Laminated Face Sheets Research Articles

Blast response of rectangular graded foam sandwich plate with fiber-metal laminate face-sheets

In this paper, the dynamic response of a fully clamped rectangular graded foam sandwich plate (GFSP) with fiber-metal laminate (FML) face-sheets under impulse loading is studied analytically and numerically. Due to the fibers having intricate layups, there are various difficulties in developing an analytical model that can accurately analyze the structural properties of fiber layups. In this work, the bound and membrane mode solutions for the blast response of a rectangular GFSP with FML face-sheets are obtained on the basis of the modified rigid-plastic model by introducing the number of fiber layups, metal volume fraction, composite density coefficient, and composite strength coefficient. In addition, finite element analysis is performed using ABAQUS/Explicit software. Analytical predictions agree very well with numerical results. The effects of metal volume fraction, composite coefficients of density and strength, thickness and average yield strength of the graded foam, and gradient property of the foam on the blast response of GFSP with FML face-sheets are discussed. It is demonstrated that the proposed analytical model can be efficient in predicting the blast response of rectangular GFSP with FML face-sheets.

Low-velocity impact of sandwich beams with fibre-metal laminate face-sheets considering local denting effect

In this work, the dynamic response of the clamped sandwich beams with fibre-metal laminate face-sheets under low-velocity impact is analytically and numerically studied. Analytical solutions for the dynamic response of clamped FML sandwich beams under low-velocity heavy-mass impact are developed based on modified rigid-plastic material approximation. Analytical results are compared with numerical ones, there is a good agreement between the two. The effects of foam strength, strength ratio of metal layer to composite layer, and composite volume fraction on structural response are discussed in detail. It is shown that foam strength has a substantial impact on the local denting deformation whereas strength ratio of metal layer to composite layer has a considerable impact on the overall bending of FML sandwich beams.

Vibration and damping characteristics of auxetic honeycomb sandwich panels with polyurea-metal laminate face sheets

Vibration and damping characteristics of auxetic honeycomb sandwich panels with polyurea-metal laminate face sheets

Efficient design of composite honeycomb sandwich panels under blast loading

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

Multi-objective optimization of composite sandwich structures using Artificial Neural Networks and Genetic Algorithm

Sandwich structures offer significant opportunities to improve the performance of many industrial applications such as aerospace, automotive, and marine. The design of a composite sandwich structure is often challenging because it is driven by the balance between the weight and cost of these structures. In this paper, a multi-objective optimization model using a Genetic Algorithm (GA) and an Artificial Neural Network (ANN) is presented to evaluate a new optimization approach in terms of weight and cost minimization for the composite sandwich structures. Classical lamination and beam bending theories were used, along with Monte Carlo simulation, to generate the design data for the proposed composite sandwich structure, which is applied as a floor panel for a high-speed train. Multilayer feedforward neural networks were used for predicting safety factors, cost, and weight of the designed structure based on the following inputs: core density, core thickness, face sheet materials’ combinations, and applied load. The trained Neural Network model was able to predict the considered results with a good performance metric, namely the coefficient of determination (R2 = 0.99) and the Mean Square Error (MSE = 1.3·10−5).Multi-objective optimization for cost and weight minimization was performed with a Genetic Algorithm using the derived ANN model. The obtained Pareto front provided several non-dominated optimal points leading to insights on the optimization process. The Finite Element Method (FEM) was used to model the key points of the optimal designs (i.e. the design with the lowest cost, weight, and Pareto optimal points). The FEM and optimization results had a maximum deviation of about 8.9%, indicating a good agreement between the two techniques.The newly elaborated methodology demonstrates a new approach for obtaining the optimum design of the investigated composite sandwich structure constructed from honeycomb core and laminated face sheets in terms the cost and weight. The study concluded that the use of Carbon Fiber-Reinforced Plastic (CFRP) or Fiber-Metal Laminate (FML) face sheets results in significant weight savings of about 59.5% and 48.6%, respectively, compared to an all-aluminum sandwich structure.

Explosive blast loading effect on transient mechanical responses of aircraft panels with curvilinear fibers: 3D elasticity approach

In the present paper, for the first time, the dynamic loading effect on transient bending and stress distributions of aircraft nanocomposite sandwich panels including curvilinear fibers are presented and explained. Face sheets of the panel contain curvilinear fibers with an orientation angle varies linearly with respect to the horizontal coordinate. The core layer is made of polymer matrix reinforced by graphene platelets (GPLs) with uniform and random orientation distribution. 3-D elasticity theory is used to formulate the transient problem of the panel. The model of the panel is so general to include different time-dependent loads, especially explosive ones. A three-dimensional layerwise-differential quadrature method (LW-DQM) together with a non-uniform rational B-spline-based multi-step time integration scheme is employed to investigate the transient responses of the sandwich panel with variable stiffness composite laminated face sheets (VSCL-FS) and graphene platelets reinforced porous core (GPLR-PC) under dynamic loading. The convergence behavior of the method is examined numerically and to assure its accuracy, the results in the limit cases are compared with those available in the literature. Finally, through the parametric studies, the effects of core porosity distribution and amounts, GPLs weight fraction and boundary conditions on the transient responses of the sandwich panel with VSCL-FS and GPLR-PC subjected to explosive blast loading are investigated. The results show that the addition of GPLs to the core layer decreases the transverse displacement but increases the peak values of the stress components. Also, the core porosity increases the transverse displacement and the stress components. However, it has not significant effect on the period of oscillation of the field variables under explosive blast loading. On the other hand, the curvature of the fibers does not considerable effect on the plate response and on the period of oscillation of the field variables under explosive blast loading

Failure characterisation of sandwich beams using integrated acoustic emission and digital image correlation techniques

The paper presents the experimental study of the failure behaviour of sandwich beams subjected to bending. The samples examined are sandwich beams made of polyethylene terephthalate foam core and glass fibre-reinforced polymer laminate face sheets. In a series of experiments, it has been proposed to integrate diagnostic techniques with acoustic emission and digital image correlation to accurately track the cracking process on the surface as well as in the entire volume of the beam. The research programme carried out allowed observing various modes of failure in composite specimens. The results obtained showed that the integration of acoustic and optical diagnostic techniques provided complementary results and can be used successfully for failure monitoring in sandwich beams.

Buckling and Postbuckling of Laterally Pressured Sandwich FG-GRC Laminated Toroidal Shell Segments with Corrugated Core in Thermal Environment

The nonlinear buckling behaviors of sandwich functionally graded graphene reinforced composite (FG-GRC) laminated toroidal shell segments with corrugated core under lateral pressure in thermal environment are reported in this study. Three distributed types of the FG-GRC face sheets and two forms of corrugation including the trapezoidal and round corrugations are considered. By adding the thermal forces into an existing equivalent technique, the behavior of the corrugated core is modelled. The nonlinear formulations can be obtained by using the nonlinear Donnell shell theory taking into account the shell-foundation interaction. The Ritz energy procedure is used for three states of deflection to obtain the postbuckling curve expressions of the load-maximal deflection. The bifurcation buckling type of critical buckling pressure is obtained in the explicit form. The numerical examinations present the significant effects of corrugated core and FG-GRC laminated face sheets on nonlinear buckling behaviors of shells.

Dynamic performance of ultralight corrugated sandwich plate with FML face-sheets impacted by FSP-foam composite projectile

Ultralight corrugated sandwich constructions have shown great promise as multifunctional structures capable of simultaneous load-bearing, shock mitigation and ballistic resistance, yet little is known about the synergetic effects of combined shock and fragment loadings on their performance. This study presented a combined experimental and numerical investigation of corrugated-core sandwich plate with ultra-high molecular weight polyethylene (UHMWPE) fiber metal laminate (FML) face-sheets subjected to combined shock and fragment impact. The combined loading was achieved using a laboratory-based experimental technique previously proposed by the present authors, i.e., the impact of fragment-foam composite projectile fired from a light gas gun. Corrugated-core sandwich plates with both FML face-sheets and metallic face-sheets were prepared, and their ballistic/blast resistances and deformation/failure modes were characterized experimentally. Three-dimensional finite element simulations were performed and validated to provide further insight into the underlying mechanisms of dynamic responses under combined loading. Compared with the reference sandwich plate with metallic face-sheets, stacking UHMWPE composite sheets into the face-sheets not only maintained the blast-induced deflection but also improved the ballistic limit against the fragment simulation projectile (FSP). The synergetic effect of combined loading could weaken the penetration resistance and increase the permanent deflection, but the tearing cracks caused by combined loading could be significantly inhibited by the use of FML face-sheets. In addition, the impact sequence of foam and fragment affected the ballistic resistance of corrugated-core sandwich plate with FML face-sheets.

Investigation of viscoelastic properties in composite sandwich panels subjected to low-velocity impact: Experimental and numerical approaches

This study investigates the effect of viscoelastic properties in the numerical modeling of foam-filled sandwich panels when their composite facesheets are exposed to low-velocity impact loading. A finite element (FE) model is developed using the software package of ABAQUS and used to investigate the effect of both considering and ignoring the time-dependent behavior of composite laminate facesheets as well as the foam core. Material constitutive equations, damage characteristics, and failure modes are defined in a FORTRAN user-subroutine VUMAT. To characterize the material behavior of both polyurethane foam and glass/epoxy composite material, a set of experimental tests are conducted under compression, tension, and stress relaxation modes. To validate the numerical results, low-velocity impact tests at two energy levels of 9.81 and 17 joules are carried out on sandwich panels with foam core. The results of numerical simulations are found to be in good agreement with the experimental test results. It is shown that ignoring the viscoelastic properties in the composite laminate and the foam core can lead to deviations of up to 7% and 25%, respectively, from experimental results. The analysis reveals that, ignoring the viscoelastic behavior along the fiber-direction in the composite facesheets does no change the results considerably. The viscoelastic properties perpendicular to the fibers, however, has a more noticeable effect on the results due to the prevalence of the properties of the polymeric resin in that direction.

Development and evaluation of the sandwich open-hole flexure test

An open-hole flexure test method has been developed to assess the notch sensitivity of sandwich composites under flexural loading. This test method, recently standardized as ASTM D8453, utilizes the current long beam four-point flexure fixture with the addition of a centrally-located open through-hole in the standard specimen. Previous research has identified an open-hole diameter that minimized finite-width effects while producing a statistically significant reduction in strength. Finite element analyses focused on quantifying interaction between the open-hole stress concentration and the load span length, hole location tolerance, and misalignment of the specimen and fixture. The effect of non-linear geometry due to large deflection was investigated and limits prescribed for linear geometry assumptions to remain valid. The sandwich configurations investigated consisted of a Nomex honeycomb core and carbon/epoxy facesheet laminates with a range of material orthotropy ratios. A series of mechanical tests were performed to evaluate the proposed specimen design, and the existing test fixture and procedure. The first set of experiments were performed to assess the notched strength sensitivity to the load span length. A second set of experiments assessed the effect of different core densities and thicknesses.

Impact Resistance of a Fiber Metal Laminate Skin Bio-Inspired Composite Sandwich Panel with a Rubber and Foam Dual Core

This paper reports the development of a novel bio-inspired composite sandwich panel (BCSP) with fiber metal laminate (FML) face sheets and a dual core to improve the low-velocity impact behavior based on the woodpecker's head layout as a design template. The dynamic response of BCSP under impact load is simulated and analyzed by ABAQUS/Explicit software and compared with that of the composite sandwich panel (CSP) with a single foam core. The impact behavior of BCSP affected by these parameters, i.e., a different face sheet thickness, rubber core thickness and foam core height, was also reported. The results show that BCSP has superior impact resistance compared to CSP, with a lower damage area and smaller deformation, while carrying a higher impact load. Concurrently, BCSP is not highly restricted to any particular region when dealing with stress distributions. Compared to CSP, the bottom skin maximum stress value of BCSP is significantly reduced by 2.4-6.3 times at all considered impact energy levels. It is also found that the impact efficiency index of BCSP is 4.86 times higher than that of CSP under the same impact energy, indicating that the former can resist the impact load more effectively than the latter in terms of overall performance. Furthermore, the impact resistance of the BCSP improved with the increase in face sheet thickness and rubber core thickness. Additionally, the height of the foam core has a notable effect on the energy absorption, while it does not play a significant role in impact load. From an economic viewpoint, the height of the foam core retrofitted with 20 mm is reasonable. The results acquired from the current investigation can provide certain theoretical reference to the use of the bio-inspired composite sandwich panel in the engineering protection field.

Investigation of mechanical characterization of hybrid sandwich composites with syntactic foam core for structural applications

In this work, mechanical performance on sandwich composites consisting of syntactic foam filled with hollow glass microsphere in an epoxy resin matrix as the core material and hybrid kenaf/glass fibers face-sheet based composites panel is studied. The main purpose of this work is to design a suitable lightweight composite panel material for structural application. Four different sequences of face-sheet reinforcement (e.g., kenaf-kenaf; glass-glass; glass-kenaf, and kenaf-glass) were adopted. In this study, the mechanical properties and failure modes are carefully investigated. The sandwich composites were characterized by compressive, tensile, and flexural properties. The results showed that compressive strength was highest at the “kenaf-glass” face-sheets, tensile strength was highest at “glass-glass” face-sheets, and flexural at “glass-glass” face-sheets with 52.1%, 67.6%, and 74.4% increase to “kenaf-kenaf” face-sheets, respectively. The tensile strength and modulus values with the specific strengths and modulus values showed that the mechanical properties of the sandwich composites can be influenced by hybridizing the face-sheet laminates of the composite. This shows that kenaf fiber has limited strength when used as reinforcement alone but gave an excellent performance when combined with glass fiber.

A study on the damage tolerance of durable redundant composite sandwich joints

A patented Durable Redundant Joint (DRJ) concept featuring multiple adhesive load-paths, via a novel composite preform insert, is being considered for joining composite sandwich panel segments. Applications are wide ranging from spacecraft bus structure to launch vehicle primary structure (i.e. interstage cylinders and payload fairings). Numerical and experimental investigations were performed to assess the DRJ’s performance. A fracture-based approach was used to evaluate this design. Ply-level mechanical properties for the material systems were generated, and a double cantilever beam coupon was designed and tested to estimate the Mode I critical energy release rate for the interface between two different composite prepreg material systems. The DRJ was tested and compared to testing of the more conventional splice joint (CSJ) design. Polytetrafluoroethylene (PTFE) inserts were used at the free edges of the joints to simulate debonds between the doubler and facesheet laminates. The DRJ coupons reached 32% greater in-plane tensile failure load compared to the CSJ coupons. Furthermore, the predicted increased strength for the DRJ design compared to the CSJ design was in remarkably good agreement with test data. Using the insight gained from these studies, three design attributes were investigated relative to increasing damage tolerance characteristics of the DRJ: (1) Insert stiffness, (2) Relative length between the doubler and the insert, and (3) The use of tapers at the ends of doublers.

Development and evaluation of the sandwich open-hole compression test

An open-hole compression test method has been developed to assess the notch sensitivity of sandwich composites under compression loading. This test method, in the process of being standardized by ASTM International, utilizes end loading as well as knife-edge side supports to provide out-of-plane restraint to specimen buckling. Finite element analyses focused on identifying a sandwich specimen geometry that minimized finite-width and finite-length effects on the stress concentration produced by the centrally-located through-hole. Geometric variables included the specimen width-to-hole diameter (w/D) and length-to-hole diameter (l/D) ratios. The sandwich configurations investigated consisted of a Nomex honeycomb core and carbon/epoxy facesheet laminates with a range of material orthotropy ratios. Numerical results were used to identify a candidate sandwich specimen geometry and optimal strain gage placements for use in specimen alignment. A series of mechanical tests were performed to evaluate the proposed specimen design, the proposed test fixture, and the recommended test procedure. The first set of experiments were performed using specimens with different hole diameters but the same specimen width and length. A second set of experiments used specimens with different lengths but with the same specimen width and open-hole. In addition, the use of specimen end potting of the core region was investigated to prevent facesheet separation and end brooming.

Plastic behavior of sandwich beams with fiber metal laminate face-sheets and metal foam core: Combined local denting and overall deformation

In this paper, the plastic behavior of a fully clamped sandwich beam with fiber metal laminate (FML) face-sheets and metal foam core under transverse loading is analytically and numerically studied. Based on the modified rigid plastic model, the analytical solution for large deflection of FML sandwich beams under transverse loading is given, in which the local denting deformation is considered. Finite element results are conducted, and analytical solutions capture numerical results reasonably. The influences of material and geometrical parameters on the plastic behavior of FML sandwich beams are considered. The results show that the present analytical model can be used to predict the plastic behavior of fully clamped FML sandwich beams considering the local denting deformation.

Dynamic response of slender multilayer sandwich beams with fiber-metal laminate face-sheets subjected to low-velocity impact

Low-velocity impact of slender multilayer sandwich beams, which formed by fiber-metal laminate (FML) face-sheets and metal foam cores, is theoretically and numerically investigated. Based on the modified rigid plastic model, the analytical solution for dynamic response of the slender multilayer FML foam sandwich beam under low-velocity impact is obtained. Numerical calculations are conducted, the analytical solutions capture numerical results. Effects of the strength ratio of composite and metal layers, core strength, and metal volume fraction are discussed for impact resistance of multilayer FML foam sandwich beams. Finally, the optimal design map by minimizing the mass of multilayer FML foam sandwich beam is conducted.

Comparative experimental study into the explosive blast response of sandwich structures used in naval ships

Naval ships can be constructed using sandwich composite structures with the core material being polymer foam or balsa wood. Naval ships are at risk from explosive blasts from underwater and airborne munitions, and therefore the sandwich structures used must be resistant to extreme deformation and damage caused by blast loads. An experimental study is presented comparing the explosive blast response of sandwich composite panels with a polymer foam (PVC) core or balsa core with polymer laminate facesheets reinforced carbon or glass fibres. These materials studied are representative of sandwich structures used on naval ships. Sandwich panels were subjected to small-scale explosive air blasts of increasing shock wave impulse loads. The out-of-plane deformation and damage was influenced by both the facesheet laminate material and the core material. The fibreglass laminate facesheets were more resistant to blast-induced damage than the carbon fibre facesheets. The blast damage to the facesheet-core interfaces and within the core was more extensive using balsa compared to polymer foam. The study provides new insights into the relative blast performance of different types of sandwich structures used in naval ships.

The Plastic Behavior in the Large Deflection Response of Fiber Metal Laminate Sandwich Beams under Transverse Loading.

The plastic behavior in the large deflection response of slender sandwich beams with fiber metal laminate (FML) face sheets and a metal foam core under transverse loading is studied. According to a modified rigid–perfectly plastic material approximation, an analytical model is developed, and simple formulae are obtained for the large deflection response of fully clamped FML sandwich beams, considering the interaction of bending and stretching. Finite element (FE) calculations are conducted, and analytical predictions capture numerical results reasonably in the plastic stage of large deflection. The influences of metal volume fraction, strength ratio of metal to composite layer, core strength, and punch size on the plastic behavior in the large deflection response of FML sandwich beams are discussed. It is suggested that, if the structural behavior of fiber-metal laminate sandwich beams is plasticity dominated, it is similar to that of metal sandwich beams. Moreover, both metal volume fraction and the strength ratio of metal to composite layer are found to be important for the plastic behavior in the large deflection response of fiber metal laminate sandwich beams, while core strength and punch size might have little influence on it.

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.