Corrugated Sandwich Structures Research Articles

Low-velocity impact failure of foam-filled GFRP trapezoidal corrugated sandwich structures

In this paper, a new lightweight sandwich structure with polyurethane foam filled glass fiber reinforced polymer (GFRP) trapezoidal corrugated sandwich structure is fabricated. Based on the low-velocity impact tests, the impact failure performance and energy absorption efficiency of polyurethane foam filled sandwich structures are investigated. Low-velocity impact tests were carried out on the node and base positions of the foam filled trapezoidal corrugated sandwich structure by using a drop hammer test machine, and the set impact energy range was 25 J – 150 J. Experimental results show that when the impact energy is the same, the maximum impact load and maximum energy absorption generated by the node impact are greater than the base impact, which proves that the node position has better impact resistance and energy absorption effect than the base position. In addition, by comparing the displacement-time curves of foam filled and unfilled sandwich structures, it is found that when the impact energy is the same, the slope of the displacement-time curve of unfilled specimen is greater than that of foam filled specimen. Therefore, within the same time, the deformation of unfilled specimen is larger than foam filled specimen during the impact process, which demonstrates the effectiveness of polyurethane foam filling on the gain of sandwich structure.

Cushioning performance design of meta-sandwich structures inspired by Kirigami

ABSTRACT Novel ultralight meta-sandwich structures inspired by Kirigami (MSS) are proposed in this study. The topological designs of uniform (MSS-U) and non-uniform (MSS-N) sizes are studied based on the inconsistent distribution of the biomaterials. First, MSS-U and MSS-N are manufactured using laser powder bed fusion (LPBF) technology, and energy absorption prediction formulas are successfully derived by extracting the experimental deformation features. It is found that MSS-N exhibits a higher energy absorption level than MSS-U. Compared to the conventional corrugated sandwich structures (CSS), the MSS achieves better crashworthiness indicators and more folding numbers. Moreover, the parameter effect of the MSS is analysed, and the minimum/maximum thickness and folding angle significantly influence the crashworthiness responses. The mechanical properties of MSS-N can be regulated by changing the folding angle while maintaining the same thickness. The MSS proposed in this study can achieve a higher energy absorption efficiency at the same density compared to other existing mechanical structures. Interestingly, the feasibility of applying MSS to automobiles and plant protection drones is verified by changing the materials and macro-configurations. The design concept presented in this study provides a promising method for obtaining sandwich structures with excellent cushioning properties for engineering protective equipment.

Analytical investigation of hygrothermal effects on failure mechanisms of adhesively bonded corrugated sandwich structures under three-point bending

This research paper presents an analytical mechanics model for studying the degraded failure mechanics of an adhesively bonded corrugated sandwich structure (ABCSS) subjected to three-point bending and hygrothermal ageing loads. The model incorporates a detailed stress state model that considers the stress distribution of the adhesive layer, including the adhesive fillet, to more accurately reflect the failure mechanics of ABCSS. The Fickian Diffusion model and a degradation coefficient are used to describe the characteristics of water diffusion and hygrothermal mechanical degradation for the adhesive joint in ABCSS. The hygrothermal ageing experiments are conducted by immersing the ABCSS into deionized water and 5 wt% NaCl water, followed by three-point bending tests after hygrothermal ageing. The proposed two-step finite element (FE) method is developed to simulate both moisture diffusion and three-point bending test. The presented FE method is validated through comparison with corresponding experimental results, then it is utilized to demonstrate that the proposed analytical model is accurate enough in initial failure modes and initial failure loads predictions. At last, the hygrothermal effects on degraded stress distribution and degraded failure performance are investigated through analytical method, and the degraded failure mechanics maps are constructed to further visually demonstrate failure mechanics with the aid of the analytical model.

Laser powder bed fusion of multilayer corrugated sandwich structures: Mechanical properties and failure mechanisms under bending loadings

Laser powder bed fusion of multilayer corrugated sandwich structures: Mechanical properties and failure mechanisms under bending loadings

Numerical study of heat transfer and load-bearing performances of corrugated sandwich structure with open-cell metal foam

Critical engineering applications require lightweight components that can effectively dissipate heat and provide sufficient load-bearing capacity. Examples of such applications include the jet blast deflector (JBD) on an aircraft carrier and engine combustion chambers in supersonic vehicles. While lightweight corrugated sandwich structures (CSSs) exhibit excellent load-bearing capacity, their heat transfer capacity falls short. To overcome this limitation, a strategy of filling the CSS with an open-cell metal foam (MF) is proposed to create a sandwich structure with ultralight load bearing and heat transfer capabilities. Numerical simulations were conducted to study the heat transfer and load-bearing performance of this new structure. The findings indicate that the use of a MF significantly improves the heat transfer capabilities of the CSS. Compared to the CSS, the Nusselt number of MF and CSS-foam composite at a Reynolds number of 240 were enhanced by 51.3% and 102.3%, respectively. The overall thermal performance of CSS-foam composites was optimized under the same pumping power constraints. In turbulent conditions, the overall thermal performance of CSS-foam composites was 5.9% to 55.4% higher than that of CSS in turbulent conditions. Furthermore, the simulations showed that when the CSS was subjected to static and quasi-static compression, the maximum von Mises stress occurred at the connection between the panel and the web.

Experimental Study on Low-Velocity Impact Performance of GFRP Trapezoidal Corrugated Sandwich Structures

Glass fiber trapezoidal corrugated sandwich structures are composed of trapezoidal cores and glass fiber-reinforced polymer (GFRP) panels. A series of low-velocity impact tests were conducted to investigate the impact resistance performance, considering the effects of impact position, impactor shape, and impactor diameter on the damage mechanism of sandwich structures. When the impactor shape and impact energy remain constant, the maximum impact load at the node impact point is higher than at the base, while the displacement of impact at the base is significantly higher than that at the node. Secondly, when the impactor diameter and energy of the impactor are the same, the hemispherical impactor requires less penetration energy to impact the sandwich structure compared to the flat impactor. Comparing the shape of the impactor, it is found that the smaller the contact surface of the impactor, the more concentrated the stress, and the lower the required penetration energy. Finally, when the impactor shape and impact energy are the same, as the diameter of impactor increases, the damage expansion during impacting on the sandwich structure becomes more sufficient, resulting in decreased impact displacement and smaller impact damage caused to the sandwich structure.

The compressive performances of 3D-printed micron-size corrugated sandwich structures

Micron-scale grid-shaped, V-shaped and U-shaped corrugated sandwich structures are fabricated by 3D printing technology and present different mechanical properties from those made by traditional method. Their peak stresses and elastic moduli could be fitted to cubic functions. The compression performance of the multilayer grid-shaped sandwich can be determined by the relative mechanical strength of layers. Adding a layer on a grid-shaped sandwich has no significant influence on the peak stress, but can enhance the elastic modulus by about 60.9 MPa. The deformation modes of multilayer V-shaped and U-shaped sandwiches can be determined by the load carrying path and the relative mechanical properties between interlayers and cores. The elastic modulus of V-shaped sandwich is enhanced with the increase of layer number, while the elastic modulus of U-shaped sandwich decreases with the increase of layer number. The peak stress and the elastic modulus of a four-layer V-shaped sandwich can reach 9.85 MPa and 261.09 MPa, and those of a four-layer U-shaped sandwich can reach 4.79 MPa and 119.18 MPa. The result reveals the principles that the reduced structural size and suppressed debonding, the structures and the load carrying path, and materials, influence the failure mode and mechanical properties of the corrugated sandwiches.

Impact resistance of composite circular corrugated core sandwich structures

In this study, we used HyperMesh and LS-DYNA software, based on the MAT54 model and Chang-Chang failure criterion, to establish a finite element model of composite corrugated sandwich structures, and introduced a progressive damage model. The impact resistance of the corrugated sandwich structure was studied by analysing the residual velocity of the projectile, the impact force of the target plate, and the failure mode. The impact resistance of the corrugated sandwich structure was analysed when four types of composite materials were used as the front and back panels of the corrugated sandwich structure. The results showed that, compared with the metal aluminium panel, the impact resistance of the structure was high when ultra-high molecular weight polyethylene (UHMWPE) fibres were used as the positive panel. When the composites were used as the back panel, although the residual velocity was lower than metal aluminium, the impact force was higher than metal aluminium, with more serious damage form of the target plate. Thus, the impact resistance of composite front panel/metal aluminium core/metal aluminium back panel sandwich structure was better than the all-metal aluminium corrugated sandwich structures. The results of this paper can provide a reference for the design of novel lightweight multifunctional structures.

Damage in hybrid corrugated core sandwich structures under high velocity hail ice impact: A numerical study

Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight. In this study, a nonlinear finite element (FE) model is developed to investigate the dynamic response and damage behavior of hybrid corrugated sandwich structures subjected to high velocity hail ice impact. The impact and breaking behavior of hail are described using the FE-smoothed particle hydrodynamics (FE-SPH) method. A rate-dependent progressive damage model is employed to capture the intra-laminar damage response; cohesive element and surface-based cohesive contact are implemented to predict the inter-laminar delamination and sheet/core debonding phenomena respectively. The transient processes of sandwich structure under different hail ice impact conditions are analyzed. Comparative analysis is conducted to address the influences of core shape and impact position on the impact performance of sandwich structures and the corresponding energy absorption characteristics are also revealed.

Radar-stealth and load-bearing corrugated sandwich structures with superior environmental adaptability

The engineering design of lightweight multifunctional composite structures is an attractive research subject with enormous potential in the aerospace and marine fields. Nevertheless, the mechanical and electromagnetic performance of variable-curvature structures has been seldom investigated. Herein, a novel multifunctional sinusoidal corrugated sandwich structure with impedance-type frequency selective surface (FSS) is proposed to provide superior out-of-plane load-bearing capacity and broadband microwave stealth performance. A precise theoretical model is proposed to predict the out-of-plane compressive strength of sinusoidal corrugated structures. The model is based on the Timoshenko beam theory and a modified plastic hinge theory, considering the actual stress distribution on the cross-section. The selective laser sintering (SLS) method is employed to fabricate a series of specimens with different structural parameters. The simulation analysis and experimental results suggest that the proposed mechanical model possesses high precision and wide applicability. The proposed multifunctional sandwich structure has an average ultimate compressive strength of 1.106 MPa and broadband microwave stealth (maximum reflectivity of −8.8 dB in 2–18 GHz). Environmental factors are found to have little effect on microwave reflectivity, including out-of-plane compressing (2 dB), frosting (0.5 dB) and holing (0.5 dB). The present study provides an example of broadband microwave stealth and load-bearing structure with superior environmental adaptability.

Experimental and numerical study on the low-velocity impact response of thermoplastic composite corrugated sandwich panels

Composite corrugated sandwich structures have a wide range of applications in aerospace field, and the loss of structural load carrying capacity due to low-velocity impact damage has become one of the main threats in practical applications. In this study, the impact resistance of corrugated sandwich panels prepared from thermoplastic composites (TPC) under low-velocity impact loading was investigated. Through a series of drop-weight experiments and finite element simulations, the impact response process and damage morphology of the thermoplastic composite sandwich panels were obtained, and the effects of different impact energy and different core arrangements on the energy absorption performance of the structure were explored. Finally, a parametric analysis of the perpendicularly-arranged double-layered corrugated sandwich panel was carried out. The results show that thermoplastic composite sandwich panels exhibit an overall collapse response rather than localised damage, and the structure maintains good integrity and stability. The perpendicularly-arranged sandwich panels rely on the orthogonal configuration characteristics to provide optimum impact load carrying capacity, their impact resistance can be further improved by increasing the thickness of top face-sheet and reducing the thickness of the middle face-sheet at the same time. This provides a basis for promoting the application of TPC in engineering and the design of sandwich structures.

A dimension-reduction based Chebyshev polynomial method for uncertainty analysis in composite corrugated sandwich structures

A prediction method for the ultimate load of composite corrugated sandwich structures (CCSS) was established based on the dimension-reduction method and Chebyshev polynomial. First, an ultimate load response function of the CCSS was reduced in dimension on basis of the univariate method. The original response function was converted to the sum of univariate functions of all random variables. Chebyshev polynomial was used to fit all univariate functions, and the univariate Chebyshev approximate model (UCAM) of the response function was obtained. Second, the fitting accuracy of the UCAM was analytically compared with the Kriging model, radial basis function, and response surface methodology. Finally, the effect of the order on the fitting accuracy of UCAM was studied. The UCAM has higher fitting accuracy and calculation efficiency compared with the other three approximate models. When the order of UCAM is lower than ninth-order, the larger the order, the higher the fitting accuracy. And the order and the fitting accuracy are no longer positively correlated when the order exceeds ninth-order. The order is recommended to choose an odd-order when using UCAM to solve the uncertainty problem.

Coupled Eulerian-Lagrangian (CEL) characterization of slamming response and failure mechanism on corrugated sandwich structures

This paper aims to numerically investigate the dynamic response and failure mechanism of corrugated composite metal sandwich structures under slamming impact. Firstly, a slamming model is established based on Coupled Eulerian-Lagrangian (CEL) method and verified through the comparison with the published results. Subsequently, the influence of slamming velocity and deadrise angle on hydrodynamic response are studied through the monitoring of hydrodynamic force, deflection and pressure distribution. Finally, ultimate damage mode and critical failure mechanism are characterized by a VUMAT subroutine developed based on Hashin failure and Yeh delamination criterion. Results indicate that the final failure is regional collapse, accompanied with fiber rupture of bottom skin, plastic hinge of aluminum core and obvious damage of upper skin. The collapse propagates gradually from the lower 1/3 (β=5°) to the upper 1/3 (β=10°) of sandwich structure, indicating that the increase of deadrise angle is beneficial to the delay of final failure. The dominate damage mode changes from widespread matrix damage (V = 6 m/s and V = 8 m/s) to concentrated fiber fracture damage (V = 10 m/s), illustrating that the influence of slamming velocity is mainly reflected in damage degree. Stripe distributed matrix tension damage is the critical damage mode, which may led to resulting damage aggravation and core-skin delamination.

Crashworthiness analysis and optimization of bionic corrugated sandwich structures

To improve the crashworthiness of thin-walled sandwich structures, a series of bionic corrugated sandwich structures with triangular elements (the height-to-width ratios of the elements are defined as γ) were designed inspired by the structures of shrimp chelas, including single-layer, double-layer and three-layer corrugated sandwich structures (γ1, γ2 and γ3 denotes the height-to-width ratios of single-layer, double-layer and three-layer elements, respectively). To analyze the deformation and mechanical response of the bionic thin-walled structures, the finite element method was adopted based on LS-DYNA and HyperMesh. By taking the initial peak load Fp and specific energy absorption Es as crashworthiness indexes, the influences of γ on the crashworthiness of the corrugated sandwich structures were discussed. The crashworthiness of the single-layer sandwich structures becomes worse gradually when the parameters γ exceed a certain value. For the double-layer sandwich structures, the influences of the parameters γ2 in the lower layers on the crashworthiness is greater than that of the parameters γ1 in the upper layers.. The Fp decreases by 37.8% with the increase of γ2, which means the greater γ2 of the lower layer is beneficial to improve the crashworthiness of the structure. For the three-layer sandwich structures, the influence of γ on crashworthiness indexes was investigated by range and variance analysis methods. The results show that the γ3 has the most significant influence on Es, and the significance level reaches 0.1. Finally, the optimal parameters of the bionic corrugated sandwich structures were obtained by using the multi-objective particle swarm optimization method based on a polynomial regression (PR) meta model. The optimal results show that the crashworthiness of the single-layer corrugated sandwich structures improves with the increase of γ. For the double-layer corrugated sandwich structures, The γ of the lower layer affects the crashworthiness more significantly than the γ of the upper layer. The three-layer corrugated sandwich structure with lower γ has higher Es. The optimal dimensions of the single-layer, double-layer and three-layer structures are γ = 0.8; γ1 = 0.5 and γ2 = 1.2; γ1 = 0.6, γ2 = 0.6 and γ3 = 0.9, respectively. The above results are helpful for the design of the thin-walled sandwich structures.

Failure analysis of bio-inspired corrugated sandwich structures fabricated by laser powder bed fusion under three-point bending

Corrugated sandwich structures have been widely used in aviation and aerospace industries due to their perfect mechanical properties. In our work, the theoretical derivation, experimental and finite element method (FEM) were applied to investigate the failure mechanisms and processes of bio-inspired corrugated sandwich structures (BCSS) manufactured by laser powder bed fusion (LPBF) under three-point bending. The results show that the failure maps of BCSS with different structural parameters can be obtained based on the theoretical model, and the panel buckling is the fundamental failure mode because it takes up most of the area of failure maps. Moreover, the panel buckling cannot cause the BCSS to fail, and the panel yielding or core buckling is the fatal failure mode for the structures whose initial failure mode is the panel buckling. Furthermore, the experimental and FEM results agree well with those of analytical predictions.

Bending performance and failure behavior of 3D printed continuous fiber reinforced composite corrugated sandwich structures with shape memory capability

Here, a co-extrusion-based 3D printing technology was applied to integrally manufacture continuous fiber reinforced composite trapezoidal corrugated sandwich structures (CFRCTCSs) with shape memory capability. The theoretical models were developed to analyze the bending performance and failure behavior of the 3D printed CFRCTCSs with various geometric configurations and verified by three-point bending tests. Good agreement between the predictions and the experimental measurements was achieved. Considering four dominant failure modes including face yielding, face buckling, core shear failure and indentation collapse, the failure maps based on the analysis models were constructed to highlight the failure mechanism of CFRCTCSs and provide a practical guide for the design of lightweight sandwich structures. Shape recovery tests were performed to confirm the shape memory capability of the 3D printed CFRCTCSs. Finally, the comparison of the bending properties with several competing structures indicates that the 3D printed CFRCTCSs possess the potential to provide new opportunities for lightweight systems and multifunctional applications.

Equivalent models and mechanical properties of bio-inspired corrugated sandwich structures subjected to bending loads

Corrugated sandwich structures have been widely used in aerospace and aviation fields due to their excellent performances. In this paper, a new bio-inspired corrugated sandwich structure is designed based on the microstructure of cybister elytra. Moreover, the homogenization method is used to simplify models and the equivalent material parameters are derived by analytical formulation and finite element method (FEM). The mechanical properties of bio-inspired corrugated sandwich structures fabricated by selective laser melting (SLM) and equivalent models are also investigated subjected to bending loads by FEM and experiments. The results show that the bio-inspired corrugated sandwich structure can be equivalent to the orthotropic model better. Increasing the core height, thickness of the core and panel will improve the bending stiffness obviously. The simulation results are consistent with analytical formulation. But the experimental results are little greater due to the dimension deviation between the fabrication and design. Moreover, the equivalent calculation has a much higher accuracy with a relative deviation less than 10%.

The effect of adhesive fillet on mechanical performance of adhesively bonded corrugated sandwich structures: an experimental–numerical study

ABSTRACTAdhesive fillet has been proposed to improve the mechanical performance of adhesively bonded corrugated sandwich structures, but limited research can be found focusing on the effect of adhesive fillet on the stress state within the ABCSS. In this work, an experimental-FE modelling work was carried out to study the effect of adhesive fillets on the mechanical performance of adhesively bonded corrugated sandwich structures (ABCSS) under 3-point bending load. Three-point bending tests were conducted for model verification in the numerical analysis procedure on adhesively bonded corrugated sandwich structures. Additionally, load–displacement curves have been deduced to determine the load-bearing capacity and failure performance of the corrugated sandwich structures. Cohesive Zone Model (CZM) was adopted for damage analysis in the adhesive layer as well as the fillet, while detailed discussion on the stress distribution caused by various adhesive fillet geometrical dimensions was also addressed. It can be judged that increasing the fillet size can provide a smoother transition between the adhesive layer and adherend, and thus reduce the stress concentration at the edge of the overlap region. It was concluded that enhancing the size of adhesive fillets led to the better mechanical performance of the adhesively bonded corrugated sandwich structure.

Characterisation on the influence of curing history on the mechanical performance of adhesively bonded corrugated sandwich structures

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

Heat transfer mechanism and characteristics of lightweight high temperature ceramic cellular sandwich

Consider the severe thermal loads in thermal engineering applications of lightweight ZrO2 and ZrB2 corrugated sandwich structures, here, their heat transfer mechanism and characteristics are originally explored in this work. Finite element (FE) models for heat transfer of ZrO2 and ZrB2 sandwiches, sandwiches filled with insulation material and the corresponding bulk ceramics are respectively well established. The insulation efficiency, temperature gradient, thermal short effect and thermal-mechanical coupling effect are well calculated and analyzed. It is found that cavity radiation heat flux is increased with the height, leading to low insulation efficiency. The insulation material can block the cavity radiation, and hence can remarkably enhance the insulation efficiency and improve the temperature uniformity. Low temperature gradient is found in ZrO2 and ZrB2 sandwiches, while, remarkable temperature gradients are found in sandwiches filled with insulation material. With the increasing height, the insulation effect is improved, while the mechanical properties are weakened, suggesting pronounced thermal-mechanical coupling effect between loading bearing capacity and insulation effect. The heat transfer mechanism and characteristic revealed here provide the thermal basis for engineering applications of the ZrO2 and ZrB2 cellular sandwiches.