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The 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.

The 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.

It 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.

This 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.

The purpose of this paper is to develop a general mathematical model for the evaluation of the bending and vibration responses of the skew sandwich composite plate using higher-order shear deformation theory. The sandwich structural components are highly preferable in modern engineering application because of their desirable structural advantages despite the manufacturing and analysis complexities. The present model is developed to solve the bending and vibration problem of the skew sandwich composite plate with adequate accuracy numerically in the absence of the experimental analysis.

The skew sandwich composite plate structure is modelled in the present analysis by considering laminated face sheet in conjunction with isotropic and/or orthotropic core numerically with the help of the higher-order mathematical model. Further, the responses are computed numerically with the help of in-house computer code developed in matrix laboratory (MATLAB) environment in conjunction with finite element (FE) steps. The system governing equations are derived via variational technique for the computation of the static and the frequency responses.

The skew sandwich composite plate is investigated using the higher-order kinematic model where the transverse displacement through the thickness is considered to be linear. The convergence and the validation study of the bending and the frequency values of the sandwich structure indicate the necessary accuracy. Further, the current model has been used to highlight the applicability of the higher-order kinematics for the evaluation of the sandwich structural responses (frequency and static deflections) for different design parameters.

In the present paper, the bending and the vibration responses of the skew sandwich composite plate are analysed numerically using the equivalent single-layer higher-order kinematic theory for the isotropic and the orthotropic core numerically with the help of isoparametric FE steps. Finally, it is understood that the present model is capable of solving the sandwich structural responses with less computation cost and adequate accuracy.

The purpose of this paper is to investigate the feasibility of using rapid prototyping (RP) technologies (stereolithography (SLA), fused deposition modeling (FDM), and three‐dimensional printing (3DP)) for fabrication of the core of a composite sandwich structure.

Control cores of a flat geometry were fabricated from epoxy using SLA and from acrylonitrile butadiene styrene (ABS) plastic using FDM. Corrugated geometry cores were fabricated using SLA, FDM, and 3DP. Carbon‐epoxy composite sandwich structures were fabricated from all cores using a wet‐hand layup process with vacuum cure. The performance of each core was measured using a bend test to determine bending stiffness and failure load.

Based upon bending stiffness and failure load, composite sandwich structures utilizing epoxy cores fabricated via SLA outperformed composite sandwich structures utilizing plaster powder and ABS plastic cores. Composite sandwich structures with corrugated ABS plastic cores outperformed those with flat ABS plastic cores by a margin well beyond that predicted by theory in both bending stiffness and failure load.

The marked improvement in stiffness and failure load of the composite sandwich structures with corrugated ABS plastic cores over those with flat ABS cores is not explained by the theoretical improvement due to an increased area moment of inertia and increased surface area. Additional research in the failure mechanism is warranted.

The ability to easily create complex core geometries will allow for the ability to place enhanced structural features in the regions of high stress.

This paper demonstrates that cores fabricated via RP technology and containing enhanced structural features are suitable for carbon‐epoxy composite sandwich structures.

Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore aims to give the reader an encyclopaedic view on the subject. The bibliography at the end of the paper contains 2,025 references to papers, conference proceedings and theses/dissertations dealing with the analysis of beams, columns, rods, bars, cables, discs, blades, shafts, membranes, plates and shells that were published in 1992‐1995.

Gives a bibliographical review of the finite element analyses of sandwich structures from the theoretical as well as practical points of view. Both isotropic and composite materials are considered. Topics include: material and mechanical properties of sandwich structures; vibration, dynamic response and impact problems; heat transfer and thermomechanical responses; contact problems; fracture mechanics, fatigue and damage; stability problems; special finite elements developed for the analysis of sandwich structures; analysis of sandwich beams, plates, panels and shells; specific applications in various fields of engineering; other topics. The analysis of cellular solids is also included. The bibliography at the end of this paper contains 655 references to papers, conference proceedings and theses/dissertations dealing with presented subjects that were published between 1980 and 2001.

Defects can be caused by a number of factors, such as maintenance damage, ground handling and foreign objects thrown up from runways during an in-service use of composite aerospace structures. Sandwich structures are capable of absorbing large amounts of energy under impact loads, resulting in high structural crashworthiness. This situation is one of the many reasons why sandwich structures are extensively used in many aerospace applications nowadays. Their non-destructive inspection is often more complex. Hence, the choice of a suitable non-destructive testing (NDT) method can play a key role in successful damage detection. The paper aims to discuss these issues.

A comparison of detection capabilities of selected C-scan NDT methods applicable for inspections of sandwich structures was performed using water-squirt, air-coupled and pitch-catch (PC) ultrasonic techniques, supplemented by laser shearography (LS).

Test results showed that the water-squirt and PC techniques are the most suitable methods for core damage evaluation. Meanwhile, the air-coupled method showed lower sensitivity for the detection of several artificial defects and impact damage in honeycomb sandwiches when unfocussed transducers were used. LS can detect most of the defects in the panels, but it has lower sensitivity and resolution for honeycomb core-type sandwiches.

This study quantitatively compared the damage size indication capabilities of sandwich structures by using various NDT techniques. Results of the realised tests can be used for successful selection of a suitable NDT method. Combinations of the presented methods revealed most defects.

This paper aims to present the procedures necessary to determine the insert allowable for a composite sandwich, considering that the inserts were the most commonly used means to install equipment on the composite structure of Clean Sky 2 (CS2)-RACER compound helicopter.

The installation of the equipment inside of the airframe shall comply with the certification regulations, especially in relation to the inertial factors. Establishing of the needed number of inserts to fix the equipment is directly linked to the allowable coming from coupon tests. The materials and test procedures to which they were subjected are part of the process qualification used in the development of the CS2-RACER Main Fuselage. The samples were tested in two different static mechanical loadings, consisting of pull-out insert and shear-out insert tests. The mechanical behaviour and failure mechanism of the materials were evaluated using optical and scanning electron microscopy.

The insert installation on the sandwich structure influences the behaviour and mechanical properties during pull-out and shear-out testing.

The limited data available in standardized documents related to insert testing makes it difficult to compare results with certified baseline values.

To reduce the effort of selecting the optimized insert system, specific parameters are included in analytical pre-sizing, i.e. type of loads, geometry, materials, failure modes, special conditions such as manufacturing and testing.

The results of the study presenting the design, manufacturing and mechanical testing of pull-out and shear-out inserts used in composite materials sandwich-type coupons provide valuable information regarding the insert allowable determination.

The main idea is the comparison between composites including natural fibres (such as the linoleum fibres) and typical composites including carbon fibres or glass fibres. The comparison is proposed for different structures (plates, cylinders, cylindrical and spherical shells), lamination sequences (cross-ply laminates and sandwiches with composite skins) and thickness ratios. The purpose of this paper is to understand if linoleum fibres could be useful for some specific aerospace applications.

A general exact three-dimensional shell model is used for the static analysis of the proposed structures to obtain displacements and stresses through the thickness. The shell model is based on a layer-wise approach and the differential equations of equilibrium are solved by means of the exponential matrix method.

In qualitative terms, composites including linoleum fibres have a mechanical behaviour similar to composites including glass or carbon fibres. In terms of stress and displacement values, composites including linoleum fibres can be used in aerospace applications with limited loads. They are comparable with composites including glass fibres. In general, they are not competitive with respect to composites including carbon fibres. Such conclusions have been verified for different structure geometries, lamination sequences and thickness ratios.

The proposed general exact 3D shell model allows the analysis of different geometries (plates and shells), materials and laminations in a unified manner using the differential equilibrium equations written in general orthogonal curvilinear coordinates. These equations written for spherical shells degenerate in those for cylinders, cylindrical shell panels and plates by means of opportune considerations about the radii of curvature. The proposed shell model allows an exhaustive comparison between different laminated and sandwich composite structures considering the typical zigzag form of displacements and the correct imposition of compatibility conditions for displacements and equilibrium conditions for transverse stresses.

The purpose of this study was to introduce three-dimensional printing (3DP) of functionally graded sandwich foams (FGSFs). This work was continued by predicting the mechanical buckling and free vibration behavior of 3DP FGSFs using experimental and numerical analyses.

Initially, hollow glass microballoon-reinforced high-density polyethylene-based polymer composite foams were developed, and these materials were extruded into their respective filaments. These filaments are used as feedstock materials in fused filament fabrication based 3DP for the development of FGSFs. Scanning electron microscopy analysis was performed on the freeze-dried samples to observe filler sustainability. Furthermore, the density, critical buckling load (P_cr), natural frequency (f_n) and damping factor of FGSFs were evaluated. The critical buckling load (P_cr) of the FGSFs was estimated using the double-tangent method and modified Budiansky criteria.

The density of FGSFs decreased with increasing filler percentage. The mechanical buckling load increased with the filler percentage. The natural frequency corresponding to the first mode of the FGSFs exhibited a decreasing trend with an increasing load in the pre-buckling regime and an increase in post-buckled zone, whereas the damping factor exhibited the opposite trend.

The current research work is valuable for the area of 3D printing by developing the functionally graded foam based sandwich beams. Furthermore, it intended to present the buckling behavior of 3D printed FGSFs, variation of frequency and damping factor corresponding to first three modes with increase in load.

The purpose of this paper is to present experimental investigations on the structural behaviour of composite sandwich panels for civil engineering applications. The performance of two different core materials – rigid plastic polyurethane (PU) foam and polypropylene (PP) honeycomb – combined with glass fibre reinforced polymer (GFRP) skins, and the effect of using GFRP ribs along the longitudinal edges of the panels were investigated.

The experimental campaign first included flatwise tensile tests on the GFRP skins; edgewise and flatwise compressive tests; flatwise tensile tests on small‐scale sandwich specimens; and shear tests on the core materials. Subsequently, flexural static and dynamic tests were carried out in full‐scale sandwich panels (2.50×0.50×0.10 m³) in order to evaluate their service and failure behaviour. Linear elastic analytical and numerical models of the tested sandwich panels were developed in order to confirm the effects of varying the core material and of introducing GFRP ribs.

Tests confirmed the considerable influence of the core, namely of its stiffness and strength, on the performance of the unstrengthened panels; in addition, tests showed that the introduction of lateral reinforcements significantly increases the stiffness and strength of the panels, with the shear behaviour of strengthened panels being governed by the ribs. The unstrengthened panels collapsed due to core shear failure, while the strengthened panels failed due to face skin delamination followed by crushing of the skins. The models, validated with the experimental results, allowed simulating the serviceability behaviour of the sandwich panels with a good accuracy.

The present study confirmed that composite sandwich panels made of GFRP skins and PU rigid foam or PP honeycomb cores have significant potential for a wide range of structural applications, presenting significant stiffness and strength, particularly when strengthened with lateral GFRP ribs.