Sandwich Parts Research Articles

An assessment of PLA/wood with PLA core sandwich multilayer component tensile strength under different 3D printing conditions

Material extrusion is increasingly used to make functional parts in small batches that are challenging to produce with traditional machining. Also, intensive efforts are being made to develop new eco–friendly materials. This work investigates the strength of multilayer samples made in sandwich form with 4–5–4 layers of 0.3 mm layer thickness, externally with polylacticacid wood (PLA/wood, 61.5 % of specimens' material) and internally with pure PLA (38.5 % of specimens' material), under tensile loads. The intent is to investigate the possibility of manufacturing biocompatible components that take advantage of the excellent surface properties of wood externally and the durability properties of PLA internally. For this purpose, a designed experiment following the Taguchi L9 orthogonal array was prepared, and nine samples were fabricated: three with pure PLA, three with a sandwich PLA/wood–PLA–PLA/wood form, and three with composite PLA/wood form. Printing speed and temperature were varied during the experiment, and the results were examined using the analysis of means and residuals. Sandwich specimens improve tensile strength and elastic modulus by 100 % and 50 % compared to PLA/wood components while exhibiting slightly better surface roughness parameters, i.e., Ra and Rz, about ∼10 % lower values. Additionally, even if PLA parts showed better strength and surface texture than sandwich parts (∼100 % and ∼56 % higher tensile strength and elastic modulus), they had lower performance in terms of PLA–PLA/wood material ratio, i.e., 160 % more PLA than sandwich parts. The findings of this research, with the potential to design functional and sustainable new products with optimal performance, are significant and can be exploited in various industries.

Multi-material and thickness optimization of a wind turbine blade root section

Structural optimization has been shown to be an invaluable tool for solving large-scale challenging design problems, and this work concerns such optimization of a state-of-the-art laminated composite wind turbine blade root section. For laminated composites structures, the key design parameters are material choice, fiber orientation, stacking sequence, and layer thickness, however a framework for treating these simultaneously in optimization, on the current wind turbine blade scale, has not been demonstrated. Thus, the motivation and novelty of the present work is providing and demonstrating a general gradient-based approach applicable to wind turbine blades, where the key design parameters and structural criteria, i.e., buckling, static strength, and fatigue damage, are considered for multiple design load cases. The optimization framework is based on a variation of the Discrete Material and Thickness Optimization approach, where the thickness is directly parametrized, allowing for appropriately treating the sandwich parts of the blade. It is demonstrated how optimization leads to a design consisting of complex variable-thickness laminates, a good overall distribution of the structural criteria in the model, and a significant reduction in mass compared to the initial design.

Investigation on Flexural Property of Sandwich 3D Printed PLA Components - A Review

Making a product from design to finished product is difficult and time consuming job in conventional manufacturing process but in additive manufacturing (AM) it is an easy process. In AM technologies Fused Deposition Modeling (FDM) is an important printing technology to produce components using thermos plastics. Up to date AM technologies are used to make parts in single material, by using this additive manufacturing sandwich parts can be fabricated to improve flexural property of the material. A lightweight core and two thin solid face sheets with strong flexural rigidity at the top and bottom make up sandwich constructions. Sandwich structures have a core that can be developed and updated to meet our needs, which offers up new possibilities in a variety of disciplines. This method can be done with a variety of filaments, PLA having properties such as biodegradability, lack of disagreeable odor when heated, and usual environmental compatibility throughout its life cycle. PLA also produces 10 times less potentially harmful ultra-fine particles than Acrylonitrile Butadiene Styrene. This article concentrated review on PLA and PLA composite materials to improve flexural property

Prepreg, carbon fiber, thermoset autoadhesive resin for sandwich structures: advantages, disadvantages and manufacturing challenges

It’s thoroughly known that sandwich structures in aeronautical sector are formed by a core material, which more usual format is honeycomb, between two facings or skins made from several prepreg material layers.  Nevertheless in order to obtain an adequate adherence between core and prepreg most of thermoset resin systems need the presence of a film adhesive placed among the core and prepreg to favour the adhesive menisci formation inside core cells. Main benefit asociate to autoadhesive prepregs usage in sandwich parts is adhesive elimination from part configuration which translates in a weight reduction of the structure. Present article is centered in autoadhesive prepreg materials 180º cure. After more than 3 years of work with several composite materials manufacturers and AIRBUS, key process parameters in an industrial environment have been defined along with basic characteristics in order to guarantee internal quality of the elements

Survey on compression property of sandwich 3D printed PLA components

Additive Manufacturing (AM) is a trending technology to manufacture functional parts from 3D design to real-time products. Lightweight structure with expected mechanical property is a difficult task in conventional manufacturing. In aircraft, interior design parts should have high-strength parts with a low weight ratio. The high strength to low weight ratio can be developed using different materials, but the influenced factor is cost. Making a sandwich component is one of the best methods to fabricate the parts with high strength to low weight ratio. Sandwich structure is one type of design that can be fabricated using additive manufacturing with different materials. Sandwich structures comprise three components: a lightweight core and two face sheets at the top and bottom. Many materials can be used in this technique to produce sandwich parts, but this article focused on existing PLA and its composites. PLA is widely renowned for its characteristics and environmental awareness. This review is focused on the compression property investigation of the 3D printed Sandwich Structure and methods to improve the mechanical property of 3D printed parts.

Structural performance of 3D-printed composites under various loads and environmental conditions

Sandwich-structured composites are in high demand in various industries, and additive manufacturing has proven its ability to meet this demand. As a result of the advances in three-dimensional (3D) printing techniques, 3D-printed polymers have received considerable attention in fabrication of sandwich structures with complex geometries. This paper is concerned with design, manufacturing, and analysis of the 3D-printed sandwich-structured components which experienced various loadings and environmental conditions. The core structure plays a major role in the in-plane behavior of lattice composites, therefore in this study, sandwich specimens with two types of core topologies made of two common and similar 3D printing filaments, acrylonitrile butadiene styrene (ABS) and acrylonitrile styrene acrylate (ASA), were manufactured. Based on the applications of sandwich-structured parts, they might experience different temperatures in their service life. In order to determine effects of thermal environment, we conducted accelerated thermal aging within temperatures of 22-60 °C, which is below glass temperature of the examined materials. Based on a series of three-point bending tests, the failure behavior of the original and aged components are determined, and the effects of temperature change on the bending behavior of 3D-printed sandwich parts are discussed. The experimental practice revealed that ASA with honeycomb core specimens indicated highest stability under bending load after thermal aging. The current study sheds lights on durability of 3D-printed sandwich structural elements, and the obtained results demonstrate feasibility of 3D printing technology in fabrication of thermal-stable sandwich structures.

Defects investigation in thermal insulation coatings with microwave imaging based on a 22 GHz holographic radar

The evaluation of microwave (MW) imaging radar capabilities in non-destructive tests to detect internal structures or defects in the inner volume of thermal insulation coating has been carried out. The MW imaging with high spatial resolution has been performed with holographic subsurface radar operated in the frequency range from 22.2 to 26.2 GHz. The investigation of this non-destructive testing (NDT) technology is important to evaluate the feasibility for quality check of assembled polyurethane sandwich parts for thermal insulation. The samples of polyurethane foam thermal insulation have been fabricated in collaboration with a manufacturing industry of household appliances to have a representative set of real defects. The images obtained are of high quality and easy to be interpreted as they reveal the shapes and plane positions of the defect into samples with thickness up to 90 mm.

Manufacture and test of C/C–SiC sandwich structures

Sandwich structures based on C/C–SiC composites (carbon fibre-reinforced carbon with silicon carbide matrix), manufactured using the liquid silicon infiltration (LSI) process and an in situ joining method, offer high specific stiffness and strength, low thermal expansion, high environmental stability, and temperature resistance. Potential application areas are thermal protection systems (TPS) for spacecraft, optical benches in satellites, and hot structures in aerospace. In this work, C/C–SiC sandwich parts of two different geometries, small sandwich samples and large sandwich structures, were manufactured and tested. Carbon fibre-reinforced polymer (CFRP) plates for the skin panels as well as for the cores were made via warm pressing of prepregs based on a 2D carbon (C) fibre fabric, preimpregnated with phenolic resin. After pyrolysis, carbon fibre-reinforced carbon (C/C) core structures were built up and joined to C/C skin panels. Finally, the resulting C/C sandwich preforms were infiltrated with molten silicon (Si), building up a silicon carbide (SiC) matrix. The resulting C/C–SiC sandwich parts were tested in four-point and three-point bending. The applied forces and the correspondent displacements and strain of the skin panels were determined. The bending and shear stiffness as well as bending moment were evaluated through analytical and finite-element (FE) simulation approaches. Furthermore, failure modes of the sandwich samples were analysed. Sandwich stiffness and ultimate bending moment obtained in the bending tests were close to the expected theoretical values, calculated on the basis of the material properties and the sandwich geometry.

One Step Production of High-performance Sandwich Components

The combined PU spray and wet pressing process allows the manufacture of parts with high lightweight potential. The process can be used for the production of sandwich parts with compact continuous fiber reinforced PU outer layers and a process integrated formation of the foam core. Compared with established production processes for structural sandwich parts, the integration of the foam core formation in a wet pressing process is highly efficient and economical especially for complex structural parts.

Analysis of the forming behaviour of in-situ drawn sandwich sheets

Abstract One way to produce metal fibre-reinforced plastic-metal sandwich parts is to inject the polymer between the sheets during deep drawing. A new process has been designed in which parts with an interlayer of glas fibres including a thermoplastic matrix and two metallic sheets can be produced by combining deep drawing and thermoplastic-resin transfer moulding (T-RTM). With the possibility of forming sandwich sheets with a wide range of states of the interlayers’ viscosity and due to the polymerisation of the monomers between the sheets, the process combines a lot of advantages but also faces challenges due to the viscous fluid interlayer being hindered from squeezing out. This contribution analyses the dependency of the interlayer on the forming behaviour of the sheets in this process. When forming circular cups with aluminium (AA5182) sheets and a viscous interlayer of different heights, the effect of bulging could be observed which affects a free formed shape during forming. The viscous interlayer does not remain at the same position during forming which leads to an inhomogeneous total blank thickness of the part. In experiments and FE simulations a shape with bulged zones could be observed. An analytical approach for the prediction of these bulge heights has been developed so that both bulge dome heights could be predicted analytically. This approach is verified by experiments and numerical simulations. The results serve to set the process window for the in-situ hybridisation method in which the starting point of injection, volume fraction of the thermoplastic matrix in the fibres, mechanical properties of the materials, and geometrical parameters can be adjusted so that this effect is reduced.

Mold technology for mass production of continuous fiber-reinforced sandwich parts

Abstract In order to reduce cycle times, increase functional integration and automation further, the innovative gap impregnation process and mold technology was developed at the Institute of Plastics Processing at RWTH Aachen University (Germany) in collaboration with industry partners. The novel process enables an automated production of continuous fiber-reinforced sandwich composite structures in integral design with high surface quality in short cycle times, which is demonstrated by manufacturing a carbon fiber-reinforced plastic (CFRP) engine hood. For the first time, the gap impregnation and mold technology makes it possible to manufacture large-scale, three-dimensionally shaped sandwich components in one shot and in short cycle times at similar mechanical properties compared to the reference steel hood. Furthermore, a weight reduction of about 60% to only 5 kg was achieved for the CFRP engine hood. This paper focuses on the systems engineering of the RTM-related gap impregnation process. The focus is on the utilized mold concepts for the pressurized air-assisted ejector pins, vacuum-tight sealing, the motion concept of the mold halves, resin traps, sensors for process control and the specially treated mold surfaces for class A surface components. Additionally, the main procedures, capabilities and characteristics of this innovative process are discussed.

Design and analysis of the flat honeycomb sandwich structures

Structural sandwich is a unique form of the composite structure, and it finds a widespread use in the aerospace industry, where weight saving is a primary concern. The major difference between analysis procedures for sandwich construction and those for homogeneous structural elements is the inclusion of core shear effects on deflection, buckling and stress. The design procedure given in this article is intended to guide the designer in sizing the sandwich parts for primary loading properly. These procedures are usually iterative, and optimum design may require the design of several face-core combinations. Comparing the results obtained through the analytical procedure and Finite Element Analysis (FEA) one can conclude their good agreement. Differences for most of the results are from 10% to 15%, which is quite satisfactory, taking into account that the analytical models are formed on the basis of a number of assumptions and approximations.

Principal component analysis for fast and automated thermographic inspection of internal structures in sandwich parts

Abstract. Rising demand and increasing cost pressure for lightweight materials – such as sandwich structures – drives the manufacturing industry to improve automation in production and quality inspection. Quality inspection of honeycomb sandwich components with infrared (IR) thermography can be automated using image classification algorithms. This paper shows how principal component analysis (PCA) via singular value decomposition (SVD) is applied to compress data in an IR-video sequence in order to save processing time in the subsequent step of image classification. According to PCA theory, an orthogonal transformation can project data into a lower dimensional subspace with linearly uncorrelated principal components preserving all original information. The effect of data reduction is confirmed with experimental data from IR-video sequences of simple square-pulsed thermal loadings on aramid honeycomb-sandwich components with CFRP/GFRP (carbon-/glass-fiber-reinforced plastic) facings and GFRP inserts. Hence, processing time for image classification can be saved by reducing the dimension of information used by the classification algorithm without losing accuracy.

Modeling of the performance reduction of Macro Fiber Composites for use in numerical forming simulation of piezoceramic-metal-compounds

With the objective of producing aluminum sandwich parts with a sensor and actuator functionality, a production method was proposed which uses an adhesive for the integration of a piezomodule. Complex shapes may cause a reduction in the performance of piezomodules. Uniaxial and biaxial transducer tensile tests and accompanying optical strain measurements were carried out to evaluate the residual performance taking into account the strain load combination. The model validation showed a very good agreement between forming experiment and numerical simulation. The simulation model including the functionality reduction enables the performance of the actuator to be predicted after the forming stage for complex shaped parts has been completed.

Characterization of surface defects on composite sandwich materials based on deflectrometry

This paper presents a new characterization technique to measure and quantify surface defects in composites. During manufacturing of composite sandwich parts, imperfections appear on the skins due to molding parameters such as temperature, pressure and humidity. Recurring imperfections observed on the surface of composites include surface porosities, resin shrinkage and gloss variation. Although several methods to characterize such defects were developed in the past, visual inspection remains widely used in the industry. In this paper, two different types of surface defects often encountered in the composite industry are measured: surface porosities and resin shrinkage. The proposed measurement method uses an optical system based on deflectometry. Unlike other methods, this technique provides real-time mapping of reflected light intensity. It also provides surface curvature variation which is the most relevant criterion for surface appearance analysis. The results further suggest that setting a threshold on a given parameter (e.g. total surface area of porosities per unit area of sample) and using a fully automated procedure would make this approach very efficient for quality control operations of composite parts.

Characterisation of Strength Behaviour of Aluminium Foam Sandwiches Under Static Load

Abstract: Cellular metals, particularly aluminium foams, are increasingly used in automotive, railcar and aircraft industries due to their advantages such as low density, comparatively high stiffness, noise damping or non‐flammability. From this point of view a new powder‐compact forming and foaming technique has been developed to manufacture 3D‐aluminium foam sandwich (AFS) parts for components of railcars without glued joint between the foamed core layer and both cover sheets. Three different stages of foam expansion have been analysed to describe the material properties. We have characterised samples made of plane AFS panels by compression, bending and shear tests. The shear strain is optically measured by digital image correlation to estimate the shear modulus of foamed sandwiches. Furthermore, these experimentally determined values and curves are the basis for the verification and optimisation of finite element models by design of experiments. As a result of this work, recommendations could be derived for improving technological parameters.

Properties and Manufacturing of Sandwich Parts with Phenolic Foam Cores

Phenolic resins are noted for their outstanding fire properties. Foams produced of this material combine these properties with other qualities such as low density and low thermal conductivity, a combination that makes them particularly attractive for aviation applications. With the further development of the foam systems, phenolic foams are nowadays available with acceptable mechanical properties, too. This paper looks at the property spectrum of these new foams in more detail. Taking the example of an overhead storage compartment door for a passenger aircraft, the article also shows how these foams are processed and what properties can be achieved and expected for such parts. The One Step Sandwich Moulding (OSSM) process is a technique that allows dry textiles to be impregnated with the foam system, giving a sandwich laminate with a foam core and a fabric skin in a single step.

Manufacture of Aluminum Foam Sandwich (AFS) Components

Much work has been done to find commercially efficient applications for metal foams produced using the powder metallurgical route. Most of these efforts have not been successful, because foam quality could not be reproduced reliably and production methods were too inefficient. This article describes the conditions under which aluminum foam sandwich parts may be put into series production in an economical way.

Manufacturing of three dimensional sandwich parts by direct thermoforming

Sandwich panels have been used extensively in the transportation industry. However, as geometric complexities increase, the manufacturing techniques require longer cycle times and significantly increased labour. Press forming of initially flat thermoplastic sandwich panels is a new cost-effective way of obtaining a complex part in a one-step process. Nonetheless, the heterogeneous nature of the sandwich panels requires accurate control of the processing stage, and the complex geometry of the final part can lead to wrinkling of the faces and local collapse of the core during forming. Therefore, the potential for complex shape forming of thermoplastic sandwiches, based on a polyetherimide (PEI) foam core combined with PEI warp-knitted reinforced skins, has been investigated. An experimental approach associated with numerical simulations was used to define appropriate processing windows. Selective heating of the face sheets and the foam core was achieved, and parts were successfully thermoformed. The developed materials and process have open up new perspectives for use within the transportation industry.

Simulation of superplastic forming/diffusion bonding with finite-element analysis using the convective coordinate system

Abstract Superplastic-forming processes are simulated with finite-element analysis in the convective coordinate system. The finite-element code developed is applied to blow-forming processes for demonstration of its validity by predicting the optimum forming pressure cycle. The numerical results provide the pole height and intermediate deformed shapes with variation of the forming time, as well as thickness distribution. The results are compared with those from the experiment and finite-element analysis with a continuum element. The finite-element code is applied to the analysis of a superplastic-forming/diffusion-bonding (SPF/DB) process of four-sheet sandwich parts. The result shows that the deformed shape with the three-dimensional analysis is different from that with the two-dimensional plane strain because of the end effect, and so is the thickness distribution. The analysis enables accurate prediction of thickness distribution, which is necessary for the good design of multi-sheet sandwich parts such as an aircraft part.