Face Sheet Thickness Research Articles

Evaluation of test methods and face-sheet thickness effects in damage tolerance assessment of composite sandwich plates

Composite sandwich materials provide high bending performance-to-weight ratios. However, these materials are vulnerable to impact damages which can drastically reduce their load-bearing capability. Presently there is a lack of standardised test methods for impact assessment. This study compares three different test methods for impact assessment; single skin compression after impact (CAI-SS), sandwich compression after impact (CAI-SW) and four-point bending-after-impact (BAI). The CAI-SS test method shows high compressive strength and strain at failure and the tesr is relatively easy to evaluate. For finite size plates with significant impact damage, the CAI-SS test method is recommended for post impact strength assessment. For large sandwich panels with relatively small impact damages the CAI-SW test method could be more relevant since it includes effects of panel asymmetry generated from the impact damage. The BAI test method may be recommended as an alternative to CAI but quite long specimens are required in order to assure compressive failure in the tested face-sheet, making the test both demanding and expensive. On the other hand, lower load levels are required to break the specimens and there is less need for precise machining during specimen manufacturing. A finite element model including progressive damage evolution was used to estimate the post impact strength. The simulations showed generally good agreement with the experiments.

Vibration analysis of sandwich beam with honeycomb core and piezoelectric facesheets affected by PD controller

Free vibration analysis of a sandwich beam with honeycomb core and piezoelectric face sheets, which is rested on the viscoelastic foundation is investigated. The thermal environment and the electric field are applied to this structure. Also, it is affected by the proportional-derivative (PD) controller. The amount of gain in this controller can affects the vibration frequency. The displacement components are expressed by improved high-order sandwich panel theory (IHSAPT) that considers continuity conditions for transverse shear stress at the interfaces and the zero transverse shear stresses conditions on the upper and lower surfaces of the beam and core flexibility. The motion equations are derived and solved by Hamilton's principle and Navier's method, respectively. This paper examines the effects of various parameters, such as the internal aspect ratio and the cell angle/thickness of the honeycomb core, temperature variations, viscoelastic environment, electric load, and control gain on its natural frequencies. The results show when the honeycomb core's to face sheet's thickness ratio increases, the beam dimensionless frequency increases, too. Also, by increasing the internal aspect ratio of honeycomb core, the frequency of sandwich beam decreases. The results of this study can be used to vibration control in aerospace engineering and constructions.

Effect of Structural Differences on the Mechanical Properties of 3D Integrated Woven Spacer Sandwich Composites.

Three-dimensional integrated woven spacer sandwich composites have been widely used as industrial textiles for many applications due to their superior physical and mechanical properties. In this research, 3D integrated woven spacer sandwich composites of five different specifications were produced, and the mechanical properties and performance were investigated under different load conditions. XR-CT (X-ray computed tomography) images were employed to visualize the microstructural details and analyze the fracture morphologies of fractured specimens under different load conditions. In addition, the effects of warp and weft direction, face sheet thickness, and core pile height on the mechanical properties and performance of the composite materials were analyzed. This investigation can provide significant guidance to help determine the structure of composite materials and design new products according to the required mechanical properties.

Analytical non-linear analysis of functionally graded sandwich solid/annular sector plates

Nonlinear behavior of functionally graded (FG) sandwich circular sector plates with simply supported radial edges under transverse loading is investigated using the first-order shear deformation theory with von Karman geometric nonlinearity. The nonlinear governing equations are reformulated and solved via single-parameter perturbation and Fourier series methods. Verification is performed by comparing numerical results with the available ones in the literature and the ones obtained via ABAQUS code. The effects of non-linearity, material constant, lay-up, and boundary conditions on bending of FG sandwich sector plates with FG core/homogenous face sheets and metallic core/FG face sheets are studied. It is shown that in sandwich plates with an FG core, the deflection and maximum tensile stress decrease by using thinner homogenous face sheets and in ones with a metallic core, increasing the thickness of FG face sheets reduces the maximum tensile and compressive stresses, while the total thickness is considered the same in all layups. Furthermore, in bending analysis of FG sandwich sector plates, linear theory is adequate for w/h<1 in plates with free circular edges, it is solely applicable for w/h<0.2 in plates with clamped circular edges and is inadequate for analysis of fully simply supported FG sandwich sector plate.

The energy absorption behavior of novel composite sandwich structures reinforced with trapezoidal latticed webs

Abstract This article proposed an innovative composite sandwich structure reinforced with trapezoidal latticed webs with angles of 45°, 60° and 75°. Four specimens were conducted according to quasi-static compression methods to investigate the compressive behavior of the novel composite structures. The experimental results indicated that the specimen with 45° trapezoidal latticed webs showed the most excellent energy absorption ability, which was about 2.5 times of the structures with vertical latticed webs. Compared to the traditional composite sandwich structure, the elastic displacement and ultimate load-bearing capacity of the specimen with 45° trapezoidal latticed webs were increased by 624.1 and 439.8%, respectively. Numerical analysis of the composite sandwich structures was carried out by using a nonlinear explicit finite element (FE) software ANSYS/LS-DYNA. The influence of the thickness of face sheets, lattice webs and foam density on the elastic ultimate load-bearing capacity, the elastic displacement and initial stiffness was analyzed. This innovative composite bumper device for bridge pier protection against ship collision was simulated to verify its performance. The results showed that the peak impact force of the composite anti-collision device with 45° trapezoidal latticed webs would be reduced by 17.3%, and the time duration will be prolonged by about 31.1%.

Layer-wise solutions for variable stiffness composite laminated sandwich plate using curvilinear fibers

This paper deals with the vibration analysis of variable stiffness composite laminated (VSCL) sandwich plates. The VSCL sandwich plate is composed by soft core and two laminated face sheets, in which the face sheets are considered with curvilinear fiber. The layer-wise plate theory and p-version of finite element method are used to solve the problem formulation. In layer-wise theory, each layer modeled separately as a one p-element and the continuity of displacement fields is based on a linear zig-zag variation of displacements through the thickness of the layers. The obtained results of present model are compared and validated with available solutions, such as equivalent single layer theories, layer-wise theory and three-dimensional theory for sandwich plate with constant stiffness. The frequencies and mode shapes are examined for different physical and mechanical parameters such as plate thickness, core to face sheets thickness ratio, orientation angle of curvilinear fibers, stacking sequence and boundary conditions. New layer-wise solutions for thin and thick VSCL sandwich plate are offered, in which can be used to establish benchmarks for future comparisons.

Resistance of all-metallic honeycomb sandwich structures to underwater explosion shock

All-metallic honeycomb sandwich structure is a new kind of ship protection structure, which has a broad application prospect in the field of ship protection. However, there is not enough research on the dynamic response of honeycomb sandwich structures under the actual underwater explosion load. The dynamic behavior and protective performance of honeycomb sandwich structures subjected to underwater explosion load were investigated, both experimentally and numerically in this paper. A backplane stiffened honeycomb sandwich structure and the corresponding buoyant box were designed and fabricated for the subsequent experimental study in a large open water pool. The structural response was numerically simulated using the coupled acoustic-structural approach (integrated in commercial FE code ABAQUS/Explicit). The numerical simulation results are in good agreement with the experimental measurements. Then, the deformation process and energy absorption characteristics of the honeycomb sandwich structure subjected to underwater explosion load were investigated. The effects of the load parameter (impact factor) and two geometric parameters (i.e., facesheet thickness ratio and core relative density) on the dynamic response of the sandwich structure were analyzed. Finally, the Pareto optimal designs with minimize value of non-dimensional areal density and minimize value of non-dimensional maximum deformation of the central point on back facesheet were obtained using the NSGA-Ⅱ algorithm. The results show that with the increase of impact factor, the overall deformation of the structure increases significantly. The honeycomb core is the main energy absorbing substructure during this process, and its energy absorption ratio gradually decreases. With the increase of either face sheet thickness ratio or core relative density, the deformation of the structure first decreases and then increases, accompanied by changes in deformation modes. The influence of core relative density is more significant. The optimized structures obtained from multi-objective optimal design effectively reduce the areal density and the maximum deformation, which can be used as a reference for the future design of honeycomb sandwich structures.

Predictions of the elastic modulus of trabecular bone in the femoral head and the intertrochanter: a solitary wave-based approach.

This paper deals with the numerical prediction of the elastic modulus of trabecular bone in the femoral head (FH) and the intertrochanteric (IT) region via site-specific bone quality assessment using solitary waves in a one-dimensional granular chain. For accurate evaluation of bone quality, high-resolution finite element models of bone microstructures in both FH and IT are generated using a topology optimization-based bone microstructure reconstruction scheme. A hybrid discrete element/finite element (DE/FE) model is then developed to study the interaction of highly nonlinear solitary waves in a granular chain with the generated bone microstructures. For more robust and reliable prediction of the bone's mechanical properties, a face sheet is placed at the interface between the last chain particle and thebone microstructure, allowing more bone volume to be engaged in the dynamic deformation during interaction with the solitary wave. The hybrid DE/FE model was used to predict the elastic modulus of the IT and FH by analysing the characteristic features of the two primary reflected solitary waves. It was found that the solitary wave interaction is highly sensitive to the elastic modulus of the bone microstructure and can be used to identify differences in bone density. Moreover, it was found that the use of a relatively stiff face sheet significantly reduces the sensitivity of the wave interaction to local stiffness variations across the test surface of the bone, thereby enhancing the robustness and reliability of the proposed method. We also studied the effect of the face sheet thickness on the characteristics of the reflected solitary waves and found that the optimal thickness that minimizes the error in the modulus predictions is 4mm for the FH and 2mm for the IT, if the primary reflected solitary wave is considered in the evaluation process. We envisage that the proposed diagnostic scheme, in conjunction with 3D-printed high-resolution bone models of an actual patient, could provide a viable solution to current limitations in site-specific bone quality assessment.

Harmonic analysis of annular sector sandwich plate using FEM

In present study, vibration and harmonic behaviors of annular sector sandwich plate of two orthotropic composite materials are analyzed using FEM technique. Sandwich plate made of two face sheet and one core sheet in middle has been modelled using an ANSYS APDL FEM tool. A suitable finite element model is developed and proposed based on first order shear deformation theory. The model has been discretized using appropriate elements i.e. 8-node solid 185 for core sheet and SOLSH190 for face sheet from the ANSYS element library. Effect of varying face sheet thickness is demonstrated on vibration as well as harmonic behaviors of sandwich plate and related findings are discussed briefly. Effect of sector angle has also been demonstrated. The authenticity of the proposed methodology has been verified by comparing the simulation results with available literature. It can be observed that the results obtained are in good propinquity and presently proposed model shows the results with adequate accuracy.

On the structural parameters of honeycomb-core sandwich panels against low-velocity impact

This paper presents a combined experimental and numerical study on the low-velocity impact behavior of honeycomb-core sandwich panels with different structural parameters, including facesheet thickness, core height, honeycomb cell size, and cell wall thickness. Impact tests were conducted at four different energies using a drop-weight impact facility, and the deformation and damage characteristics of the tested sandwich panels were analyzed by microscopic X-ray computed tomography. The experimental results revealed two distinct failure modes of sandwich panels: namely mode A, with localized damage in both facesheets and core, which is dominated by indentation; and mode B, which is characterized by global bending deflection of the facesheets and overall core crushing. It was found that a sandwich panel with thin facesheets and a high-density honeycomb core (e.g. with a small cell size and/or a thick cell wall) tended to fail in mode A, but core height did not influence the failure mechanism notably. Furthermore, finite element modeling was carried out to gain further understanding of the effects of these structural parameters. The perforation resistance and energy absorption capacity were significantly enhanced with increasing facesheet thickness. Whereas reducing the cell size and/or thickening the cell wall resulted in lower perforation resistance. When the total thickness of facesheets remained a constant, the impact behavior of the sandwich structure could be optimized by controlling the thickness ratio of the front to back facesheets. Finally, cost efficiency analysis was performed to achieve a rational design of the sandwich structure considering both the impact performance and cost.

WITHDRAWN: Optimization design of vibration characterizations for functionally graded porous metal sandwich plate structure

In this study, numerical analysis is developed to optimize natural frequencies of sandwich plate functionally graded plate with porosity demonstrated by formulating several MOGA methods (Multi-Objective Genetic Algorithm) design optimization parameters. First, we proposed a new analytical model and analyzed the resultant effects for different parameters. The second results have been validated by comparison to results from detailed finite element (FE) models. Finally, a design of experiments (DOE) based response surface optimization method combined with ANSYS software 2020 R2 is used to maximize fundamental frequencies while minimizing the mass and cost of the FG sandwich plate. Constraints of the maximum natural frequency are imposed. ANSYS DesignXplorer Add-in for Excel in combination with dxrom software used to approximate solutions. A 3D model of the FG system was constructed and meshed with 8-node SOLID186 elements using the default grid. The input parameters are the face sheet thickness, core height, porosity ratio, and power-law index. By considering 100 design points, the first six natural frequencies of a functionally graded sandwich plate are obtained and analyzed. A numerical analysis is performed on the sandwich plate's examples with various boundary conditions, power-law index, FG core thickness, porosity parameter, and slenderness ratios. The calculated results are compared with those solved analytically to show the current approach's accuracy and effectiveness, and the optimized natural frequencies of sandwich plates are also investigated. A predicted error for each parameter can also be recorded. An accepted agreement can be observed between analytical and numerical results with a maximum percentage discrepancy of 5%.

Dynamic deflection and contact force histories of graphene platelets reinforced conical shell integrated with magnetostrictive layers subjected to low-velocity impact

The present paper concerns low-velocity impact for nanocomposite sandwich truncated conical shells (NSTCS). Graphene platelets (GPLs)-reinforced as core layer is covered through magnetostrictive layers as face sheets. The supposed impacts are applied over the above face layer and further, the interaction among impactors as well as NSTCS is assumed utilizing novel equivalent three-degree-of-freedom (TDOF) with spring–mass–damper (SMD) model. For modeling the core layer and face sheets mathematically, higher-order shear deformation theory (HSDT) besides first-order shear deformation or Mindlin theory (FSDT) is utilized, respectively. To presume this sandwich structure much more realistic, the Kelvin–Voigt model will be used. According to Hamilton’s principle concerning continuity boundary conditions, the governing equations are obtained. Utilizing differential cubature (DC) as well as Bolotin procedures, the governing equations will be solved. In this work, different variables covering various boundary edges, Controller, cone’s semi vertex angle, damping,​ feedback gain, the proportion of core to face sheets thickness, dispersion kinds of GPLs and their volume percent, and their effects on low-velocity impact analysis of the sandwich structure will be investigated. To indicate the accuracy of applied theories as well as methods. the results are collated with another paper. It is found that increment of GPLs volume percent leads to rise the deflection as well as maximum contact force whereas contact duration is reduced.

Influence of stitching on the fracture of stitched sandwich composites

Sandwich composites consist of two rigid outer facesheets that are bonded to a lightweight internal core. Although they have a high stiffness-to-weight ratio, these structures have low interlaminar strengths, which may lead to core-to-facesheet separation when subjected to out-of-plane stresses. In this study, sandwich composites with carbon/epoxy facesheets and a 110 kg/m3 foam core, were manufactured with through-the-thickness reinforcements, or stitches, using a vacuum-assisted resin transfer molding process. A design of experiments approach was used to investigate the influence of stitch parameters (stitch density, linear thread density, and facesheet thickness) on fracture energy. Single cantilevered beam tests were performed to obtain the mode I dominant fracture energy for each treatment combination. This study reveals and discusses the unique fracture surface morphologies associated with stitch processing parameters for a sandwich composite. For increased fracture toughness, the optimum stitch parameters for different linear thread densities are captured in the response surface model.

A parametric study on the design factors influencing the thermal performance of nickel alloy C263 sandwich panels

ABSTRACT To protect the airframe and the payload of hypersonic cruise vehicles from aerothermal heating and aerodynamic loading, metallic thermal protection systems (MTPS) are intended to be used. MTPS are composite structures containing a combination of insulating material and two sandwich panels placed on top and bottom of it. There are numerous design factors influencing the (a) thermal performance and (b) density of these sandwich panels (SP). In the current study, the effect of six important geometric design parameters of nickel alloy C263 sandwich panel viz., (A) core cell shape, (B) core cell size, (C) core cell height (D) core sheet thickness, (E) top and (F) bottom face sheet thickness were evaluated and analysed using Taguchi-based design of experiments (DOE) approach. The results obtained were analysed using standard statistical analysis techniques in order to identify the optimum combination of design parameters and to ascertain the influence of each aforementioned design parameters on the performance of C263 sandwich panels. Further, the optimum combination of sandwich-panel design parameters that provides the best thermal performance with lowest density has been identified using an algebraic model and validated. The results obtained are presented and discussed here.

A continuum shell element in layerwise models for free vibration analysis of FGM sandwich panels

A finite element model based on continuum shell elements available in ABAQUS software has been developed for the free vibration analysis of FGM sandwich panels. Applications to sandwich plates with different combinations of FGM core and/or FGM face sheets satisfying through-the-thickness material gradations in the form of either power (P-FGM) or sigmoid (S-FGM) or exponential (E-FGM) distributions are considered. A user-defined material subroutine UMAT was used to implement functionally graded properties of the constitutive FGM layer. Numerical studies are given for free vibrations of sandwich plates subjected to different boundary conditions and with different structural parameters such as span to thickness, face sheet–core–face sheet thickness and aspect ratios, and volume fraction exponent. The studies showed very good agreement between the present results and those existing in the literature that confirmed the accuracy of the developed model. A series of numerical solutions obtained in the research extends the results of testing examples and may serve as additional benchmark data for other researchers.

Characterization of the vibration, stability and static responses of graphene-reinforced sandwich plates under mechanical and thermal loadings using the refined shear deformation plate theory

An analytical investigation was carried out to assess the free vibration, buckling and deformation responses of simply-supported sandwich plates. The plates constructed with graphene-reinforced polymer composite (GRPC) face sheets and are subjected to mechanical and thermal loadings while being simply-supported or resting on different types of elastic foundation. The temperature-dependent material properties of the face sheets are estimated by employing the modified Halpin-Tsai micromechanical model. The governing differential equations of the system are established based on the refined shear deformation plate theory and solved analytically using the Navier method. The validation of the formulation is carried out through comparisons of the calculated natural frequencies, thermal buckling capacities and maximum deflections of the sandwich plates with those evaluated by the available solutions in the literature. Numerical case studies are considered to examine the influences of the core to face sheet thickness ratio, temperature variation, Winkler- and Pasternak-types foundation, as well as the volume fraction of graphene on the response of the plates. It will be explicitly demonstrated that the vibration, stability and deflection responses of the sandwich plates become significantly affected by the aforementioned parameters.

A Critical Review of Recent Research of Free Vibration and Stability of Functionally Graded Materials of Sandwich Plate

In the past few decades, due to the unique material properties of functionally graded materials (FGM’s), they have been used in various engineering industries. This article aims to introduce an overview of the existing literature on the area of application, stability, and free vibration analysis of FGM structures conducted by some recent research studies and to provide a comprehensive overview of the development, application, different numerical representation of materials, demonstrating procedures and arrangement technique and solution method of FGM rectangular plate. It focuses on the influence of many parameters on natural frequencies and buckling loads, such as aspect ratio, power-law index, porosity distribution throughout the thickness of the plate, and face sheet thickness. This research also involves various analyses and numerical techniques for vibration and buckling analysis of the FGM sandwich plate. Furthermore, some important notes and suggestions are put forward for future work trails in this field. It is found that there is an exceptionally restricted path to investigate the same above analysis for the FGM sandwich plate with the porous metal dependent on various parameters such as gradient index, aspect ratio, face sheet thickness, porous factor, FGM layers thickness, and the number of layers.

RETRACTED ARTICLE: Dynamic simulation of moderately thick annular system coupled with shape memory alloy and multi-phase nanocomposite face sheets

The current research work analyzes dynamics of a sandwich disk which is gently thick. The mentioned sandwich structure has honeycomb core, a couple of middle layers having fibers of shape memory alloy (SMA), and a couple of external layers of multi-scaled hybrid nanocomposite (MHC) considering in-plane force. The core in the shape of honeycomb is manufactured of aluminum due to its high stiffness and less density compared with other materials. Applying energy methods called the principle of Hamilton, we obtained governing motion equations of the mentioned structure and solved them using First-order shear-deformation-theory (FSDT), as well as generalized-differential-quadrature-method (GDQM), respectively. To layers’ joint, the compatibility equations have been taken into account. Then, a parametric mathematical manipulation has been conducted to analyze the impacts of fibers of SMA, boundary conditions (BCs), internal loads, honeycomb network angle, ratio of external to internal radiuses, ratio of thickness to length of the honeycomb, weight fraction of CNTs, angle of fibers, ratio of honeycomb to face-sheet thickness on the frequency of the multi-phase sandwich disk. The outcomes derived reveal that for any amount of internal pressure and each BCs, the relation of the honeycomb’s thickness ratios to MHC layer ( $${h}_{H}/{h}_{t}$$ ) and sandwich structure’s frequency is similar to quadratic function. Further results show that the effects of the fibers’ angle on the frequency can be ignored for larger $${h}_{H}/{h}_{t}$$ amounts.

Experimental study on the fatigue performance of aluminum foam sandwich with 304 stainless steel face-sheet

This work focused on aluminum foam sandwich (AFS) with different foam core densities and different face-sheet thicknesses subjected to constant amplitude three-point bending cyclic loading to study its fatigue performance. The experiments were conducted out by a high frequency fatigue test machine named GPS-100. The experimental results showed that the fatigue life of AFS decreased with the increasing loading level and the structure was sensitive to cyclic loading, especially when the loading level was under 20%. S-N curves of nine groups of AFS specimens were obtained and the fatigue life of AFS followed three-parameter lognormal distribution well. AFS under low cyclic loading showed pronounced cyclic hardening and the static strength after fatigue test increased. For the same loading level, effects of foam core density and face-sheet thickness on the fatigue life of AFS structure were trade-off and for the same loading value, the fatigue life of AFS increased with aluminum foam core density or face-sheet thickness monotonously. Core shear was the main failure mode in the present study.

Vibration analysis and control of micro porous beam integrated with FG-CNT distributed piezoelectric sensor and actuator

In this study, the active control and vibration analysis of a micro sandwich beam based on modified couple stress theory (MCST) are investigated. The core of sandwich structure is porous and the face sheets are made from piezoelectric material and reinforced by carbon nanotubes. The generalized rule of mixture is employed to predict the mechanical and electrical properties of a micro sandwich composite beam. Based on Hamilton's principle, the governing equations of motion for a micro Reddy beam are derived and active control is considered by the state space representation of the system. The results of this research show that the porosity coefficient, porosity distributions, carbon nanotubes (CNTs) volume fraction, CNTs distributions, the material length scale parameter and different face sheet and core thicknesses effect on the natural frequencies, the resonance phenomenon, settling time and deflection response of system. This research can provide a valuable background for further experimental studies as a basic investigation for applications of a micro sandwich beams in the field of micro robots. Also the results are potentially useful for active control, preventing the resonance phenomenon, design and optimization of micro sandwich beams.