Thick Sandwich Research Articles

Integrating parametric HFGMC and isogeometric RZT[formula omitted] for multiscale damage modeling of composite structures: A numerical and experimental study

In this research effort, a novel multiscale analysis scheme is proposed for damage modeling of composite laminates, sandwich structures, and stiffened plates relying on capabilities of the parametric HFGMC and isogeometric RZT{3,2} formulations. The Ramberg Osgood (RO) model is incorporated into the micromechanics model to reflect polymer matrix material nonlinearities on the overall homogenized composite behavior. Carbon fibers are assumed to behave in a linear transversely isotropic manner. The higher order RZT{3,2} theory employed at the macro level facilitates efficient applicability of the model to thick composite laminates and soft core sandwiches. On the other hand, it generates all three-dimensional stress components and thus ensures dimensional consistency between micro and macro levels. Numerical discretization and prediction of RZT{3,2} kinematic variables are enabled by performing NURBS based isogeometric analysis (IGA) thereby enhancing modeling efficacy to a significant degree. Soft core plasticity and failure in the composite are evaluated at the macro level through the RO model and Hashin criteria, respectively. Applicability of the method is presented for thin and thick flat composite and sandwich laminates; and further extended to stiffened plates via developing a multipatch formulation. A comprehensive validation of our analysis is conducted by comparing the results with established benchmarks from the literature, experimental data, and three-dimensional finite element method (3D-FEM) simulations. Initially, a moderately thick, simply supported square laminate under transverse loading is examined, a common verification benchmark. Then, results from standard mechanical tests, including tensile, shear, and four-point bending tests on thin laminates, followed by experiments on moderately thick sandwich structures subjected to four-point bending, are presented. Finally, the analysis is extended to a stiffened plate under uniform pressure, demonstrating the method’s accuracy and applicability across diverse structural configurations.

Failure mode maps for glass fibre-reinforced polymer/polyvinyl chloride foam-cored sandwich structures

Purpose This study aims to understand how the facesheet size, orientation and core size influence the analytical failure mechanism mode of glass fibre reinforced polymer (GFRP)/polyvinyl chloride (PVC) sandwich structures subjected to three-point bending. The purpose of this study was to develop failure-mode map of GFRP/PVC sandwich structures. Sandwich structures with different facesheet and core thicknesses were used to develop the failure map. Design/methodology/approach The sandwich structure and facesheet were fabricated using a vacuum-assisted resin infusion method with core sizes of 10, 15 and 20 mm and facesheet thicknesses of 1.5 and 3 mm and were arranged in three different orientations: angle-ply, cross-ply and quasi-isotropic. The key failure modes that occur in sandwich structures were used to predict possible failures in the developed material. Analytical equations were used in MATLAB for each observed failure mode. The probable failure modes, namely, face yielding, core shear and indentation equations, were used to construct the failure maps and were compared with the experimental data. Findings The boundary of the two failure modes shifts with changes in the facesheet and core thicknesses. The theoretical stiffness of sandwich panels was higher than the experimental stiffness. Based on strength-to-weight ratio, specimens E10-4, A15-8 and E20-8 exhibited the best optimum values owing to their shorter distance to the boundary lines. Originality/value In this study, a failure map was used to predict the possible failure modes for different GFRP facesheet orientations and thicknesses and PVC core thickness sandwich structures. Little is known about the prediction of the failure modes of unidirectional GFRP arranged in different orientations and thicknesses and PVC core thicknesses for sandwich structures. Few studies have used failure mode maps with unidirectional GFRP oriented in angle-ply, cross-ply and quasi-isotropic directions as a facesheet for sandwich structures compared to bidirectional mats. This study can serve as a guide for the correct selection of materials during the design process of sandwich structures.

Nonlinear free vibration analysis of moderately thick sandwich plates with viscoelastic core using finite strip method

Nonlinear free vibration analysis of moderately thick sandwich plates with viscoelastic core using finite strip method

An enhanced higher-order finite element formulation for wrinkling analysis of thick sandwich plates

Sandwich structures are susceptible to wrinkling when subject to in-plane compressive loads, which threatens structural safety. To accurately investigate the failure behavior, the following work is to be required. Firstly, the wrinkling behavior of sandwich plates is a typical three-dimensional (3D) issue. To consider a 3D effect, an enhanced higher-order finite element formulation including transverse normal strain has been proposed for the first time. Utilizing the proposed finite element formulation, a refined quadrilateral element model has been constructed. Secondly, the buckling and wrinkling behaviors of square sandwich plates have been investigated. The performance of the proposed model has been evaluated by comparing it with the quasi-3D solutions, the results obtained from the 3D finite element method (3D-FEM), and other models. The differences between the buckling and wrinkling failure behaviors have been carefully explained. Thirdly, the effects of boundary conditions on buckling and wrinkling deformation have been explored in detail. By utilizing the proposed model, the translation mechanism between the buckling and wrinkling deformations of sandwich plates under different boundary conditions has been revealed, which can help other investigators to well understand the buckling and wrinkling behaviors of sandwich plates. It can be shown that the wrinkling behaviors of thick sandwich plates occur earlier than the buckling behaviors when the thickness ratio of core to face panel is more than 35. Besides, it also can be shown that the buckling and wrinkling loads decrease gradually with the relaxation of the boundary restriction.

Vibration analysis of graphene-reinforced porous aluminum-based variable-walled thickness sandwich joined conical-conical panel with elastic boundary conditions using differential quadrature method

In this paper, a unified solution is proposed to investigate the vibration characteristics of the variable-walled thickness graphene-reinforced porous aluminum-based (GRPA) sandwich joined conical-conical panel (JCCP) with the arbitrary elastic support boundary conditions by using the differential quadrature method (DQM). The two surfaces of the sandwich JCCP are made of metallic aluminum and the central core layer is the GRPA. The core thickness of each conical plate varies linearly with its generatrix. Three types of the graphene distributions and two types of porosity distributions are considered along the core thickness direction. Based on the first-order shear deformation theory (FSDT), von-Karman strain displacement relationship, constitutive relationship and Hamiltonian principle, the partial differential governing equations of motion are obtained for the variable wall thickness GRPA sandwich JCCP. Using the DQM, the dynamic equation is discretized into the ordinary differential equation. The matrix of the characteristic equation is analyzed to solve the frequencies and mode shapes of the variable wall thickness GRPA sandwich JCCP. The effects of the spring stiffness, boundary conditions, graphene distributions, porosity distributions and geometric parameters on the vibration properties are studied for the variable wall thickness GRPA sandwich JCCP with two interesting elastic supported boundary conditions. At the same time, this article provides a useful approach for studying the arbitrary boundary coupled plate and shell structures with the variable wall thickness.

Design of energy-absorbing bionic workstation table for trains and research on occupant collision injury

Secondary impact is a significant contributor to occupant injuries in train crashes. To mitigate collision injuries, a workbench with energy-absorbing properties was developed, drawing inspiration from leaf-vein and honeycomb structures. A local collision model of a dummy compartment was established to evaluate the impact of different sandwich thicknesses on occupant injuries. By optimizing the wall thickness of the energy-absorbing sandwich, the optimal gradient parameters were determined. The assessment of occupant collision injury from the workstation table with a graded wall thickness sandwich was conducted using the LSTC Hybrid III 50th seating dummy. The results demonstrate that the workstation table influences the occupant's movement posture during a collision, preventing head impact with the tabletop. Apart from slightly elevated leg injuries in the dummy, which remained within permissible values, the head, neck, and chest injuries were reduced by 98.45%, 48.17%, and 81.18%, respectively.

Nonlinear dynamic response and bifurcation of variable thickness sandwich conical shell with internal resonance

Nonlinear dynamic response and bifurcation of variable thickness sandwich conical shell with internal resonance

Effective multiscale structural analysis of thick sandwich structures with 3D woven composite face sheets and a soft core based on coupled micromechanics and refined zigzag theory

In this study, a novel multiscale analysis technique is presented for predicting the mechanical behavior of 3D woven composites. To this end, the model of the representative unit cell (RUC) is generated using SOLIDWORKS computer-aided design package by taking the optical microscopic images as a reference. The fiber volume fractions (FVF) of the impregnated yarns are calculated using the roving parameters and the dry fiber density for each tow separately. Homogenized properties are obtained by utilizing the finite element analysis (FEM) software ABAQUS. The proposed method simplifies the meso-modeling process of 3D woven composites as it does not require CT scanning for geometry generation or sophisticated localized fiber volume fraction measurements. The verification of the current model is carried out both in the meso scale where the RUC surface strains are compared with DIC results and in the macro scale where tensile and flexural tests are simulated and compared with the experiments. Finally, the applicability of this method is demonstrated through an assessment study of the 3D woven composites as facesheets in thick sandwich structures in an isogeometric refined zigzag framework.

Load bearing investigations on novel Acrylonitrile butadiene styrene‐carbon quantum dots 3D printed core/bamboo fiber polyester sandwich composite for structural applications

AbstractIn this research, a novel 3D printed core and natural fiber polyester composite skin based thick sandwich panel was developed as structural material for domestic and commercial infrastructure applications. The main objective of this research was to analyze how the carbon quantum dots (C‐dots) from agriculture waste strengthen the softer thermoplastic acrylonitrile butadiene styrene (ABS) core and overall sandwich panel's load bearing properties. The core of sandwich was prepared using additive manufacturing method whereas the skin was developed by hand layup method. According to the results the C‐dots of 20 phr into the ABS improved the compression properties of core in both flatwise and edgewise directions. A highest tensile and flexural strength of skin was observed to be 114 and 146 MPa respectively. The addition of C‐dots improved the load bearing effect and also restricts the deformation against load. This performance improved novel 3D printed core and bamboo fiber skin sandwich could be used as an alternative construction and building material where the commercial plywood and other forms of powder wood face damages via weather and termite issues.Highlights Higher filler volume of up to 20 phr of carbon quantum dots in acrylonitrile butadiene styrene (ABS) were developed Novel 3D printed thin walled core of 1 mm diameter was developed using carbon quantum dots and ABS. Bamboo fiber‐polyester skin with highest tensile strength of 114 MPa was developed. Improved flatwise compression and tensile strength were achieved for ABS core with 20 phr of Carbon quantum dots Flexural strength and edgewise compression properties were improved with 20 phr of Carbon quantum dots in ABS

Layerwise models for supersonic flutter analysis of viscoelastic sandwich panels with curvilinear fibre composite skins

In this work, an assessment of layerwise finite element models for supersonic flutter analysis of soft core viscoelastic sandwich panels is presented, making use of various kinematic descriptions involving shear deformation theories and Lagrange z-expansions with thickness stretching, progressively refined to render numerically accurate and computationally efficient solutions. Numerical applications of sandwich panels include either viscoelastic or purely elastic core with skins of metal or laminated composite, using unidirectional or curvilinear fibres, considering thin and moderately thick panels, with core thickness ratios ranging from narrow to wide cores. A comprehensive assessment of the models predictive capabilities in free vibration analysis is carried out by comparison with three-dimensional exact solutions and numerical methods available in the literature. Even though it is concluded that layerwise first-order modelling, with no thickness stretching, ensures a fair compromise between numerical accuracy and computational efficiency in the aeroelastic flutter analysis of thin sandwich panels, layerwise high-order theories accounting for thickness stretching are rather necessary for the proper modelling of moderately thick sandwich panels, with either viscoelastic or purely elastic core.

Vibrational behavior of a 3D printed biomimetic dual‐core composite sandwich beam: An experimental and numerical study

AbstractComposite sandwich structures have been used in various applications like aerospace, automotive, and maritime sectors. The process of identifying the core design and the selection of a prominent core is crucially important in sandwich structures. In this study, biomimetic core development and vibration responses of composite sandwich beams with a dual biomimetic honeycomb core are investigated. The composite face layers are fabricated by the hand lay‐up method, and the fused deposition modeling is used to 3D print the PLA honeycomb cores. Based on ASTM‐E1876 and the alternative dynamic approach, the face layer elastic properties and rigidity modulus of the cores are evaluated, respectively. The numerical simulation is used to predict the sandwich panels' natural frequencies and mode shapes and verified with experimental results. There was an excellent agreement between the calculated and experimental natural frequencies. Due to the presence of the core and enhanced rigidity modulus, the dual lamellar honeycomb core sandwich beam produces the highest natural frequencies among all‐composite sandwich beams, followed by the dual regular honeycomb, single lamellar honeycomb, and single regular honeycomb cores. The geometric parametric studies, including core thickness, length‐to‐breadth ratio, lamination schemes, support conditions, and transverse vibration responses were also analyzed for different sandwich patterns. As a result of this work, thick composite sandwich panels in aeronautical and marine structures can be replaced with dual biomimetic core structures. The study highlights the fact that the dual‐core sandwich beam provided greater modal frequency than the single‐core beam with the same weight proportions.Highlights Pistachio nut shell‐based biomimetic honeycomb core has been developed. Alternative dynamic approach is used to find sandwich‐core shear properties. Lamellar‐infused biomimetic model yields higher shear modulus and stiffness. Dual‐core beam having high flexural stiffness enhances the natural frequency. Various parametric studies were analyzed for different sandwich patterns.

Experimental verification of FRP bridge deck's monitoring system based on DFOS sensors

AbstractThe paper presents the smart FRP composite bridge panel called „OptiDeck“ with integrated distributed fibre optic sensors (DFOS), to monitor the panel's behavior. The panel is intended for use in newly build and refurbished road bridges. From structure point of view the uniqueness of the presented solution results from innovative technological production process to create a honeycomb core in thick sandwich panel. In order for the monitoring system to cover the entire surface of the panel and to detect local damage, it was necessary to use a modern solution based on geometrically continuous DFOS system. The DFOS system serves as the structure health monitoring (SHM) system, which has been tested during the production and laboratory testing of a prototypes in natural scale. The advantages of DFOS measurements are well known and applied in many civil engineering applications. However, the potential benefits are still not fully utilized. Finally the experimental verification of the DFOS system integrated with the FRP deck panel is presented.

Dough‐Like Aramid Nanofiber Putty‐Assisted Design of Free‐Standing Liquid Metal‐Based Films for Ultrahigh Electromagnetic Interference Shielding

Gallium‐based liquid metal (LM) is expected to be an ideal candidate for flexible electromagnetic interference (EMI) shielding materials in wearable electronics due to its excellent electrical conductivity and extraordinary fluidity. However, it is difficult to fabricate LM as a free‐standing material due to its high surface tension and unmanageable fluidity, as well as its poor compatibility with other materials. Herein, a processing strategy is developed to fabricate free‐standing LM‐based films by vacuum filtration with the assistance of dough‐like aramid nanofiber (ANF) putty. The ANF putty improves the compatibility of ANF and LM, and also greatly improves the stability, reliability, and processability of ANF. Rational design of the structure enables the preparation of LM/ANF films with ANF as the nanobridge connecting LM micro/nanodroplets, and ANF‐LM‐ANF sandwich films with ANF as the shells, LM layer as the core. The LM/ANF film (tensile strength: 5.4 MPa) exhibits an ultrahigh EMI SE of up to 105.9 dB (8.0–12.4 GHz) at a thickness of 60 μm. While the ANF‐LM‐ANF sandwich film has higher mechanical strength (33.1 MPa), and also has good EMI shielding properties. The average EMI SE of the 10 μm thick sandwich film exceeds 45 dB in the X‐band.

Experimental characterization of impact damage in foam-core sandwich structures using acoustic emission, optical scanning and X-ray computed tomography techniques

Sandwich structures used in transportation and energy industries are commonly subjected to low-velocity impact in the course of manufacturing, service and maintenance, which can lead to the premature degradation of structural stiffness and strength. A single non-destructive evaluation technique is often difficult to provide a comprehensive assessment on impact damage from online to offline and from visible to invisible. In the present study, acoustic emission (AE), three-dimensional (3D) optical scanning and X-ray computed tomography (CT) techniques are combined to provide a systematic approach for damage characterization of thick foam-core sandwich panels under low-velocity impact. In the tests, the mechanical responses such as force-time and force-displacement curves are obtained from the testing system. The AE technique is adopted to monitor damage initiation and evolution in situ; optical scanning and X-ray computed tomography techniques are used for off-line damage identification and quantification. The results show that the AE signal waveform stream, cumulative counts and cumulative energy correlate well with the mechanical responses of the sandwich panel under the low-velocity impact, enabling capture of valuable information for online damage monitoring. Unlike general cases, the AE signals generated from low-velocity impact are found to be presented in strong bursts of nearly coincident events in the short duration. Therefore, the distributions of AE amplitude and peak frequency between adjacent AE counts are extracted to study the different damage modes and damage mechanisms. The X-ray computed tomography images enable to precisely visualize the fracture behaviors of the PET foam-core inside the sandwich panel in a nondestructive fashion, which evidently supports the AE and optical scanning results. The study is anticipated to demonstrate effectiveness and capability of the proposed experimental methodology for damage detection and characterization on sandwiched composite structures subjected to impact loading.

Dynamic response of honeycomb cored sandwich panels under high velocity impact: A numerical study

To investigate the impact resisting behavior of honeycomb cored sandwich panel under the bullet attacks, birds and debris, computational analysis of ballistic impact tests have been performed. The honeycomb sandwich panel with SS 316L front and back sheets are used owing to its better impact resistance, high ductility and superior strength for impact resisting applications. The Ballistic test simulations under a wide range of 150 to 800 m/s have been carried out on a SS 316L sandwich panel embedded with Aluminum alloy (AA 3003) honeycomb core using ABAQUS/Explicit software. For this, 12 mm thick sandwich panel and three types of bullet profiles namely conical, hemispherical and blunt are considered. The initial and residual velocity obtained from the simulation is used for computing the dynamic energy absorption of the panels. The significance of projectile velocity, nose shape on overall energy absorption capacity of the panel have been thoroughly investigated. The sandwich panel reportedly absorbed 20.6% and 41.2% higher energy when impacted with blunt projectile than those impacted with hemispherical and conical bullets. Moreover, an almost linear increase in the overall energy absorption capacity of the panel have been observed by increasing the striking sheet thickness.

Vibration characteristics of arbitrary thick sandwich beam with metal foam core resting on elastic medium

An analysis is performed in this research to obtain the natural frequencies and mode shapes of a thick sandwich beam with metal foam core. Different types of foams are considered for the sandwich beam where distribution of pores is a functionally graded patterns. The governing equations of the sandwich beam are established by means of a shear and normal deformable thick beam model. This theory considers the thickness stretching and admits the nonuniform through-the-thickness shear strain. The governing equations of the sandwich beam are established which are four in number by means of the Hamilton principle. The established equations are solved for the case of thick sandwich beams resting on elastic foundation via the Navier solution method. Results of this study are first compared with the available data in the open literature and after that novel results are given to explore the effects of different parameters on the vibration characteristics of the sandwich beam. It is shown that porosity of the core is an important factor on vibration characteristics of sandwich beam with metal foam core.

Flexible, robust, sandwich structure polyimide composite film with alternative MXene and Ag NWs layers for electromagnetic interference shielding

The design and fabrication of electromagnetic interference shielding films with a novel structure to eliminate undesirable electromagnetic pollution is an important research direction. However, it is still a challenge to combine and organize nanofillers in different dimensions into the structured network in polymer-based electromagnetic interference (EMI) shielding composites. In this work, a sandwich structure polyimide (PI) composite film with alternative 2D-MXene network and 1D-Silver nanowires (Ag NWs) network was prepared through the “electrospinning-immersion-hot pressing” method. With the increase of Ag NWs content, the EMI shielding effectiveness (SE) gradually increases while maintaining good flexibility and mechanical robustness. The EMI SE and the tensile strength of 150 μm thick sandwich composite film can reach up to 79.54 dB and 39.82 MPa, respectively. The prepared flexible and robust PI composite film with a sandwich structure has high EMI SE with less metal content, which can provide guidelines for the development of high-performance EMI polymeric films with potentials in wearable devices and equipment.

A strategy improving stiffness to resist local vibration of sandwich plates by extended Legendre higher-order model

Sandwich structures have been increasingly used in aerospace engineering, while local vibration modes of sandwich plates might occur earlier than global vibration modes attributing to the weak stiffness of the core layer, and it is difficult to predict such vibration modes. Therefore, local vibration modes are often discarded in the process of structural design, so that potential dangers might be encountered when the frequency of external load is close to the natural frequency of local vibration. To avoid such an issue, an extended Legendre higher-order theory (ELHT) is developed to accurately forecast the local dynamic behaviors of sandwich plates for the first time. Subsequently, an effective multi-objective optimization platform will be constructed to optimize the distribution of graphene-nanoplatelets (GPLs) in the core layer, so that natural frequencies of local vibration modes will be improved and largely more than the fundamental frequency. The B-spline basis functions are employed to describe various GPLs distributions, which is more convenient to produce original data for the machine learning method in the optimization process. Then, extreme gradient boosting optimized by Sparrow Search Algorithm (SSA-XGBoost) is utilized as the high-fidelity surrogate model to construct the objective functions to accelerate the interaction of the ELHT and non-dominated sorting sparrow search algorithm (NSSSA). By optimizing for minimum global and local fundamental frequency ratio and total mass of GPLs reinforced sandwich plates, the Pareto-optimal solutions are obtained from the present algorithm which can give an alternative suggestion for the future designer to ensure the structural dynamic safety of thick sandwich plates.

Free vibration analysis of functionally graded sandwich plates using a new discrete kirchhoff four node quadrilateral element

In the present work, a four node quadrilateral element is developed for the free vibration analysis of functionally graded moderately thick sandwich plates. The element has seven degrees of freedom per node namely, two in-plane displacements, the transverse displacement, two rotations of mid plane and two transverse shear strain components at the mid plane. In the present study, two models of the material property variation through the thickness, namely; power law model and Mori-Tanaka model are considered. The results for sandwich plates with different thickness configurations and with different boundary conditions are compared with the available analytical and finite element results. For some cases, the present results of the non-dimensionalised frequencies are compared with those obtained using commercial software ANSYS. It is observed that the performance of the present element is quite satisfactory for the sandwich plates considered in this study.

A hybrid CPU–GPU solver based on three-dimensional spectral Chebyshev technique for determining the dynamic behavior of thick sandwich panels

In this study, static and vibration behavior of a curved thick sandwich-structured composite composed of a honeycomb core layer and two face-sheets reinforced with carbon nanotubes is investigated. The governing equations are derived using three-dimensional elasticity equations and Hamilton’s principle. The problem domain is discretized following Gauss–Lobatto sampling approach. To numerically solve the governing equations, a spectral method based on Chebyshev polynomials is used and a CPU–GPU based hybrid solver is developed. The presented approach is validated by comparing the predicted natural frequencies and deformation of the structure to those obtained from finite element analysis. The results show that in-house CPU–GPU based spectral solution approach decreases the computational duration remarkably and predicts the dynamic and static behavior of the system accurately. Since composite materials offer great flexibility in tailoring the dynamic behavior of the structure, an optimization study is also performed to benefit from the developed computationally efficient solver. In this study, the CNT orientations are selected as design variables to maximize the fundamental frequency of the structure. Based on the analyzed cases for different thickness ratios, curvature amounts, volume content, and distributions of CNTs, it is shown that the vibration behavior of the structure can be significantly tailored.