the single plate, i.e., 4. The ratio of the weight of the sandwich panel to that of the single plate having the same length of the panel side and the different thickness, which becomes same deflection compared to the sandwich panel, was found to be smaller as the length of the panel side becomes longer. This effect of weight reduction was possible to be estimated analytically. Smaller value of scaling exponent of the sandwich panel compared to that of single plate was found be related with that the normal force applied to the panel was effectively converted to the shear force at the bonding interface between the core and the bottom plate.

In this work, bending properties of five-layer sandwich panels with corrugated three-layer core are investigated both numerically and experimentally. Sheet metal forming is employed to construct the corrugated core and three-point bending tests are performed to experimentally evaluate the bending behavior of the panels. Besides, reliable finite element model is developed and validated by the experimental results. The results show that the phase difference of the external core has no considerable effect on the panel behavior. Next, the effect of orientation for the corrugated cores is studied for two 0/90/0 and 90/0/90 layups. The results show that bending rigidity of 90/0/90 is greater than other case due to more bending rigidity of the external cores. To design an optimum sandwich panel, genetic algorithm is utilized by constraining the mass and height of the panel. For optimization purpose, an analytical formulations that is validated by presented experimental and numerical results are used. Based on optimization results, optimized sandwich panel is constructed and exposed to TPB test. Good agreement is observed between all the numerical, analytical and experimental methods. The results indicate that the optimized configuration can achieve notable higher bending resistance in the same weight especially for the 90/0/90 case. Finally, an isotropic multilayered sandwich panel is introduced and optimized to overcome the drastic anisotropic properties of corrugated cores. The optimized isotropic panel have equal bending rigidity in two principal axes of the panel. [ABSTRACT FROM AUTHOR]

The mechanisms of projectile penetration of composite sandwich panel with empty, trapezoidal corrugated cores have been experimentally investigated. The panels have been designed to investigate the influences of specific parameters, like the fiber type of corrugated core, the projectile nose shape and the stacking sequence of face-sheets, on the impact performance from the aspects of sequential deformation, failure modes and associated mechanisms. Experimental results demonstrated that usage of Twill glass fiber in corrugated core is attained highest performance in term of energy absorption and residual velocity for the fully perforated specimens. Comparisons of panels with different stacking sequences for face-sheets verify that the corrugated core composite sandwich structures with ( 0 ° ∓ 45 ° 90 ° ) s stacking sequence is indicated the highest energy absorption. This panel is displayed a superior resistance over the ones with other stacking sequences. The hemispherical projectile is showed no deviation from the direct line of path flight relative to the conical and blunt projectile in the high velocity impact test. Moreover, the deviation of the projectile decreases the damage area in specimens. [ABSTRACT FROM AUTHOR]

The present research work investigated on the behavior of corrugated core composite sandwich panel (CCCS) with composite face-sheets reinforced by pseudo-elastic NiTi shape memory alloy (SMA) wires subjected to high-velocity impact experimentally. The number of SMA wires, their location, and their pre-strain percentage are the parameters studied in this investigation. The sandwich specimens were made by woven glass fibers/epoxy composite face-sheets strengthened by the SMA wires and Aluminum corrugated core and prepared using the wet hand lay-up method. Their behavior is evaluated under high-velocity impact test by a gas gun impactor testing machine. According to the results obtained, a significant change in the amount of energy absorption of the specimens containing SMA wires is observed. By increasing the number of the SMA wires, the energy absorption by the specimen is increased, but by pre-straining the SMA wires, the effect in energy absorption is significant. Also, when the projectile hits the SMA wire in CCCS, better properties in energy absorption can be observed. The results show that the energy absorption increased from 117.247 J for the specimen without the SMA wire to 128.749 J for the six SMA wires specimen. On the other hand, by applying the pre-strain to the SMA wires, the residual stresses in the specimens and hence the energy absorption in the specimen with six SMA wires with 3% pre-strain increased to 142.57 J. [ABSTRACT FROM AUTHOR]

A sustainable alternative for wood waste is turning them into structural panels since it adds value to the raw material and contributes to the sector's circular economy. Strand-based composites such as oriented strand board is a natural fit for these wood wastes. A molded core composite with sandwich geometry with trapezoidal core guarantees significant increases in the stiffness of the panel, enabling its use as structural components in civil construction. Therefore, in this study, the mechanical properties of OSB sandwich panel with trapezoidal core produced with Balsa wood (Ochroma Pyramidale) waste agglomerated with bicomponent castor oil polyurethane resin (phenol free) were evaluated. The results indicate that the panel under study presented properties in the longitudinal direction that enable its use as a structural component. [ABSTRACT FROM AUTHOR]

In this paper, a shear stiffness model for corrugated-core sandwich structures is proposed. The bonding area is discussed independently. The core is thought to be hinged on the skins with torsional stiffness. The analytical model was verified by FEM solution. Compared with the previous studies, the new model can predict the valley point of the shear stiffness at which the relationship between the shear stiffness and the angle of the core changes from negative correlation to positive correlation. The valley point increases when the core becomes stronger. For the structure with a angle of the core smaller than counterpart for the valley point, the existing analytical formulations may significantly underestimate the shear stiffness of the structure with strong skins. The results obtained by some previous models may be only 10 persent of that of the present model, which is supported by the FEM model. [ABSTRACT FROM AUTHOR]

All-metallic truncated conical sandwich shells with corrugated cores (TCSS) were investigated for crashworthiness under quasi-static oblique compression using a combined experimental and numerical approach. Subsequently, multi-objective optimization design of the TCSS was also performed by adopting the algorithm of NSGA-II to achieve maximum specific energy absorption (SEA) and minimum peak force ( F P ). Compared with a monolithic shell, the TCSS exhibits much higher SEA and lower F P under oblique loading, especially with its semi-apical angle set around 10° to 15°. The results provide valuable guidance for the application of truncated conical sandwich tubes in protective engineering, such as vehicle crashworthiness. [ABSTRACT FROM AUTHOR]

This paper reports the deflection behavior of the sandwich panel with corrugated core of trapezoidal cross section. The size of the top and bottom plates were 200 mm square, and the height of the sandwich panel was fixed at 13.6 mm. The models for finite element method were created by taking into account the geometrical limitations of the corrugated core due to the space between both plates and the manufacturing condition. The four sides of the sandwich panel were rigidly fixed, and a uniformly distributed load was applied to the surface of the top plate. The deflection always became maximum at the center of the panel. The analysis was performed by changing the inclination angle of the trapezoidal patterns of the core. It was found that there is an inclination angle of the patterns at which the deflection of the sandwich panel becomes minimal. The deflection of the corrugated core itself increased with decrease in the inclination angle of the trapezoidal patterns. On the other hand, the shear stress developed in the plates and the core increased with decrease in the inclination angle, which had the effect of reducing the deflection of the sandwich panel. It was found that these synergistic effects cause the minimal inclination angle occur. Moreover, the anisotropy of deflection of the sandwich panel, which is the difference in the deflection depending on the selected two sides of the panel when the relative two sides are fixed and loaded, was investigated. It was found that the anisotropy of deflection also became smaller at the inclination angle of the trapezoidal patterns at which the deflection of the panel became minimal.

Corrugated sandwich panels are widely used in engineering applications for their excellent energy absorption and lightweight. In this research, the mechanical response of aluminum corrugated sandwich panels subjected to three-point bending is investigated experimentally, numerically, and theoretically. In the experiments, the sandwich panels were loaded under two conditions, namely base indentation and node indentation. A parametric study is conducted by ABAQUS/explicit to investigate the effects of geometric configurations (corrugation angle, core height, and core thickness) on the deformation mode, peak force, and energy absorption. Both peak force and specific energy absorption vary with the geometric parameters. Theoretical models are further developed to predict the force–displacement curves of the panels under the two loading conditions. The theoretically predicted crushing force is in good agreement with both the experimental and simulated results. Finally, the non-dominated sorting genetic algorithm II is adopted to optimize the geometric configuration to improve the specific energy absorption and reduce the weight of corrugated sandwich panels. [ABSTRACT FROM AUTHOR]

All-metallic sandwich-walled cylindrical and conical structures for aerospace applications often require simultaneous excellent vibration and load-carrying capacities. In the present study, the free vibration and axial compression behaviors of cylindrical and truncated conical sandwich shells with corrugated cores are investigated using a combined experimental and numerical approach. Excellent agreement between experimental measurements and finite element simulations for representative vibration and axial compression characteristics is achieved. Parametric studies based on the response surface model are subsequently performed to quantify the influence of key geometrical parameters on vibration and axial compression performance. A multi-functional collaborative design to meet the requirement of high load-bearing capacity subjected to the constraint of low natural frequency is also carried out, which demonstrates the unique advantages of the novel sandwich-walled shells for aeronautical and astronautical applications. [ABSTRACT FROM AUTHOR]

This research aims to improve the blast performance of trapezoidal corrugated core sandwich panel under air blast loading. A finite element model for the prediction of dynamic responses of trapezoidal corrugated core sandwich panel was first proposed and validated by experiments. Based on the simulation results, kriging models were established to approximate the relationships between design variables and blast performances, and correlation analyses were carried out to investigate the effects of the design variables on the maximum back face deflection and specific energy absorption. It is found that any decrease in maximum back face deflection would always lead to undesirable deterioration in specific energy absorption, and the correlation relationships are associated with the stand-off distance. Using the developed kriging models, multi-objective design optimization was performed to seek trade-off solutions for the trapezoidal corrugated core sandwich panel under specific and variable stand-off distances. Results show that the design on Pareto fronts depended upon stand-off distance. Comparisons of the blast performance between optimized designs and initial designs turned out that there indeed existed a great potential in performance improvement. Importantly, careful examination of the responses of the optimized designs revealed some valuable design methods which should be useful for the engineering applications of trapezoidal corrugated core sandwich panel. [ABSTRACT FROM AUTHOR]

This paper aims to construct a lightweight and durable structure with different designs and construction methods using materials with low-weight characteristics and appropriate strength. In this regard, sandwich panels were made in filled and unfilled sine and square corrugated core, and for comparison of some mechanical behaviors of made specimens with each other, three-point bending tests were performed. Obtained results indicated that the use of polyurethane foam will significantly increase the energy absorption of the structure and extend the life of the structure. The amounts of absorbed energy of the foam-filled samples are 2 and 2.5 times of the foam-free ones for sine and square corrugated cores, respectively. Finally, a numerical analysis based on finite element solution using ABAQUS software by applying the properties of the samples was performed. [ABSTRACT FROM AUTHOR]

The effect of the parameters of the Johnson and Cook material model on the direct impact crushing behaviour of a layered 1050 H14 aluminium corrugated structure was investigated numerically in LS-DYNA at quasi-static (0.0048 m s−1) and dynamic (20, 60, 150 and 250 m s−1) velocities. Numerical and experimental direct impact tests were performed by lunching a striker bar onto corrugated samples attached to the end of the incident bar of a Split Hopkinson Pressure Bar set-up. The numerical impact-end stress-time and velocity-time curves were further compared with those of rigid-perfectly-plastic-locking (r-p-p-l) model. Numerical and r-p-p-l model impact-end stress analysis revealed a shock mode at 150 and 250 m s−1, transition mode at 60 m s−1 and quasi-static homogenous mode at 20 m s−1. The increase of velocity from quasi-static to 20 m s−1 increased the numerical distal-end initial peak-stress, while it almost stayed constant between 20 and 250 m s−1 for all material models. The increased distal-end initial peak-stress of strain rate insensitive models from quasi-static to 20 m s−1 confirmed the effect of micro-inertia. The numerical models further indicated a negligible effect of used material models on the impact-end stress of investigated structure. Finally, the contribution of strain rate to the distal-end initial peak-stress of cellular structures made of low strain rate sensitive Al alloys was shown to be relatively low as compared with that of strain hardening and micro-inertia, but it might be substantial for the structures constructed using relatively high strain rate sensitive alloys. [ABSTRACT FROM AUTHOR]

The behavior of different structures subjected to blast loads is always an important factor to study. Sandwich panels have a wide range of applications in different fields of engineering and the construction of some industrial and military structures. These panels are made of two sheets and an intermediate core. The core has a significant role in reducing the deflection and enhancing energy absorb of structure. In this article, the effect of the shape of the corrugated panel and the type of panel materials is investigated. Hence, the reaction of aluminum and steel sandwich panels subjected to blast loads has been investigated. In the process of analysis, four kinds of profiles, which are: rectangular, trapezoidal, triangular and elliptical, are considered as panel cores. the most deflection was for rectangular profiles and the least deflection was for triangular ones. Those panels which are completely made of aluminum or the panels with steel cores can sustain more strain energy by their back sheets. all the panels that are completely made of aluminum have more damped energy than others. Those panels which have only aluminum sheets or aluminum cores are placed next to whole aluminum panels in order to damped energy level. In the study of the joint effect of the type of materials and the shape of the core panel, the panel with the upper and back of the steel and aluminum core with the triangular shape has the most desirable.

With the extension of the applications of sandwich panels with corrugated core, sound insulation performance has been a great concern for acoustic comfort design in many industrial fields. This paper presents a numerical and experimental study on the vibro-acoustic optimization of a finite size sandwich panel with corrugated core for maximizing the sound transmission loss. The numerical model is established by using the wave-based method, which shows a great improvement in the computational efficiency comparing to the finite element method. Constrained by the fundamental frequency and total mass, the optimization is performed by using a genetic algorithm in three different frequency bands. According to the optimization results, the frequency averaged sound transmission of the optimized models in the low, middle, and high-frequency ranges has increased, respectively, by 7.6 dB, 7.9 dB, and 11.7 dB compared to the baseline model. Benefiting from the vast number of the evolution samples, the correlation between the structural design parameters and the sound transmission characteristics is analyzed by introducing the coefficient of determination, which gives the variation of the importance of each design parameter in different frequency ranges. Finally, for validation purposes, a sound insulation test is conducted to validate the optimization results in the high-frequency range, which proves the feasibility of the optimization method in the practical engineering design of the sandwich panel.

A novel sandwich panel with double-directional corrugated core is proposed in this paper. This complex-corrugated core makes the conventional detailed finite element analysis of large structures a tough work. Thus, an equivalent homogeneous method is proposed, the key of which is to obtain the equivalent property of this novel structure. The equivalent elastic modulus considering the effect of geometrical parameters is analytically derived and verified by finite element method. Besides, equivalent shear modulus and Poisson's ratios are obtained by finite element method. Three-dimensional detailed and equivalent models are established for further validation of this equivalent homogeneous method. Results show that elastic modulus predicted by analytical formulas is in good agreement with that by finite element method no matter how geometrical parameters change. It has been proved that stretching deformation is dominating in thickness direction, and only corrugation along loading direction can bear the load. The proposed novel sandwich structure owns better mechanical property than the conventional one with single-corrugated core. The result by equivalent model agrees well with that by detailed model, which means that this equivalent homogeneous method can well predict the macroscopic property of this novel structure. [ABSTRACT FROM AUTHOR]

In this study, a closed-cell aluminum foam was filled into the interspaces of a sandwich panel with corrugated cores to form a composite structure. The novel structure is expected to have enhanced foam-filled cores with high specific strength and energy absorption capacity. An out-of-plane compressive load under low-velocity impact was experimentally and numerically carried out on both the empty and foam-filled sandwich panels as well as on the aluminum foam. It is found that the empty corrugated sandwich panel has poor energy absorption capacity due to the core member buckling compared to that of the aluminum foam. However, by the filling of the aluminum foam, the impact load resistance of the corrugated panel was increased dramatically. The loading-time response of the foam-filled panel performs a plateau region like the aluminum foam, which has been proved to be an excellent energy absorption material. Numerical results demonstrated that the aluminum foam filling can decrease the corrugated core member defects sensitivity and increase its stability dramatically. The plastic energy dissipation of the core member for the foam-filled panel is much higher than that of the empty one due to the reduced buckling wavelength caused by the aluminum foam filling. [ABSTRACT FROM AUTHOR]

Stress analysis of adhesively bonded joints of sandwich structures is more complex. Only a few research works have studied this subject. The major obstacle is finding the stress distribution at the adhesive layer of sandwich structures under different loading conditions. This paper presents a study on stress distribution at the adhesive joints of the corrugated sandwich structure subjected to three-point bending using the cohesive zone model. Firstly, three cases of sandwich models with different types of glue on both longitudinal and transverse loading directions were calculated using cohesive zone model, and then the corresponding experiments were carried out and compared to prove the FEM results to validate the results through both load-displacement curves and failure deformation modes. Secondly, the cohesive zone model simulation was used to obtain the detailed stress distribution at the bonding joint with the effect of four major geometrical parameters: adhesive layer thickness, corrugated panel thickness, face panel thickness and adhesive joint width. Lastly, the results of stress analysis showed that the stress distribution is not uniform and is highly affected by the bonding joint's geometrical parameters, adhesive layer thickness and adhesive joint width. [ABSTRACT FROM AUTHOR]

Cone-shaped sandwich structures are extensively employed in various fields due to their excellent bearing efficiency and designability. In this work, the design approach and integrated manufacturing method for the carbon fiber reinforced plastic (CFRP) corrugated sandwich truncated cone (CSTC) are proposed to improve the anti-debonding ability and ensure the reliability of the sandwich cone. First, the theoretical model for the stiffness of the CSTC is derived, in which the conservative prediction and the upper limit considering the fiber orientation of the cone are derived. The multiple failure modes of the CSTC under axial compression are theoretically established. Then, the failure mechanism map of the CSTC is established to forecast the possible failure modes. The typical failure modes of local buckling, face fracture, and core buckling are captured by experiments and finite element analysis (FEA). The theoretical model of the stiffness and failure modes is verified by the experiments and FEA. The effect of the semi-vertex angle and circumferential cell number on the failure modes is revealed. Furthermore, a more comprehensive failure mechanism map is generated by altering the geometric parameters of the CSTC. The failure modes of Euler buckling and global buckling are acquired by the comprehensive failure mechanism map and verified by FEA. Finally, the optimum design of the CSTC structure is performed. The results show that the failure mode of face fracture has the best bearing efficiency. This research provides a solid foundation for designing and applying lightweight CSTCs in constructions, such as the adapter of launch vehicles. [Display omitted] • The structure design method and integrated preparation technology of CFRP corrugated sandwich truncated cone are proposed. • The theoretical models of the stiffness and failure modes of the CSTC under axial compression are derived and verified. • The conical sandwich structure is more prone to global buckling with the increase of the semi-vertex angle. • It is found that the failure mode of face crushing has the highest bearing efficiency in structural optimal design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wood veneers can be used to manufacture corrugated cores of sandwich panels. • Geometric imperfections of the corrugated core reduce its mechanical properties. • Cracks and wood defects will not significantly reduce the mechanical properties of the panels. • The density of panels with a corrugated core is three times lower than solid panels. The environmental issue in engineering approaches is critical due to the requirements of the circular economy. The main emphasis in this work was the experimental and numerical investigation method of wooden sandwich structures' bending characteristics with the corrugated core. It included the effect of natural, randomized gaps in veneer. In addition, the influence of the re-bending of the damaged beam on its mechanical properties was also investigated. The results show that beams are an excellent construction material. The modulus of elasticity of the beams, till failure, ranged from 1580 to 3247 MPa, and the bending strength from 3.3 MPa to 7.9 MPa. In the second bending test, these values decreased after revealing new cracks in the core. It has been shown that the greater the share of gaps, the lower the modulus of elasticity of the beams, the lower the strength, and the lower the value of the destructive force of the beam. Numerical calculations showed that the virtual beam model without imperfections and gaps was characterized by a maximum force of 11.5 % higher than the best beam with imperfections and gaps. The prepared numerical model correctly determined the damage in the core and confirmed its applicability in engineering practice. [ABSTRACT FROM AUTHOR]

Corrugated cardboard has waved cores with small flutes that prevent the use of detailed numerical models of whole structures. Many homogenization methods in the literature overcome this drawback by defining equivalent homogeneous plates with the same mechanical behaviour at a macro-mechanical scale. However, few homogenization works have considered complete structures, focusing mainly on beams or plates. For the first time, this study explores the application of homogenization approaches to larger structures as an aid in their design process. We also considered triple-wall boards rather than single- and double-wall configurations commonly addressed in the literature. To this end, we adapted the homogenization methods proposed by Talbi and Duong to analyze thin-walled stools made of triple-wall corrugated cardboard. Using a progressive design process, we performed an efficient stool design by removing material zones with lower stresses, with 35% less material, 35% lower vertical deflections, and 66% lower stresses than the initial design. Unlike other corrugated cardboard stools, this design comprises just one folded piece instead of three, thus saving storage space. These results demonstrate the utility of homogenization techniques as an aid in the design process of whole structures made of corrugated cardboard. Further research will consider buckling analysis.

This paper presents a finite element based parametric study of the dynamic response and strength of sandwich steel beams with either sinusoidal or trapezoidal corrugated core subjected to impulsive blast loads. The sandwich steel beams consists of flat top and bottom substrates made of Steel 1018 and four core layers of Steel 1008. The core layers are arranged with uniform and non-uniform thicknesses. The finite element model is validated with a set of shock tube experiments and thus makes it feasible for a present parametric design study of core configurations. Sinusoidal and trapezoidal core shapes as well as various core thickness arrangements are taken into consideration for comparing core crushing and buckling behavior and their performances in mitigating blast load effects onto the main structure. A unit-cell beam and a fully clamped sandwich beam are studied to elucidate the effect of core shapes and arrangement onto its dynamic response. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of curing history on the strength behaviour and cohesive properties of adhesively bonded corrugated sandwich structures with a structural adhesive. Three-point bending tests under both longitudinal and transverse loading directions were taken into account. The selected curing histories of adhesively bonded corrugated sandwich structures were: a) 2 h at temperature of 40 °C; b) 2 h at 40 °C and then 2 h at 60 °C; c) 2 h at 40 °C, then 2 h at 60 °C and 1 h at 80 °C. To predict adhesive joint mechanical behaviour with different curing conditions, bulk tensile, Double Cantilever Beam, and End-Notched Flexure tests were conducted for material characterisation and verification of the subsequent developed numerical analysis. The glass transition temperatures (T g) of the adhesive with different curing histories were determined using differential scanning calorimetry method. Crack propagation and stress distribution in the adhesive layer was simulated using the bilinear traction-separation law of Cohesive Zone Model. The predicted critical ultimate loads and the corresponding failure modes were proved to be in good correlation with the experimental observation. The presented study revealed that gradual step-wise increasing in curing temperature and duration can effectively strengthen the mechanical performance and fracture resistance of adhesively bonded corrugated sandwich structures. • Experimental characterisation on the effect of curing histories on the material properties of structural adhesive. • FE prediction on the mechanical performance of ABCSS with different curing histories under three-point bending load. • The predicted ultimate loads and failure modes of ABCSS were analysed, showing the dangerous locations of failure occurrence. [ABSTRACT FROM AUTHOR]

A combined theoretical, numerical and experimental investigation of the integrated thermal protection system based on C/SiC composite corrugated core sandwich plane structure was conducted. Corrugated core sandwich plane structure was made from carbon fiber reinforced silicon carbide composite by a hot compression molding combined with precursor infiltration and pyrolysis method. The equivalent thermal conductivity prediction method for the C/SiC composite corrugated core sandwich plane was developed, and its heat transferring behavior was numerical analyzed. Based on the theory and numerical analysis, a novel integrated thermal protection system, which was consisted of three parts: C/SiC composite corrugated core sandwich plane, insulated aerogel filling in the core, and insulated aerogel adhering onto the down surface of the down facesheet, was designed, manufactured and examined by simulated atmospheric re-entry wind tunnel test. It was believe that this novel design of integrated thermal protection system is a potential thermal protection system for the next generation hypersonic flights. [ABSTRACT FROM AUTHOR]

The impact strength, energy absorption, and failure modes of hybrid sandwich panels with corrugated aluminum core and laminated composite face-sheets are investigated. Numerical simulation of hail impact of hybrid sandwich panels is presented using LS-DYNA software. The effects of hail projectile shape, face-sheet stacking sequences, and reinforcement type on the impact response of sandwich panels are investigated. The standard test specimens of the composite face-sheets are manufactured and experimentally evaluated to obtain required mechanical properties of the lamina for hail impact simulation. The results presented herein revealed that [ 90 ° / ∓ 45 ° / 0 ° ] s laminated composite face-sheets achieved the lowest damage. The hail projectile with sharper nose created higher damage on hybrid sandwich panels. The glass/epoxy face-sheets of corrugated core hybrid sandwich panel presented a significant improvement in impact response and failure modes compare to carbon/epoxy. [ABSTRACT FROM AUTHOR]

Novel ultralight all-metallic truncated conical sandwich shells (TCSS) with corrugated cores are designed and fabricated using the molding process. Quasi-static axial compression tests are performed to investigate the crushing behaviors of the proposed structure, with focus placed upon its peak strength and energy absorption capacity as well as the interaction effect of its face-sheets and corrugated core during the crushing process. Detailed parametric study with three-dimensional finite element simulations is subsequently carried out to further explore the failure mechanisms as well as the influence of key geometrical parameters. Finally, the response surface models of specific energy absorption (SEA) and peak force (PF) are established with key design variables, and the Pareto fronts in terms of maximum SEA and minimum PF are obtained. Relative to monolithic conical shells having equal mass, the SEA of the TCSS is significantly greater while the PF is smaller, attractive for energy absorption applications demanding high levels of crashworthiness. • Novel all-metallic truncated conical sandwich shells with corrugated cores are proposed. • The structure has coupling effect during crushing process, which shows better energy absorption characteristics. • Quasi-static axial compressive behaviors including collapse modes and deformation mechanisms are systematically studied. • Parametric discussion and multi-objective optimization is performed. [ABSTRACT FROM AUTHOR]

This study examined the applicability of the equivalent core concept, which replaces a discrete core with a homogenized solid core representing its elastic properties, on a large-scale structure. To this end, numerical verifications were performed for corrugated core structures at two levels, the specimen level and structural level. Before the verifications, analytical equations were gathered from previous reports to obtain the homogenized elastic properties of corrugated cores. At the specimen-level verifications, the maximum deflections of the corrugated core panel specimens subject to three-point bending were calculated with sandwich beam theory, finite element models with discretely modeled cores and equivalent cores. For the structural-level verifications, the maximum deflection and natural frequency were computed from a discrete finite element model and an equivalent model of a railway car body structure. The results revealed that the equivalent models gave excellent agreement with the theoretical values if the same underlying boundary conditions were used; however, greater discrepancies were observed with the discrete models. In addition, for the structural-level verifications the equivalent core model reasonably approximated the discrete model with marginal accuracy. Therefore, employing the equivalent core concept can be expected to save computational costs in the initial design stage of large-scale structures. [ABSTRACT FROM AUTHOR]

Abstract Increasing the development in industrial technology and need for energy absorption, lightweight and cost effective composite materials such as composite sandwich panels have been in the center of attention. In this paper energy absorption properties of proposed composite sandwich panels with different corrugated core geometries under quasi static out of plane loading conditions is experimentally investigated. Three different corrugated shapes, i.e. rectangular, trapezoidal and triangular fabricated with the same thickness are used. The specimens were subjected to three different quasi-static compression loading condition i.e. concentrated, linear and planar. The effect of the number of unit cells and corrugated core geometries in determining the overall deformation and local collapse behavior of the panels also investigated. Based on the comparative results, it is found that three unit cell rectangular corrugated geometry possessed the best performance than other types of corrugated core geometries. Moreover, through visual observation the damage mechanisms under loading conditions and subsequent failure modes are inspected. Plastic buckling of cell walls and foam densification identified as the initial failure modes and by continuing the loading, fiber breakage, localized delamination as well as debonding between the skins and the core were the main damage mechanisms in these corrugated systems. Highlights • Characterization the effects of different corrugated core on energy absorption of sandwich panels. • Damage mechanism identification of sandwich panels under compressive loading conditions. • Performance of woven glass fibers as corrugation elements for infilled sandwich panels. [ABSTRACT FROM AUTHOR]

A series of experimental tests have been carried out on three types of novel sandwich panels mainly designed for application in lightweight mobile housing. Two types of the panels are manufactured entirely from wood-based materials while the third one presents a combination of plywood for surfaces and corrugated thermoplastic composite as a core part. All sandwich panels are designed to allow rapid one-shot manufacturing. Mechanical performance has been evaluated in four-point bending comparing the data to the reference plywood board. Additionally, finite element simulations were performed to evaluate global behavior, stress distribution and provide the basis for a reliable design tool. Obtained results show sufficient mechanical characteristics suitable for floor and wall units. Compared to a solid plywood board, sandwich alternative can reach up to 42% higher specific stiffness, at the same time maintaining sufficient strength characteristics. [ABSTRACT FROM AUTHOR]

Abstract Ultralight all-metallic sandwich cylindrical shells with corrugated cores are designed and fabricated using a method involving tamping and shape correction. Quasi-static axial compressive behaviors of the sandwich shells are investigated using a combined experimental, theoretical and numerical approach. Based on the analytical model and numerical approach, systematic parametric study is carried out to explore the effects of key geometrical parameters on the failure load and energy absorption capacity. Minimum weight design as a function of the failure load is subsequently carried out for the proposed sandwich shell. As an attempt for further performance enhancement, the foam-filled corrugated-core sandwich cylindrical shell is proposed and a preliminary experimental study is carried out. The superiority of sandwich shells over monolithic shells in terms of initial failure load and energy absorption is clearly demonstrated, potentially important for applications demanding simultaneous ultra-lightweight, load-bearing and energy absorption. Graphical abstract Unlabelled Image Highlights • Novel all-metallic sandwich cylindrical shells with corrugated cores are proposed. • Quasi-static axial compressive behavior including initial collapse and folding deformation is studied. • The superiority of sandwich shells over monolithic shells in terms of initial failure load and energy absorption is dramatic. [ABSTRACT FROM AUTHOR]

This paper addresses the dynamic loading characteristics of the shock tube onto sandwich steel beams as an efficient and accurate alternative to time consuming and complicated fluid structure interaction using finite element modeling. The corrugated sandwich steel beam consists of top and bottom flat substrates of steel 1018 and corrugated cores of steel 1008. The corrugated core layers are arranged with non-uniform thicknesses thus making sandwich beam graded. This sandwich beam is analogous to a steel beam with web and flanges. Substrates correspond to flanges and cores to web. The stress-strain relations of steel 1018 at high strain rates are measured using the split-Hopkinson pressure. Both carbon steels are assumed to follow bilinear strain hardening and strain rate-dependence. The present finite element modeling procedure with an improved dynamic impulse loading assumption is validated with a set of shock tube experiments, and it provides excellent correlation based on Russell error estimation with the test results. Four corrugated graded steel core arrangements are taken into account for core design parameters in order to maximize mitigation of blast load effects onto the structure. In addition, numerical study of four corrugated steel core placed in a reverse order is done using the validated finite element model. The dynamic behavior of the reversed steel core arrangement is compared with the normal core arrangement for deflections, contact force between support and specimen and plastic energy absorption. [ABSTRACT FROM AUTHOR]

Abstract The crushing behavior of a multilayer 1050 H14 aluminum corrugated core was investigated both experimentally and numerically (LS-Dyna) using the perfect and imperfect models between 0.0048 and 90 m s−1. The dynamic compression and direct impact tests were performed in a compression type and a modified Split Hopkinson Pressure Bar set-up, respectively. The investigated fully imperfect model of the corrugated core sample represented the homogenous distribution of imperfection, while the two-layer imperfect model the localized imperfection. The corrugated core experimentally deformed by a quasi-static homogenous mode between 0.0048 and 22 m s−1, a transition mode between 22 and 60 m s−1 and a shock mode at 90 m s−1. Numerical results have shown that the stress-time profile and the layer crushing mode of the homogeneous and transition mode were well predicted by the two-layer imperfect model, while the stress-time profile and the layer crushing mode were well approximated by the fully imperfect model. The fully imperfect model resulted in complete sequential layer crushing at 75 and 90 m s−1, respectively. The imperfect layers in the shock mode only affected the distal end stresses, while all models implemented resulted in similar impact end stresses. The distal end initial crushing stress increased with increasing velocity until about 22 m s−1; thereafter, it saturated at ~2 MPa, which was ascribed to the micro inertial effect. Both the stress-time and velocity-time history of the rigid-perfectly-plastic-locking model and the critical velocity for the shock deformation were well predicted when a dynamic plateau stress determined from the distal end stresses in the shock mode was used in the calculations. [ABSTRACT FROM AUTHOR]

Profiled hollow core sandwich panels (SPs) and their components (outer layers and core) were manufactured with ponderosa and lodgepole pine wood strands to determine the effects of low-velocity impact forces and to observe their energy absorption (EA) capacities and failure modes. An instrumented drop weight impact system was applied and the tests were performed by releasing the impact head from 500 mm for all the specimens while the impactors (IMPs) were equipped with hemispherical and flat head cylindrical heads. SPs with cavities filled with a rigid foam insulation material (SPfoam) were also tested to understand the change in EA behavior and failure mode. Failure modes induced by both IMPs to SPs were found to be splitting, perforating, penetrating, core crushing and debonding between the core and the outer layers. SPfoams absorbed 26% more energy than unfilled SPs. SPfoams with urethane foam suffer less severe failure modes than SPs. SPs in a ridge-loading configuration absorbed more impact energy than those in a valley-loading configuration, especially when impacted by a hemispherical IMP. Based on the results, it is evident that sandwich structure is more efficient than a solid panel concerning impact energy absorption, primarily due to a larger elastic section modulus of the core’s corrugated geometry. [ABSTRACT FROM AUTHOR]

A preliminary experimental evaluation of duration of load and creep effects of lightweight wood-strand sandwich panels (lwW-SSP) was conducted following ASTM D6815-09 to determine the equivalence to the duration of load and creep effects of visually graded lumber as specified in Practice D245. The modulus of rupture (MOR) of lwW-SSP was obtained using four-point bending tests to evaluate their creep and load behavior at three stress levels (15, 40 and 65% of MOR). Two different widths were considered to observe the effect of this parameter. lwW-SSP preformed well under long-term loads, as tertiary creep was not observed at all stress levels and the strain rate decreased over time. The panels met the criteria specified in the standard. None of the specimens failed, the creep rate decreased and the fractional deflection was <2. Accordingly, the duration of load factors of visually graded lumber is applicable to these panels. For the theoretical evaluation of solid wood behavior, viscoelastic models can also be applied to describe the creep behavior of lwW-SSP with wood-strand corrugated cores. An exponential viscoelastic model consisting of five elements accurately approximates the experimental creep behavior of three-dimensional (3D) core sandwich panel. [ABSTRACT FROM AUTHOR]

Optimal structure of thermal barrier skins used for rescue vehicles experiencing extreme conditions is developed. The conditions include extreme arctic cold and possible extreme heat of burning oil. The skin structure includes fibrous insulation material as well as external active cooling system using sprinklers. Optimal design variables, for the best combinations of the thermal and mechanical performances – the panel geometry and the discharge density – are examined by the analytic and numerical means. It is shown that the high discharge density in the cooling system may be necessary not only for the thermal protection, but also to provide the strength of the panel elements. In particular under the considered loading conditions, the solution of the optimization problem with all constraints exists only for the enough high discharge density due to the thermal buckling of the web elements inside the panel under non-uniform heating. [ABSTRACT FROM AUTHOR]

Graded lightweight structure is a new trend to improve energy absorption capacity of such structural materials. This study aims at the influence of property gradients on the overall behavior of graded multilayer sandwiches with corrugated cores under impact loading. The design of the property gradient of graded multilayer sandwiches as well as the manufacturing of different corrugated cores is presented at first. The graded multilayer sandwich is tested under various experimental configurations at rather low (9 m/s) and high (38 m/s) impact velocities. It turned out that no influence of gradient is found for low impact velocity because a quasi-static equilibrium state is reached. However, at high impact velocity, the test revealed a significant difference between different property gradient profiles. Numerical models are also built to simulate those tests. It allows for the further numerical analysis on a larger range of gradient profiles and higher impact velocities. A general trend for the design of the graded multilayer sandwiches with corrugated cores to improve energy absorption efficiency is proposed, which consists of placing the weakest layer near the protected structure and the hardest layer near the impacted end of the graded sandwich. [ABSTRACT FROM AUTHOR]