Face Sheet Thickness Research Articles

Low speed impact on sandwich beam with flexible core and face sheets reinforced with FG-CNTs

Purpose The purpose of this study is to model the theory of the low-velocity impact (LVI) process on sandwich beams consisting of flexible cores and face sheets reinforced with functionally graded carbon nanotubes (CNTs). Design/methodology/approach A series of parameters derived from molecular dynamics are used to consider the size scale in the mixture rule for the combination of CNTs and resin. A procedure involving the use of the first-order shear deformation theory of the beam is used to provide the displacement field of the sandwich beam. The energy method and subsequently the generalized Lagrange method are used to derive the motion equations. Due to the use of Hertz’s nonlinear theory to calculate the contact force, the equations of motion are nonlinear. Validation of the problem is carried out by comparing natural frequencies with other papers. Findings The influence of a series of parameters such as CNTs distributions pattern in the face sheets, the influence of the CNTs volume fraction and the influence of the core thickness to the face sheets thickness ratio in the issue of LVI on sandwich beams with clamped-clamped boundary conditions is investigated. The result shows that the type of CNTs pattern in the face sheet and the CNTs volume fraction have a very important effect on the answer to the problem, which is caused by the change in the value of the Young’s modulus of the beam at the contact surface. Changes in the core thickness to the face sheets thickness ratio has little effect on the impact response. Originality/value Considering the important application of sandwich structures in vehicles, aviation and ships, in this research, sandwich beams consisting of flexible core and CNTs-reinforced face sheets are investigated under LVI.

Dynamic response and energy absorption of aluminum foam sandwich under low-velocity impact

Aluminum foam sandwich (AFS) are widely used in energy absorption because of their light weight and excellent energy dissipation capabilities. In this study, energy absorption, deformation modes, and dynamic response of AFS under low-velocity impact are investigated using experimental and numerical approaches. Dynamic impact tests are performed utilizing a drop hammer impact test on AFS with different core densities, face sheet thicknesses, and impact energy. Based on the 3D Voronoi foam model, a full-scale finite element model (FEM) is developed to simulate the mechanical response of AFS under low-velocity impact, and verified by experimental results. The contributions of different AFS components to energy absorption at various impact velocities are further analyzed, along with the effects of face sheet thickness distribution. The results indicate that the performance of the face sheet and core and the impact energy have a remarkable influence on the low-velocity impact response and damage modes of the AFS. The type of structure configuration, “thin top and thick bottom,” enables the AFS better play its energy absorption while ensuring the overall light weight. This study provides a reference for the design and optimization of the face sheet thickness of AFS when it is used as an energy-absorbing member and improves their design efficiency.

Quasi-static three-point bending of sandwich panels with Miura-ori cores

Collapse mechanisms of sandwich panels with Miura-ori cores are analysed and classification of the deformation regimes under three-point bending is proposed. It is revealed that the homogenisation approach to the core material properties is not applicable to the deformation of panels with relatively strong origami cores due to the immediate simultaneous local deformations of the core and face sheets. To describe this deformation regime, an analytical model based on the development of new stationary hinge lines in Miura-ori cells and rigid motion rotation of the adjacent planes is proposed. The model pertains to a single degree-of-freedom model governed by the global bending angle of the panel. On the other hand, the homogenisation approach to the core material properties proved to be applicable to bending analysis of panels with relatively soft Miura-ori cores. This approach is used to analytically obtain the collapse load related to several deformation modes. Parametric FE analysis is conducted to further explore the deformation regimes of panels with different face sheet thicknesses.Experiments were conducted to validate the finite element studies and analytical models. A good agreement between the analytically predicted collapse forces and those obtained by the FE simulations is shown. Deformation mode maps are constructed based on the analytical and FE analyses in terms of the face sheet thicknesses and core strength.A brief comparison between the bending strength of sandwich panels with Miura-ori cores and panels with PVC and honeycomb cores is presented, demonstrating the superiority of the honeycomb cores loaded in the out-of-plane direction. On the other hand, the possibility of the development of high shear strains in metallic Miura-ori cores without damage gives them advantages compared to three-point bending of panels with low density PVC foam cores.

Failure mechanisms of asymmetric sandwich panels subjected to low-velocity impact: An explicit wave dominating damage model

Asymmetric sandwich panels (ASPs) with tapered transitions are effective configurations for connecting them with other structural elements. However, fiber reinforced composite panels are susceptible to impact events and thus it is imperative to gain a comprehensive understanding of the impact failure mechanisms of ASPs. This article investigates the failure mechanisms of ASPs subjected to low-velocity impacts experimentally and numerically. Low-velocity impact tests are conducted at two energy levels to induce barely visible impact damage (BVID) and visible impact damage (VID). A non-linear finite element (FE) model is developed to elucidate the damage behavior and failure mechanisms of ASPs. The numerical results are compared with experimental data to validate the FE model. Additionally, a parametric study is undertaken to explore the failure mechanisms of ASPs subjected to penetration. This study also investigates the influence of impactor diameter, impactor angle, foam core thickness, face sheet stacking sequence, and face sheet thickness on impact response through numerical simulations. The reported results hold potential significance for safety design ASPs.

Modified couple stress theory (MCST) and refined zigzag theory (RZT) for wave propagation of embedded smart sandwich plates with magnetorheological fluid core and viscoelastic FG-CNTRC magnetostrictive face sheets

This paper discusses the wave propagation of a magnetorheological fluid (MRF) micro sandwich plate with magnetostrictive face sheets embedded in the Kerr foundation. The face sheets are reinforced with functionally graded carbon nanotubes (FG-CNT). It was hypothesized that the distribution of carbon nanotubes would be functionally graded along the thickness of face sheets in various patterns such as uniform distribution (UD), and three type of functionally graded (FG), that is, FG-O, FG-X, and FG-AV. The properties of the magnetostrictive layer are considered viscoelastic based on the Kelvin-Voigt model. The refined zigzag theory (RZT) is utilized to simulate displacements of the plate due to the sandwich nature of the system. The modified couple stress theory (MCST) is utilized to predict the influence of small-scale parameter. The equations of motion for the micro sandwich plate are derived by Hamilton's principle, and analytical solutions are utilized to acquire the phase speed, escape, and cut-off frequencies. After model verification, extensive analytical results are presented in detail. They demonstrated that the wave characteristics of the system are influenced by the micro sandwich plate parameters. Consequently, the dimensionless phase speed rises 66% via increasing the magnetic field magnitude from 12.5 to 17.5 G.

Metal-faced sandwich composite panels: A review

This review paper discusses the challenges in improving the mechanical and structural performance of metal-faced sandwich composite panels while reducing weight and cost. It focuses on the core and facesheet structural trends of metal-faced sandwich panels, highlighting innovative design concepts and mechanical performance with respect to failure modes. The paper categorizes recent core geometries used in metal-faced sandwich structures into three types: cellular foam cores, two-dimensional periodic cores, and three-dimensional periodic cores, each with unique characteristics and advantages. The performance of metal sandwich panels with different core structures in response to various mechanical tests is also summarized, including high and low-velocity impact, flexural, and blast and fire resistance. The review emphasizes that the core geometry, facesheet thickness, and core-face interfacial bonding of sandwich composites play a critical role in determining their structural performance and potential applications. Overall, this review paper provides valuable insights into the challenges of improving the mechanical and structural performance of metal-faced sandwich composite panels and highlights the importance of innovative design concepts for achieving optimal performance.

Experimental study of 3D printed carbon fibre sandwich structures for lightweight applications

Honeycomb sandwich structures are widely used in lightweight applications. Usually, these structures are subjected to extreme loading conditions, leading to potential failures due to delamination and debonding between the face sheet and the honeycomb core. Therefore, the present study is focused on the mechanical characterisation of honeycomb sandwich structures fabricated using advanced 3D printing technology. The continuous carbon fibres and ONYX-FR matrix materials have been used as raw materials for 3D printing of the specimens needed for various mechanical characterization testing; ONYX-FR is a commercial trade name for flame retardant short carbon fibre filled nylon filaments, used as a reinforcing material in Morkforged 3D printer. Edgewise and flatwise compression tests have been conducted for different configurations of honeycomb sandwich structures, fabricated by varying the face sheet thickness and core cell size, while keeping the core cell thickness and core height constant. Based on these tests, the proposed structure with face sheet thickness of 3.2 mm and a core cell size of 12.7 mm exhibited the highest energy absorption and prevented delamination and debonding failures. Therefore, 3D printing technology can also be considered as an alternative method for sandwich structure fabrication. However, detailed parametric studies still need to be conducted to meet various other structural integrity criteria related to the lightweight applications.

Three-point bending response and energy absorption of novel sandwich beams with combined re-entrant double-arrow auxetic honeycomb cores

The response and energy absorption of novel sandwich beams with combined re-entrant double-arrow auxetic honeycomb (RDAH) cores subjected to three-point bending were studied experimentally and numerically. Two typical sandwich beams loaded at different loading positions were considered. Quasi-static three-point bending experiments were conducted to obtain the failure modes and force–displacement curves. The reliable numerical simulation models were further established based on experimental validations. The results indicate that when the loading roller is located directly above the re-entrant cell, the RDAH core sandwich beam has better load-carrying and energy absorption capacity. Subsequently, the influence of face sheet distribution, cell-wall thickness, impact velocity and cell configuration on the structural response were explored. For the sandwich beams with same total mass, the arrangement where the thickness of the front face sheet is larger than that of the back face sheet is beneficial for improving the load-carrying and energy absorption capacity. In addition, the cell-wall thickness has an influence on the local deformation mode of the sandwich beam, and increasing its value can produce more stable deformation and improve the load-carrying capacity. Increasing impact velocity has a significant influence on the initial deformation but little influence on the final deformation of the sandwich beams. As the impact velocity increases, the total energy absorption of the sandwich beam gradually increases, and the negative Poisson's ratio characteristic of the core still exists. Compared to the traditional re-entrant honeycomb (RH) core sandwich beams, RDAH core sandwich beams have better energy absorption capacity and bending resistance.

Blast performance of 3D-printed auxetic honeycomb sandwich beams

Little research has been conducted on comparing the blasting characteristics between the regular hexagonal and auxetic honeycomb sandwich beams (RHSBs and AHSBs). To address this gap in knowledge, the study utilised both experimental and numerical analyses. The HSBs consisted of steel top and rear face sheets bonded to a stainless- steel honeycomb core. The parameters considered in this test included the core configuration (regular vs. auxetic hexagonal) and face-core bonding method (adhesive vs. integrated). Results revealed that at scaled distances of 0.8617 m/kg1/3 and 0.7971 m/kg1/3, the AHSB core exhibited a reduction in mid-span displacement of only 3.3 % and 3.7 %, respectively, compared to the RHSB core. However, the compression value of the AHSB core significantly exceeded that of the RHSB core by 171.5 % and 161.5 %, respectively. This finding indicates that auxetic honeycomb cores possess enhanced energy absorption capacity to withstand blast loading. In addition, using unbonded face sheets increases the range of local cell deformation and decreases the global flexural bending by 22.66 % and 24.14 % at scaled distances of 0.8617 m/kg1/3 and 0.7971 m/kg1/3, respectively, compared to the AHSBs with face sheet debonding. To further investigate the damage mechanism of HSBs subjected to blast loading, a well-validated finite element model was employed. Notably, parametric simulations demonstrated that the dynamic behaviour of AHSBs under blast loading is significantly influenced by cell wall thickness, face sheet thickness, and cell angle.

Failure analysis of sandwich beams under three-point bending based on theoretical and numerical models

Abstract This article presents a comprehensive study on the failure behavior of foam core sandwich beams under three-point bending using theoretical analysis and finite element methods. A displacement formula for the foam sandwich beam is derived, considering the shear deformation of the foam core. Based on this formula, the deflection is obtained using energy and Rayleigh–Ritz methods. The failure loads of face yielding, core shearing, and indentation are combined to construct a failure mechanism map. The proposed theoretical model is then compared with existing theoretical analyses, demonstrating higher prediction accuracy. To investigate nonlinear damage and size effects, a series of finite element analyses is conducted. The results suggest that increasing the face sheet thickness has a greater impact on the ultimate load capacity, while the foam core thickness is more effective in enhancing bending stiffness.

Energy dissipation mechanism and ballistic characteristic optimization in foam sandwich panels against spherical projectile impact

This study systematically examines the energy dissipation mechanisms and ballistic characteristics of foam sandwich panels (FSP) under high-velocity impact using the explicit non-linear finite element method. Based on the geometric topology of the FSP system, three FSP configurations with the same areal density are derived, namely multi-layer, gradient core and asymmetric face sheet, and three key structural parameters are identified: core thickness (tc), face sheet thickness (tf) and overlap face/core number (no). The ballistic performance of the FSP system is comprehensively evaluated in terms of the ballistic limit velocity (BLV), deformation modes, energy dissipation mechanism, and specific penetration energy (SPE). The results show that the FSP system exhibits a significant configuration dependence, whose ballistic performance ranking is: asymmetric face sheet > gradient core > multi-layer. The mass distribution of the top and bottom face sheets plays a critical role in the ballistic resistance of the FSP system. Both BLV and SPE increase with tf, while the raising tc or no leads to an increase in BLV but a decrease in SPE. Further, a face-core synchronous enhancement mechanism is discovered by the energy dissipation analysis, based on which the ballistic optimization procedure is also conducted and a design chart is established. This study shed light on the anti-penetration mechanism of the FSP system and might provide a theoretical basis for its engineering application.

Energy absorption of polyurethane filled Al 6061 honey comb sandwiched structure

The energy absorption characteristics of composites are developed for applications likely to be subjected to sudden or prolonged impacts. In lightweight applications, the possibilities of Al 6061 composites are being explored with various known materials with similar properties. Three materials of low densities but high strength was combined: hexagonal honeycomb Al 6061 core was sandwiched with polyurethane foam and embedded within two glass fiber-reinforced polymer plates. L-9 orthogonal array Taguchi DOE was adopted for the design of the experiment varying the polyurethane mixture, core height, and face sheet thickness using the three-factor method. From the output of the Taguchi DOE, twenty-seven samples were fabricated. In order to determine the force-displacement relationship for each of the test samples, a three-point bending test was performed on a universal testing machine. Energy absorption (EA) and crushing force (CF) were determined from the force and displacement values. These values were then optimized to minimize the PCF while maximizing EA. Numerical analysis performed correlated with the results from experimental samples after testing. Since energy absorption is a measure of applied force and the resulting displacement on a material, the energy absorption characteristics were discussed.

Dynamic response of foam-filled X-type sandwich beam under low-velocity impact

The dynamic response of a fully clamped foam-filled X-type sandwich beam under low-velocity impact is studied analytically and numerically. The analytical model is developed for the dynamic response of the sandwich beam with foam-filled X-type core under low-velocity impact based on the yield criterion. The numerical calculations are carried out, and analytical results are in good agreement with numerical ones. The effects of face-sheet thickness, X-type folding plate thickness and foam strength on the impact resistance of the foam-filled X-type sandwich beam are discussed. It is shown that face-sheet thickness, X-type folding plate thickness, and foam strength have noticeable effects on the low-velocity impact response of the foam-filled X-type sandwich beam. The present analytical model can be used to predict the low-velocity impact of the foam-filled X-type sandwich beam.

Additively manufactured cure tools for composites manufacture

This research presents a novel framework for the design of additively manufactured (AM) composite tooling for the manufacture of carbon fibre-reinforced plastic composites. Through the rigorous design and manufacture of 30 unique AM tools, the viability of a design for AM framework was evaluated through measuring the performance with respect to geometrical accuracy and thermal responsiveness, and simulating the tool specific stiffness. The AM components consisted of a thin layup facesheet, stiffened by a low density lattice geometry. These tools were successfully used to layup and cure small composite components. The tooling was highly thermally responsive, reaching above 93% of the applied oven heating rate and up to 17% faster heating rates compared to similar mass monolithic tools. The results indicate that thermal overshoot has a greater dependence on the lattice density while the heating rate was more sensitive to the facesheet thickness. Lattice densities of as little as 5% were manufactured and the best overall geometry was a graded gyroid lattice with thicker walls near the surface and thinner walls at the base, attached to a 0.7 mm thick facesheet. The outputs from this research can provide a new route to the design and manufacture of mould tools, which could have significant impacts in the composites sector with new, lighter, more energy efficient tooling.

Effects of parameters on postbuckling failure of composite sandwich panels loaded axially: Function form and applications

Based on the refined first-order shear theory (simplified zig-zag model), using quasi-conforming finite element method with path-following and switching approach, the postbuckling behaviors and postbuckling bearing capacity (PBC) of composite sandwich panels (CSPs) axially loaded were studied and discussed in detail. To utilize the carrying potential of CSPs in postbuckling, the effects of the key parameters on postbuckling behaviors of the CSPs were analyzed by finite element method. The numerical results show that the PBC of CSPs increases with the increase of face sheets thickness, core thickness and core shear modulus, but it is insensitive to the change of the side length ratio. The enhancement of core shear strength can increase the PBC of CSPs and change the failure mode, but it is found there is a threshold value, beyond which, the PBC will no longer or slightly increases with the increase of core shear strength. The failure of CSPs is mainly determined by the tensile strength in the direction perpendicular to the fiber. Finally, a parameter selection optimization approach is proposed to effectively improve the PBC of CSPs under axial compression.

Dynamic responses of metal foam sandwich beam under repeated impacts considering impact location and face thickness distribution

Owing to the excellent mechanical performance, the metal foam sandwich structures have potential applications in the design of protective equipment, which can improve the impact resistance of engineering structures. In this paper, the nonlinear finite element model is employed to investigate the dynamic behaviors of metal foam sandwich beam (MFSB), and the accuracy of the finite element method is verified by repeated impact tests. In addition, the effects of impact location and face thickness on the dynamic behavior of the MFSB are examined. Results show that, as the distance from the impact position to the middle span of the beam increases, the deflections of face sheets decrease gradually, and the loading and unloading stiffness increases. The thickness of front face sheet affects the depth of indentation, while the total thickness of the front and back face sheets decides the overall deformation, loading and unloading stiffness. Overall, as the impact number increases, the influences of impact location and face thickness on the dynamic behavior of MFSB enhances gradually.

Multi-objective optimization of multi-core composite aluminum honeycomb sandwich panels for improved crashworthiness

This article presents the low-velocity impact response of the multi-core aluminum honeycomb sandwich panel with composite face sheets using LS-DYNA-based finite element simulation. The effect of geometric parameters like cell size, cell height, cell thickness, and facesheet thickness, on structural response, is explored. The interaction effect of these geometric parameters, effect of number of layers/cores and characteristic force-time and energy-time curves for multilayer composite sandwich panels are also studied. Finally, these geometric parameters are optimized for better crashworthiness designs, followed by crashworthiness design recommendations.

A sequential mixed-integer programming method for concurrent optimization of core topology and face sheet thickness of a sandwich beam

A method is proposed that allows for the concurrent optimization of core topology and face sheet thickness of a sandwich beam under compliance constraints. The problem is solved using a novel mixed-linear extension of the Topology Optimization of Binary Structure (TOBS) topology optimization method aiming to minimize the total mass of the beam. The method has been demonstrated on a clamped beam example and the results have been compared to results from topology optimization of the core with a range of a priori fixed face sheet thicknesses. It is shown that the new method, starting from a fully populated core, finds a minimum mass that is lower than but in the neighbourhood of the best results from the topology optimization with fixed face sheet thicknesses. By varying the compliance constraint it is shown that the core topology approaches an ideal corrugated geometry as the compliance constraint is relaxed. The trends observed in the results are compared to analytical models for an idealized core.

Mechanical responses of CFRP/PVC foam sandwich plate impacted by hailstone

Mechanical responses of sandwich plate with carbon fiber reinforced polymer (CFRP) laminate as face-sheets and polyvinyl chloride (PVC) foam as core, which is promising in the lightweight design of high-speed maglev trains, was studied for the case of hailstone impact. Nine 500 × 500 mm sandwich plate specimens of three face-sheet thicknesses 1, 2 and 3 mm and a constant core thickness 30 mm were fabricated and tested under the impact of ice spheres of 50 mm in diameter propelled by the first-stage light gas gun. Three impact speeds, i.e. 30, 60 and 90 m/s, of the ice spheres and three incident angles, i.e. 0°, 30° and 45°, were investigated. For all cases, no macro failures were observed, but invisible damages, i.e. delamination in the upper face-sheets and indentation of the foam core, were found by high resolution ultrasonic testing. The experimental results were then used to calibrate the corresponding numerical model, based on which a thorough parametric analysis was performed to show the full dynamical responses of CFRP/PVC foam sandwich panels under hailstone impact. It is found that the foam cushion could effectively protect the rear face-sheet and increasing the ratio of span to thickness of the panel could reduce the damage degree due to the change of failure mode from local to global.

Effect of truss core on sound radiation behavior of sandwich plate structures under structure borne excitation

Compared with traditional honeycomb and stiffened sandwich structures, lattice-based structures are considered an ideal substitute for traditional core structures due to their high stiffness and other potential multifunctional application characteristics. Based on that, the sound radiation characteristics of the sandwich plate with different truss cores under structure borne excitation were investigated in the current paper, wherein three truss cores, including pyramidal, tetrahedral and 3D-kagome cores types, are considered. The governing equations for the vibration and sound radiation analysis of the sandwich plate structure are carried out using the static equilibrium method, and then solved via the Navier approach and Rayleigh integral. By comparing the experimental results, the validity of the proposed theoretical model is verified. The theoretical model is subsequently used to investigate the influences of truss core geometric parameters and types, face sheet-core face sheet thickness ratio and aspect ratio on sandwich plate sound radiation characteristics. The results indicate that, in the range [ 5 ∘ ≤ θ ≤ 52 ∘ ] and [ 52 ∘ < θ ≤ 85 ∘ ] , the tetrahedral and 3D-Kagome core types have the maximum natural frequency values, respectively, while the resonance peaks of sound pressure level curves move to lower frequency region with the increase in truss core radius and face sheet-core face sheet thickness ratio, and the sandwich plate with the 3D-kagome core shows better sound radiation characteristics in the wide frequency range.