Papers by Keyword: Sandwich

Abstract: In view of obtaining a step bunched morphology on large 4H-SiC surfaces, a sandwich configuration is investigated. A piece of silicon is melted between two 4H-SiC 4° off wafers, allowing a better spreading of the liquid than a Si drop approach. This successfully leads to highly step-bunched surfaces, though with irregular steps. The most regular step and terrace stuctures were found to be the result of epitaxial growth via a dissolution-precipitation process occuring from the edges to the center of the wafers. This is probably caused by radio-frequency induced electromagnetic convection within liquid Si. This process is quenched when using smaller liquid thickness.

Abstract: As the demand of the automotive and aerospace industries for lightweight and cost effective materials increases, it is necessary to combine different materials with respect to their lightweight and functional properties. The combination of polymer-steel-sandwich composites - which consist of a polymer core structure (transferring shear loads) and two metal face-layers (absorbing tensile and compression loads occurring at bending) - suite the need of minimizing weight per area under bending loads. The reduction of process steps can be achieved by connecting the face layers and core in-situ via an in-mold assembly process using variothermal processing. The injection mold hereby is heated near the melt temperature of the polymer with a variothermal water processing unit. Via contact heating inserted steel blanks are heated to the same temperature as the mold. This process enables the combination of the metal surface with the polymer core by infiltrating the micro or nano scale structure, which is generated by laser structuring or nano coating. Through the increased mold/blank surface temperature induced via variothermal heating the melt viscosity is lowered. This decreasing viscosity of the polymer melt hereby enables a higher degree of infiltration of the laser structured and nano coated blanks. This improved infiltration behavior is a key factor for the adhesion of the sandwich components and beneficial for the composites strength. Within this work two steel blanks are inserted into the mold to manufacture sandwich structures with steel face layers and a polymer (here: polylactidacid; PLA) core. As these sandwich composites are prone to bending failure, the 4-point-bending test is used to characterize the mechanical properties of this hybrid structure. The two surface treatments will also be compared concerning their mechanical interface properties with a shear edge test. The additional reduction on the polymer melt viscosity by means of gas inducing with chemical blowing agent is investigated on the laser structured surfaces only. To investigate the influence of the polymers melts viscosity on the bonding properties chemical blowing agent is added for some blanks.

Abstract: Based on the first order shear deformation plate theory (FSDT) in the present studie, static and dynamic behavior of carbon nanotube-reinforced composite sandwich plates has been analysed. Two types of sandwich plates, namely, the sandwich with face sheet reinforced and homogeneous core and the sandwich with homogeneous face sheet and reinforced core are considered. The face sheet or core plates are reinforced by single-walled carbon nanotubes with two types of distributions of uniaxially aligned reinforcement material which uniformly (UD-CNT) and functionally graded (FG-CNT). The analytical equations are derived and the exact solutions for bending and vibration analyses of such type’s plates are obtained. The mathematical models provided and the present solutions are numerically validated by comparison with some available results in the literature. Influence of Various parameters of reinforced sandwich plates such as aspect ratios, volume fraction, types of reinforcement and plate thickness on the bending and vibration analyses of carbon nanotube-reinforced composite sandwich plates are studied and discussed. The findings suggest that the (FG-CNT) face sheet reinforced sandwich plate has a high resistance against deflections compared to other types of reinforcement. It is also revealed that the reduction in the dimensionless natural frequency is most pronounced in core reinforced sandwich plate.

Abstract: The manufacturing processes for sandwiches made with aluminum or steel sheets are differentiated by their various melting ranges. Sandwiches with aluminum face sheets have recently been produced using to the so-called AFS technology, which includes a rolling process. However, if it is desirable to avoid rolling to reduce costs and allow for quick and flexible responses to the needs of the customer, the manufacturing process must be redesigned.

Abstract: The aim of the present work is to study the linear free symmetric vibration of three-layer sandwich beam using the energy method. The zigzag model is used to describe the displacement field. The theoretical model is based on the top and bottom layers behave as Euler-Bernoulli beams while the core layer as a Timoshenko beam. Based on Hamilton’s principle, the governing equation of motion sandwich beam is obtained in order to calculate the linear frequency parameters. Two types of boundary conditions simple supported-simple-supported (SS-SS) and clamped-clamped (C-C) under the influence of materials properties and geometrical parameters are studied. The validation of results is done by comparing with another studies, which available in the literature and found good agreement between the studies.

Abstract: The combination of metals and fiber reinforced plastics is also known as hybrid metal composites. They offer the fusion of the good static mechanical properties of the fiber reinforced plastics and the good dynamic mechanical properties of the metal. For that reason, parts made of hybrid metal composites are predestined for the use as load relevant parts. The purpose of this study was to develop new technologies for semi finished hybrid metal composite materials. Thermoplastic Fiber-Reinforced Composites (TP-FRC) were arranged with new, isotropic, closed pore Aluminum Foam (AF) structures to an Extrinsically Combined Composite Sandwich (ECCS) by adhesive bonding. They form the basis for novel weight-optimized as well as cost-effective applications. The entire manufacturing process for the continuous semi-finished product was examined and verified according DIN EN 2563. This was done with regard to subsequent characterization by the specific bending modulus and specific bending stiffness. The examinations show a high bending stiffness and high strength structures combined with excellent damping properties at high damage tolerances. These are the most requested in automotive applications.

Abstract: The present article addresses the evaluation of the electro-mechanical (E/M) impedance method as a Structure Health Monitoring (SHM) method to detect and classify damage, more specific, the debonding of a face layer.In the study the considered structure is simplified as a circular sandwich panel of constant thickness, consisting of isotropic face layers and a honeycomb core.The debonding is assumed to be circular and situated at the center of the panel, only variable in its radius.The article starts with a brief introduction to the basic idea of SHM and the fundamentals of the E/M impedance method.Further, the idealized setting is investigated by two sets of experiments whose results are analyzed by typically used damage metrics and by considering both analytical and numerical models.A coupled-field FEM model is developed and compared to the experimental results.Furthermore, an analytical model is derived to evaluate the experimental and numerical results.All results are presented and discussed extensively on pursuing the objective to detect and classify the size of a debonding.Finally, it is shown how a model based approach can predict the presence but also the size of a debonding in the considered sandwich panels based on the E/M impedance measurements.

Abstract: Hybrid sheet metal composites do show advantages compared to monolithic materials when strength, stiffness, and damping characteristics are set to a global optimum. Even though the mechanical properties of hybrid sheet metal composites have been improved in recent years, the application of such hybrid materials in the automotive industry is not well-established due to insufficient knowledge about their forming characteristics (e.g. in deep drawing process). Stiffness increasing composites consist of two metal sheets and a viscoelastic damping layer in-between: the outer sheet reveals stamped beads which increases stiffness of composite while the inner sheet serves as cover sheet. This paper deals with challenges of formability of stiffness increasing composites in industrial deep-drawing processes. The main concern is dimensional stability and accuracy of those layered materials after finishing the forming process. In order to ensure accuracy of formed parts, a methodology was developed for increased quality of sheet metal composites. Depending on the drawing limit ratios and blankholder forces, which evaluate the drawability of component in general, the drawing limit ratio is influenced for profound or insufficient residual bead heights and widths. Besides insufficient bead height, which causes a reduction in moment of inertia, inner marks on the visible outer sheet hamper a broad application in practical use. Finally, paper provides detailed recipies for manufacturing and tool layout for deep drawing objectives of such composite material.

Abstract: This study is aimed to discuss structural behavior of steel reinforced sandwich concrete beams (SWB) consisted of skins and a core. The skins were made of ordinary concrete and a core was of pumice lightweight concrete. The SWB skin compressive strengths of 30 MPa and the core compressive strength of 15 MPa were considered. Twelve SWB specimen of 150x250x2500 mm with 50 mm skin thickness and 150 mm core thickness were cast and tested after curing process under flexural points loading as simply supported beams. All the beams considered were reinforced with 3D12 mm deformed bar and 8 mm stirrups with 3 spacing variations. Shear span depth ratio (a/d) of 1.8, 2.3, 2.8, and 5.4 were also considered to reflect the behavior between short and slender beams. Results showed that the flexural behavior of sandwich beams were identical with normal or lightweight concrete beams behavior. Ultimate moment of beam section slightly increased with increasing the shear span to depth ratio, which were varies between 1.26 and 2.31 of the calculated moment. The yield moment to the ultimate moment ratio vary between 0.83 and 0.99. The ductility was increased with the decreased shear reinforcement spacing. The shear strength increased as the spacing of shear reinforcement decreases in almost all a/d variations. Shear strength was also increased with the increase of a/d ratio for short beam and the other hand shear strength decreased with the increasing a/d.

Abstract: There is a continuing interest in using laminated materials for the production of lightweight parts, the resulting parts having the same functionality and even an increased stiffness and length of operation compared to conventional materials. The present paper aims to study the forming behavior of the laminated materials that requires the unfolding of tests to determine the tensile mechanical properties and the intrinsic properties, determining the forming limit curves by means of the Nakajima test and the analysis of the behavior at unconventional incremental forming.