Composite Sandwich Panels Research Articles

Theoretical and experimental investigations on control parameters of piezo-based vibro-acoustic modulation health monitoring of contact acoustic nonlinearity in a sandwich beam

Contact-type defects are prevalent in composite constructions and sandwich panels due to failure mechanisms such as bolt loosening and delamination. Contact acoustic nonlinearity is a manifestation of such defects that nonlinear health monitoring systems can detect. Vibro-acoustic modulation (VAM) is a well-established technique for the early detection of nonlinear defects in structures. It employs bi-tone excitation to reveal damage-induced nonlinearity, which results in the appearance of sidebands in the response spectrum. The objective of this research is to use PZT-based excitation to monitor bolt loosening in a sandwich beam in real-time. To address the limited capacity of the PZT transducers to excite the nonlinear mechanism, a sensitivity analysis (SA) for input factors of VAM testing was conducted to improve damage detection using the results. The Morris approach is used to investigate the sensitivity of VAM damage metrics derived analytically in the frequency domain. To reduce the number of tests required for the experimental SA, the response surface methodology (RSM) is applied. The analysis of variance and Fischer's statistics are used to calculate the SA of experimental damage indices. In RSM computations, the discrete influence of excitation frequencies on the modulation sidebands is addressed. For reliable SA of experimental results, the effect of background noise is taken into account. The findings of this study may be applied to the selection of appropriate damage metrics in real-world applications of VAM health monitoring systems, as well as the effective tuning of input control parameters to maximize damage detectability.

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.

Composite sandwich structures: review of manufacturing techniques

PurposeThe purpose of this review paper is to provide a review of the most recent advances in the field of manufacturing composite sandwich panels along with their advantages and limitations. The other purpose of this paper is to familiarize the researchers with the available developments in manufacturing sandwich structures.Design/methodology/approachThe most recent research articles in the field of manufacturing various composite sandwich structures were reviewed. The review process started by categorizing the available sandwich manufacturing techniques into nine main categories according to the method of production and the equipment used. The review is followed by outlining some automatic production concepts toward composite sandwich automated manufacturing. A brief summary of the sandwich manufacturing techniques is given at the end of this article, with recommendations for future work.FindingsIt has been found that several composite sandwich manufacturing techniques were proposed in the literature. The diversity of the manufacturing techniques arises from the variety of the materials as well as the configurations of the final product. Additive manufacturing techniques represent the most recent trend in composite sandwich manufacturing.Originality/valueThis work is valuable for all researchers in the field of composite sandwich structures to keep up with the most recent advancements in this field. Furthermore, this review paper can be considered as a guideline for researchers who are intended to perform further research on composite sandwich structures.

Low-Velocity Impact Response of Sandwich Composite Panels with Shear Stiffening Gel Filled Honeycomb Cores

Low-Velocity Impact Response of Sandwich Composite Panels with Shear Stiffening Gel Filled Honeycomb Cores

Experimental studies on crashworthiness analysis of a sandwich composite panel under axial impact: A comprehensive review

Experimental studies on crashworthiness analysis of a sandwich composite panel under axial impact: A comprehensive review

Preliminary study on defect detection for sandwich composites using Impact-Echo method

The sandwich composites in this study are laminated structures with two outer thin glass fiber reinforced panels and one or more thick lightweight foam panels as the core material. Such sandwich composites are often used in wind turbine blade. The Impact-Echo method using a microphone as a receiver was used to test the sandwich composite panel specimens. The signals were analysed in the frequency domain and normalized by the Rayleigh wave amplitude. Preliminary results show that thicker plates generally have a lower maximum peak frequency (MPF) for specimens without defects, but MPFs are more unstable due to the higher number of layers of the inner foam plate. Internal defects generated by excavating the core material, with lateral dimensions as small as 20 mm, can be identified from lower MPF and higher maximum peak amplitude in the normalized amplitude spectrum.

FINITE-ELEMENT ANALYSIS OF HYBRID GRID-STIFFENED HONEYCOMB CORE SANDWICH PLATES FOR STRUCTURAL PERFORMANCE ENHANCEMENT

Use of honeycomb sandwich structures is increasing in many engineering applications in aircraft, automobile, and other industries, due to their high flexural strength-to-weight ratio. Naturally, the challenge on further increasing their strength-to-weight ratio is an active research objective in this area. Grid stiffeners are known for their high bending strength. Hence, to combine the advantages of both of the honeycomb core and grid stiffeners, this paper investigates the possibility of enhancing the structural performance of composite sandwich panels by using a hybrid-grid-stiffened honeycomb sandwich composite panel. Towards this, an ortho-grid structure is considered to be combined with the honeycomb core, to raise the overall stiffness. Response under static uniformly distributed transverse load is simulated using finite-element software ANSYS to compare the performance of sandwich structures of different types of core, namely, aluminum grid-stiffened core, aluminum honeycomb core, and an aluminum hybrid-ortho-grid-stiffened honeycomb core. Based on this FE analysis, the mechanical characteristics like bending stiffness, transverse displacement, and specific bending stiffness are evaluated for these three types of sandwiches, to compare their performance. Some further parametric studies are also carried out. The results from the present research indicate that the grid-stiffened-honeycomb core is a bit heavier than honeycomb core, but load-carrying capacity and more importantly the specific strength is considerably improved. This promises to improve the overall properties of sandwich structures.

INVESTIGATION IN TO THE STATIC AND DYNAMIC PROPERTIES OF LIGHTWEIGHT STRUCTURAL SANDWICH PANEL

Analytical investigations on the static and dynamic behaviour of light weight structural sandwich panels, which are widely employed in maritime, aircraft, transport, and mechanical/civil engineering applications, are provided. These light, thin-walled structures can vibrate ferociously and are sensitive to even the smallest disturbances. So, the main goal of this work is to improve sandwich panels' static and dynamic behaviour by investigating various face sheets and core materials. Studies on carbon-based polymer nanocomposite are currently generating more interest because to its favourable thermal, electric, magnetic, and structural characteristics. In this study, functionally graded carbon nanotube reinforced polymer composite faces with a 3D graphene foam core and functionally graded carbon nanotube reinforced polymer composite faces were all used to make the sandwich panels. Also, the thermal stresses created in this structure when these panels are exposed to a thermal environment have a significant impact on the dynamic behaviour. Hence, the honeycomb core and polymer composite sandwich panels with reinforced FG-CNT face sheets are examined in various thermal environments. This study examines the properties of forced and free vibration to analyse the dynamic behaviour of a structure

Dynamic Behavior of Composite Sandwich Panel with CFRP Outer Layers

Sandwich panel with laminate faces is used for free vibration analysis. The periodic microstructure and Mori- Tanaka model are used for homogenization of unidirectional fiber reinforced composite. The Shear Deformation Theory is considered for analytical and numerical analysis. FEM in ANSYS is used for numerical analysis. The effect of sandwich design parameters such as panel length, core thickness and fiber reinforced angle on vibration response is investigated. Natural frequencies of sandwich panel versus sandwich design parameters are presented in graphical form. From the results can be concluded that sandwich design parameters affect the natural frequencies of sandwich panels, and this effect is important for designing of sandwich panels under dynamic load.

Construction, Testing and Evaluation of a Honeycomb Structured 3D Printed Sandwich Panel under Various Load Circumstances

Composite sandwich panels are progressively being employed in the aircraft industry for floor panels, compartment partitions, bulkheads and even the skin and wings of aircraft. Lightweight structures are essential for aircraft operations because they allow for faster take-off and landing. The sandwich panel comes into play in this situation. Composites with stiff, high-strength skin facings are bonded to a low-density core to form multi-layered materials with a high mechanical strength. Using finite element analysis and experimental equipment, composite sandwich panels are constructed, tested and evaluated under various load circumstances. The panel's expected compressive strength and flexural stiffness values were then calculated for various operating conditions. A mean difference of 0.28 is seen between the stresses in both x and y directions of the panel over a loading range of 1kg to 60kg. The standardised values of the strains were used to compare them using Bayesian estimation, which outperforms the t test. Ec increases by nearly 20 times when the side length is increased by 10% compared to when the side length is increased by 50%. For a given span length and when an is fixed, the flexural stiffness at f1=0.002 is nearly 2 times higher than that at f1=0.006. Although there are differences in the displacements and strains, the overall trend is fairly pleasing. The exact numerical conditions were not produced due to the experimental challenges, but the loading and displacements were equal.

Parameterization of core plug replacement properties for flexural performance optimization of repaired composite honeycomb sandwich panel

As lightweight structures, composite sandwich panels are distinguished by their significant flexural performances, which make them suitable for lightweight design applications, especially in the aerospace industry. These structures are very prone to different damages, which affects the structure’s performance. In this study, the numerical three-point bending test is carried out to evaluate the flexural performance of the damaged and repaired panel by comparing it with the intact panel values. The response surface methodology (RSM) is then adopted to analyze the core plug replacement properties’ effect on the flexural performances of the repaired honeycomb sandwich panel. Adequate models between the core plug replacement design parameters and the repaired panel flexural responses are built and discussed. In addition, aiming to determine the optimized core plug replacement parameters of the proposed repaired panel flexural performances, an optimization technique is implemented.

Analysis of Hard Point Mechanical Behaviour Due to Variations of Potting Agent Volume on a Composite Sandwich Panel

Composite sandwich panels are widely used in lightweight structures, especially in aerospace, automotive, and marine industries. They are chosen mainly because of the superiority of their specific stiffness as compared to solid panels. Stingray, a solar car designed by the UiTM Eco-photon team, applied this technology for its lightweight property. However, the honeycomb sandwich constructions were susceptible to localized load. Thus, load attachment points using metal inserts, also known as ‘hard points’, were introduced. In this study, the behaviour of hard points based on three volume variations of the potting agent was investigated. ESA recommended static pull-out tests to be conducted on the sandwich panels composed of Nomex honeycomb core, two laminates of carbon fibres/epoxy composite as the face-sheets to determine the failure load of the hard points. A finite element simulation using ANSYS was also performed to determine the displacement of the inserts in presence of normal-to-plane load. The results include load versus extension curves obtained by both methods. Potting agents were found to elevate the stiffness and the strength of the inserts by some degree. Therefore, the application of these hard points on the solar car was found to be effective.

Quasi-static and blast resistance performance of octet-truss-filled double tubes

Thin-walled filled tube is a common energy absorbing and buffering structure. In this study, an octet-truss-filled double tubes structure was presented by filling an octet-truss core into double tubes. The quasi-static mechanical behavior of the octet-truss-filled double tubes was analyzed by both FEM and experiment and the blast resistance performance of the composite sandwich panel (CSP) with proposed octet-truss-filled double tubes core was analyzed by FEM. For comparison, the mechanical behaviors of random closed-cell foam-filled double tubes and square honeycomb-filled and hexagon honeycomb-filled double tubes were also studied. Results show that the specific energy absorption (SEA) value of octet-truss-filled double tubes under quasi-static was 49.5%, 19.0%, 18.4% and 8.7% higher than empty single outer tube, the empty double tubes, the random closed-cell foam-filled double tubes and the square honeycomb-filled and hexagon honeycomb-filled double tubes. In the blast resistance study, the proposed structure was simplified and arrayed to study its performance in the blast resistant CSP by numerical simulation. The maximum displacement of the midpoint of the back plate of the octet-truss-filled double tubes was 30%, 19.2%, 11.2% and 8.9% smaller than the maximum value of the CSP with single tube core, the CSP with double tubes core, the CSP with random closed-cell foam-filled double tubes core and the square honeycomb-filled and hexagon honeycomb-filled double tubes core. The effects of equivalent explosion load, plate thickness and side length of octet-truss on the blast resistance performance of the CSP were discussed. This study provides a fresh idea for the design of more efficient energy absorption and blast resistant structure.

Nonlinear dynamic and forced vibration characteristic analysis of sandwich panel with double-U auxetic core and GPLRC facing sheets embedded with piezoelectric layers

The aim of the present research is to investigate the nonlinear dynamic and forced vibration of a composite sandwich panel embedded with piezoelectric layers under thermo-harmonic loading. The panel consists of a double-U auxetic honeycomb core made of aluminum alloy and graphene platelet reinforced composite (GPLRC) skins at the top and bottom surfaces. According to Gibson’s formula, the effective material properties of facing sheets and double-V auxetic core are considered. The nonlinear equations are obtained by applying Hamilton’s principles via von Karman’s nonlinear theory and higher-order shear deformation theory (HSDT). The governing equations of motion are solved by employing the differential quadrature method (DQM) and homotopy perturbation method, respectively. The accuracy of the current results has been verified by comparison with others in the literature. Finally, the influence of different parameters such as applied voltage, magnetic potential, temperature rise, different boundary conditions, and geometric parameters of core on the nonlinear frequency-amplitude response of cylindrical panels are analyzed. The numerical results show negative effect of temperature increment, positive influence of ratio of thickness to inclined length, core thickness, amplitudes of segments, considerable effect of the magnetic potential as well as small effect of applied voltage on the nonlinear vibration of sandwich panel. Finally, the important findings of this research indicate that the magnetic potential, amplitude segment, and length to inclined cell rib length have significant effects on nonlinear dynamic deflection and frequencies-amplitude response. Based on the results of this article, designers can develop different parts of aircraft.

Numerical and experimental study on mechanical properties of glass fiber‐reinforced polymer sandwich structure with polyurethane foam‐filled M‐shaped core

AbstractTruss‐like core sandwich panels made of glass fiber‐reinforced polymer (GFRP) composite are extensively exploited in numerous industrial and non‐industrial applications. Most of the time, these structures are exposed to extreme and heavy loads and damaged. Therefore, the mechanical properties of composite sandwich structures are important issue that should be addressed by engineers. For this purpose, the mechanical properties of a GFRP composite sandwich structures with polyurethane foam‐filled M‐shaped core are numerically and experimentally determined in this research. The sandwich panels manufactured for this study are composed of GFRP as fibers and resin epoxy as matrix material. In order to determine the bending and compressive response of the GFRP composite structures, three‐point bending and compression tests are performed using a SANTM ATM‐140 universal testing machine. A finite element method is developed to validate the precision of the experimental results. It is recognized that the finite element data are in remarkably great agreement with those obtained by experimental tests. Hence, the finite element analysis and experiment method could be utilized to predict the mechanical properties of the GFRP composite sandwich panels.

Modal properties investigation of a carbon/glass fiber-reinforced polymer composite sandwich structure with lozenge-like core: An experimental and finite element simulation

The vibration properties of a carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP) composite sandwich panels with lozenge-like core and free-free boundary conditions are experimentally determined in this research. The sandwich panels manufactured for this study are composed of CFRP, GFRP, and epoxy resin. A modal experiment is performed using a modal hammer with an acceleration sensor to obtain modal properties of the structure, including natural frequencies, damping ratio, mode shapes, and frequency responses. Eventually, the comparison of vibration characteristics of the CFRP sandwich panel with the GFRP sandwich panel with almost identical geometry is discussed in detail. Furthermore, a finite element simulation is developed to validate the precision of the experimental data. It is recognized that the finite element results are in remarkably good agreement with those obtained by modal experiments. Hence, the finite element analysis and experiment method could be utilized to predict the modal properties of the CFRP and GFRP composite sandwich panels.

Static analysis of corrugated lattice-core sandwich panels using VAM-based model

To investigate the mechanical properties of the composite sandwich panel with complex single- and double-layer corrugated lattice-cores (CSP-CLCs), a simplified analytical frame is developed by decoupling the original 3D model into a unit cell-based analytical model (providing equivalent plate properties) and a 2D reduced-order equivalent model (2D-REM) based on the variational asymptotic method (VAM). The validity of the equivalent plate properties and the equivalent model for CSP-CLCs is compared with the three-dimensional refined plate model (3D-RPM) under different cases, including static analysis under tension–bending coupling, global buckling analysis, second-order analysis, and local field recovery. The results of 2D-REM agreed with those of 3D-RPM, and the calculation time is greatly reduced. Subsequently, the effect of geometric parameters on the effective performance was comprehensively investigated, which helped to improve the mechanical properties of corrugated lattice-core sandwich plates. The innovation is that the present 2D-REM achieves a good balance between effectiveness and accuracy. Furthermore, the tailoring of unit cells can provide convenience for parameter analysis.

Failure mechanisms of fluted-core sandwich composite panels under uniaxial compression

Fluted-core sandwich composite structures are major load-bearing components used in launch vehicles. Herein, analytical models were proposed to investigate the failure mechanisms of fluted-core sandwich composite panels, including global buckling, local buckling, and material failure. Failure mode maps of fluted-core sandwich panels were constructed to analyze the intrinsic impact mechanism of geometric parameters on failure behavior. Integrated fluted-core sandwich composite panels were then fabricated by adopting the integrated forming process and co-cured method. Uniaxial compression tests and finite element simulation were also conducted to verify the analytical predictions with good consistency. The effects of the geometric variable on both load-bearing capacity and failure modes of the structures were explored. The results indicated the occurrence of global buckling at small distances between the top and bottom face sheets, resulting in undesired load-carrying capacities. The decrease in width of short span or increase in thickness of face sheets prevented such local-buckling behavior, resulting in material failure. The triangular-shaped core with zero short spans was identified as a better option for material failure as dominant failure mode for designing load-bearing sandwich panels. These findings look promising for lightweight and load-carrying applications, providing a reliable reference for the initial design of such sandwich structures.

Manufacturing, thermoforming, and recycling of glass fiber/ PET/ PET foam sandwich composites: DOE analysis of recycled materials

AbstractThis article presents efficient methods to manufacture, thermoform, and recycle sandwich composites consisting of glass fiber (GF)/polyethylene terephthalate (PET) composite skins and a PET foam core. Sandwich composite panels were manufactured using a hot press, which involved heating and pressing from the upper and lower platens inducing thermal fusion between the skin and the foam core. The formability of the sandwich composite panels using a hot press and a pocket‐shaped mold was simulated to determine the forming conditions. And the formability of the sandwich composite panels was tested using the simulation results. Recycling of the sandwich composite panels was achieved using recycling molds to perform heat compression. The excess PET was separated from the GF/PET composite and re‐impregnated with the remaining GF and PET. As a result of recycling, recycled PET and PET/GF composite were obtained. Design of experiments (DOE) analysis was conducted to analyze the recycled properties and to identify which factors affected these properties. These results were re‐plotted according to DOE priority ranking to identify the changes in the properties of the recycled materials per factor. Compared to the original properties, the mechanical and thermal properties including modulus, ultimate tensile strength, melting temperature and crystalline temperature were ~ 95 and ~ 99% preserved. These findings are expected to contribute towards the development of recyclable sandwich composite panels with reduced mass production cost, which are easily formed, used and recycled.

Study of Ultrasonic-Guided Wave Interaction With Core Crush Damage for Nondestructive Evaluation of a Honeycomb Composite Sandwich Panel

AbstractHoneycomb composite sandwich structures are extensively used for the manufacturing of many different components of aerospace, automobiles, wind turbine blades, and marine ship hull structures. Despite its widespread use and advantages, the honeycomb core is frequently damaged during production and operation, even if the damage is not visible on the face-sheet. In this study, an ultrasonic-guided wave (GW) propagation technique is utilized for robust and reliable nondestructive evaluation of a honeycomb composite sandwich panel (HCSP) in the presence of core crush damage. A 2D semi-analytical model was developed to understand the dispersion characteristics in the HCSP and to identify various modes of GW propagation in the signals. Extensive numerical simulations are carried out using abaqus to study the guided wave interaction with core crush damage. For this purpose, two numerical models were considered (a realistic model with both crushed core and cavity, and a simplified model that only comprises the cavity) and experimentally validated using a contact-type transducer. The presence of core crush damage in an HCSP increases the amplitude and group velocity of the primary antisymmetric mode, and this characteristic has been used for localization of the core crush region in the HCSP. Finally, a damage detection algorithm using signal difference coefficient is presented for successful localization of the core crush region within a square monitoring area. Unlike other studies reported in the literature, we demonstrate the utility of the simplified numerical model for studying GW interactions with core crush defect and experimentally validate the nondestructive evaluation (NDE) technique to localize core crush defect on an HCSP.