Face Sheets Research Articles

Aero-Hygro-Thermoelastic size-dependent analysis of NCMF-reinforced GNPs sector microplates located between piezoelectric patches in supersonic flow considering surface stress effects

Lately, metal foams have been widely used in various engineering structures due to their exceptional mechanical properties, including their lightweight. However, scientists have proposed adding nano-fillers like graphene nanoplatelets (GNPs) to overcome the issue of low stiffness caused by increased porosity. Hence, aerodynamic stability and vibrational behaviors of nanocomposite metal foams (NCMF)-reinforced GNPs sector microplate with piezoelectric/metallic face sheets are provided in this work. The microstructure is sited on Kerr elastic substrate and also is in a hygro-thermo-electrical media, subjected to supersonic flow based on first-order piston’s theory (FPT). Gaussian random field (GRF), Halpin-Tsai, and extended rule of mixture (ERM) in conjunction with Gurtin-Morduch, modified strain gradient theories, and Hamilton’s principle are used to derive the governing equations and linked boundary conditions. Generalized differential quadrature (GDQ) scheme is chosen to attain the results. By validating the results’ precision, the effects of different parameters on the natural frequencies (NFs) and critical aerodynamic pressures (CAPs) are observed. It is perceived that adding GNPs enhances both NFs and CAPs significantly, and increasing porosity up to seventy percent, leads the results to drop. Various industries use simpler models to evaluate the microstructure, therefore the present model can pave the way for future uses and push the boundaries of knowledge in these industries based on the results it produces.

Dynamic response of square sandwich panels with stagger-layered honeycomb cores under intensive near-field air blast loading

Metallic honeycomb sandwich panels have been widely used in energy dissipation due to large plastic deformation under impact/blast loading. In this paper, the dynamic response of a honeycomb sandwich panel with stagger-layered core under intensive near-field air blast loading is investigated. Comparative experiments are conducted for stagger-layered and typical honeycomb sandwich panels with the same geometrical size and mass. Numerical simulation has been undertaken based on the experiments. Numerical results coincide well with experimental results on the deformation/failure modes and center-point deflection of back face sheet. The influence of layer number as well as the geometrical parameters on the energy absorption ability of sandwich panels is clarified. Results show that stagger-layer arrangement of honeycomb core greatly improves energy dissipation capability of sandwich panels compared to typical one with the same mass. The increase of layer number and cell size benefits this effect. These findings indicates that core stagger-layer arrangement is a well choice to improve energy dissipation ability of sandwich panels under air blast loading, especially for highly intensive near-field blast loading.

Nonlinear geometric fluid-structure interaction model of multilayered sandwich plates in contact with unbounded or bounded fluid flow

Based on the Kirchhoff-Love theory and von Kármán's geometric nonlinearity, the nonlinear vibration analysis of multilayered sandwich plates under ideal flow is presented. Rectangular plates are considered to be laminated of orthotropic composite layers as upper and lower face sheets as well as a central lightweight core made of functionally graded (FG), anisogrid lattice or metal foam materials. Three coupled equations of motion are reformulated into one decoupled governing equation in terms of transverse deflection (w) using the method of inverse differential operator. For the first time, an impermeability condition is developed that considers the moderately large deflection of the contact surface in order to correct the pressure distribution of fluid flow. Based on the potential flow theory, closed-form expressions of hydrodynamic pressure are obtained for different fluid boundary conditions including infinite depth of fluid, flow bounded by a rigid wall and flow between two identical elastic plates. Then, the Galerkin and multiple-scale perturbation methods are used to obtain closed-form solution of nonlinear natural frequency in terms of maximum vibration amplitude. Finally, case studies are presented to investigate the effects of geometric ratios, boundary condition, material distribution, layup, characteristics of flow and geometric nonlinearity on the response quantities. Findings indicate that the large deformation term in the developed impermeability condition has significant effect on the pressure distribution and its effect is more pronounced for thicker plates with larger mode number in the flow direction. Therefore, the novel nonlinear fluid-structure interaction model should be considered to study flow-induced dynamic behavior of sandwich plates with different boundary conditions. In addition, the snap-through behavior is seen in the nonlinear frequency-upstream speed curves and the incipient points of dynamic instability can vary remarkably with the fluid boundary conditions.

FINITE ELEMENT ANALYSIS FOR DYNAMIC RESPONSE OF VISCOELASTIC SANDWICHED STRUCTURES INTEGRATED WITH ALUMINUM SHEETS

Passive vibration attenuation of modern mechanical structures is one of the most essential technologies applied to the arsenal of modern mechanical structures. In this work, dynamics analysis is performed on viscoelastic (VE) sandwich beam and plate by using finite element method. The proposed structure is composed of a VE core and aluminum face sheets as substrate layers on both sides of the structure. Small-strain VE material is modeled based on complex constant moduli model and numerical method is used to develop the finite element (FE) shear model based on first-order shear deformation theory (FSDT) and Hamilton principle. In modal analysis, model-effective mass analysis is performed to investigate its dominant mode shape and sweet spot at resonance using C3D20 and CPS8 elements. The former is indicated as a 3-D element with 20 nodes while the latter is indicated as a 2-D plane strain element with eight nodes. In harmonic analysis, resonance frequency is obtained based on mode superposition method to evaluate the steady-state response of VE sandwich beam via maximum deformation. Thereafter, the results are compared against analytical solutions from the literature. Moreover, a parametric study shows that the natural frequency of the beam did not change with the increase in core thickness. However, normalized loss factor of VE sandwich beam is directly proportional to VE damping factor and the thickness of VE core layer. Based on frequency response function, the results of resonance frequencies for VE beam are in the range of modal natural frequency.

Nonlinear low-velocity impact response of sandwich beams with FG porous aluminum core reinforced by GPLs

Sandwich beam structures facing low-velocity impact frequently throughout their life cycle, making it necessary to investigate the impact response of these structures to enhance their design and reliability in service. In this paper, sandwich beam structures subjected to nonlinear low-velocity impacts are investigated, comprising a functionally graded (FG) porous aluminum core reinforced by graphene platelets (GPLs) and two aluminum alloy face sheets. The mechanical properties of FG-GPLRC core are predicted by a generalized Halpin-Tsai model, which takes porosity into account, where the material properties of the closed-cell aluminum alloy foam are established on experimental data. The numerical investigations are conducted using the finite element method and apply the Hertz contact law. The simulation results indicate that the FG-X pattern, where the porosity coefficients are designed to have the maximum values at the top and bottom layers, while to have the minimum values at the mid-plane layers, exhibits the best impact resistance, and that the incorporation of GPLs enhances the impact response. Furthermore, the findings suggest that the thickness of the core has no impact on the duration of the initial impact. Moreover, an increase in impactor velocity, density and radius results in an increase in both deflection and contact force.

Hybrid Fuzzy PID Sound Radiation Control of a Functionally Graded Porous GPL-Reinforced Plate with Piezoelectric Sensor and Actuator Layers

This paper is the first attempt to investigate the sound radiation control of a functionally graded porous graphene platelet-reinforced composite (FGP-GPLRC) plate integrated with piezoelectric face sheets. A spatial state-space formulation based on the linear 3D piezoelasticity theory is utilized to derive a semi-analytic solution for the coupled vibroacoustic response of the simply-supported arbitrarily thick composite plate. A comprehensive parametric study examines the effect of GPLs’ distribution, weight fraction, and porosity parameters of the core layer on the radiated sound power. Then, the best material configuration is selected to be actively controlled. A hybrid Fuzzy Proportional-Integral-Derivative (FPID) controller, which utilizes an FPID controller integrated with a classical PID controller, is employed to mitigate sound radiation from the smart sandwich plate via the volume velocity approach. The gain parameters of the proposed controller are tuned using the Bat optimization algorithm. Finally, the performance of the active control strategy in attenuating radiated sound power is investigated through several numerical simulations. Results show the proposed control scheme's robustness and rapid disturbance rejection performance.

Natural frequency analysis of sandwich plate with auxetic honeycomb core and CNTRC face sheets using analytical approach and artificial neural network

In this paper, an analytical investigation is presented on the natural frequency analysis of sandwich plate resting on Winkler-Pasternak type elastic foundations in thermal environment. The sandwich plate consists of an auxetic honeycomb core with negative Poisson's ratio, which is assumed to perfectly bond to two carbon nanotube reinforced composite (CNTRC) face sheets to ignore potential interface effects or imperfections in bonding. The material properties of CNTRC are assumed to be temperature dependent. The volume fraction of carbon nanotube (CNT) varies through the thickness dimension according to linear functions with five different distribution patterns of CNT including UD, FG-O, FG-V, FG-Λ and FG-X. The governing equations of motion are derived based on the Reddy's first order shear deformation plate theory and Hamilton's principle, and the expression of the natural frequency is performed via Galerkin method. Artificial neural network (ANN) model is established to accurately predict the natural frequency of the sandwich plate on the basis of 1450 data points collected from analytical results. The effects of various material and geometrical parameters on the natural frequency of the sandwich plate are investigated in details.

Understanding the coaxial optical coherence tomography signal during the laser welding of hidden T-joints

In the case of “hidden” T-joints, the nonvisible web sheet is welded through the face sheet. Positioning tolerances and movement due to the distortion of the web sheet represent the main challenges to maintain on track during laser beam welding. This study investigated the assumption that keyhole monitoring based on optical coherence tomography (OCT) could be utilized for seam tracking by detecting critical misalignments between the laser beam and the web sheet position. It hereby analyzed whether an emerging misalignment between the laser beam and the web sheet could be discerned in the OCT data before the laser beam misses the web sheet and penetrated only the face sheet. This prediction represents a key requirement for the industrial use of this approach. To this end, this study investigated the welding of hidden T-joints with angular and parallel offsets of the laser path relative to the web sheet centerline while recording with OCT. The interface zone between the web and face sheets was recorded by a high-speed camera to detect the transmission of laser radiation through a lower keyhole opening. It was shown that a lower keyhole opening, in combination with transmitted radiation, was advantageous for the reliable detection of an emerging misalignment. This lower keyhole opening can occur lateral to the web sheet prior to a misalignment, therefore enabling a prediction of spot misalignments via OCT. The welding parameter dependent maximum distance of the laser spot edge to the web sheet edge at detection was 0.1 mm in this study.

On the vibrations of sandwich structure with magneto-electro-rheological core and composite face sheet via mesh-free method

Multidirectional functionally graded materials due to high-mechanical resistance with other extraordinary properties in each direction have received much attention in recent years. Thus, in the current research, a numerical solution is presented to study the fundamental frequency characteristics of an MD-FG sector annular plate in a supersonic airflow. For obtaining exact displacement fields, the refined zig-zag theory is employed to obtain the transverse shear strain through layers of the composite lamina. A quasi-3D new refined theory is presented to model the displacement fields of the current sandwich structure. The Legendre-radial point interpolation method shape function is used to estimate the displacements while the mesh-free strong form approach discretizes the equations of motion and boundary conditions. Finally, the results show that Mach number, free stream speed, air yaw angle, temperature, and aerodynamic pressure have important roles in the dynamic stability performance of the sandwich sector annular plate in supersonic airflow. The results of the current report can be used in various high-temperature multidirectional compositionally graded materials for future works.

Local impact resistance of curved sandwich panel with Miura-ori foldcore

Curved sandwich structures have demonstrated great potential for engineering applications. However, little study on the impact resistance of the curved Miura-ori sandwich structure is found. In this study, the curved sandwich panel with a curved Miura-ori foldcore (CPCM) is proposed and its impact resistance is numerically investigated. The force displacement history, energy absorption, specific energy absorption, residual velocity of the projectile and the displacement of the rear face sheet are used to evaluate the performances of the CPCM. Various loading scenarios including different impact velocities and positions, different projectile sizes and geometries are considered. Moreover, the curved sandwich panel with a curved honeycomb core (CPCH) that have similar specifications and the same relative density as the CPCM is simulated as well for comparison. It is found that the CPCM shows excellent impact resistance with a ballistic limit around 61 % higher than that of the CPCH. Its energy absorption capacities and impact resistance are improved under blunt projectile impact. However, when the impact velocity is above the ballistic limit, the energy absorption EA of the CPCM remains at a constant level, irrespective of the impact velocity.

Improving the blast resistance of sandwich structures by tailoring honeycomb core through varying cell size and vertex-derivative approach

Honeycomb sandwich panels (HSPs) with efficient core design have the potential to enhance blast resistance to tackle increasing blast threats by terrorist attacks. In this work, an innovative vertex-derived approach is introduced to enhance the blast resistance of HSPs. First, a quarter model of regular quadrilateral core HSP structures (RQH) with a cell size of 30.5 mm (10 × 10) was simulated with various amounts of TNT charges(1,2,&3 kg) kept at a height of 100 mm using the CONWEP algorithm available in ABAQUS/Explicit. The results obtained through simulation were validated with the tested results available in the literature. The study was extended by varying the cell sizes of 61 mm (5 × 5), 15.25 mm (20 × 20), and 7.625 mm (40 × 40) for comparison purposes. Further, honeycomb cores were tailored with the vertex-derived approach to enhance the blast resistance characteristics of RQH structures. The explosion resistance was assessed in terms of the deformation of the face sheets and dissipated energy through plastic deformation (PDE) of the face sheets and core. The result proved that the cell size variation and vertex-derived hierarchical core improved the blast resistance and the energy dissipation capacity of the RQH. The obtained results demonstrated that RQH with a 15.25 mm cell size (20 × 20) was found to have a good blast resistance at low and high-intensity blasts compared to other core sizes. The results also proved that the vertex-derived hierarchical topology enhanced the blast resistance of RQH under the same geometric parameters. The results demonstrate that employing vertex-derived hierarchical topology can enhance the blast resistance of HSPs.

Experimental investigation on impact behavior of curved sandwich composites with chiral auxetic core

The purpose of this study is to evaluate and compare the capability of impact energy absorption of the sandwich panels with various chiral auxetic cores. To this end, flat and curved panels were subjected to impact testing at varying energy levels. Glass fiber-reinforced epoxy composites and PLA material were used as the skins and core of the examined sandwich panels, respectively. The face sheets were produced by the hand-layup method and the auxetic cores with tetrachiral, anti-tetrachiral, and hexachiral configurations were printed using a 3D printer. The wall thickness, node diameter, and ligament length of the cells, as well as the core thickness, were kept constant for all the studied core structures. Flat and curved sandwich panels were obtained by combining the skins and cores produced in flat, 100 mm, 125 mm, and 160 mm radii of curvature with the epoxy used in skin production. Drop weight tests were carried out at impact energies of 10, 25, and 80 J. The contribution of the auxetic core configuration and panel curvature to the impact behavior of the sandwich panel was evaluated by examining the relationships between contact forces and deflection and by the analysis of the energy absorption and failure mode. The comparative evaluations showed that the auxetic core structure and the curvature of the panel have a significant effect on the impact properties of the sandwich panels. It was also observed that the use of tetrachiral cores could be the ideal design option for flat panels loaded at the perforation energy level. For curved panels, it was determined that the use of a hexachiral core configuration was advantageous in terms of more energy absorption capability, while the use of an anti-tetrachiral core structure was more effective in terms of specific energy absorption.

On the selected problems of time-dependent dynamics of composite truncated conical shells-like aerospace structures

In this paper, the nonlinear dynamic responses of ring-stiffened truncated conical sandwich shells-like aerospace structures fabricated by perfectly bonded graphene platelets (GPLs) reinforced composite porous core and face sheets (GPLRC-PC-FS) under asymmetric internal ring-shaped moving load are investigated. The sandwich shells have edge point supports, which are simulated using the translational and rotational artificial springs. In addition to the open cell porosities, closed cells are also considered and analyzed. The spatially discretized nonlinear motion equations are derived based on the first-order shear deformation theory (FSDT) under the von Kármán geometric nonlinearity assumptions using the Ritz method with Chebyshev polynomials as its admissible basis functions. Then, Newmark's time integration scheme along with the Newton–Raphson method is employed to obtain the shell dynamic responses. After demonstrating the robustness and accuracy of the approach, the influence of rings number, their size and arrangement, core porosity distribution and structure, face sheets, GPLs parameters, moving load velocity and boundary conditions on the shell responses are studied. The results show that the shell dynamic behaviors are significantly affected by porosity, but almost are independent of the type of porosity distribution pattern and its structure (open and closed cell porosities). It is shown that the shell deflection can be minimized by suitably choosing the number of rings, their dimensions and arrangement. Moreover, the nonlinear behaviors of the shells have a significant correlation with the number of point supports and by adjusting the support stiffnesses, the nonlinear dynamic responses of the shells can be reduced.

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

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

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

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

Structural response of steel sandwich panels with PUR foam core subjected to edgewise compression: Experimental, numerical, and analytical considerations

With the objective of leading to innovative lightweight structural components in the construction sector using sandwich panels with polyurethane foam and steel face sheets, different studies were conducted on such structures, including experimental, numerical, and analytical campaigns. The experimental campaign includes the mechanical characterisation of the constituent materials and the edgewise compressive test of small-scale sandwich panels. The test protocols are detailed, and their influence on the results is assessed. Through the use of digital image correlation recordings, deformation patterns and failure mechanisms in the constituent materials and the composite structure are identified. Material constitutive models are calibrated based on the experimentally obtained results. The accuracy of such models is first evaluated against the stress–strain curves recorded during the experiments. In the second stage, the response of the sandwich panels subjected to edgewise compressive loading is simulated. A parametric analysis on the sensitivity of the numerical models to the initial geometrical imperfections is shown to be fundamental to capturing the behaviour of the sandwich panels. Furthermore, the experimental and numerical results are compared to analytical solutions of the problem of the edgewise compression of sandwich panels. Finally, a thorough discussion of the obtained experimental, numerical and analytical results is presented, along with comparisons to results available in the literature.

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

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

Nonlinear free vibration analysis of internal thickness-tapered multi-layered composite rectangular plates undergoing moderately large deflections

Thickness-tapering in multi-layered composites is achieved by terminating the plies at discrete locations. This allows for effective material utilization and significant weight savings and is adopted in applications involving multi-layered composites that demand variation in thickness such as helicopter yokes, flexbeams and rotor blades, aircraft wing-skin structures and turbine blades. In the present work, the nonlinear free vibration of such tapered composites undergoing moderately large deflections is investigated for the first time. A general nonlinear finite element formulation for tapered multi-layered composite plates based on Reddy's higher-order shear deformation theory and considering Von Karman nonlinearity is developed. Newton–Raphson scheme in conjunction with Newmark time-integration technique is employed to obtain the time response. The developed model is validated against available results in the literature and through experimentally obtained linear natural frequencies of a honeycomb sandwich plate with tapered face sheets. Parametric studies are conducted to deeply understand the nonlinear dynamic behaviour of tapered composite structures. The investigation reveals that tapered multi-layered composite plates exhibit higher nonlinearity compared to uniform plates thus necessitating the consideration of nonlinear effects in the analysis of such structures.

Traumatic brain injuries caused by knockout in Japanese amateur boxers: A questionnaire-based survey.

The aim of the present study is to conduct a trauma and disability survey in amateur boxers and show the actual conditions of injuries based on the current situations. We have obtained 663 valid responses from male and female boxers. In the questionnaire survey who was carried out on a Web questionnaire form. The questions involve that Face Sheet (gender, height, weight, athletic experience, etc.) and prepared 10 questions about trauma and impairment, 7 questions with concussion or damage on head. and, set 11 self-evaluations, which the boxers assessed their boxing skills. The subjects include amateur boxers who are all high school students (15 years old) and retired boxers. We had analyzed relation between the skills and the injuries. And, main outcome was that make a measure to setting whether or not questionnaires have been knockout (KO) as a variable, we applied a method of multiple logistic regression analysis. Moreover, as for the group who got KO in the past, we have also applied multiple regression analysis by using stepwise regression to factors affecting numbers of symptoms. The number of hits they experienced was smaller in international tournament matches, and the odds rate for KO was 0.669. And, KO experience group was compared with non-KO experience group, and the factors influencing the number of severity symptoms were examined. As a result, 2 factors were selected what "Seriousness in practice" and "Fighting spirit in games". It might be possible that the relation between the experience of being KO and self-assessment of boxing performance.

Further Investigation of Impedance Eduction in a Grazing Flow Duct Facility

An established protocol for impedance eduction is based on a search procedure in which wall impedance in a duct propagation model is varied to obtain an acoustic field converging with one measured in a grazing flow duct. Here, an acoustic velocity potential formulation for the finite element model propagation model is extended to examine the relative effectiveness of driving the model with measured acoustic pressure at the source and termination and driving with acoustic pressure at the source and closing the computational domain with measured termination impedance. Also assessed is the appropriate location of measurement microphones to satisfy plane wave requirements for the computational model. Source acoustic pressure and termination impedance driving the propagation model produce superior eduction results with lower residual error, though the model driven with pressure at both the source and termination produces acceptable spectra. The microphone location in the gazing flow test facility is judged to be adequate for the range of grazing flow Mach number and frequency considered. Examination of impedance spectra for a range of lining samples has revealed a correlation of a decrease in spectrum quality, measured by observed data scatter, with a decreasing face sheet open area ratio and therefore with increasing lining nonlinearity.