This paper investigates the buckling behavior of carbon fiber reinforced polymer honeycomb sandwich cylindrical shells (HCSs) under external pressure, with emphasis on the buckling response and the effects of geometric parameters. Two groups of HCS specimens with identical mass but different honeycomb cell sizes were designed and fabricated. Hydrostatic pressure tests were conducted to obtain their ultimate buckling loads. Additionally, a finite element model was developed in ABAQUS, and its accuracy was validated against the experimental results. The validated model was further employed to reveal the damage evolution process and the effects of key geometric parameters on buckling capacity. The results show good agreement between the experimental and numerical results, indicating that the proposed model can accurately capture the buckling characteristics of HCSs under external pressure. The final failure of the structure results from the coupled effects of progressive fiber damage, matrix damage, and structural instability. Compared with an equal-mass single-layer composite cylindrical shell (SCS), the HCS exhibits a higher ultimate buckling load and superior buckling resistance. These findings provide useful guidance for the design and optimization of composite honeycomb sandwich cylindrical shells used in marine pressure structures.
This paper focuses on providing a novel analytical model which can be used to predict the stiffness and ultimate load of a blind rivet connection for sandwich panel under tensile pull-out load. The analytical model is based on the component method which is adapted by Eurocode for the design and analysis of structural connections. The present study appears to represent the first attempt to apply this approach to such joints. It can be used for three failure modes of the connection, which are the sandwich panel PIR core fracture, sandwich panel top facing failure and blind rivet failure. The combined deformation of the sandwich panel and the local deformation of the top facing around the blind rivet, which is observed both in the experimental tests and finite element (FE) analysis, is simplified and incorporated in the analytical model. The result of the analytical model is compared with both experimental test result and data shows good agreement.
In this paper, two plate-added configurations of the corrugated sandwich structure (CSS) were proposed: the interlocked corrugated sandwich structure (ICSS) and the non-interlocked one (NICSS). Plates and corrugations were slotted and interlocked to form the ICSS, and they were merely assembled to form the NICSS. The compressive performance and enhancement mechanisms of the ICSS and NICSS were investigated experimentally and numerically. The results showed that due to the buckling suppression provided by the corrugations, the specific compressive strengths of the ICSS and NICSS were 80.3% higher than that of the CSS. Due to the buckling suppression provided by interlocking, the energy absorption per mass of the ICSS was 241.6% and 13.8% higher than that of the NICSS and CSS, respectively. Further corrugation angle analysis revealed that when corrugation angles ≤60°, the ICSS exhibited 4% higher specific compressive strength than the NICSS, due to the load-bearing contribution of the corrugations enhanced by interlocking. Among the typical sandwich structures, the optimal ICSS exhibited relatively high compressive performance, indicating engineering application potential.
Natural frequency variability across nominally identical aluminium honeycomb sandwich panels from a single production batch is dominated by differences in adhesive quantity, not by face sheet or core geometry, a finding with direct implications for manufacturing quality control and structural dynamic prediction. This finding applies to the commercial aluminium/polyurethane honeycomb sandwich system investigated and is not expected to generalise to film-adhesive aerospace systems. This study quantifies this relationship experimentally across 35 commercial panels from the same production batch using three field-compatible measurement methods. First, a portable single-microphone acoustic test, requiring no contact sensors or multi-channel analyser, identifies panel natural frequencies with correlation r = 0.984 against laboratory experimental modal analysis (mean percentage error 1.1%, RMSE < 0.5 Hz), validating its suitability as a field-deployable alternative. Second, a weight-balance method derives total adhesive mass per panel from scale measurement and image-measured geometry, yielding a signal-to-noise ratio of 8.9 for between-panel ranking. Third, automated edge cross-section image processing quantifies face sheet thickness (coefficient of variation 2.7%) and core height with sub-pixel precision. Combined, a precision scale and an edge-imaging camera predict 84% of first-mode frequency variance across the batch R 2 LOO = 0.839 without any vibration measurement, demonstrating a practical baseline for factory-floor quality screening. Adhesive quantity, not face sheet thickness, is identified as the dominant source of natural frequency variability, with total panel weight ( r = −0.855, p < 0.001) being the single most reliable frequency predictor.
Hypersonic vehicles operate under severe aerodynamic-thermal coupled loading conditions during flight. The air rudder, as a key component for attitude control, is also subjected to significant aerothermal loads and therefore requires both high stiffness and lightweight characteristics. In this study, a unit cell of the air-rudder sandwich structure is selected as the research object. Structural parameter analysis under thermo-mechanical coupling is conducted, and a radial basis function surrogate model is then constructed, and the pointer algorithm is employed for structural optimization to reveal the interaction mechanisms among structural parameters. Results indicate that the skin thickness is the key parameter controlling deformation resistance. Increasing the skin thickness improves the cell stiffness and enhances the cooperative effects of variables such as radial ribs. As the projected cell area increases, the coupling effect among structural parameters becomes stronger. The optimized cellular configurations obtained under five constraint conditions validate these findings. Different performance objectives correspond to distinct optimal designs, achieving a weight reduction of 8.25%-28.29% while maintaining deformation resistance, thereby providing a basis for further high-performance design of air-rudder sandwich structures.
Core shape has a significant impact on sandwich composites’ mechanical and impact properties. The four fundamental topologies of sandwich composite structures—honeycomb, re-entrant, grid, and full-shape—were examined experimentally in this study. The face sheets were made of carbon fiber/epoxy laminates, whereas the core material was polyvinyl alcohol (PVA). Sandwich panels were created by bonding the additively generated core components between the composite face sheets. The specimens’ structural behavior was assessed using three-point bending, dynamic mechanical analysis (DMA), low-velocity impact (LVI), and Charpy impact tests. According to the bending data, the re-entrant core showed the maximum bending strength and elongation at break, showing better deformation capability, while the full-shape core showed the best bending modulus because of its continuous structure. The full-shape configuration produced the maximum peak force of around 15 kN, according to low-velocity impact tests, while the re-entrant core’s auxetic deformation mechanism produced the highest energy absorption capacity of about 88 J. On the other hand, under high strain-rate loading conditions, the honeycomb core had the highest Charpy impact energy and specific impact energy values. The findings show that in sandwich composite constructions, core geometry is crucial for regulating stiffness, damage tolerance, and energy absorption methods.
This paper presents a comparative analysis of discrete and continuous models for the pyramidal lattice truss core in sandwich plates. The study focuses on determining the fundamental vibration frequency as the basis for model comparison. The finite element method, implemented in ANSYS, was employed to address the dynamic problem. The sandwich plate with a pyramidal lattice truss core was modeled using shell and beam finite elements, while the continuous core plate was represented with shell and solid volume finite elements. The effects of the number of pyramidal cells, core thickness, and lattice truss core strut diameter on the fundamental frequency were examined. Fundamental frequencies obtained from both core models were compared, revealing that the continuous core model consistently overestimates the fundamental frequency. Additionally, a design algorithm for sandwich plates with a pyramidal lattice truss core was developed. The procedures for finite element model generation, fundamental frequency calculation, and structural design were implemented using APDL.
Honeycomb sandwich structures have been investigated for a variety of applications, particularly as blast resistant structures because of their excellent strength to mass ratio. The current study investigates the response of a stainless-steel sandwich panel, with hollow core, foam filled core, and gel filled core under air blast load using Finite Element (FE) analysis. Johnson-Cook (J-C) material model is used to estimate the plastic failure characteristics of steel under air-blast explosion of 1, 2 and 3 kg of trinitrotoluene at a stand-off distance of 100 mm. The air-blast simulation is achieved using the Conventional Weapons Effect Program (CONWEP) code developed by US army corps. A parametric study for the gel filled model is carried out by varying the core thicknesses and the blast-point stand-off distances (SoD) with respect to the front plate deflection (FPD), back plate deflection (BPD), and energy absorption. A strain rate analysis of sandwich structure is conducted for the hollow core and foam core models, wherein the strain rate for the hollow core panel is varied from 0.1/s - low strain rate (LSR) to 3500/s - high strain rate (HSR), and for the foam core model, it is varied from 0.004/s (LSR) to 12,000/s (HSR). It is found that the back plate deflection obtained from the HSR model in both cases is significantly smaller compared to the LSR model.
This study presents an experimental and numerical investigation of the crashworthiness behavior of the closed-cell aluminum foam-filled hexagonal honeycomb structures under quasi-static compression. Honeycomb cores made from AA3003-H18 aluminum alloy with cell sizes of 12 mm and 19 mm were filled with closed-cell aluminum foam of 200 kg/m3 density, to evaluate the effect of cell geometry and cell wall thickness (0.05-0.2 mm) on key crashworthiness parameters i.e. peak crushing force (Fpeak), mean crushing force (Fmean), total energy absorption (EA), specific energy absorption (SEA), and energy distribution in linear, plateau and densification region. Quasi-static compression tests were conducted using a Universal Testing Machine (UTM), while numerical simulations were carried out using the explicit finite element code LS-DYNA (R). Numerical results show good agreement with the experimental results, with crashworthiness parameter precision of above 90%, thus validating the numerical simulation approach. Compared to empty honeycomb structures, the foam-filled configurations indicate enhanced performance. In all configurations, the plateau region consistently represented the primary phase of energy absorption, comprising more than 50% of the total energy. At thinner walls, 19 mm cells benefited from greater foam volume and foam-wall interaction, while at higher thicknesses, 12 mm cells achieved superior performance through stable plastic folding. These results provide insights into the foam-filled honeycomb composites as efficient crashworthy structures for automotive, aerospace, and protective applications.
Composite sandwich structures are widely used in weight-critical applications such as aerospace and automotive engineering due to their high strength-to-weight ratio. This study investigates the flexural performance of sandwich structures fabricated with 3D-printed glass fiber-reinforced nylon (GF-PA6) cores, comparing fully printed composite sandwich structures (PCSS) to hybrid composite sandwich structures (HCSS) reinforced with woven carbon fiber/epoxy face sheets. Two core geometries, triangular and tri-hexagonal, were fabricated at infill densities of 20% and 40% using fused filament fabrication (FFF). HCSS configurations were produced by bonding carbon fiber/epoxy face sheets to the printed cores via vacuum-assisted wet layup. All specimens were tested under three-point bending per ASTM C393, with stress characterization performed using sandwich beam theory applied consistently to both PCSS and HCSS configurations. HCSS specimens achieved facing stress values of 184.40-349.70 MPa, compared to 86.96-103.35 MPa for PCSS, with the failure mode transitioning from brittle fracture in PCSS to progressive classical sandwich failure in HCSS, involving local face-sheet indentation, core shear failure, face-core debonding, and fiber pull-out. Increasing infill density from 20% to 40% produced significantly larger improvements in facing stress in HCSS (+57.1% and +89.6% for triangular and tri-hexagonal geometries, respectively) than in PCSS (+8.3% and +18.8%), confirming that a denser core more effectively transfers load to the carbon fiber face sheets. A density-dependent trade-off between strength and energy absorption was observed, with 20% infill HCSS exhibiting greater displacement capacity and energy absorption despite lower facing stress. These findings highlight the effectiveness of combining 3D-printed fiber-reinforced thermoplastic cores with high-stiffness composite face sheets, and provide insight into how core density and architecture govern flexural performance and failure behavior in additively manufactured sandwich composites.
This study investigates the compressive buckling behavior of composite plates adhesively bonded to rectangular sandwich panels. The critical buckling loads are determined using the Generalized Differential Quadrature Method (GDQM) based on the First-Order Shear Deformation Theory (FSDT), which incorporates compatibility conditions at the adhesive interface. The governing relations of the lap-joint setup are formulated based on the principle of minimum potential energy (MPEP). The effects of several parameters, including sandwich core thickness, boundary conditions, and face sheet and plate materials are evaluated. The adhesive layer response under buckling conditions is also examined. Parametric studies are conducted on multilayer composites made of glass/epoxy, carbon/epoxy, and aramid/epoxy, bonded with epoxy, AV-138, and IPCO-9923 adhesives. The influence of material properties, joint overlap, geometric aspect ratio, adhesive-to-plate thickness ratio, and boundary constraints on the critical buckling capacity is comprehensively assessed. Additionally, adhesive failure is evaluated to ensure it does not precede structural buckling. The findings show that a thicker core leads to higher critical buckling loads and shifts the buckling zone from the sandwich panel to the composite plate. Higher overlap ratios and stiffer upper and lower face sheet materials significantly enhance the buckling capacity. Among the tested configurations, unidirectional carbon/epoxy laminates bonded with AV-138 adhesive exhibit the highest critical buckling loads. The analytical findings are validated through finite element simulations using ABAQUS, showing excellent agreement with the proposed model.
The utilisation of composite sandwich structures in high performance applications is gaining growing attention due to its superior stiffness to weight ratio and enhanced energy absorbing characteristics. Pertaining to this, the present study focuses on designing a dual-core hybrid composite sandwich structure comprising aluminium honeycomb (AH) and PVC foam cores, placed between the carbon fiber reinforced polymer (CFRP) face sheets. To investigate the structural performance of the developed sandwich panel (C1/AH + PVC 20 /C2), low velocity impact tests were conducted at energy levels varying from 12 J to 150 J, exhibiting damage from rebound to total perforation. The impact response of the panels was evaluated using force-displacement and energy-time curve. Furthermore, different damage mechanisms involving indentation, inter-layer delamination, core crushing, and fibre fracture were examined through post-impact visual inspection to characterize the energy absorbing behaviour of the sandwich panel. Additionally, three different stacking arrangements of the dual-core sandwich panels (DCSP) were investigated at an impact loading of 150 J, resulting in complete perforation. For the same impact load, the effect of foam core thickness was studied along with a comparative analysis of single and dual core configuration. Among all the sandwich structures, the panel having a symmetric foam arrangement i.e. C1/PVC 10 +AH + PVC 10 /C2 performed better with energy absorption efficiency of 83.9%. It also exhibited highest specific energy absorption of 1.41 J/g at the perforation impact energy. Overall, this work provides a valuable insight in developing a dual-core composite sandwich configuration designs having a strong potential for the application in impact resistant structures such as aircraft fuselage, satellite and UAV protective skin panels, as well as in lightweight high speed automotive crashworthy components, where the combination of progressive energy dissipation through core crushing and improved load distribution can enhance the energy absorption capacity and delayed damage failure.
Honeycomb sandwich panels are widely used in aerospace, automotive, and marine applications. To meet the demands of complex loading conditions and specialized application scenarios requiring flexibly tunable advanced structures, an adjustable-similarity-ratio nested folded honeycomb core was developed by integrating the adjustable similarity ratio nested hierarchical and folding design strategies. Numerical simulations were conducted to investigate the low-velocity impact response of sandwich panels with cores of varying geometric parameters under different impact velocities. The local crash efficiency (LCE) and energy balance models were employed to evaluate deformation resistance, while specific penetration energy was analyzed. The new structure can ensure that the external dimensions remain unchanged, and the mechanical properties can be altered by changing the nesting similarity ratio. Analysis demonstrates that the nested folded honeycomb sandwich panels can achieve 25.5% and 85.6% enhancements in resistance to local deformation and global stiffness, respectively, compared to traditional honeycomb sandwich panels. At high impact velocity, structures with vertical folding and high nesting similarity ratios demonstrated the maximum specific penetration energy, being 1.076 times that of nested honeycomb and 1.248 times that of traditional honeycomb structures, respectively. The deformation process and energy absorption characteristics of the nested folded honeycomb structure provide valuable guidance for the design of new energy-absorbing materials.
Sandwich panels in engineering applications are typically subjected to varied support and loading scenarios. However, traditional core designs based on predefined geometries often exhibit significant performance deterioration when service conditions shift. This study employs a parametric level set-based topology optimization method to maximize core stiffness under multiple representative conditions. Numerical results demonstrate that both support conditions and loading patterns have a decisive influence on global stiffness; the four-edge fixed configuration with concentrated loading achieves the highest stiffness, while the four-corner supported configuration with uniformly distributed loading exhibits the lowest stiffness due to restricted load-transfer efficiency. Unlike studies limited to comparing fixed topological families, the proposed framework automatically generates a synthesized honeycomb-like structure (SHLS) with adaptive load-transmission paths under multi-condition. Three-point bending simulations and experiments on selective laser melting (SLM)-fabricated AlSi10 Mg specimens reveal that, at identical core thickness, the proposed core achieves the highest specific stiffness and the highest specific energy absorption (SEA). Compared with traditional honeycomb-like structure (THLS) and honeycomb structure (HS), the specific stiffness of the SHLS is enhanced by up to 27% and 5%, respectively. Numerical simulations and experimental results exhibit high consistency throughout the loading process, confirming the reliability of the modeling framework.
Fused Deposition Modelling (FDM) additive manufacturing is being used more and more to create lightweight polymeric composites. However, because of the intricate dynamics of interfacial bonding, processing parameter optimization for multi-material sandwich structures continues to be a special challenge. This work systematically investigates the tensile and flexural behaviour of 3D-printed polylactic acid (PLA) and carbon fibre-reinforced PLA (PLA-CF) sandwich specimens using a Taguchi L27 orthogonal array design. Layer height (0.20, 0.25, 0.30 mm), infill pattern (Gyroid, Tri-Hexagon, Honeycomb), and printing speed (125, 175, 225 mm/s) are among the control elements assessed. Multiple linear regression, analysis of variance (ANOVA), and signal-to-noise ratio plots were used to analyse the generated dataset for Young's modulus, ultimate tensile strength (UTS), elongation at failure, and flexural characteristics. The statistical findings show that the infill pattern, which accounts for 48-80% of the property variance, is the most important element influencing mechanical performance. Quantitatively, the Triply Periodic Minimal Surface (TPMS) Gyroid pattern optimized tensile stiffness and ductility, whereas the Honeycomb core architecture produced the highest flexural strength and maximum ultimate tensile strength (similar to 28.5 MPa) because of effective planar stress distribution. Maintaining an ideal intermediate printing pace revealed to be physically necessary to guarantee correct interlayer fusion and avoid heat degradation during extrusion, even though variations in printing speed showed a slight statistical impact on the total property variance. Moreover, the stiffness and pseudo-ductility of the components were mostly affected by layer height. The suggested combination of sandwich architecture and parameter optimization offers a very efficient way to modify the mechanical performance of PLA-based composites for lightweight structural applications, which is supported by fractographic observations demonstrating improved interlayer bonding and fiber-matrix interaction under ideal conditions.
This study aims to enhance the impact damage resistance of 3D spacer woven composites. The novelty of this study is tailoring both core cell geometry and face sheet architecture of 3D spacer woven composites. The 3D square spacer composites exhibited superior impact resistance compared to the 3D triangular spacer composites at both 20 J and 40 J energy levels. This behaviour was attributed to the increased resilience and more flexible response of the 3D square spacer core structure. The impact resistance of the 3D spacer composites also increased with the reinforcement of 2D woven composites. The lowest deformation was achieved for the composites reinforced with satin 2D woven composites, which was related to the higher stiffness provided by the low-crimp satin weave under impact load, compared to the plain and twill weaves.
While topology optimization has gained substantial popularity in recent times, its application in the design of functionally graded auxetic sandwich beams is still relatively limited. This study presents a topology optimization framework for the design of functionally graded auxetic honeycomb sandwich beams and systematically investigates their flexural behaviour, energy absorption characteristics, and deformation modes under three-point bending loading. To support the optimization process, expressions for the homogenized in-plane mechanical properties of honeycomb cellular materials with various microstructures maintained within a fixed unit cell confined space were derived analytically and validated experimentally. Topology-optimized, standard auxetic, and Poisson’s ratio-coupled hybrid sandwich beams were numerically modelled and comprehensively compared under identical relative density and boundary conditions. The topology-optimized sandwich beams demonstrate superior performance across all sandwich beams, achieving superior flexural stiffness, load bearing, and energy absorption capabilities while exhibiting a combined local-global deformation mode that engages a substantially greater number of unit cells compared to the predominantly localized deformation observed in standard beams. Von Mises stress analysis confirms broader spatial stress engagement and more efficient material utilization in the topology-optimized beams. Moreover, the hybrid sandwich beams outperform the standard sandwich beams in flexural and energy absorption properties. Unit cell orientation in standard beams and the relative positioning of unit cells in hybrid sandwich beams are identified as significant design parameters influencing flexural properties. These findings demonstrate that integrating an auxetic lattice core with topology optimization constitutes an effective and versatile strategy for designing lightweight sandwich structures with enhanced mechanical performance.
This study introduces a refined methodology for modeling water diffusion in polymeric foams. The approach is grounded in Darcy’s law, which governs diffusion in porous media. A modified diffusion law is proposed to describe the complex interplay between the foam’s mechanical state and the dynamics of water transport. The resulting diffusion kinetics follows a three step mechanism controlled by a parameter that captures the interaction between Darcy-governed diffusion and diffusion influenced by mechanical properties. Notably, at low values of this parameter, the kinetics closely approximate those predicted by Fick’s laws. The framework is further extended to sandwich structures composed of composite skins and a polymer foam core. In this configuration, the diffusion process proceeds in two distinct phases: an initial pseudo-step corresponding to skin saturation, followed by diffusion within the foam core. A series of experimental studies corroborate this intricate diffusive behavior, underscoring the robustness and applicability of our model.
Composite sandwich structures are widely used in unmanned aerial vehicle (UAV) components due to their high stiffness-to-weight ratio; however, their vulnerability to impact-induced damage remains a major limitation for structural reliability. Conventional sandwich panels with uniform foam or honeycomb cores often experience either excessive indentation or brittle collapse under low-velocity impact, leading to significant degradation of post-impact stiffness. Although impact damage mechanisms in sandwich composites are well established, experimental validation of hybrid graded core architectures at full structural scales remains limited. In this study, a combined experimental and numerical investigation is conducted to evaluate the impact response and residual bending performance of hybrid graded sandwich panels for UAV applications. Sandwich panels incorporating carbon-fiber-reinforced polymer (CFRP) face sheets and three core configurations, namely uniform foam, uniform honeycomb, and hybrid graded foam-honeycomb, were subjected to a 25 J low-velocity impact followed by residual three-point bending tests. The results demonstrate that the hybrid graded configuration significantly improves impact tolerance by promoting progressive damage evolution. The graded panels exhibited a sustained force plateau, higher energy absorption (48.6 J), and effective damage confinement (similar to 4 cm2), compared with lower energy absorption (28.5 J for foam and 35.4 J for honeycomb) and larger delamination areas (8 cm2 and 12 cm2) in conventional cores. Residual bending tests revealed stiffness retention approximately 90%, substantially higher than that of uniform core configurations. These improvements arise from both core architecture and the controlled interaction of face-sheet damage, core crushing, and limited delamination governing post-impact load transfer. Finite element simulations developed in Abaqus/Explicit accurately reproduced the impact response and damage evolution, with deviations within similar to 11%. This study provides a validated full-scale demonstration of hybrid graded sandwich structures for UAV applications and establishes a quantitative correlation between damage morphology and residual structural performance, offering practical design guidance for impact-tolerant lightweight structures.
