Composite Sandwich Structures Research Articles

Mechanical characteristics of auxetic composite honeycomb sandwich structure under bending

Auxetic honeycomb sandwich structures (AHS) composed of a single material generally exhibit comparatively lower energy absorption (EA) and platform stress, as compared to traditional non-auxetic sandwich structures (TNS). To address this limitation, the present study examines the use of aluminum foam (AF) as a filling material in the re-entrant honeycomb sandwich structure (RS). Filling the AHS with AF greatly enhances both the EA and platform stress in comparison to filling the TNS with AF, while the auxetic composite honeycomb sandwich structure effectively addresses interface delamination observed in traditional non-auxetic composite sandwich structures. Subsequently, the positive–negative Poisson’s ratio coupling designs are proposed to strengthen the mechanical features of a single honeycomb sandwich structure. The analysis results show that the coupling structure optimizes the mechanical properties by leveraging the high bearing capacity of the hexagonal honeycomb and the great interaction between the re-entrant honeycomb and the filling material. In contrast with traditional non-auxetic sandwich structures, the proposed auxetic composite honeycomb sandwich structures demonstrate superior EA and platform stress performance, suggesting their immense potential for utilization in protective engineering.

Slate–Cork Laminate Enhanced with Silicone for Habitat Industry Application

This study investigates the feasibility of using a composite material comprising slate reinforced with cork sheets for architectural purposes like facades and wall coverings. The research involves the comprehensive characterisation of both slate and cork materials along with the evaluation of the silicone adhesive used in their bonding process, specifically Sikasil® HT from SIKA®. It was found that both slate and cork exhibited low wettability, which was enhanced through cold plasma treatment. Subsequently, a composite sandwich structure was fabricated and subjected to impact testing in a drop tower, along with fire resistance evaluations. The fire tests revealed that when subjected to a flame of 900 °C for 15 min, the slate alone heated rapidly, reaching 500 °C within 3 min on the side opposite to the flame. However, the sandwich structure reached 260 °C on the cork side (opposite to the flame) at 7.5 min, maintaining this temperature until the deterioration or detachment of the cork between 11 and 12 min. This provided insulation and delayed ignition. The sandwich structure maintained its fire resistance due to the insulating properties of cork and the superior thermal resistance of silicone compared to other adhesives up to 260 °C. Overall, the results suggest the potential suitability of this sandwich structure for architectural applications. Its favourable adhesion properties and acceptable fire resistance indicate that it could serve as a viable alternative for construction materials in architectural contexts.

Curved Polymeric Sandwich Composites Subjected to Air Shock: An Experimental Investigation

Abstract Background The vulnerability of polymeric composite sandwich structures in marine applications to air explosions highlights a significant gap in our understanding of the dynamic behavior of the curved sandwich structures, which is essential for design improvements. Objective This study aims to explore the dynamic response and failure mechanisms of curved sandwich composite panels subjected to air-blast loading, providing insights into their structural integrity under such conditions. Methods Experiments were performed using laboratory-simulated air shocks generated by a shock tube, employing high-speed photography and digital image correlation to measure deflections on the back surface of the panels. The panels, made with PVC closed-cell foam cores of two densities (H45 and H130), were tested across three curved geometries (radii of 112 mm, 305 mm, and infinity) under various boundary conditions. Results Findings indicate an increase in deformation with a decreased radius of curvature under simple support conditions, a trend that reverses under arrested displacement conditions. Moreover, a reduced radius significantly enhances panel strength and resistance to interfacial damage, with the primary failure mode transitioning from core shear cracking to interfacial debonding as core density increases. Conclusions The study reveals that the radius of curvature, boundary conditions, and core density significantly affect curved sandwich panels’ dynamic response and performance. Panels with smaller radii and higher core densities exhibit increased strength, though boundary conditions introduce variable effects on deformation behavior.

4D printed shape memory bismaleimide resin with high storage modulus and low shrinkage rate via second-stage curing

In recent years, the field of shape memory materials with active deformation capabilities has experienced rapid development. However, bismaleimide, as a widely used structural material in the aerospace industry, has been neglected in the field of shape memory. This work designed a UV-crosslinked network with 1-vinyl-2-pyrrolidone monomer, and prepared 4D printed smart structures based on shape memory bismaleimide resin through UV-assisted DIW printing. 4D printed semi-interpenetrating network polymer materials were obtained through a two-stage UV-thermal curing process, resulted in an increase in the material's glass transition temperature to a maximum of 187.4 °C. The storage modulus was improved to 5229 MPa. More important, we achieved a lowest shrinkage rate (0.21 %) of 4D printed polymer. The composite sandwich structure with electrical-driven shape memory performance was printed by double-sided printing of bismaleimide resin on conductive carbon fabric. 4D printed composite structure realizes in-situ self-blocking secondary curing, deformation process after curing. This significant progress provides a promising prospect for remote controllable and precise driving in the aerospace field.

Mechanical responses and damage characteristics of the high-velocity impact of ice projectiles on foam sandwich structure

The integration of composite sandwich structures in aircraft design necessitates consideration of hail impacts within aerospace applications. This investigates the dynamic response and damage characteristics of a carbon fibre/PMI foam sandwich structure under hail impact through both experimental and numerical simulation methods. These methods analyse the impact velocity, fibre panel thickness, and angle of incidence of the ice projectiles. The study establishes relationships among various parameters such as ice projectile impact force, foam absorption energy, and target plate deformation in relation to the impact velocity and angle of incidence. The damage sustained by the carbon fibre/PMI foam sandwich (CPS) structure due to ice projectile impact was systematically categorized and examined. Additionally, the effects of normal and tangential impact velocities on the target plate's dynamic response during oblique impacts were investigated. This research serves as a valuable reference for understanding the dynamic response and damage characteristics of composite foam sandwich structures subjected to ice projectile impacts, With a focus on the carbon fibre/PMI foam sandwich structure.

Fabrication and mechanical properties of thermoplastic corrugated sandwich panel with enhanced face‐core interface

AbstractThermoplastic sandwich structures are widely utilized in engineering fields due to their high specific strength and stiffness, recyclability, and impact toughness. The face‐core interface strength is crucial to maximize the performance benefits of sandwich structures. Two sizes of corrugated sandwich panels with hot‐melt bonding and resistance welding connection methods were fabricated. The mechanical properties of sandwich panels were compared using a combination of experimental, numerical, and analytical investigation. Edgewise compression (EC) and 3‐point bending (3 PB) tests were conducted to obtain load–displacement curves and investigate different failure modes of sandwich panels. The peak edge compression and bending loads of the resistance welded structures were 42% and 92% higher, respectively, and the face‐core interface was always well‐connected compared to those of the hot‐melt bonding. The results indicate that the resistance welding method can be utilized as a core bonding technique for thermoplastic composite sandwich structures and has great potential for aerospace application.Highlights A method that includes hot‐melt bonding and resistance welding are develop to produce thermoplastic composite corrugated sandwich panels (TPC‐CSPs). The TPC‐CSPs fabricated by resistance welding exhibit superior interface connection performance compared to hot‐melt bonding and this method enhance the structural load bearing capacity. The numerical and analytical method were presented to investigate the failure model, which was consistent with the experimental results.

Dynamic response of GFRP/Nomex honeycomb sandwich panels subjected to multiple hail impacts – An experimental study

AbstractNowadays, more and more aircraft components are made of composite sandwich structures, and ice impacts are prone to cause internal damage to composite sandwich structures, so it is crucial to study the impact of hail on composite sandwich structures. Since hail impacts may occur several times at a single point, an experimental approach was used to investigate the dynamic response of GFRP/Nomex honeycomb sandwich panels under multiple hail impacts. The dynamic response of the structure was investigated in terms of response rate and deflection‐profile curves using 3D digital image correlation methods, and the effects of impact energy, hail size, and number of impacts on the impact resistance of the honeycomb sandwich structure were explored. The results show that the dynamic response process of sandwich panels can be categorized into the ball‐and‐crown phase, the rebound phase, and the vibration phase. Under the same impact energy, the impact of small‐sized hailstones is more threatening to honeycomb sandwich panels. As the number of impacts increases, the maximum deflection value of the back panel first increases uniformly, and when the layered damage area reaches the threshold value, fiber stripping occurs, and the increment of the maximum deflection value increases significantly.Highlights Since hail impacts may occur several times in real situations, this study conducted multiple impact experiments for one impact site. The dynamic response and damage pattern of the GFRP/Nomex honeycomb sandwich panels under multiple hail impacts were also investigated. The dynamic response process of GFRP/Nomex honeycomb sandwich panels was categorized into three phases: ball‐crown stage, rebound stage, and vibration stage. With the increase of the number of impacts, fiber stripping and fiber break damage began to occur when the layered damage area of the panel reached the threshold value. The honeycomb core has three main failure modes: cell wall folds, cell wall fracture, and cell wall debonding at the TGPW interface. Small‐diameter hails pose a more significant threat of damage to honeycomb sandwich panels at the same impact energy.

Sandwich-Structured Mxene/Waste Polyurethane Foam Composites For Highly Efficient Electromagnetic Interference, Infrared Shielding and Joule Heating.

Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high-efficiency EMI shielding and IR stealth materials of sandwich-structured MXene-based thin foam composites (M-W-M) via filtration and hot-pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of "film-foam-film", the M-W-M composite exhibits a high EMI shielding effectiveness of 83.37dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7-14µm and thermal conductivity (0.19W m-1 K-1), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M-W-M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.

A combination of “Inner - Outer skeleton” strategy to improve the mechanical properties and heat resistance of polyimide composite aerogels as composite sandwich structures for space vehicles

Low density aerogels with high fatigue resistance are widely used in the manufacturing of core material structures in aircraft fuselage to be able to tolerate the extreme environment of aerospace. However, most organic aerogel materials have poor energy absorption of external impact forces, and are prone to irreversible deformation, such as contracture and collapse in the process of long-term service. In order to solve this problem, a new type of thermosetting-thermoplastic polyimide composite aerogel was prepared, with its microstructure presenting the coexistence of the inner and outer skeletons. The intermolecular forces promoted the assembly of the soft thermoplastic layer and the strong thermosetting layer in the thermodynamic process with 4.63–6.55 μm range. The hard-soft layer structure improved the compressive and the shear load bearing capacities by bending of the panel (Compressive modulus is 1.60 MPa–3.52 MPa, tensile modulus is 1.04 MPa–1.45 MPa). Its permanent degradation less than 1.5 % after 500 cycles at 30 % strain. C–CPIAs also exhibited excellent heat resistance and thermal insulation performances, with a T5% value of 612 °C (C-CPIA-2), Tg of 458 °C (C-CPIA-3). The sandwich materials can be used as outer protective composite material of aircraft fuselage for future deep space missions.

Mussel-inspired antimicrobial and antireflective Ag-NPs/PDA/SiO2 coatings via interfacial functionalization

Utilizing surface chemical engineering to endow interfacial special functionalities is effective for fabricating antireflection coating with antibacterial activity. Herein, we present a mussel-inspired dopamine (DA) interfacial functionalization strategy to modify porous silica antireflection coatings, forming a sandwich composite structure composing an antireflective, intermediary, and antibacterial layer. The low refractive index antireflective coating formed by porous silica with developed pore structure greatly improves the light transmittance, and provides a trace of moisture and oxygen channels to facilitate the activation of Ag-NPs, significantly increases the antimicrobial efficiency of the coatings. PDA helps Ag-NPs to be uniformly dispersed and anchored on the surface of the silica, which significantly enhances the antibacterial performance and durability. In addition, the introduction of PDA reduces the surface roughness of the coating, thus reducing light scattering and attenuating the negative effect of Ag-NPs on light propagation. Under the optimal conditions, the antibacterial rate of GSPA-0.1–10 exceeds 99.9999 % (E. coli and S. aureus antimicrobial rate > 99.9999 % at 40 min and 3 h, respectively), and the light transmittance was maintained above 96 %. This work demonstrates a synergistic interaction between porous silica and PDA, which will provide a new approach for the functionalization of porous antireflective coatings.

Functionally varied negative-stiffness metamaterial core sandwich structures with three-phase bending deformation

Abstract This paper introduces a novel class of negative-stiffness (NS) core sandwich composite structures that exhibit unique mechanical performance, including shape recovery, superelasticity, and energy absorption (EA) in bending and shear mode. The core of these structures consists of a periodic cellular arrangement of double-curved beams that undergo consecutive local snap-buckling transitions between multiple equilibrium states, enabling the structures to change shape reversibly between their initial and deformed configurations. To characterize the force-displacement relationship of the core, a comprehensive analysis was conducted using a combination of 3D printed models and finite-element simulations. The metamaterial core with gradient-thickness negative-stiffness beams were examined under uniform compression, demonstrating that the snap-through behavior of the curved beams was intricately controlled by the beam thickness in each row. The numerical simulations accurately predicted the deformation characteristics of the graded cellular core, supporting the design of a metamaterial core with functionally varied beam thickness for nonuniform transverse loading. This led to spatially controlled NS core material with specific EA of around 50 J kg−1 and an apparent core shear strength of 0.1 MPa, all mainly within the reusable elastic regime. The resulting sandwich structures efficiently mitigated the localized effect from concentrated compressive forces and achieved complete snap-through buckling in all curve beams. Three-point bending response revealed three distinct phases of flexural deformation: the local facial bending phase, the sequential core-snapping superelastic phase, and the global bending phase.

Multifunctional design of hierarchical corrugated metamaterial absorber realized by carbon fiber stitching

Carbon fiber (CF) which has both mechanical and electromagnetic (EM) characteristics can achieve multiple functions by special designing, such as load bearing and EM wave absorption. In this work, based on the excellent mechanical properties of hierarchical corrugated sandwich structure (HCSS), a novel CF interlaminar reinforced hierarchical corrugated metamaterial absorber (HCMMA) is constructed. By stitching CF arrays onto the core member face of HCSS, the spoof surface plasmon polaritons (SSPPs) structure is constructed, endowing HCSS with EM wave absorption ability and enhancing its interlaminar mechanical properties. Simulation and experimental results show that the proposed structure achieves efficient absorption (average over 90 %) of 4 - 12 GHz EM wave with an incident angle of 0 - 60°, which realized by the dielectric loss of EM wave and local strong E-filed formed by SSPPs structure. In addition, the stitching of CF arrays effectively limit the local buckling-debonding deformation region of the core member face, which greatly improves its mechanical performances. Thereby the compressive strength and specific compressive strength of the proposed structure is increased by 32.7 % and 16.7 %, respectively. Based on the multifunctional design characteristics of CF, the proposed structure effectively expands the application of composite sandwich structures in the field of multifunctional design.

Accurate free and forced vibration behavior prediction of functionally graded sandwich beams with variable cross-section: A finite element assessment

The current investigation proposes an enhanced finite element beam model to assess the dynamic behavior of functionally graded sandwich beams with variable cross-sections. By integrating the shear effect, this beam model integrates both C0 and C1 continuities to generate elementary matrices using an efficient three-unknown shear deformation beam theory. The model focuses on advanced sandwich beams with functionally graded material face-sheets and metallic cores, exploring various geometric arrangements. The originality of this study addresses variable cross-sections in sandwich beams, evaluating the influence of material composition and geometric configurations on free and forced vibration responses, including different boundary conditions. The methodology uses the eigenvalue method for examining free vibration and applies Newmark’s algorithm for solving forced vibration problems. The current model expands the scope of analysis compared to previous models that primarily focus on uniform cross-sections and conventional material distributions. The developed model incorporates non-uniform geometrics, material gradient parameters, and advanced finite element analysis to enhance precision and efficacy through detailed parametric investigations and comparisons with existing literature. This contribution significantly improves the mechanical modeling of composite sandwich structures, particularly those incorporating functionally graded materials and complex geometrical aspects.

Study on the Energy Absorption Characteristics of Different Composite Honeycomb Sandwich Structures under Impact Energy

A honeycomb structure is a sandwich structure widely used in fuselage, among which the hexagonal honeycomb core is the most widely used. The energy absorption characteristics and impedance ability of the structure are the main reasons that directly affect the energy absorption characteristics of the honeycomb sandwich structure. Therefore, it is necessary to study the out-of-plane mechanical properties of the composite honeycomb sandwich structure. Based on the numerical simulation results, the energy absorption characteristics of several composite honeycomb sandwich structures are verified by drop hammer impact experiments. The research shows that the transient energy absorption characteristics of the composite honeycomb sandwich structure are mainly related to the cell size of the honeycomb structure. The smaller the size of the front cell, the stronger the overall impact resistance; the strength of the composite honeycomb sandwich structure exceeds that of 7075 aluminum alloy-NOMEX and carbon fiber-NOMEX honeycomb sandwich structures. In this paper, the energy absorption characteristics of composite honeycomb sandwich structures under different impact energy are compared and studied. The displacement, force and energy curves of energy absorption characteristics related to time variables are analyzed. The difference in protective performance between the composite honeycomb sandwich structure and existing airframe structure is compared and studied. The optimal structural design parameters of composite honeycomb sandwich under low-speed impact of drop hammer are obtained. The maximum energy absorption per unit volume of the designed honeycomb sandwich structure is 171.7% and 229.8% higher than that of the NOMEX-AL and NOMEX-C structures. The 6.4 mm and 3 mm cell sizes show good characteristics in high-speed buffering and crashworthiness. The composite honeycomb sandwich airframe structure can improve the anti-damage performance of the UAV airframe structure, ensure the same thickness and lightweight conditions as the existing honeycomb sandwich airframe structure, and improve the single-core bearing mode of the existing airframe structure.

Compressive Strength and Elastic Modulus of a 3D Woven Glass/Polyester Fire-Retardant Sandwich Composite

A 3D woven sandwich composite structure has been widely used in various fields due to its advantages in terms of its strength-to-weight ratio. The adoption of lightweight materials in the railway industry for train carriages is aligned with United Nations Sustainable Development Goal 11, as this fosters the development of sustainable transportation by reducing carriage weight, enhancing fuel efficiency, minimizing component wear, and mitigating air pollution. This study explores the effect of the addition of aluminum trioxide (ATH) filler on the core structure, density, compressive strength, elastic modulus, and the number of added layers of 3D woven core fabric with 2D woven face sheets. Sandwich composites were produced with varying ATH loads of 30%, 40%, and 50%. We also varied the number of 3D woven core fabric layers in the composite sandwich (one, two, three, and four layers) and the 2D preform (one on the upper side, two on the upper side, and one on the upper + two on the lower sides) used as a face sheet thickener. The results showed that the addition of ATH filler increased the composite density. The addition of up to 40% ATH improved the strength and elastic modulus of the composite, while excessive loading led to a decrease in both properties. Variation of the 3D and 2D preform layers also improved the compressive strength and elastic modulus. We conclude that 3D woven sandwich composites incorporating 40% ATH, multilayered 3D woven core fabric, and 2D woven fabric face sheet thickener represent promising materials for use in the railway industry.

A flexible wearable phase change composite with electro-/photo-thermal heating for personal thermal management and human body motion detection

There is an urgent need to develop flexible materials with electrothermal/photothermal conversion and energy storage/release capabilities to meet the requirement of wearable personal thermal management (PTM) and health monitoring. Here, sandwich-structured phase change composites (SSPCCs) with PTM and health monitoring were prepared through film-forming and pressing process, in which a poly (ethylene vinyl acetate) (EVA)/poly (ethylene glycol) (PEG) composite was the middle layer, and waterborne polyurethane (WPU)/carbon nanotubes (CNTs) films were the top and bottom layers. The electrical conductivity and tensile strength of the two outer layers with 3 phr CNTs can achieve 2.83 S/m and 12.96 MPa, respectively. Due to the multiple synergistic effects of sandwich structure, the SSPCCs exhibit excellent flexibility with an elongation at break of approximately 1173 %, good stability and durability of 500 cycles and admirable electro-/photo-thermal heating performance (∼40 °C at 7 V or NIR light power of 50 mW/cm2). In addition, the inner layer, where the flexible EVA hold PEG well, has a melting latent heat of 71.45 J/g and freezing latent heat of 65.79 J/g in the phase change process as the mass ratio of PEG reached 50 wt%. The prepared composites show good abilities of information encryption and motions monitoring, which turns out great promising applications in wearable personal thermal management and medical devices.

Efficient design of composite honeycomb sandwich panels under blast loading

Hybrid composite honeycomb sandwich structures (HCHSS) were employed due to high specific strength and stiffness and higher impact resistance property required for the aerospace and defence fields. The numerical modelling of the efficient HCHSS was developed for the core, front and back face plate using the C3D8R elements to determine the realistic failure behaviour for the honeycomb sandwich structure. The ConWep blast simulation loading was applied for the HCHSS. Advanced composite materials were used for the blast analysis of the HCHSS (carbon/epoxy, graphite/epoxy, woven basalt fibres/polypropylene and woven Kevlar fibres/polypropylene). The damage initiation and damage propagation based progressive damage modelling was developed and implemented in the VUMAT code for composite materials to determine the actual failure behaviour of the HCHSS. The face sheets used in this model were of a stainless-steel alloy AL-6XN. The sandwich structure was subjected to blast loads of 1, 2 and 3 kg of TNT and their performance was compared w.r.t both front and back-face deflection. The effectiveness of sandwich panels was further examined by altering the thickness of the core. Fibre-metal laminates (FML) were used in place of the steel face sheets in the panel in order to minimise its mass, and a thorough analysis of the panel’s mass in relation to its peak deflection was carried out. Upon analysing the results, it was noted that the panel with the basalt fibre reinforced polymer (BFRP) core gave the best results compared to other composite materials. For a blast load of 3 kg TNT, the peak back face deflection (PBFD) of HCHSS with a BFRP core decreased by 10.64%, 7.61% and 4.75%, respectively, compared to panels with CFRP, GFRP, and KFRP cores. The peak deflection of the panel decreased as the BFRP core thickness increased. The energy absorption capacity of the panel also increased with increasing thickness. Additionally, it was found that panels with BFRP cores and KFRP-steel laminate face sheets provided the optimum balance of strong blast resistant performance and light weight. Compared to the metallic (steel) sandwich panel, the mass of the sandwich panel with KFRP-steel laminate face sheets and BFRP core was reduced by 33%, but at the same time, its PBFD increased by almost 50%.

Depositing gradient thickness silver film on CNF/rGO/polyimide surface to form a sandwich structure for efficient electromagnetic interference shielding

Deployable satellites in space are exposed to high-frequency electromagnetic interference (EMI) for long periods of time, resulting in shortened lifetimes, so there is an urgent need for supportive electromagnetic shielding materials. To address this limitation, our team has developed innovative ultrathin carbon nanofiber/reduced graphene oxide/polyimide (CNF/rGO/PI) composites. It has excellent strength, shape memory properties, thermal stability and wide temperature range tolerance. Among them, polyimide with 4 % CNFs and 4 % rGO (CGPI44) has the best performance. Gradient-thick Ag films are deposited on both sides of the CGPI44 substrate by magnetron sputtering to form sandwich structure composites. With a sputtered Ag thickness of only about 5 μm and a total thickness of 0.146 mm, the material exhibited an extremely high electrical conductivity and excellent EMI shielding effectiveness (SE) of up to 112 dB in the 8.2–12.4 GHz band. Finite element analysis is performed to calculate the electric field strength and energy distribution. By providing a feasible scheme for highly effective shielding of high-frequency EMI, this approach will promote research on magnetron-sputtered polymer composites in the field of electromagnetic shielding.

Cryogenic insulation performance of polyimide foam-filled fluted-core composite sandwich panels

Foam-filled composite sandwich structures have demonstrated superior thermal insulation performance, making them highly suitable for cryogenic tanks in launch vehicles. This study focused on the cryogenic insulation characteristics of carbon fiber-reinforced plastic (CFRP) fluted-core sandwich panels filled with polyimide foam. The fluted-core sandwich panel was simplified into a homogeneous multilayer plate to establish a one-dimensional heat transfer theoretical model. This model was used to predict steady-state temperature approximate solutions by linearizing the temperature-dependent thermal conductivity. The sandwich specimens were fabricated using an integrated forming co-cured method. Self-developed cryogenic insulation experiment and finite element simulations were conducted to acquire temperature distributions and validated the precision of the theoretical model. Results showed that the specimens achieved insulation temperature difference exceeding 143.05 °C, with effective thermal conductivity reaching 0.0326 W/(m·°C), significantly lower than that of CFRP. The temperature distributions along the thickness direction displayed a nonlinear increasing trend. The cryogenic thermal short effect was noticeable at the junction of the bottom facesheet and web. An analysis of geometric parameter influences revealed that increasing the short span, core height, or reducing web thickness could enhance thermal insulation characteristics with minimum effective thermal conductivity of 0.0276 W/(m·°C) and lead to a more uniform distribution of bottom temperatures with minimum temperature difference of 3.30 °C. These findings provide a foundational analysis for designing cryogenic insulation structures.

Mechanical Behavior of Bio-Inspired Honeycomb-Core Composite Sandwich Structures to Low-Velocity Dynamic Loading.

In order to improve the impact resistance of sandwich panels under low-velocity impact, the lotus leaf vein is selected as a biological prototype to design a bio-inspired honeycomb (BIH) sandwich panel. ABAQUS is used to establish and effectively verify the finite element (FE) model of the BIH sandwich panel. To systematically compare and study the mechanical properties of BIH and conventional hexagonal honeycomb sandwich panels under low-velocity impact, the maximum displacement of face-sheets, the deformation mode, the plastic energy consumption and the dynamic response curve of the impact end are presented. At the same time, the performance differences between them are revealed from the perspective of an energy absorption mechanism. Furthermore, the influence of the circumscribed circle diameter ratio of the BIH trunk to branch (γ), the thickness ratio of the trunk to branch (K) and the impact angle (θ) on impact resistance is studied. Finally, the BIH sandwich panel is further optimized by using the response surface method. It can be concluded that, compared to conventional hexagonal honeycomb sandwich panels, the addition of walls in the BIH sandwich panel reduces the maximum deformation of the rear face-sheet by 10.29% and increases plastic energy consumption by 8.02%. Properly adjusting the structural parameters can effectively enhance the impact resistance of the BIH sandwich panel.