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In this study, PMI foam and aluminum foam are used as reinforcement materials for filling the cells of carbon fiber-reinforced composite square honeycomb sandwiches (CSHSs), forming two new sandwich structures, namely, PMI foam-reinforced CSHS (PRCSHS) and aluminum foam-reinforced CSHS (AFRCSHS). The impact resistance and residual flexural performance of the composites is compared by using low-velocity impact (LVI) and three-point bending (3 PB) experiments. The different impact energy levels of 25 J, 50 J, 65 J, and 100 J are applied. The impact and bending failure process and failure mechanism are analyzed using a combination of industrial computed tomography (ICT) and scanning electron microscopy (SEM). PRCSHS and AFRCSHS are compared for various enhancement effects and their resulting lightweight features. The residual flexural and impact resistance properties of the two sandwiches improved significantly. Compared with CSHS, the maximum impact load of PRCSHS and AFRCSHS increased by 115.6% and 78.9%, respectively. Moreover, the impact energy absorption, residual flexural load, and residual flexural energy absorption increased by 30.9% and 21.3%, 80.7% and 58.5%, and 173.1% and 84.3%, respectively. The PRCSHS was noticeably lightweight, but AFRCSHS was not sufficiently lightweight. The qualitative results of comparison of the two reinforcement materials in this study can be extended to other carbon fiber-reinforced all-composite 2D honeycomb sandwiches. [ABSTRACT FROM AUTHOR]

This study introduces a novel three-dimensional orthogonal accordion structure (3D-OAS) as the cellular core of sandwich panels, achieving multi-directional zero Poisson's ratio through the orthogonal combination of two-dimensional accordion structures. To analyze its static characteristics effectively, a two-dimensional equivalent Reissner–Mindlin model (2D-ERM) was established utilizing the variational asymptotic method (VAM). The accuracy of 2D-ERM was confirmed by conducting three-point bending tests on 3D-printed specimens and analyzing the in-plane and out-of-plane deformation results of the 3D finite element model (3D-FEM). The comparison of global displacement contours and path-displacement curves between 3D-FEM and 2D-ERM showed a high level of agreement in predicting static deformation. The equivalent stiffness of SP-3D-OAS steadily increased as the inclined angle deviates by 90-degree, irrespective of whether it pertains to the convex or concave angle. Evaluation of deformability in sandwich panels with different cellular core forms revealed superior comprehensive performance in 3D-OAS, followed by 3D-YRS and 3D-XYAS, with a reduction of 16.41% and 17.35% in specific stiffness, respectively. Compared to the 3D-FEM, 2D-ERM significantly reduces computation time without compromising engineering accuracy. The research results provide a useful reference for optimal design of sandwich panels with multi-directional ZPR cellular core. [Display omitted] • Introducing 3D-OAS with multi-directional ZPR effect in sandwich panels. • Validating the accuracy of the equivalent model through 3-point bending test. • The panel's stiffness increases as the inclined angle deviates from 90-degree. • Extending strut in the 3D-OAS improves the panel's specific stiffness. • 3D-OAS exhibits a more uniform distribution of local stress–strain fields. [ABSTRACT FROM AUTHOR]

An auxetic material can use the negative Poisson ratio to make the impact area denser and better absorb energy. This unique behavior can be exploited for building sandwich panels that absorb more energy per unit of weight. This work proposes a methodology to design lightweight auxetic-core sandwich panels with enhanced impact energy absorption capability. The method is based on an optimization framework whose function is a parameterized Finite Element model of a 3D auxetic structure. Metamodeling is used instead of direct optimization. The performance of different surrogate models, including Artificial Neural Networks, are computed and the best-ranked model is used for the subsequent optimization task carried-out with the aid of a genetic algorithm. The applicability of the framework is demonstrated by creating a sandwich panel with a 3D reentrant auxetic core subjected to a ballistic load, which is 36% lighter than the baseline design and 28% thinner than the literature reference honeycomb sandwich. [ABSTRACT FROM AUTHOR]

• Self-balancing hyperboloid multilayered sandwich panel was designed and prepared. • Performances under CHEMICAL and simulated nuclear explosion tests were revealed. • Self-balancing hyperboloid multilayered sandwich promotes explosion resistance. • Fills of polyethylene foams serve to enhance the structure's blast resistance. • The structure is lighter but has smaller deflection even the pressure is greater. This study introduces an innovative protective structure featuring a hyperbolic multilayered sandwich design with hybrid cores. The structure integrates orthogrid and fold-cores, which can be supplemented with polyethylene foams to enhance energy absorption. Experimental evaluations, including chemical explosions and simulated nuclear blasts, were conducted on these self-balancing hyperboloid folded-core sandwich panels (SHFSPs). The results indicate that the SHFSPs successfully resisted the impact of 0.7386 m/kg1/3 and a simulated nuclear explosion with a peak pressure of 0.75 MPa, showing no signs of damage. Additionally, after filled with foam, the SHFSPs endured a chemical explosion of 0.5894 m/kg1/3 and a simulated nuclear blast with a peak pressure of 0.80 MPa, remaining undamaged. This study underscores the SHFSPs' potential as a robust blast-resistant solution, suitable for a variety of engineering applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Building and construction waste contributes to global carbon emissions, leading to the need to seek alternative materials that are more environmentally friendly. Mycelium Biocomposite (MB) is a sustainable material that utilizes agricultural waste as its main substrate and can be degraded after-use. This study aimed to investigate mechanical performance of additional layers in sandwich panel fabrication of MB. The experiment was conducted in two phases including (1) Composite 1: Oil Palm Empty Fruit Bunch (OPEFB) fiber layer with pine resin and (2) Composite 2: MB sandwich panel. In Composite 1, the mechanical test results showed the S50 sample (50 % fiber and 50 % resin) had the highest tensile strength of 0.18 N/mm² and was selected as the surface layer. In Composite 2, the variable of layer binder was produced using mycelium hyphae (MB-M) and resin (MB-R). The results of the physical, mechanical, and thermal properties tests were compared with the JIS A 5905:2003 standard and previous studies. The MB sample (no layer) had the best mechanical and thermal conductivity values due to the binding method effects, such as flexural strength at 25.38 N/mm² and bending strength at 0.53 N/mm². MB-M showed incomplete drying that caused lower tensile strength and higher thermal conductivity. Meanwhile, MB-R showed mechanical values similar to MB, such as flexural strength at 21.22 N/mm² and bending strength at 0.52 N/mm². Yet, MB had higher thermal conductivity, where MB-R showed 0.1558 W/mK and MB showed 0.1037 W/mK, due to Composite 1 addition. This study suggests the development of MB thermal values and considers its application as non-structural insulation panels. • Sustainable alternative material: Mycelium Biocomposite (MB) with additional layer in sandwich panel fabrication. • Oil Palm Empty Fruit Bunch (OPEFB) with pine sap bioresin binder as additional layer. • Investigating physical, mechanical and thermal properties of Mycelium Biocomposite (MB). • Mycelium Biocomposite (MB) sample with no additional layer has a high mechanical and thermal conductivity value. • MBs exhibit potential as renewable materials and alternative insulation panels for non-structural insulation panels. [ABSTRACT FROM AUTHOR]

The paper investigated the experimental study of composite spherical-roof contoured-core (SRCC) sandwich panels under a V-shaped quasi-static indentation (QSI) test. The carbon fiber, glass fiber, aramid fiber, hybrid carbon/aramid, and glass fiber chopped strand mat sheets were used to manufacture the composite cores, which used the hand layup and hot compression techniques. The polylactide (PLA) core was fabricated using fused deposition modelling (FDM). The V-shaped indenter had a 65° angle and was set at 1 mm/min as indentation speed in the experimental test. It was found that the maximum indentation deflection was 35.49 mm on the SRCC sandwich panel with a hybrid carbon/aramid core compared to other composite cores. Furthermore, it was localized fiber fracture, matrix damage, delamination, inwards fronds, and debonding damage mode on composite SRCC sandwich panels, which was visually shown at the central SRCC core unit cell. It is highlighted that aramid fiber and hybrid carbon/aramid materials can provide outstanding impact characteristics, which have great potential to be used as impact-resistant sandwich structures. [Display omitted] • Composite spherical-roof contoured core (SRCC) sandwich panels are manufactured. • The impact damage of composite sandwich panels is determined under the V-shaped quasi-static indentation loading. • The hybrid carbon/aramid SRCC core sandwich panel exhibits the maximum indentation deflection of 35.49 ± 2.63 mm. • Carbon fiber-reinforced plastic SRCC core sandwich panel had the highest peak load mass ratio value of 17.92 ± 0.32 N/g. [ABSTRACT FROM AUTHOR]

This study investigated the in-plane shear responses of four types of connectors (single-strand truss, double-strand truss, grid-type, and I-shaped) in precast concrete sandwich panels (PCSPs). The influence of connector type, connector arrangement, and wythe material on the shear performance was discussed through in-plane shear tests and finite element analysis. The failure modes and test results of the four types of connectors were closely related to their shear resistance mechanisms. Changing the connector arrangement method from continuous along the length to discrete arrangement improved connector damage extent and toughness index (TI). The substitution of ordinary concrete with ECC or UHPC in wythes can prevent the wythes failure and enhance peak load (P m). The finite element (FE) model using the Hashin damage model and randomly generated fibers can accurately capture the shear response of the connectors within PCSP. The damage factor was introduced for quantitative analysis of the damage processes in connectors and wythes and corresponding damage evolution model was developed. Furthermore, the damage evolution model was applied to characterize the degradation of shear stiffness in the load-slip curve, and a load-slip theoretical model that accounted for the progressive development of damage was established. • Two novel connectors, the grid-type connector and the I-shaped connector, were introduced. • In-plane shear performance of four types of connectors in PCSPs made of high-performance concrete was investigated. • A damage factor was introduced to quantitatively analyze the damage process of connectors and wythes. • A load-slip theoretical model that accounted for the progressive development of damage was established. [ABSTRACT FROM AUTHOR]

The novel sandwich panel with egg-shaped honeycomb-grid core (SP-EHC), formed by chamfering the grid walls, can achieve a balance between lightweight and high-strength, as well as promote effective ventilation and drainage due to the semi-closed honeycomb design. To determine the panel's equivalent stiffness properties, an asymptotic analysis of the energy functional stored within the periodic unit cell is conducted. On this base, a 2D pseudo-equivalent model (2D-PEM) in the form of the Reissner–Mindlin model was formulated. The pseudo-excitation method was employed to analyze the self-power spectral density function and root mean square response of the 2D-PEM under random vibration. The accuracy and effectiveness of the model were validated through comparisons of the three-point bending experimental results of the 3D-printed specimen, exhibiting relative errors of 2.95%. In addition, free and random vibration analyses were conducted on the hybrid SP-EHC to further validate the model. Furthermore, the influence of material and structural parameters on specific stiffness, natural frequencies and first velocity RMS was systematically investigated. The findings reveal that enhancing the grid wall's chamfering ratio is beneficial in achieving the desired objectives of lightweight and high-strength. In addition, compared to sandwich panels with orthogonal and pyramid grid cores, this improvement positively impacts the vibration characteristics of the sandwich panel. These findings offer valuable insights for the future design and optimization of such sandwich panels. [Display omitted] • A novel chamfered grid wall design creates a semi-closed egg-shaped honeycomb-grid core. • Static and dynamic analysis employ a 2D pseudo-equivalent model established using the VAM. • The impact of material and geometric parameters on the effective performance of SP-EHG is investigated. • The dynamic performance of SP-EHG is significantly influenced by the chamfering ratio. • SP-EHG combines lightweight composition and multifunctional characteristics. [ABSTRACT FROM AUTHOR]

The low stiffness resulting from substantial core porosity within the re-entrant honeycomb sandwich panel can be addressed by introducing rib-reinforcements. To investigate its static and vibration characteristics, an energy-based 2D equivalent-homogenization model (2D-EHM) was derived through asymptotic analysis of the leading terms in the governing equations considering the energy-related characteristics. The accuracy of the constructed model for predicting the elastic bending performance of the sandwich panel was verified by comparing the results of a three-point bending experiment with 3D-printed specimens. Comparative analysis with a 3D FE model demonstrates that the 2D-EHM exhibits maximum errors of only 4.65% and 6.46%, respectively, in analyzing static deformation and natural frequency while improving computational efficiencies by up to 59- and 173-folds. Parameter analysis reveals that the performance of SP-RRH is minimally affected by the reinforcement-to-honeycomb wall thickness ratio. However, its performance is compromised when the honeycomb walls align in an equilateral triangle with the reinforcing walls. Comparing specific stiffness as well as static and vibration characteristics of sandwich panels with different core configurations (including traditional and diamond reinforced re-entrant honeycombs) shows that inclusion of rib reinforcements enhances deformation resistance and natural frequencies through increased specific stiffness. These findings provide valuable insights for optimizing design of re-entrant honeycomb sandwich panels. [Display omitted] • VAM-based 2D model of SP-RRH accurately validated against 3D-FEM results. • Equivalent stiffness obtained via asymptotic analysis of unit cell's energy functional. • The tailorability of the unit cell facilitates the customization of its properties. • Rib-reinforcing walls enhance deformation resistance of sandwich panels. • The performance of SP-RRH is influenced by equilateral triangular cellular structure. [ABSTRACT FROM AUTHOR]

Composite materials are very attractive options for aerospace and aeronautical industries particularly because of their high strength to stiffness ratio. The main design requirements for any space craft or aircraft is the strength to weight ratio. The composite material become significant mainly because these materials can be designed based on the material required properties. Today we find a huge variety of composite materials like Fiber Reinforced Composites, Particle Reinforced Composites, Sandwich Panels, Metal Matrix Composites, and Ceramics Matrix Composites differing substantially in build-up, matrix and reinforcement type, fiber reinforced composites are very common in space industry applications. Composites are non-magnetic making them a desired material for aircraft applications. This paper is further extension of Ref. [7] to calculate the weight reduction of a single windowpane. Spider silk has properties which make it stiffer than Kevlar and steel. This material could drastically reduce the amount of material used in various engineering fields like civil, mechanical etc. In this paper we analyse a structural model of an aircraft windowpane and the results are compared against the standard material currently used in industry. The excellent elastic properties of spider silk material making it an ideal fiber material for composites. The composite material has spider silk fibers as reinforced material and epoxy as matrix material. Reduced weight calculations without compromising the performance of the structure has been carried out in this research paper. • Reinforcing composite material with epoxy as matrix material and spider silks and reinforced fibers. • Calculating the physical and mechanical properties of composite material based on matrix and fiber material. • Demonstration of weight reduction of Airplane's windowpane without compromising its strength. • Reduced thickness of windowpane by lowering the number of laminates in the composite material model. • Increased strength to weight ratio of composite materials compared to acrylic material. [ABSTRACT FROM AUTHOR]

• Analytical modeling of 3D-printed FG lattice-core sandwich in thermal environment. • Homogenization-based rapid prediction for strut stress in various FG lattice cores. • Effect of ambient temperature and gradation mode on strut stress of FG sandwich. 3D-printed sandwich panels with functionally graded (FG) lattice cores have garnered widespread attention owing to their outstanding mechanical performance. However, the straightforward interplay between the service environment, strut structure, and their mechanical behavior has not been systematically explored. In this study, an analytical two-step prediction modeling is developed to efficiently obtain the mechanical response of 3D printed sandwich panels with FG lattice cores. Initially, the effective elastic moduli of FG lattice cores are identified based on finite element (FE) analysis. The stress and deformation of the core-homogenized sandwiches in thermal environments are predicted using the higher-order shear deformation theory. Subsequently, the de-homogenization is employed to calculate strut stresses. The prediction shows excellent agreement with the FE results in the literature. Furthermore, parametric analysis is performed to uncover the impact of crucial variables on the strut stresses within the FG lattice cores. The results show that the strut stress decreases with the increased transverse layer number and power index, while increasing with the higher ambient temperature, length-to-thickness ratio, and thermal expansion of the sandwich panels. The proposed model can serve as an efficient tool for the design and printing of high-performance lattice-core sandwich panels. [ABSTRACT FROM AUTHOR]

Sandwich panels with a hierarchical core facilitate the optimal utilization of limited materials to enhance bearing capacity in strategic locations. Nevertheless, the complex sub-structural cells have hindered extensive investigation into their static and modal characteristics. The objective of this study is to obtain the effective plate properties by homogenizing the representative unit cell and subsequently applying them to a two-dimensional equivalent single layer model (2D-ESL) based on the variational asymptotic method (VAM). Furthermore, three-point bending test of 3D-printed specimen and 3D detailed finite element results are employed to confirm the predictions of 2D-ESL under various load and boundary conditions. The effects of material factors (such as fiber volume fraction and layup configuration) and structural parameters (including aspect ratio, hierarchy ratio, and slenderness ratios of ribs and ligaments) on the equivalent stiffness and modal characteristics are also examined. Moreover, sandwich panels with different hierarchical configurations (including 2, 3 and infinite segments within the inclined ribs) are investigated to provide valuable insights for selecting appropriate hierarchies based on specific conditions. Notably, the transition from polyline to arc-shaped segments has been proven to effectively mitigate local stress concentration, leading to a more uniform distribution of local displacement. • Hierarchical core optimizes material utilization or enhanced bearing capacity. • The unit cell is homogenized to determine the equivalent plate properties. • 2D-ESL can improve computational efficiency while ensuring sufficient accuracy. • SP-HDH can achieve optimal bending stiffness at the slenderness ratio of 0.26. • HDH with different segment configuration offer insights for hierarchy selection. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel dual-sub-fold Miura foldcore is proposed by introducing sub-fold into the cell walls of conventional Miura foldcore. • The improvement in initial peak force and average force are demonstrated in novel Miura compared to the conventional Miura. • The novel Miura are found to exhibit a predictable and stable deformation mode for a wide range of geometric parameters. A modified Miura foldcore geometry was developed by introducing sub-folds into the cell walls of a conventional Miura foldcore. Similar to other sub-fold Miura foldcores, stable plastic hinge lines were generated at sub-fold sites under the guidance of the sub-folds and transformed into traveling hinge lines or stationary hinge lines in the subsequent crushing process. Therefore, in comparison to the conventional foldcore, the dual-sub-fold Miura foldcore exhibited a higher average crushing force with an improvement of 60.8 % in the optimum case. The dual-sub-fold Miura foldcore exhibited relatively lower stiffness at the sub-fold sites, effectively reducing the initial peak crushing force. This reduction in peak crushing force reached a maximum decrease of 70 %. Moreover, this dual-sub-fold foldcore was glued to two parallel rigid plates (top and bottom), making it more suitable for engineering applications. The parametric study indicated that the dual-sub-fold Miura foldcore exhibited predictable and stable deformation modes. It was found that the average crushing force could be effectively enhanced by reducing the core folding angle, elevating the sub-fold position, decreasing the sub-fold size, and elongating the foldcore. The theoretical model for predicting the energy absorption performance of the foldcore was also established. [ABSTRACT FROM AUTHOR]

• The strip method of reverberation-ray matrix (S-MRRM) is presented for the first time. • The S-MRRM solves the limitations of MRRM boundary simply supported and sector modeling. • Dynamic model of sandwich sector- rectangular coupled plates is developed. • Accurate dynamic prediction of sector- rectangular coupled plates under impact is achieved. • Influences of material parameters on the transient and steady-state responses are revealed. This paper proposes a general method for analyzing the dynamic response characteristics of sector- rectangular coupled plates subjected to external impacts. This method combines the method of reverberation-ray matrix (MRRM) with the strip transfer function method, referred to as the strip method of reverberation-ray matrix (S-MRRM). The traditional MRRM has some limitations for the dynamic modeling of the sector structure and also requires the Lévy-type exact solution, leading to simply supported boundary conditions in certain direction of the structure. The present method can not only address the aforementioned limitations but also maintain the efficiency advantage of the wave method for solution. The investigated structure consists of sandwich panels composed of functionally graded carbon nanotube reinforced (FG-CNTRC) panels and the three-dimensional graphene foam (3D-GrF) core. The structure is discretized into several strip elements by the strip transfer function method, and the whole dynamic model of the structure is obtained through matrix assembly. The motion differential equation in matrix form is derived by using Hamilton principle, followed by obtaining the matrix-form wave number equation. Upon deriving the wave solution of the structure based on this equation, the transient and steady-state responses of the structure are obtained by employing MRRM. Convergence analysis is conducted on these calculation results, followed by comparison with FEM results to validate its prediction accuracy. Finally, through a comprehensive parametric study, the impacts of various factors such as CNTs distribution form, CNTs volume fraction, 3D-GrF pore distribution form, 3D-GrF porosity, and sandwich panel thickness ratio on both transient and steady-state responses of these structures were investigated, thereby providing guidance for engineering applications. [ABSTRACT FROM AUTHOR]

• An innovative negative Poisson's ratio arc curve structure is proposed. • On the basis of the honeycomb core with a negative Poisson's ratio arc curve structure, an embedded tube is added. • The analysis model is established and verified by experimental and simulation results. • Through sound absorption experiments and compression experiments, it is confirmed that the structure has excellent sound absorption and energy absorption performance. A negative Poisson's ratio arc curve Helmholtz resonator structure is proposed to address the difficulty of achieving perfect low-frequency absorption in traditional absorbing structures at ultra-subwavelength scales for subaqueous low-frequency sound waves. The shape of the embedded tube is designed as a circular tube and a regular hexagonal tube, with the two shapes symmetrically distributed about the center of the circle. Furthermore, the traditional concave sandwich structure with negative Poisson's ratio has been modified to ensure outstanding sound absorption performance while preserving the overall dimensions. The structure is simulated using the finite element software COMSOL and validated through experiments using a standing wave tube absorber test. The experimental and simulated results show a high level of consistency. The findings demonstrate that the arc-shaped Helmholtz resonator structure with a negative Poisson's ratio significantly lowers the resonant absorption peak frequency of the Helmholtz resonator. This modification allows the structure to exhibit exceptional sound absorption performance within the frequency range of 520–930 Hz, with an average sound absorption coefficient surpassing 0.9, achieving near-perfect absorption of sound waves. The absorber structure achieves an absorption peak of 0.99 at a frequency of 740 Hz, with a thickness that is ultra-subwavelength, being only 1/15 of the corresponding wavelength for the absorption peak frequency, demonstrating its deep subwavelength dimensional characteristics. Even when the structure's height is 30 mm, there is still a wide absorption band, with a bandwidth ratio of 68 % (sound absorption coefficient > 0.5). Furthermore, an energy absorption characteristic analysis is conducted on the negative Poisson's ratio arc curve Helmholtz resonator structure, showing that the energy absorption performance is almost the same between structures with and without microperforated plates. Therefore, creating micro-perforations on the panel does not affect the energy absorption characteristics of the structure. [ABSTRACT FROM AUTHOR]

• A new non-uniform rectangular honeycomb sandwich panel is designed based on Bezier curves to enhance material utilization. • The effective elastic constants of non-periodic honeycombs are obtained through the geometric equivalent method and the strain energy-based homogenization method. • The analytical solutions of bending and buckling responses of the non-uniform rectangular honeycomb sandwich panel are derived by using parabolic shear deformation theory. • The weight/performance multi-objective optimization design of the non-uniform rectangular honeycomb sandwich panel is conducted. Honeycomb sandwich panels have a wide range of applications in aerospace, marine and energy industry due to their high stiffness-to-weight ratio. In this study, a new non-uniform rectangular honeycomb core is presented to promote its material utilization ratio. The non-uniform wall of honeycomb core is described using Bezier curves, and the effective elastic constants are obtained by both the geometric equivalent method and the strain energy-based homogenization method. To analyze the bending and buckling behaviors of the sandwich panel, the parabolic shear deformation theory is adopted, and the governing equations are derived by employing Hamilton's principle. Then, the closed-form solutions of bending and buckling responses of the non-uniform rectangular honeycomb sandwich panel are derived. Furthermore, multi-objective design formulations are established, with the objectives of minimizing the weight and deflection, and maximizing the critical buckling load. Illustrative examples demonstrate that the non-uniform design of the honeycomb core can remarkably increase the material utilization rate and improve the mechanical performance of sandwich panels. [ABSTRACT FROM AUTHOR]

• Developed novel thermal insulation sandwich panels containing ELV waste in manufacturing plant. • Performed laboratory evaluations to test thermal conductivity of ELV-based sandwich panels. • Better thermal performance achieved for sandwich panel encapsulated with ELV PC and PU waste. • Evaluated transparency level of the developed sandwich panels using haze meter. Recycling automotive waste has increasingly become an alternative solution towards producing sustainable materials given the rising issue of raw material shortages and waste management challenges at global level. The improper end-of-life vehicle (ELV) waste management poses detrimental impacts on the environment. This paper proposes a novel method to develop thermal insulation sandwich panels using ELV waste, motivated by the critical needs of creating high-performance thermal insulation for buildings. Six sandwich panels (P1-P6) of different weight and ratio of shredded ELV particles were manufactured. The sandwich panels structure was made of three layers: a core, and a glass face sheet bonded to each side. The core structure composed of Polycarbonate (PC) from headlamp lenses and polyurethane (PU) from seat, bonded using resin casting approach. Thermal conductivity of the samples was measured using guarded hot-plate apparatus. Results corroborated that thermal conductivity of ELV-based sandwich panels reduced remarkably compared to panel without ELVs, recorded at 15.51% reduction. Composition gives the best thermal performance was made of mixed ELV core materials of ratio 50%PC:50%PU, it has a thermal conductivity value of 0.1776 W/mK. The transparency data were obtained using Haze-gard plus haze meter. The best luminous transmittance value was exhibited by P2 (100% PC), 67.47%. The best clarity value and haze value were shown by P6 (25% PC: 75% PU), 55.13% and 52.6% respectively. ELV waste can be recycled to develop useful sustainable thermal insulation to improve thermal and optical transparency performance of buildings as a substitute for conventional materials which have a relevance for future façade concepts. [ABSTRACT FROM AUTHOR]

In this paper, a numerical scheme is prepared using the higher-order shear deformation type of kinematic model with the help of a coupled finite and boundary elements (FE–BE) to evaluate the vibroacoustic responses of laminated composite sandwich curved shell panels. The panel is under the influence of a harmonic point load. Further, an FE–BE combined technique is utilized to prepare a generic computer code (MATLAB environment) for the numerical prediction via the proposed mathematical formulation. The structural frequency and the subsequent sound relevant data are obtained by solving the final form of the multiphysics model. In this regard, the structural system equation is derived through Hamilton's principle and the Helmholtz wave equation for the computation of acoustic responses. The performance of the proposed scheme is established initially through the convergence and the corresponding validation studies. The comparison cases are made with the available published benchmark frequency (free vibration) as well as the acoustic data. Appropriate numbers of numerical examples are solved to draw the meaningful inferences of various factors to show the significant influences on the acoustic radiation responses of the curved sandwich panel type of structural components. The curvature ratio is showing the accentuated influences on the sound radiation responses for the low-frequency ranges whereas the increase in the thickness ratio, i.e. the ratio of core to face leads to an accentuated radiated sound power. [ABSTRACT FROM AUTHOR]

The core layer of accordion honeycomb sandwich panel (accordion HSP) exhibits exceptional affinity for one-dimensional curvature deformations due to its special zero Poisson's ratio effect. This study thoroughly examines its static and dynamic characteristics by decomposing the analysis into unit-cell constitutive modeling and a two-dimensional equivalent-oriented model (2D-EOM) through the variational asymptotic method. The unit-cell constitutive modeling enables determining equivalent stiffness properties for the 2D-EOM. To validate the accuracy and efficiency of the proposed 2D-EOM, its results are compared against those obtained from a detailed 3D finite element model, including in-plane and out-of-plane behaviors of the core layer and sandwich panel, as well as free and random vibration under diverse excitation conditions. The comparison results demonstrate a significant three-fold increase in the equivalent stiffness of the accordion honeycomb in the direction of the added ligaments, as compared to the re-entrant honeycomb. Simultaneously, the acceleration amplitude of the accordion HSP is effectively reduced by 4% due to the involvement of lower high-order frequencies, rendering it exceptionally suited for shockproof meta-structural applications. This equivalent model not only fulfills accuracy requirements but also improves computational efficiency by 15 times, providing an effective approach for preliminary design of honeycomb sandwich panels. • Exceptional affinity for 1D curvature deformations due to ZRP effect of accordion core. • Comprehensive analysis of static and random dynamic characteristics of accordion HSPs. • Enhanced computational efficiency of 2D-EOM while maintaining sufficient accuracy. • Increased stiffness achieved by incorporating ligaments into accordion honeycombs. • Reduced acceleration amplitude due to involvement of lower higher-order frequencies. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper presents a novel developed Sprayed Ultra-High-Performance Cementitious Sandwich Panel (SUHPC-SP) for structural applications. The SUHPC-SP features sprayed UHPC outer layers making it suited for structural load bearing applications, and a foamed concrete core layer offering high thermal properties. With the development of enhanced material properties and novel production methods, the established SUHPC-SP can achieve optimal mechanical performance while minimising the volumes of material required. As such, this study assesses SUHPC-SP potential to increase sustainable outputs over reference Brick and Block (B&B) construction; by quantifying and comparing the whole life cycle environmental and economic impacts of the two methods. A comparative life cycle assessment (LCA) of these types of construction products is presented for the first time in this paper. The study found that integrating SUHPC-SP over typical B&B construction can reduce environmental impacts by as much as 500% and costs by up to 180%. This informs sustainable construction decisions, offering an effective alternative to conventional inefficient building methods and materials. • The study assesses the LCA of sprayed Ultra High-Performance Cementitious Sandwich Panels (SUHPC-SP). • A comparative LCA between SUHPC-SP and brick & block construction was assessed. • Sandwich panels have the potential to reduce costs and environmental impacts. • Using SUHPC-SP over typical brick & block reduces costs by up to 180%. • Using SUHPC-SP over typical brick & block reduces environmental impacts by up to 500%. [ABSTRACT FROM AUTHOR]

• A core stagger layered strategy is proposed for the honeycomb sandwich panels. • Experiments indicate availability of the strategy and accuracy of the numerical simulation. • For a given mass and geometrical size, the increase of layer number and cell size consolidate this effect. • The strategy provides a well choice to improve protective capacity of sandwich panels under air blast loading. Metallic honeycomb sandwich panels have been widely used in energy dissipation due to large plastic deformation under impact/blast loading. In this paper, the dynamic response of a honeycomb sandwich panel with stagger-layered core under intensive near-field air blast loading is investigated. Comparative experiments are conducted for stagger-layered and typical honeycomb sandwich panels with the same geometrical size and mass. Numerical simulation has been undertaken based on the experiments. Numerical results coincide well with experimental results on the deformation/failure modes and center-point deflection of back face sheet. The influence of layer number as well as the geometrical parameters on the energy absorption ability of sandwich panels is clarified. Results show that stagger-layer arrangement of honeycomb core greatly improves energy dissipation capability of sandwich panels compared to typical one with the same mass. The increase of layer number and cell size benefits this effect. These findings indicates that core stagger-layer arrangement is a well choice to improve energy dissipation ability of sandwich panels under air blast loading, especially for highly intensive near-field blast loading. [ABSTRACT FROM AUTHOR]

Textile-reinforced cementitious sandwich are lightweight, slender, non-corrosive, and cost-effective composites that have been recently proposed for structural applications. However, its composite nature depicts a complex fracture behavior, and manufacturing defects, such as a deficient interlaminar bond, can produce premature debonding. Lateral debonding can reduce up to 70% of the maximum load. Early detection of damage is key to reduce the cost and increase the impact of repair. Nondestructive testing (NDT) techniques have widely shown their ability to characterize and detect damage in cementitious composite materials. Microwave and millimeter wave (MMW) are electromagnetic (EM) NDTs that, besides not being attenuated by the insulating core, provide non-contact and real-time measurements. However, EM-based NDTs, besides Ground Penetrating Radar (GPR), have not been sufficiently explored for damage monitoring of cementitious media. Additionally, the complex fracture behavior of the composite makes the EM wave response difficult to interpret. In this manuscript, reference and artificially debonded TRC sandwich beams are tested in three-point bending and monitored with MMW spectrometry. Digital image correlation (DIC) is employed to monitor surface strain and interpret the EM wave response of the material. Results showed the sensitivity and characterization power of MMW spectrometry to different damage mechanisms such as matrix cracking, interfacial debonding, and changes in the angle of incidence, among others. • A combined methodology based on DIC and MMW spectrometry allows for noncontact damage monitoring of TRC sandwich beams. • MMW spectrometry characterized matrix cracking, debonding, and changes in the angle of incidence in TRC sandwich beams. • A weak interlaminar bond introduces complex fracture mechanisms that can be detected with MMW spectrometry. [ABSTRACT FROM AUTHOR]

• It is observed that the bending stiffness of the panels containing hexachiral core is higher than the panels containing tetrachiral cores. • The change in the curvature of the sandwich composites affects the contact force and the amount of displacement. The contact force is less and the amount of displacement is higher in curved panels, regardless of the auxetic core configuration. • At the level of perforation energy, panels with a radius of curvature of R100 can absorb more energy than flat panels. That is, the energy absorption is increased as the curvature is increased. • In flat panels loaded at the perforation energy level, the use of a tetrachiral core is the ideal design option in terms of high energy absorption and lightness, while for panels with R100 curvature, using a hexachiral core may be good application in the field of energy absorption. On the other hand, using an antitetrachiral core for panels with R100 curvature show an increase in specific energy absorption. • The size of the damaged area on flat panels is smaller than the size of the damaged area on curved panels. In addition, the damaged area on the sandwich panel with the hexachiral core is smaller than that of the panels with tetrachiral cores and is mainly due to the higher rigidity. The purpose of this study is to evaluate and compare the capability of impact energy absorption of the sandwich panels with various chiral auxetic cores. To this end, flat and curved panels were subjected to impact testing at varying energy levels. Glass fiber-reinforced epoxy composites and PLA material were used as the skins and core of the examined sandwich panels, respectively. The face sheets were produced by the hand-layup method and the auxetic cores with tetrachiral, anti-tetrachiral, and hexachiral configurations were printed using a 3D printer. The wall thickness, node diameter, and ligament length of the cells, as well as the core thickness, were kept constant for all the studied core structures. Flat and curved sandwich panels were obtained by combining the skins and cores produced in flat, 100 mm, 125 mm, and 160 mm radii of curvature with the epoxy used in skin production. Drop weight tests were carried out at impact energies of 10, 25, and 80 J. The contribution of the auxetic core configuration and panel curvature to the impact behavior of the sandwich panel was evaluated by examining the relationships between contact forces and deflection and by the analysis of the energy absorption and failure mode. The comparative evaluations showed that the auxetic core structure and the curvature of the panel have a significant effect on the impact properties of the sandwich panels. It was also observed that the use of tetrachiral cores could be the ideal design option for flat panels loaded at the perforation energy level. For curved panels, it was determined that the use of a hexachiral core configuration was advantageous in terms of more energy absorption capability, while the use of an anti-tetrachiral core structure was more effective in terms of specific energy absorption. [ABSTRACT FROM AUTHOR]

• Dimples, protrusions and pin fins are introduced into X-lattice sandwich panels. • Mechanisms of fluid flow and heat transfer by the introduced elements are analyzed. • Introducing pin fins in Region A exhibits the best overall heat transfer performance. • A proper combination of the X-lattice and heat transfer enhancement elements is desired. The special topology of the X-lattice induces a large-scale primary spiral flow and three kinds of secondary flow skewed towards and away from the endwall regions and behind each ligament. To make full use of secondary flows produced in different regions, dimples, protrusions and pin fins are separately introduced to the endwall of a sandwich panel to further improve the overall cooling performance. Forced air convection in the six sandwich panels is numerically investigated based on a validation of the numerical model against experimental data available in the literature. Results reveal that the case with pin fins installed in the region upstream of the crosses in the X-lattice (Region A) exhibits the best overall heat transfer performance, while the case with dimples installed downstream of the crosses in the X-lattice (Region B) shows the poorest heat transfer. In terms of the pressure drop, the introduction of protrusions or pin fins in Region A slightly decreases the pressure drop within a certain range of Reynolds number, but the other four cases show an increase in pressure drop. Taking the pressure drop and heat transfer into consideration, a proper combination of the X-lattice and the elements can enhance the overall thermal performance of the sandwich panel. The modifications of the fluid flow and local heat transfer characteristics by the added elements are well analyzed to understand the underlying mechanisms. [ABSTRACT FROM AUTHOR]

Sandwich panel is a promising engineering structure, attracting more and more research attention. Most of current sandwich panels are constructed with plane skins and lattice cores via traditional fabrication processes. In this work, the skin faces of sandwich panels are designed by the freeform T-spline surfaces. The triply periodic minimal surface (TPMS) structures can be accurately generated as porous internal cores. In order to evaluate the performances of TPMS units, a cross-section analysis framework is developed. Based on that, an improved particle swarm optimization (IPSO) algorithm is discussed to seek optimal parameters. Moreover, considering the multifunctional requirements of actual applications, a constrained improved particle swarm optimization (CIPSO) algorithm is introduced to acquire both ideal mechanical and structural performances. Eventually, the designed sandwich panels can be fabricated by the state-of-the-art additive manufacturing technology. Experimental results validate the effectiveness of the presented design method and performance optimization algorithms. • A novel sandwich panel designed with TPMS cores and T-spline skin surfaces. • An analysis and optimization framework for TPMS based on the cross-sections. • An improved PSO algorithm for seeking the optimal parameters of TPMS. • A constrained improved PSO algorithm for multifunctional design. [ABSTRACT FROM AUTHOR]

• FFRP stiffness and strength increase with decreasing temperature. • FFRP-PIR SIP have an inverse relationship between temperature and load capacity. • Within service limit states, FFRP-PIR SIPs respond the same between 20 °C and −20 °C. Structural insulated panels (SIP), composed of an insulating foam core cladded with structural flax fibre-reinforced polymer (FFRP) skin, performs adequately in ambient conditions; however, natural fibres are susceptible to the environment. This study tests SIPs in different environmental conditions. Overall, the secondary tensile modulus of FFRP increased as temperature decreased, which translated to the SIP. For example, when the temperature decreased from 20 °C to −20 °C, the SIP's capacity increased by 28% and stiffness increased in the latter load-deflection response. Although this offers a larger margin of safety, there was no difference in performance across temperatures within normal service loads. [ABSTRACT FROM AUTHOR]

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 (L 1) to the regular hexagon edge length (L 0)), 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. Image 1 • A novel sandwich panel with hierarchical honeycomb core for improving blast resistance was first developed. • Parametric study on blasting resistance of the novel sandwich panel was conducted. • The novel sandwich panel has excellent blasting resistance compared with traditional sandwich panel. [ABSTRACT FROM AUTHOR]

Sandwich panel with Honeycomb Filled with Circular Tubes (HFCT) as core is numerically investigated by using ABAQUS/Explicit in this study. To calibrate the numerical model, the panels equipped with conventional hexagon honeycomb cores are modeled. Good agreement between numerical and experimental results is achieved. The sandwich panels with HFCT are compared with the sandwich panels with Honeycomb and Multi-tube cores of identical mass subjected to vertical and oblique impacts. The maximum displacement of face-sheets, plastic energy absorption, boundary reaction forces and impact load time history are calculated to assess the impact resistant capacity. The panel with HFCT core has smaller rear face-sheet displacement and higher energy absorption capacity as compared to the panels with the Multi-tube and Honeycomb core. Under oblique impact, both HFCT and Multi-tube panels have superior impact resistant capacity than the Honeycomb panel. In addition, the impact resistances of four types of multi-arc tube filled Honeycomb (HFMT) are also analysed. Their performances under vertical and oblique impacts are compared with those of HFCT. [ABSTRACT FROM AUTHOR]

• Innovative cementitious materials can be employed in lightweight structures. • Lighter roof solutions can indirectly secure existing frames and foundations. • Cement-based sandwich elements offer remarkable strength, ductility and robustness. • Preliminary attempt of technological transfer of HPFRCC from the lab to the precast plant demands attention. The two major earthquakes occurred in Northern Italy in 2012 (magnitude 6.1 and 5.8) shown that a serious debate over the structural safety of existing industrial buildings is utterly necessary, also in regions traditionally considered less exposed to the seismic hazard. A promising retrofitting strategy may be represented by the substitution of inefficient secondary roof components with innovative lightweight panels, capable of simultaneously ensuring a global reduction of the inertial forces and an increase of the building energy performances. In this paper, the structural behavior of a multilayered solution, consisting of an advanced cement-based case enclosing a thick insulating core, is presented and investigated on real-scale specimens. The mechanical characterization of the employed materials (High-Performance Fiber Reinforced Cementitious Composite and Textile Reinforced Concrete) at the laboratory level is followed by the discussion of the major challenges arisen in transferring such sensitive construction technologies to the prototyping plant. Structural performances are evaluated by means of longitudinal and transverse bending tests and simplified plane-section design approaches are finally explored and critically assessed. [ABSTRACT FROM AUTHOR]

Highlights • A ballistic pendulum was developed to implement water-backed plates to shock loading in water. • Deformation resistant capability and anti-shockwave performance of water-backed sandwich panel were investigated by 28 experiments and compared with monolithic plates. • Quantitative results, including the evolution of the deflection along radius of face-sheet and volumetric strain of honeycomb core, characterized permanent deformation of sandwich panel. • The secondary pressure wave was recorded by a sensor and analysed systematically. • A failure map was performed to identify the effect of panel configurations on structure failure mechanism at this blast magnitude. Abstract Explosion tests were performed underwater to study the blast resistance of water-backed sandwich panels. Effects on the structural response of face-sheet and core configurations, including face-sheet thickness, cell wall thickness of the honeycomb, core thickness and charge mass, were investigated by a large number of experiments. Quantitative results were obtained in the tests with corresponding sensors and further processing. Further results characterized the permanent deformation of sandwich panels. A failure mode map was adopted to identify the effect of design parameters on the structural failure mechanism at this blast magnitude. Finally, a comparison between sandwich panels and monolithic plates was performed. The comparative study provided further experimental evidence for the benefits of sandwich in water-backed configuration. Present study led to the apprehension of blast resistance of water-backed sandwich structure to underwater blast load, thereby developed useful guidelines for the design of blast-resistant structural systems. [ABSTRACT FROM AUTHOR]

• A nonlinear high-order theory is applied to model compressible core layer. • Introducing a new numerical approach, combination of DQ–Newmark method. • The programming code requires 50 percent less time than finite element solution. • Failure resistance of sandwich panel increases with increasing core density. • In the case of H100 core, the panel has most energy absorption. The current study aims to present a three-dimensional numerical analysis to predict the elastic-plastic behavior of a single-curvature, simply supported, composite sandwich panel. The PVC foam core is modeled with isotropic elastic-perfectly plastic properties based on the extended non-linear higher-order sandwich panel theory. An efficient and accurate numerical approach, a combination of differential quadrature, and Newmark methods were implemented to distinguish panel layers' deformations and stresses. The non-linear governing partial differential equations of motion are discretized and reduced to ordinary differential equations by applying the differential quadrature method (DQM) and are solved using the Newmark method. The various failure modes of the sandwich panel, including facesheet fracture, foam shear fracture, and foam yield were investigated. The stress components and transient responses obtained from the present method are compared with the finite element solutions using commercial software ANSYS and also compare with those reported in the literature and good agreement is achieved. It is observed that significantly less computational time and hardware capacity for the proposed method is required with respect to the finite element solution. A parametric study proved that sandwich panel with H100 foam core has the highest energy absorption and this parameter increases with increasing the span of the panel. [ABSTRACT FROM AUTHOR]

Abstract The objective of the research described in the paper was the structural development of a FRP composite bridge deck intended for manufacturing and application in road bridges in Poland, mainly for redecking the deteriorated bridge slabs. The appropriate shape of the sandwich bridge deck panel, its overall structure, constituent materials and the associated cost-effective manufacturing technology were determined following a comprehensive analysis of the similar solutions recently developed worldwide. In the first stage three different small-scale deck panel prototypes were designed and fabricated, assuming the various core configuration of the sandwich structure. Based on manufacturing tests and initial static tests the feasibility and stiffness of all prototypes were assessed to select the optimal deck solution in terms of material, structure and technology. In the second stage of the research a full-size 2.0 × 5.0 m bridge deck panel was designed taking into account the bridge loading according to Eurocode 1. The full-size bridge deck prototype was subjected to a series of static load tests simulating the relevant load. The tests confirmed the appropriate stiffness and load carrying capacity of the novel FRP bridge deck panel, quite similar to performance characteristics of other FRP bridge decks implemented worldwide. However, the necessary technological and research works on the novel sandwich bridge deck panel in order to increase its safety level were also outlined. [ABSTRACT FROM AUTHOR]

Abstract The dynamic response and design optimization of clamped sandwich panels comprising two aluminum alloy face-sheets and a layered-gradient closed-cell aluminum foam core subjected to air-blast loading were examined in this study. The numerical approach was first validated by blast test results of sandwich panels with monolithic aluminum foam cores, and then the dynamic responses of layered-gradient core sandwich panels were briefly discussed in terms of deflection response and energy absorption. Two surrogate model methods (i.e., response surface method – RSM, and radial basis function – RBF) were adopted to construct objective response functions, and the single-objective adaptive response surface method (ARSM) and multi-objective genetic algorithm (MOGA) were used for the defined optimization problem. The optimization results show the trade-off relationships among the maximum energy absorption, minimum structural mass and minimum deflection, and the advantage of "Pareto front" in such design circumstances. Furthermore, the applicability and accuracy of RSM and RBF agent models in the multi-objective design optimization (MDO) of sandwich panels with layered-gradient foam cores under air-blast loading were also compared and revealed. [ABSTRACT FROM AUTHOR]

Highlights • Novel sandwich structure subject to blast loading using PE4 explosives • Experimental and numerical work is covered • Thermoplastic polyurethane (TPU) is shown to be a promising material under blast • Pave the way for future design and development using this material Abstract This article presents experimental and numerical results following blast tests on a polyether grade thermoplastic polyurethane (TPU). Aluminium alloy (AA) 2024-T3 skins were used as facings to enhance the blast resistance of sandwich structures with TPU cores and varying thicknesses. The experimental results highlighted an improvement in blast resistance with the addition of skins to the TPU core. Increasing the thickness of the TPU core in the sandwich panels served to increase the blast resistance of the structure. For example a 20 mm core offered a blast resistance that was 50.2% higher than an equivalent 5 mm core and 71.2% higher than a plain (i.e. no skin) 5 mm TPU core. Numerical simulations of the blast response of the TPU panels were conducted by converting the explosive loading regime applied to the panels to a simplified pressure pulse loading. Good agreement was obtained between the numerical and experimental results for the back face deflection profiles through the central cross-sections of the panels. [ABSTRACT FROM AUTHOR]

Abstract Thin-walled energy absorbers are one of the common structures that are used in vehicle body for increasing the crashworthiness and consequently decreasing injuries. Investigated new type of thin-walled aluminum matrix and a thin-walled steel punch energy absorber structure has been investigated in this paper. Energy is absorbed as the matrix expansion followed by simultaneous matrix and punch folding. Present study proposes a sandwich panel based on expanding-folding absorber units to evaluate their crush mechanism. Parametric study has been done using finite element code LS-DYNA while experimental tests have been implemented to validate the FE model. The panels have been tested under three axial quasi-static loading conditions including a rigid half-cylinder and a rigid plate. Parametric study considers the punch angle, matrix thickness and punch thickness. The optimum structure based on energy absorption has then been used as a structural member in the sandwich panel until a panel with high specific energy absorption be introduced. Also it have been seen that all the curves for the expansion section can be estimated using polynomial second order functions, with a high accuracy. Graphical abstract fx1 Highlights • To absorb the kinetic impact energy effectively, the sandwich panels show structural need for high interconnection. • Increasing the thickness of thin-walled mandrel shows a direct effect in increasing the maximum and average forces. • Increasing the thickness of thin-walled matrix and increasing the angle of thin-walled mandrel increase the slope of the curve in expansion area. • The output diagrams for the expansion section can be estimated using specific polynomial second order functions. [ABSTRACT FROM AUTHOR]

Abstract A simple 1D nonlinear finite element model is presented for the analysis of composite foam-insulated concrete sandwich panel (FICSP) structures. The material nonlinearities of concrete wythes, steel rebar and insulation layer are considered. By employing a sinus shear deformation beam theory, the effects of transverse shear stress in concrete wythes and insulation layer are incorporated in the presented finite element formulation. The present formulation takes into account the partially composite action of FICSP structures by using the concept of distributed spring layer model. Full-scale experimental data and 3D finite element results are used to validate the developed finite element formulation. The obtained numerical results demonstrate that the presented finite element model of this study is an efficient tool to predict the detailed structural response of FICSPs till collapse stage. [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]

Abstract Damage severity of sandwich panels to underwater explosion load depend not only on the shock factors, but also on the fluid behind the structure. Underwater explosion tests were performed on water-backed sandwich panels to examine the deformation and failure of such composite structure. The dynamic blast response of water-backed sandwich panel was investigated using the LS-DYNA software. An analytical three-stage model was developed for the deformation history of water-backed sandwich panel subjected to shock loading in water. Blast resistance of water-backed sandwich panel was compared with monolithic plate of equivalent areal mass and air-backed sandwich panel with the same configurations. Water-backed sandwich panel exhibited the best deformation/damage resistant capability. Compared with air-backed sandwich panel, core material exhibited greater volumetric strain when the sandwich structure wetted on both sides. Overpressure in the water behind structure was reduced to about 7% by using sandwich structure over monolithic plate of equivalent thickness. Present study led to the apprehension of dynamic response of water-backed sandwich structure to underwater blast load, thereby developed useful guidelines for the design of blast-resistant structural systems. [ABSTRACT FROM AUTHOR]

Abstract In this study, sandwich panels with carbon/epoxy composite skins and an magnetorheological elastomer (MRE) honeycomb core in different proportions of magneto/elastomer (w/w%) are manufactured and studied numerically and experimentally. Test specimens in the beam form are subjected to free and forced vibrations and evaluated with and without the presence of an external (until 120 kA/m) magnetic field, positioned on the free end and on the center of the beam. The experimental results showed good performance in the attenuation of vibration level, especially on the fundamental vibration mode of the structures in question. The applied magnetic field on the free end of the test panel was capable of reducing until 37.45% their first natural frequency value. It can be noted from numerical and experimental results that sandwich panel with MRE honeycomb shifted the natural frequencies due to the increase of an induced magnetic field, especially for the first mode shape. [ABSTRACT FROM AUTHOR]

Highlights • A multi-scale model of heterogeneous aluminium sheets was developed using the DIGIMAT software. • Nonlinear 3D FE-analyses of quad core aluminium sandwich panels with a crack was reviewed. • The damage process was implemented in ABAQUS software. • The theoretical approach was performed using energy methods. • The fatigue damage mechanical model was developed. Abstract This paper develops a multi-scale analysis of fatigue damage behaviour of a quad-core sandwich panel with a heterogeneous aluminium alloy containing silicon in a ductile aluminium matrix. The analysis is based on the Representative Volume Element (RVE)-concept. Because of their capacity and high strength-to-weight ratio, these materials can be increasingly used in industry. Here, an elastic-plastic fracture analysis has been clearly considered on the heterogeneous aluminium undergoing tensile deformation. A nonlinear fatigue damage analysis of quad-core (WF51 PMI foam, H100 PVC foam, aluminium foam, and WF110 PMI foam) sandwich panel has been mainly investigated. The model proposed in the commercial software of ABAQUS with the robust nonlinear functions has been also implemented. The theoretical and analytical results are in good agreement with damage evolution and its variations. [ABSTRACT FROM AUTHOR]

An active protection sandwich panel utilizing expandable graphite (EG) was developed to address the release of hazardous gases during building fires involving sandwich panels, leveraging its excellent thermal performance. When exposed to heat, EG expands and forms a barrier, effectively preventing the spread of fire and blocking harmful gas emissions generated from the insulation material. Flame retardancy tests demonstrated that EG-applied sandwich panels exhibited significantly lower peak and total heat release, as well as reduced smoke generation. Quantitative analysis of gas emissions during combustion confirmed their lower toxicity levels. The cone calorimeter test revealed that the EG-applied sandwich panels showed a remarkable 67.1% reduction in peak heat release rate (HRR) and a 51% decrease in total heat release compared to panels without EG (PF). Furthermore, total smoke generation reduced by an impressive 94%. This study affirms the effectiveness of EG in improving flame retardancy and reducing harmful gas emissions in sandwich panels. In addition, there is significance in analyzed the effect of EG on improving fire resistance performance through the fractional effective dose analysis method, which assesses human respiratory tolerance to combustion byproducts. [ABSTRACT FROM AUTHOR]

• Perforation tests of integrally-3D printed trabecular core sandwiches. • The skin material was found to be rate-independent. • The rate-dependent behaviour was attributed to the core material's rate dependency. • Finite element models should be enhanced to predict the fracture behaviour. Sandwich panels are heavily used in industrial sectors where specific mechanical properties are of utmost importance due to their high weight-stiffness ratio and energy absorption capacity. Lightweight sandwich cores with bio-inspired topologies have been used as an advanced alternative to conventional bulk cores to improve performance. Nowadays, sandwich structures comprised of core and skins are typically manufactured with two different processes and are afterwards adhesively joined together. Here, with a less time-consuming and more efficient assembly procedure in mind, an integrally 3D-printing strategy is proposed. This investigation analyses the low-velocity impact and quasi-static perforation performance of sandwich core designs inspired by the beetle's forewing trabecular structure. It was found that the core material was responsible of the rate dependence observed in the force–displacement curves. More complex finite element models than those employed here are necessary to capture all the fracture modes observed experimentally. [ABSTRACT FROM AUTHOR]

• Cold-formed steel sandwich panel with a polyurethane foam core for structural floor. • Using digital image correlation technique to characterise construction materials. • Stiffness and peak load of sandwich panels subjected to edgewise compression. • Numerical modelling of cold-formed steel, polyurethane foam, composite structures. • Analytical prediction of wrinkling and global buckling loads of sandwich panels. With the objective of leading to innovative lightweight structural components in the construction sector using sandwich panels with polyurethane foam and steel face sheets, different studies were conducted on such structures, including experimental, numerical, and analytical campaigns. The experimental campaign includes the mechanical characterisation of the constituent materials and the edgewise compressive test of small-scale sandwich panels. The test protocols are detailed, and their influence on the results is assessed. Through the use of digital image correlation recordings, deformation patterns and failure mechanisms in the constituent materials and the composite structure are identified. Material constitutive models are calibrated based on the experimentally obtained results. The accuracy of such models is first evaluated against the stress–strain curves recorded during the experiments. In the second stage, the response of the sandwich panels subjected to edgewise compressive loading is simulated. A parametric analysis on the sensitivity of the numerical models to the initial geometrical imperfections is shown to be fundamental to capturing the behaviour of the sandwich panels. Furthermore, the experimental and numerical results are compared to analytical solutions of the problem of the edgewise compression of sandwich panels. Finally, a thorough discussion of the obtained experimental, numerical and analytical results is presented, along with comparisons to results available in the literature. [ABSTRACT FROM AUTHOR]

This study proposes a novel sandwich panel with an improved star-shaped honeycomb (SP-ISH) by replacing sharp corners with cubic struts and lengthening inclined ribs of traditional honeycomb. To more effectively analyze its special dynamic characteristics, the bending Poisson's ratio was derived and effective engineering constants were obtained through asymptotic analysis of the energy functional stored in periodic unit cells. Based on this analysis, a two-dimensional equivalent downscaling model (2D-EDM) was developed to investigate the free vibration of SP-ISH under various boundary conditions, and the influence of initial deformation on free vibration was also discussed. The frequency-domain and time-domain analyses were employed to identify the resonance characteristics of the SP-ISH under harmonic loading. Our findings demonstrate that 2D-EDM can accurately predict the free and forced vibration of SP-ISH and improve computational efficiency by reducing DOFs. The results indicate that the maximum resonance response was obtained by applying excitation at the center of the sandwich panel. Additionally, under cyclic loading, a sharp change in local stress amplitude was observed in the facesheet-core interface region. Compared with traditional star-shaped honeycomb, the incorporation of extended ribs and added struts could significantly reduce the maximum resonance amplitude by 3.8%. Notably, the natural frequencies of SP-ISH were affected by initial compression (up to a 40.6% reduction) and tensile deformation (up to a 26.4% increase). [Display omitted] • Improved SSH design with added cubic struts and elongated inclined ribs. • VAM-based 2D-EDM is developed for free and forced vibration of SP-ISH. • SP-ISH has superior dynamic characteristics other honeycomb sandwich panels. • Initial deformation from support movement impacts free vibration. • 2D-EDM accurately predicts resonance amplitude for various excitations. [ABSTRACT FROM AUTHOR]

• HCSP showed enhanced damage and perforation resistance under combined loading. • The enhanced damage of HCSP was caused by fracture of perforation hole. • The enhanced perforation resistance of HCSP was due to face sheets deforming. The performance of sandwich structures against individual shock loading and fragment impact loading has been extensively examined, but little is known about their performance in the presence of simultaneous shock and impact loading. Based on a recently developed composite projectile to simulate combined shock and single fragment impact loading, the performance of aluminum honeycomb core sandwich panels (HCSPs) against combined loading is methodically examined. The achieved results reveal that the combined loading exhibits a synergistic effect compared to the single loading, i.e., increased damage of the sandwich panel and enhanced perforation resistance of the sandwich panel. After that, a three-dimensional finite element simulation is performed to explore the underlying mechanism of the synergistic effect. Numerical analysis indicates that the increased damage is a result of perforation-induced reduction of load-carrying capacity of sandwich panel, while the enhanced perforation resistance is the result of deflecting-induced perforation time delay of the perforation process. Finally, the parametric investigation of sandwich geometries such as asymmetric face sheets, core density, and core height is comprehensively conducted. The gained results reveal that both performance and synergistic effect due to combined loading are sensitive to these parameters. [ABSTRACT FROM AUTHOR]

Sandwich structures are widely used in engineering as lightweight and high-strength materials. In recent years, there has been increasing attention toward new design ideas aimed at improving the adaptability and variability of sandwich structures for broader applications. This paper proposes a new stretchable sandwich structure. Experiments and finite element methods are conducted to provide the influence of stretchable design on the mechanical properties of traditional sandwich structures. Then, three novel stretchable sandwich structures with 3D lattice core layers are also designed to explore the applicability of this method. The results demonstrate that the stress and energy absorption capacity of stretchable lattice sandwich structures remains essentially constant. In addition, stretchable sandwich structures possess the capability of in-plane deformation and active bending. By combining the functional characteristics of sandwich structures and rotating polygons, stretchable sandwich structures can adjust their surface area, porosity, and in-plane negative Poisson's ratio effect while maintaining bearing capacity. This study suggests improvements in the utilization and adaptive capacity of sandwich structures in defense engineering and other applications by overcoming the problem of limited deformation faced by traditional sandwich structures. [Display omitted] • A new stretchable sandwich structure and its design method is proposed. • Three lattice sandwich structures (LSSs) are also designed to explore the applicability of this method. • The surface area of the structure can be adjusted. • The LSSs do not reduce energy absorption during in-plane deformation. • The sandwich structures have in-plane auxetic behavior. [ABSTRACT FROM AUTHOR]

• A composite lattice is proposed to combine advantage of auxetics and polyurea. • An abnormal hat-shape distortion opposite to impact direction of backplate is found. • The displacement time history of backplate center presents the shape of the letter N. • The failure modes of the auxetic cells and their distribution are revealed. • The dynamic mode of the auxetic sandwich panel subjected to explosion is presented. A series of air explosion experiments were carried out on the 3D polyurea-coated auxetic lattice sandwich panels in order to combine the advantages of auxetic materials and polyurea. The deformation, dynamic strain, and acceleration of the front and back plate were obtained. The results show that the dynamic response of the 3D polyurea-coated auxetic lattice sandwich panel could be divided into four stages: the shock wave action stage, the auxetic effect stage, the overall deformation stage, and the oscillation stage. The "N" type displacement time history of the back plate center due to the auxetic effect is found through the experiments. It is also found that the concave "hat-shaped" deformation mode of the back plate is opposite to the impact direction. This anomalous deformation mode is of great significance for impact protection. Finally, three dynamic response mode of the 3D polyurea-coated auxetic lattice sandwich panel subjected to air explosion is revealed. This study could provide a reference for the shock resistance design of structures. [ABSTRACT FROM AUTHOR]

Enhancing the stiffness of high-porosity honeycomb sandwich panels is a critical research field. To address this issue, a novel improved star-shaped honeycomb sandwich panel (SP-ISH) is designed by replacing the sharp corners with cubic struts and elongating the inclined ribs of the traditional star honeycomb. To fill the gap between global behaviors and local field distribution, an asymptotic analysis of the energy functional stored in periodic unit cells is performed. Based on the obtained effective plate properties, a two-dimensional equivalent downscaling model (2D-EDM) is developed and validated through comprehensive comparisons with results from 3D-printed experiments and 3D FE models, including assessments of static displacement, global buckling, and local field distribution. Furthermore, the effects of material and structural parameters on the effective plate properties and static performance are systematically investigated. The results reveal that the slenderness ratio of the rib and the core height-width ratio have the strongest influence on the equivalent tensile stiffness and bending stiffness, respectively. Notably, the SP-ISH outperforms other star-shaped honeycomb panels in specific stiffness, deformation resistance, and buckling load capacity due to the extended ribs and added struts. The study's findings provide valuable insights for future designs and applications of this honeycomb structure. • A novel improved SSH is designed by adding the cubic struts and elongating the inclined ribs. • The VAM-based 2D-EDM of SP-ISHs is developed and verified by comparing with 3D-FEM results. • The influence of material and structural parameters on static performance is systematically studied. • The increasing core height-width ratio can significantly enhance the deformation resistance of SP-ISP. • The cross-ply SP-ISH has high equivalent stiffness to achieve more balanced performance. [ABSTRACT FROM AUTHOR]

• A new foam-infilled corrugated FRP-steel sandwich shear wall (CFSSW) was proposed. • Shear wall specimens were tested to study the hysteretic behaviors of CFSSW. • Corrugated FRP effectively restrained the buckling of steel plate. • PET and FRP increased stiffness, bearing capacity and energy dissipation of CFSSW. • Elastic, plastic and damage stages of specimen with FRP and PET were distinguished. A new foam-infilled corrugated carbon fiber reinforced polymer (FRP)-steel sandwich shear wall (CFSSW) is proposed for steel frame structures subjected to severe wind or seismic loadings. To reduce the excessive out-of-plane buckling deformation of conventional steel plate shear wall (SPSW), corrugated FRP laminates are fixed on both sides of the steel plate (SP). Moreover, to further improve the hysteretic behavior of the shear wall, PET foam is chosen as filler between the corrugated FRP laminates and the steel plate. Three, 1/3 scaled, single-storey shear wall specimens were built by using, as wallboard, the flat steel plate, the steel plate with corrugated FRP laminates (VCP) and the foam-infilled corrugated FRP-steel sandwich plate (VCSP). Experimental tests were carried out under low-cycle horizontal loading to study their shear performance. The results show that the CFSSW structure exhibited clear stress development pattern and stable energy dissipation capacity. Only using FRP corrugated plates as buckling-restraining components, the initial stiffness, ultimate bearing capacity and cumulative energy dissipation of conventional steel plate shear wall can be improved by 22.01%, 13.93% and 49.07%, respectively. The contribution of the infilled PET foam allowed to increase the initial stiffness, bearing capacity and energy dissipation of 28.17%, 36.39% and 105.93%, respectively. Besides, with the restraining effect of only FRP corrugated laminates or both FRP and infilled PET foam, the maximum out-of-plane displacements of the steel plate under shear force were reduced by 67.9% and 92.1%, respectively. Moreover, PET foam can help FRP laminates to effectively bear the shear forces and increased the ultimate shear capacity to 5.9% higher than nominal ultimate shear capacity of the steel plate. [ABSTRACT FROM AUTHOR]