Use Of Sandwich Structures Research Articles

Indentation of sandwich beams: Comparison of Vlasov, Winkler, and shear theories with composite surfaces reinforced by CNTs and ANN model

The use of sandwich structures has spread to a wide range of fields today. As a result of their thin top and low stiffness, sandwich beams are very susceptible to local loads. One practical solution to increase the sandwich structure's indentation resistance is to add bending strength to the top. The structural properties of carbon nanotubes make them well-suited for use in polymer matrixes; their addition improves the attributes of polymers. Experimental and theoretical investigations of the sandwich structure's indentation behavior are presented in this article. As well, simulations of sandwich structures are conducted using Abaqus software. A tensile test of composite samples and Mori Tanaka's theory were used to determine the elastic modulus of epoxy resin reinforced with carbon nanotubes at different mass percentages. The elastic modulus of composites can be improved by adding carbon nanotubes up to 0.3 % by mass while the mechanical properties are reduced when more than 0.3 % of carbon nanotubes were added. Finally, the analytical solution and Abaqus modeling results for the indentation of the sandwich structure were compared with the results obtained from the experimental tests. A machine learning model is proposed for prediction of sandwich beams deflection. The results of the predictions were phenomenal, with MAE of less than 2 %. The computational costs have been compared with the experimental results, and the machine learning method is very efficient.

Investigation into Mechanical Properties and Failure Mechanisms of Novel Sandwich Composite Material with Carbon Fibre / Epoxy Facesheets and PVC Foam Core

Sandwich composite materials have seen a significant increase in use across various engineering fields and applications due to their exceptional mechanical properties, including high specific strength and bending stiffness values. Because of their high strength properties, the use of sandwich structures is preferred in different industries. It is crucial to investigate material properties of novel composites in order to estimate their failure mechanisms under different loading types. In this study, a type of sandwich composite material consisting of Carbon Fibre/Epoxy Facesheets with two different dimensions and a PVC Foam Core was designed and fabricated. The selection of PVC foam for this study is motivated by its wide use in load bearing components in different industries. The sandwich composite material used for the experiments was manufactured by using vacuum-assisted resin infusion moulding process (VARIM) by IZOREEL in Izmir, Turkey. Failure styles of the structure in compression, shearing and bending were revealed by sandwich flatwise tension, core flatwise compression, and sandwich edgewise compression tests. Facesheet bending of manufactured composites have been investigated experimentally. Tensile strength of the facesheets and sandwich material have been presented separately. The detailed formulations and procedures are provided. The obtained results are discussed, and it is seen that maximum tensile and compression stresses in the three-point bending test depend on the direction of the loading with respect to different facesheet thicknesses.

Thermomechanical Buckling Analysis of the E&P-FGM Beams Integrated by Nanocomposite Supports Immersed in a Hygrothermal Environment.

Due to the widespread use of sandwich structures in many industries and the importance of understanding their mechanical behavior, this paper studies the thermomechanical buckling behavior of sandwich beams with a functionally graded material (FGM) middle layer and two composite external layers. Both composite skins are made of Poly(methyl methacrylate) (PMMA) reinforced by carbon-nano-tubes (CNTs). The properties of the FGM core are predicted through an exponential-law and power-law theory (E&P), whereas an Eshelby–Mori–Tanaka (EMT) formulation is applied to capture the mechanical properties of the external layers. Moreover, different high-order displacement fields are combined with a virtual displacement approach to derive the governing equations of the problem, here solved analytically based on a Navier-type approximation. A parametric study is performed to check for the impact of different core materials and CNT concentrations inside the PMMA on the overall response of beams resting on a Pasternak substrate and subjected to a hygrothermal loading. This means that the sensitivity analysis accounts for different displacement fields, hygrothermal environments, and FGM theories, as a novel aspect of the present work. Our results could be replicated in a computational sense, and could be useful for design purposes in aerospace industries to increase the tolerance of target productions, such as aircraft bodies.

A new criterion to evaluate the machined surface quality of the Nomex® honeycomb materials

The use of sandwich structures based on composite and/or metallic honeycomb core has grown considerably these last years, especially for aeronautic, aerospace, naval and automotive fields. The proposed work deals with the analysis of milling Nomex® honeycomb core that usually generates poor machined surface quality and problems in assembling parts. The performance of milling process and obtained surface quality are strongly influenced by the honeycomb material properties and cutting parameters. The composite nature of the Nomex® paper forming the honeycomb structure, the thin wall thickness and its alveolar shape make the use of conventional parameters of quantifying the surface quality (as roughness) inappropriate. In this study a new method of measurement of the surface quality has been developed. This innovative approach allows simultaneously the identification and quantification of induced machining defects, as well as the evaluation of the performance of the obtained surface. A new quality criterion was then carried out to obtain the best compromise between high surface quality and optimal cutting conditions. This will improve the use of honeycomb materials in sandwich assemblies for industry. • Analysis of machining Nomex honeycomb with specific cutting tools • Obtained surface quality is strongly influenced by honeycomb material properties and cutting parameters. • Identification of a new criterion for the machined honeycomb surface evaluation • A new quality criterion makes able to choose the optimal cutting conditions.

Influence of Cutting Parameters on the Surface Quality of Two-Layer Sandwich Structures.

Hybrid sandwich structures are more and more widely used in many industries. This is mainly due to their good properties. One of the limitations regarding the use of sandwich structures is their difficult processing. Therefore, it seems reasonable to determine the influence of cutting parameters and machining configuration on the characteristic defect (phase) formed at the boundary of the materials forming a hybrid sandwich structure. This study investigates the effects of layer orientations during milling and machining parameters such as the cutting speed Vc, the feed fz and the cutting width ae. The study is conducted on a two-layer sandwich structure composed of two materials: 2024 aluminum alloy and epoxy-carbon composite with 60% of high-strength carbon fibers. A statistical analysis is performed using the Statistica program. The results show that the change in the cutting parameters has a greater impact on the formation of a defect on the surface of samples when the machining process starts on the side of the composite rather than the metal. The highest defect value is obtained for the milling from the composite layer when the process is performed with the following cutting parameters: Vc = 300 m/min, fz = 0.08 mm/tooth, ae = 5 mm.

Analysis of Sandwich Structures by the FEM

The use of sandwich structures is increasing rapidly. This paper is aimed on mechanical properties of sandwich structured composites and their usage in technical practice. The main contribution in paper is realized static analysis of simple sandwiches composed from various materials of core and face sheets. Final results of analysis were fields of data about maximum stresses, displacement fields of structural points of sandwich composite.

Numerical Simulation of Low Velocity Impact on Pin-Reinforced Foam Core Sandwich Panel

The use of sandwich structures is well established in industrial sectors where high stiffness and strength combined with lightweight are required, like in marine, wind turbine and railway applications. However, the vulnerability of sandwich structures to low-velocity impacts limits its use in primary aircraft structures. Pin reinforcement of the foam core enhances the out-of-plane properties and the damage tolerance of the foam core. In this paper, a finite element model is proposed to predict the impact behaviour of pin-reinforced sandwich structure. An approach based on the building block approach was used to develop the model. Multi-scale modelling in the impact region that considers the delamination of the face sheet using cohesive zone elements was employed to increase the accuracy of the simulation. Impact tests were performed to validate the numerical model. A good agreement between numerical and experimental results in terms of contact-force displacement history and failure mode was found.

Innovating Configuration and Mechanic Properties of Ultralight and Porous Quasi-Square-Honeycomb Sandwich Structure’ Core

A continuous interest for an extensive use of sandwich structures in automotive, aerospace and civil infrastructure has been manifested in the last years due to the main advantage of lightweight and energy absorption ability. Based on characteristics of press molding process of honeycomb sandwich structure, a new kind of quasi-square honeycomb sandwich structure is proposed. Following classical unit cell theory and energy method, the mechanical equivalent model of the quasi-honeycomb sandwich structure is established and the corresponding equivalent elastic constant formula is deduced. Taking a sandwich panel in a satellite structure as an example, from the aspect of core characteristics, mechanical properties, equivalent elastic constants of honeycomb sandwich structure, and shear modulus, the differences between square honeycomb and quasi-square-honeycomb were analyzed and studied. The results show that both equivalent elastic modules are approximately equal, but the quasi-square-honeycomb sandwich structure is endowed with higher equivalent shear modulus and lower equivalent body density, thus the total structure mass can be effectively reduced. Simulation verifies the correctness of the proposed mechanical equivalent model of the quasi-square-honeycomb sandwich structure.

Bilayered graphene/h-BN with folded holes as new nanoelectronic materials: modeling of structures and electronic properties.

The latest achievements in 2-dimensional (2D) material research have shown the perspective use of sandwich structures in nanodevices. We demonstrate the following generation of bilayer materials for electronics and optoelectronics. The atomic structures, the stability and electronic properties of Moiré graphene (G)/h-BN bilayers with folded nanoholes have been investigated theoretically by ab-initio DFT method. These perforated bilayers with folded hole edges may present electronic properties different from the properties of both graphene and monolayer nanomesh structures. The closing of the edges is realized by C-B(N) bonds that form after folding the borders of the holes. Stable ≪round≫ and ≪triangle≫ holes organization are studied and compared with similar hole forms in single layer graphene. The electronic band structures of the considered G/BN nanomeshes reveal semiconducting or metallic characteristics depending on the sizes and edge terminations of the created holes. This investigation of the new types of G/BN nanostructures with folded edges might provide a directional guide for the future of this emerging area.

Flutter and buckling characteristics and active control of sandwich panels with triangular lattice core in supersonic airflow

Abstract Sandwich structures with lattice core are novel composite structures, but the aeroelastic behaviors of them have not been fully studied. This paper is devoted to investigate the flutter and buckling properties of sandwich panels with triangular lattice core in supersonic airflow, and the active flutter and buckling control are also carried out, which can provide theoretical basis for the use of sandwich structures in the design of aircrafts. The unsteady aerodynamic pressure is evaluated by the supersonic piston theory in which the yawed flow angle is taken into account. Hamilton's principle with the assumed mode method is applied to formulate the equation of motion of the structural system. The active controller is designed by the displacement feedback method. Aeroelastic characteristics of the sandwich panels are studied, and the influences of the aerodynamic pressure on the frequency and mode shape of the panel are analyzed. The effects of yawed flow angle on the flutter properties of the sandwich panel are also analyzed. When considering the external in-plane load, the buckling behaviors of the sandwich panel are investigated. Moreover, the flutter and buckling properties between the sandwich and equivalent isotropic panels are compared to show the superior aeroelastic properties of the sandwich panels. The effects of piezoelectric patch placements on the active flutter control are analyzed. The optimal locations of piezoelectric actuator and sensor pairs are obtained by the genetic algorithm. The present study verifies that the sandwich structures have different aeroelastic and flutter suppression properties, which is useful in the research of lightweight sandwich materials.

Development of the fire-retardant sandwich structure using an aramid/glass hybrid composite and a phenolic foam-filled honeycomb

Sandwich structures are increasingly used in high-performance engineering application because of their high specific stiffness, strength, environmental resistance and thermal insulation characteristics. However, poor fire resistance is a critical problem for the use of sandwich structures in engineering applications.In this study, a fire-retardant sandwich structure was developed using a phenolic foam filled honeycomb and carbonized phenolic matrix aramid/glass hybrid composite faces. The sandwich structure was designed to satisfy the limit of critical thermal radiation to humans.To improve the post-fire properties and fire resistance of the glass/phenolic composite, a phenolic coating and an aramid/phenolic composite layer were applied on the surface. The carbonization and impregnation of the phenolic matrix of the composite were repeated twice to eliminate the matrix cracking and delamination by fire exposure. Phenolic foam-filled honeycomb core was used to reduce the thermal conductivity and increase the stiffness and strength of the sandwich. Finally, the thermal insulation and post-fire flexural properties of the sandwich structure were estimated.

Magnetocaloric effect in sandwich structures of La1–x K x MnO3 manganites

This paper reports on the results of the investigation into the magnetocaloric properties of sandwich structures of La1–xKxMnO3 manganites with x = 0.11 (LKM11), 0.13 (LKM13), and 0.15 (LKM15) in magnetic fields of up to 18 kOe. The results of the analysis of the field and temperature dependences of the magnetocaloric effect in the structures LKM11 + LKM13 and LKM13 + LKM15 have demonstrated that the use of sandwich structures increases the efficiency of magnetic cooling in a magnetic field of 18 kOe by 45%.

Improvements in the Blast-Mitigation Performance of Light-Tactical-Vehicle Side-Vent-Channel Solution using Aluminum-Foam Core Sandwich Structures

In the present work, an attempt is made to improve the blast-mitigation efficiency of our recently proposed light-tactical-vehicle side-vent-channel concept/solution. This concept/solution involves the use of side-ventchannels attached to the V-shaped vehicle underbody, and was motivated by the physical concepts and working principles of operation of the so-called “pulse detonation” rocket engines. By proper shaping of the V-hull and side-vent-channels, venting of supersonically-expanding gaseous detonation products is promoted in order to generate a downward thrust on the targeted vehicle. This, in turn, helps mitigate the blast-loads resulting from a shallow-buried mine detonated underneath a light tactical vehicle. The utility and the blastmitigation capacity of this concept were examined in our prior work using several computational and designoptimization methods and tools. The results obtained show that the side-vent-channel solution has a limited (but noteworthy) blast-mitigation capacity. In the present work, an attempt is made to improve the blastmitigation capacity of the side-vent-channel solution by substituting side-vent-channels made of sandwichstructures (consisting of steel face-sheets and aluminum-foam core) for all-steel side-vent-channels. The results obtained revealed that the use of sandwich-structures can improve blast-mitigation performance of the side-vent-channel solution, and that this improvement can be further increased through proper grading of the aluminum-foam density profile through the sandwich-structure core.

Prediction model for the impact response of glass fibre reinforced aluminium foam sandwiches

The use of sandwich structures combines low weight with high energy absorbing capacity, so they are suitable for applications in the transport industry (automotive, aerospace, shipbuilding industry), where the “lightweight design” philosophy and the safety of vehicles are very important aspects. The goal of this paper was the analysis of the bending and the low - velocity impact response of aluminium foam sandwiches reinforced by the outer skins made of glass fibre reinforced epoxy matrix. The results were compared with those obtained for aluminium foam sandwiches without glass fibre skins. An analytical model for the peak load prediction under low velocity impact was developed and the predicted values are in good agreement with the experimental measurements. The impact response of the sandwiches was investigated using a theoretical approach, based on the energy balance model and the model parameters were obtained by the tomographic analyses of the impacted panels.This combined experimental and theoretical investigation has particular importance for applications that require lightweight composite structures with a high capacity of energy dissipation, such as the transport industry, where problems of collision and crash have increased in the last years.

Study on Bending, Buckling and Free Vibration of Hard-Core Sandwich Plate Based on Revising the Soft-Core Reissner Theory

The use of sandwich structures in various engineering fields is growing rapidly because of advantageous features such as low weight and high strength-to-weight ratio.The existing theories are all based on soft core assumption. In this case, the in-plane stress and the stiffness of the core are not included. It has been shown that Ressiner theory is inadequate for the analysis of hard-core sandwich plates. Different revision factors were put forward in this paper to revise the bending, buckling and free vibration results of soft-core Reissner theory for hard-core sandwich plates. The results show that the revised results go well with the hard core theory, so that its validity is confirmed.

Development of a Mechanical Technology for Joining Sandwich Elements

Wide spread use of sandwich structures is still inhibited by the lack of a consistent joining technology one which is easy to work with, quantifiable and not dependent on special knowledge about manufacturing processes. A mechanical technology for joining sandwiches as developed in this article shall achieve these goals. The developing process follows the design methodology according to Pahl et al. [1]. The resulting systematic approach to the problem facilitated the generation of a complete solution field. This approach led to 18 promising concepts of 783 possible original solutions. Prototypes of those concepts showed that a reliable mechanical technology for joining sandwich elements is feasible.

Use of sandwich structures with ZnO:Al transparent electrodes for the measurement of the electro-optic properties of standard and fluorinated poled copolymers at λ = 1.55 μm

We report on the measurement of the electro-optic coefficient r33 of poled polymers at λ=1.55μm via the non-linear ellipsometry technique (or Teng and Man technique). Since the measurements rely on the use of sandwich structures with transparent electrodes, different types of aluminium doped zinc oxide (ZnO:Al) are taken into account in order to ensure transparency at the infrared range wavelength. Results on the disperse red 1/poly-methyl-metacrylate (DR1–PMMA) based side-chain benchmark system, with several different concentrations of active groups from 0.05 to 0.58molar, are reported and demonstrate the reliability of the technique. The measurement technique was then used to evaluate the r33 coefficient of copolymers derived from DR1–PMMA by partial fluorination (FATRIFE). In this case, we measured copolymers with three concentrations of active groups, 0.30, 0.37 and 0.56molar.

Sandwich Structures

The use of sandwich structures is increasing rapidly. It is used in many applications ranging from satellites, aircraft, ships, automobiles, rail cars, and in bridge construction to mention only a few. The purpose of the following review article is to provide a general introduction to or discussion of the structural mechanics involved in the field of sandwich structures and a sufficient number of references to enable the reader to further investigate his/her specific interests. Like all reviews, it is limited by the knowledge of the author and a reasonable length for the article. This article has 174 references.

Behaviour of core materials during resin transfer moulding of sandwich structures

The use of sandwich structures is a well documented and accepted engineering approach. Composite sandwich structures, consisting of a fibre reinforcement impregnated with resin surrounding a foam core, can be used to improve bending stiffness, thermal insulation, and specific mechanical properties at relatively low cost. Such materials can be produced by the resin transfer moulding (RTM)process by incorporating the core within the fibre preform before resin injection. However, this process may result in a number of defects including core shifting, deformation, and delamination, which will have a detrimental effect on mechanical performance. The occurrences of these defects have been studied as a function of the fibre volume fraction, resin pressure, and skin thickness. Delamination between the skin and the core is also a major concern, although this can be controlled by abrading the core surface before moulding. The effect of process parameters on moulding quality and, in particular, the response of the core during moulding and the subsequent delamination resistance of the resulting sandwich structure are presented. This is applied to a range of commercially available core materials.