Composite Face Sheets Research Articles

Dynamic responses of hybrid lightweight composite sandwich panels with aluminium pyramidal truss cores

This paper experimentally and numerically investigates the free vibration, quasi-static compressive and split Hopkinson pressure bar impact responses of hybrid composite pyramidal truss sandwich panels. Such sandwich panels made of carbon fibre composite face sheets and aluminium alloy pyramidal truss cores are fabricated using an interlocking and adhesive bonding approach. Modal tests and quasi-static compression tests are conducted. A good consistency for natural frequencies, modal shapes and static stress–strain curves of the specimen with the same specification is obtained, which ensures the good repeatability of the present specimens. Considering the effect of strain rate, a series of split Hopkinson pressure bar tests combined with numerical simulations is carried out to investigate their dynamic compression responses. A good agreement between simulation results and experimental data is observed, which shows that the adopted split Hopkinson pressure bar testing device and the modified Johnson-Cook model are reasonable and reliable. Results show that the dynamic compression modulus and strength of specimen are strongly influenced by the relative density of the truss cores and much higher than the corresponding static compression modulus and strength. Furthermore, it is also revealed that all the specimens have excellent energy absorption performance, which may have greatly advantage in shock isolation application.

On the static and dynamic stability of spherical sandwich shell panels with viscoelastic material core and laminated composite face sheets under uniaxial and biaxial harmonic excitations

The buckling and parametric resonance characteristics of laminated composite spherical sandwich shell panels with viscoelastic material (VEM) core are investigated in the present analysis considering full geometric nonlinearity in the Green–Lagrange sense. The study includes the longitudinal strain and normal strain in the transverse direction along with transverse shear deformation of the VEM core. The core displacements are considered to be varying linearly along the thickness and those of the face sheets follow first-order shear deformation theory. An eight-noded sandwich shell finite element of the serendipity family is adopted to discretize the sandwich shell panel domain. The finite element-based equation of motion is derived using Hamilton’s principle in the form of the Mathieu–Hill-type equation. The dynamic instability regions are obtained by applying Hsu’s criteria-based Saito–Otomi conditions to the transformed equation motion. An in-house finite element-based code is developed in the MATLAB platform to solve the stability problem and to establish the stability regions. A parametric study is carried out to investigate the influence of different system parameters on the critical buckling load and the parametric resonance of the sandwich shell panels. It is noted that an increase in core and constraining layer thicknesses increases the critical buckling load of the sandwich shell panels. The stability boundaries are observed to shift toward a higher-excitation-frequency region in the stability diagram with an increase in constraining layer thickness and a decrease in aspect ratio.

An Investigation on Mechanical Behavior of Tooth-Plate-Glass-Fiber Hybrid Sandwich Beams

Tooth-plate-glass-fiber hybrid sandwich (TFS) is a type of sandwich composites fabricated by vacuum-assisted resin infusion process, in which glass fiber facesheets reinforced by metal plate are connected to foam core through tooth nails. Bending properties and interlaminar properties of TFS beams with various foam densities were investigated by flexural tests and DCB (double cantilever beam) tests. The test results showed that by increasing the foam core density from 35 kg/m3 to 150 kg/m3, the peak strength of TFS beams significantly increased by 168% to 258% compared with similar sandwich beams with fibrous composite facesheets. With the change of foam density and span length, the main failure modes are core shear and facesheet indentation beneath the loading roller. The interlaminar strain energy release rates of TFS specimens also increased by increasing the density of the foam. In addition, an analytical model was used to predict the ultimate bending strength of TFS beams, which were in good accordance with the experimental results.

A Novel Acoustic Sandwich Panel Based on Sheep Wool

The aim of this paper is to propose a novel sandwich panel, which would be suitable for sound absorption and airborne sound insulation, used as applied cladding or independent lightweight partition wall. As far as the authors are concerned, this is the first sheep wool-based sandwich panel using only natural materials. The structure was prepared using hydrated lime-based composite face sheets and a sheep wool-based core. Several parameters of the sandwich panel were determined, including sound absorption coefficient, airborne sound insulation, thermal conductivity, thermal resistance, compressive strength, and bending strength, respectively. The results indicate that the maximum sound absorption value of 0.903 was obtained at the frequency of 524 Hz in the case of the unperforated sample, 0.822 at 536 Hz in the case of the sample with 10% perforations, 0.780 at 3036 Hz in the case of the sample with 20% perforations, and 0.853 at 3200 Hz in the case of the sample with 30% perforations. The registered airborne sound insulation index of the panel was 38 dB. Based on the obtained data, it can be concluded that the studied panel recorded comparable values with other synthetic noise control solutions, which are suitable as applied cladding or an independent lightweight partition wall, with good acoustic properties.

Effects of Microstructures of Foam Core on the Thermal Shock Strength of Ceramic Foam Sandwich Structures

The effects of microstructures of foam core on the thermal shock strength of the sandwich slabs are investigated by macro-micro analysis. Each slab has two ceramic matrix composite (CMC) face sheets and an open-cell ceramic foam core. Asymmetric thermal shock fracture is evaluated at the macro continuum level. The position of the danger zone varying with the thickness of face sheets is determined. The finite element (FE) model based on 3D Voronoi tessellations consists of a local micro-scale region surrounding the crack tip. For a calculated stress intensity factor in macro model, the displacements along the boundary of the local model are calculated based on linear elastic fracture mechanics. The thermal shock strength of the sandwich structure is found to be dominated by the cell regularity, the cross-sectional shape of the cell struts and the relative density of foam core. The physical mechanisms responsible for those results are identified. The effective methods to improve the thermal shock resistance of the sandwich structures with ceramic foam core are proposed.

Dynamic response of foam core sandwich panel with composite facesheets during low-velocity impact and penetration

This study aims to investigate the dynamic response of foam core sandwich panel with composite facesheets, particularly considering the penetration processes under low-velocity impact. An analytical model based on energy approach is developed to predict contact force, contact time, impactor displacement, energy absorption and failure modes. Contribution of the structural components in energy absorption is further analyzed. The predictions are compared with experimental and numerical results and reasonable agreement is achieved. The present work provides an analytical method to study the mechanisms of impact damage and energy absorption for the composite sandwich panels with closed-cell foam core.

Experimental and numerical investigation on damage behavior of honeycomb sandwich panel subjected to low-velocity impact

This paper presents the low-velocity impact behavior of sandwich panel with carbon fiber reinforced plastic (CFRP) composite facesheet and Nomex honeycomb core through experimental and numerical methods. Experiments were carried out on two thickness of honeycomb core at various impact energy levels. The dynamic response including contact force history and energy absorption as well as contact duration was recorded. The damage modes were obtained through non-destruction inspection (NDI) C-scan and microscopic observation. A refined three-dimensional finite element model combined with continuum damage mechanics (CDM) was developed with composite plies and detailed honeycomb core. Physically-based Puck’s composite failure criteria and energy based progressive damage model were used to capture the intralaminar damage initiation and evolution, respectively. The interlaminar damage of facesheet and debonding of facesheet/core interface were predicted using cohesive element. The hexagonal honeycomb cells were characterized in FE model with an elasto-plastic constitutive model and damage criterion in detail during impact. The simulation results show good agreements with experiments and the model can be used to predict the low-velocity impact response and impact damage effectively. More detailed responses, such as internal damage details, damage modes and evolution, are observed and discussed with the numerical model proposed.

Anti-impact behavior of auxetic sandwich structure with braided face sheets and 3D re-entrant cores

The effectiveness of sandwich structure with auxetic 3D re-entrant lattice core and semi-auxetic braided composite face sheets subjected to high-velocity impact have been investigated. Braided carbon fiber composite used in face sheets of sandwich structure with a through-thickness negative Poisson’s ratio significantly improves the impact performance. A semi-analytical Mori-Tanaka asymptotic homogenization, mechanics of structure genome, and multiscale finite element scheme have been applied to study the mechanical properties and auxeticity of the braided composite. The properties obtained at the lower scales are used in a macroscale progressive damage analysis and impact simulations of semi-auxetic braided composite. The results obtained have been compared with experimental data from the literature for validation. The sandwich core holds further scope for tailoring its architecture that can enhance the sandwich performance. The high-velocity steel ball impact response of the sandwich structure with two types of auxetic 3D re-entrant lattice core have been simulated and compared with a non-auxetic core. Parametric studies have been performed at the mesoscale to study the influence of lattice angle on homogenized effective properties of the core. Compared to non-auxetic foam, proposed auxetic sandwich structures are lightweight, have better energy absorption and high stiffness values in the in plane along with out-of-plane directions. A case study of trauma plate for the application of proposed auxetic lattice reinforced polyethylene composite in body armors is presented.

Nonlinear flexural analysis of sandwich beam with multi walled carbon nanotube reinforced composite sheet under thermo-mechanical loading

AbstractNonlinear flexural analysis of sandwich composite beam with multiwall carbon nanotube (MWCNT) reinforced composite face sheet and bottom sheet under the thermo-mechanically induced loading using finite element method is carried out. Solution of current bending analysis is performed using Newton’s Raphson approach by using higher order shear deformation theory (HSDT) and non-linearity with Von Kármán kinematics. The sandwich laminated composite beam is subjected to uniform, linear and nonlinear varying temperature distribution through thickness of the beam. The sandwich beam with MWCNT reinforced composite facesheet and bottom sheet is subjected to point, uniformly distributed (UDL), hydrostatic and sinusoidal loading. The two phase matrix is utilized with E-Glass fiber to form three phase composite face sheet and bottom sheet by Halpin-Tsai model. The static bending analysis is performed for evaluating the transverse central deflection of three and five layered sandwich composite beam. Transverse central deflection is measured by varying CNT volume fraction, uniformly distributed, linearly and nonlinear varying temperature distribution, thickness ratio, boundary condition, number of walls of carbon nanotube by using interactive MATLAB code.

Free and Forced Vibration Characteristics of a Flax Fibre Reinforced Composite Beam with Viscoelastic Core

Abstract In this study, free and forced vibration characteristics of a flax fibre reinforced composite beam with a viscoelastic core have been investigated using theoretical and experimental approaches. The theoretical approach involves finite element method incorporating layerwise modelling considering classical laminate theory for top and bottom composite face sheets. The transverse displacement field is assumed to be same for all the layers, whereas the axial displacement field for the viscoelastic core is linearly interpolated in terms of the displacements of the two face sheets. Natural Frequencies of the beam in cantilever configuration and transient response of the tip of the beam subjected to base harmonic excitation have been determined under the theoretical approach. The experimental approach involves sine sweep testing and base excitation testing for determination of natural frequencies and transient response of the tip respectively and the tests have been done using an electrodynamic shaker. The results obtained from both the approaches agree closely with each other and illustrate the effect of introduction of viscoelastic core in the natural fibre reinforced composite beam.

Bending and buckling analysis of sandwich Reddy beam considering shape memory alloy wires and porosity resting on Vlasov's foundation

The aim of this research is to analyze buckling and bending behavior of a sandwich Reddy beam with porous core and composite face sheets reinforced by boron nitride nanotubes (BNNTs) and shape memory alloy (SMA) wires resting on Vlasov\'s foundation. To this end, first, displacement field\'s equations are written based on the higher-order shear deformation theory (HSDT). And also, to model the SMA wire properties, constitutive equation of Brinson is used. Then, by utilizing the principle of minimum potential energy, the governing equations are derived and also, Navier\'s analytical solution is applied to solve the governing equations of the sandwich beam. The effect of some important parameters such as SMA temperature, the volume fraction of SMA, the coefficient of porosity, different patterns of BNNTs and porous distributions on the behavior of buckling and bending of the sandwich beam are investigated. The obtained results show that when SMA wires are in martensite phase, the maximum deflection of the sandwich beam decreases and the critical buckling load increases significantly. Furthermore, the porosity coefficient plays an important role in the maximum deflection and the critical buckling load. It is concluded that increasing porosity coefficient, regardless of porous distribution, leads to an increase in the critical buckling load and a decrease in the maximum deflection of the sandwich beam.

Large deflection geometrically nonlinear bending of sandwich beams with flexible core and nanocomposite face sheets reinforced by nonuniformly distributed graphene platelets

This study investigates the nonlinear bending response of a novel class of sandwich beams with flexible core and face sheets reinforced with graphene platelets that are functionally graded distributed through the thickness. Nonlinear governing equations are established based on extended high-order sandwich panel theory and Von Kármán type of geometrical nonlinearity. In this theory, the face sheets follow the first-order shear deformation theory, and the two-dimensional elasticity is adopted for the core. These nonlinear differential equations are discretized into algebraic systems by means of the Ritz-based method from which the static bending solution can be achieved. The effective Young’s modulus of functionally graded graphene platelet-reinforced composite (GPLRC) face sheets is determined through the modified Halpin–Tsai micromechanics model, and associated Poisson’s ratio is evaluated by employing the rule of mixture. Comparison studies are provided for a sandwich beam with graphene-reinforced face sheets and conventional nanocomposite beam reinforced by graphene platelets due to lack of results for introduced sandwich beams. Besides, three-point bending test was carried out in order to assure the validity of nonlinear bending analysis of a sandwich beam based on extended high-order sandwich panel theory. Afterwards, parametric studies are given to examine the influences of graphene platelet distribution pattern, weight fraction, and core-to-face sheet thickness ratio together with the total number of layers on the linear and nonlinear bending performances of the sandwich beams. Numerical results demonstrate that distributing more graphene platelets near the upper and lower surface layers of the face sheets, named X-GPLRC, is capable to improve the bending strength and decrease the local deflection of the top face sheet, and this recovery effect becomes more significant as graphene platelet weight fraction increases. The results also reveal that the graphene platelet distribution pattern of the face sheets plays an important role to decrease the transverse shear stress of the core by dispersing more graphene platelets near surfaces of the face sheets (X-GPLRC). So, reducing the local deflection of the top face sheet tends to be much more safety of the soft core from any failure. Besides, sandwich beams with a lower weight fraction of graphene platelets in face sheets that are symmetrically distributed in such a way, called O-GPLRC, are also less sensitive to the nonlinear deformation.

Free vibration analysis of rotating pretwisted composite sandwich conical shells with multiple debonding in hygrothermal environment

This paper presents a finite element based method to study the influence of elevated temperature and moisture absorption on the free vibration behavior of rotating pretwisted sandwich conical shells consisting of two composite face-sheets and a synthetic foam core. The sandwich structure is assumed to contain single or multiple debonding present either in the face-sheets or at the interface between the face-sheets and core. The finite element formulation consists of an eight-noded isoparametric shell element having five degrees of freedom at each node. Lagrange’s equation is employed to derive the governing equation for free vibration analysis at moderate rotational speeds while the multi-point constraint algorithm is used to model the debonding region present in the composite sandwich shells. Numerical results are presented to depict the effects twist angle, thickness ratio of core to face-sheets, rotational speed and single or multiple debonding on the natural frequency of the composite sandwich conical shells at elevated temperature and moisture concentration.

Analysis of Viscoelastic Functionally Graded Sandwich Plates with CNT Reinforced Composite Face Sheets on Viscoelastic Foundation

In this article, bending, buckling, and free vibration of viscoelastic sandwich plate with carbon nanotubes reinforced composite facesheets and an isotropic homogeneous core on viscoelastic foundation are presented using a new first order shear deformation theory. According to this theory, the number of unknown’s parameters and governing equations are reduced and also the using of shear correction factor is not necessary because the transverse shear stresses are directly computed from the transverse shear forces by using equilibrium equations. The governing equations obtained using Hamilton’s principle is solved for a rectangular viscoelastic sandwich plate. The effects of the main parameters on the vibration characteristics of the viscoelastic sandwich plates are also elucidated. The results show that the frequency significantly decreases with using foundation and increasing the viscoelastic structural damping coefficient as well as the damping coefficient of materials and foundation.

Stochastic low-velocity impact analysis of sandwich plates including the effects of obliqueness and twist

Abstract This paper quantifies the influence of uncertainty in the low-velocity impact responses of sandwich plates with composite face sheets considering the effects of obliqueness in impact angle and twist in the plate geometry. The stochastic impact analysis is conducted by using finite element (FE) modelling based on an eight nodded isoparametric quadratic plate bending element coupled with multivariate adaptive regression spline (MARS) in order to achieve computational efficiency. The modified Hertzian contact law is employed to model contact force and other impact parameters. Newmark's time integration scheme is used to solve the time-dependent equations. Comprehensive deterministic as well as probabilistic results are presented by considering the effects of location of impact, ply orientation angle, impactor velocity, impact angle, face-sheet material property, twist angle, plate thickness and mass of impactor. The relative importance of various input parameters is determined by conducting a sensitivity analysis. The results presented in this paper reveal that the impact responses of sandwich plates are significantly affected by the effect of source-uncertainty that in turn establishes the importance of adopting an inclusive stochastic design approach for impact modelling in sandwich plates.

Application of smart electro-rheological dampers in semi-active control of electro-rheological sandwich plates with nanocomposite facesheets rested on orthotropic visco-Pasternak foundation

In this research, semi-active control of sandwich plates with electro-rheological (ER) core and carbon nanotubes-reinforced composite facesheets using smart ER dampers is studied. Sandwich plate is subjected to the external electric field and rested on orthotropic visco-Pasternak foundation. The material properties of ER core and nanocomposite facesheets are obtained by Yalcintas model and Eshelby–Mori–Tanaka approach, respectively. The governing equations of motion are solved by a combination between finite element and Newmark methods for clamped and simply supported boundary condition. The effects of various parameters such as applied voltage, controlled electric field and initial gap of the electrodes on the vibration suppression time are discussed. The results show that the settling time of system introduced in this work is much less than previous researches in this field which is a very important advantage.

Vibration analysis of rotating fully-bonded and delaminated sandwich beam with CNTRC face sheets and AL-foam flexible core in thermal and moisture environments

In the present study, the high-order free vibration analysis of rotating fully-bonded and delaminated sandwich beams; with and without vertical contact; containing AL-foam flexible core and carbon nanotubes reinforced composite (CNTRC) face sheets subjected to thermal and moisture field are investigated by using generalized differential quadrature method (GDQM). The compressible core and face sheets of sandwich beam, respectively, are composed of Aluminum alloy foam with variable mechanical properties in the thickness direction and CNTRC with temperature dependent material properties. In this study, the high-order sandwich panel theory (HSAPT) for AL-foam flexible core and Euler-Bernoulli beam theory for CNTRC face sheets are considered. By employing Hamilton’s principle, the governing partial differential equations of motion and associated boundary and continuity conditions for various types of regions (fully-bonded, delaminated with contact, delaminated without contact) are derived and then discretized by using GDQM. The final formulations lead to 14 partial differential equations for the entire structure including five equations for fully-bonded two-headed parts of AL-foam cored sandwich beam (AL-FCSB) and four equations for delaminated middle part of AL-FCSB beam which are combined in axial and transverse deformations. A parametric study is performed to investigate the influence of some important parameters such as existence of delaminated region, type of delaminated region (with or without contact), longitudinal position of delaminated region, slenderness ratio, face sheet thickness ratio, CNT volume fraction, temperature rise, moisture concentration, rotating speed, and hub radius. The obtained results reveal that the 1st frequency of delaminated AL-FCSB beam, whether with or without vertical contact, is less remarkably than ones of fully-bonded AL-FCSB beam which its value for the case of delaminated ‘with contact’ is larger than that of ‘without contact’. Moreover, the 1st frequency variation of the delaminated AL-FCSB beam is symmetrical with regard to the longitudinal position of the debonded region such that the 1st natural frequency declines with moving the debonded region toward the center of the beam. The study of vibration behavior of rotating sandwich beams is very important in design of rotating structural systems, specially damaged ones, such as airplanes, helicopter rotor blades, and robot arms. One of the most important types of damage encountered in mentioned cases is the decomposition of two layers or delamination. Working these rotating structures in the media, are always along with variations of temperature and humidity and hence their mechanical properties may be changed due to the environment conditions.Communicated by S. Velinsky

Hygrothermal effect on vibroacoustic behaviour of higher-order sandwich panel structure with laminated composite face sheets

This article is a study of vibroacoustic behaviour of sandwich shell panels with laminated composite faces under concentrated harmonic loading in a hygrothermal environment by means of a higher-order finite-boundary element model. The system governing equations of the vibrating structure are derived using the higher-order shear deformation shell theory coupled with finite element and boundary element approach. The corrugated composite material properties due to temperature and moisture variation are included in the model macroscopically. The stiffness, mass tensors and modal values of the hygro-thermally stressed vibrating panel are first obtained and the acoustic radiation responses are then computed by solving the Helmholtz wave equation discretized on the structure boundary. The proposed scheme is implemented via a domestic MATLAB program to compute the desired responses. The results for natural frequencies, critical buckling moisture, critical buckling temperature and radiated sound power are found to be more accurate when matched with the available benchmark solutions. Additional numerical simulations are also performed with commercial software to authenticate the correctness of the present model. Finally, numerous numerical experimentations are carried out to reveal the versatility of the present scheme. The influence of hygrothermal conditions, geometrical parameters, support conditions and lamination scheme of the faces on the hygro-thermo-acoustic responses of laminated composite sandwich shell panels are probed and deliberated in detail.

Size‐dependent free vibration of sandwich micro beam with porous core subjected to thermal load based on SSDBT

AbstractIn this study, free vibration of the sandwich microbeam with porous core and FG carbon nanotubes reinforced composite face sheets which is rested on Winkler‐Pasternak substrate is investigated. It is assumed the beam is in thermal environment and is subjected to thermal load and the displacement components are described based on sinusoidal shear deformation beam theory. The small scale effects are taken into account according to the modified couple stress theory. The core and face sheets properties are diffused through the thickness. The motion equations are derived and solved using Hamilton's principle and Navier's method, respectively. Effect of different parameters such as porosity coefficient and distributions, different types of CNTs distribution, small scale and geometrical size of the beam is considered. The results show by enhancing the porosity, the frequency decreased. The findings of the current study can be used to design prominent role in modern engineering applications.

Flexural testing and analysis of full-strain-fields in sandwich composites

The objective of this work was to characterize the full-field flexural behavior of composite sandwich beams. Finite element analysis was used to estimate the behavior of sandwich beams under three- and four-point-bending tests and were compared with experimental results obtained via digital image correlation and strain-gages. Two different core thicknesses and two different sandwich lengths were used to simulate short- and long-beam. Two distinct sandwich beams were fabricated by bonding basalt fiber reinforced polymer composite face sheets (laminates) to polyurethane core and aluminum face sheets glued to polyurethane core with an adhesive film. Full-strain-fields and flexural displacements were obtained by means of strain-gages and digital image correlation technique. Experimental results were in good agreement with predictions and digital image technique attested to be a complementary method to strain-gages in experimental full-strain-fields analysis.