Papers by Keyword: Sandwich

Abstract: The lightweight potential of components made of fiber-reinforced plastic can be enhanced by use of sandwich composites. So far, limited dynamic properties of plastic-based foams have prevented the use of sandwich composites in machine applications. The combination of closed-cell aluminum foam (ALF) and carbon fiber reinforced plastic (CFRP) provides a solution to this obstacle. Aluminum foam is characterized by favorable damping properties with minimum weight and CFRP provides high strength and stiffness at similarly low density. This paper deals with the design of a hybrid sandwich composite and its interpretation by using customized FEM simulations.Producing this kind of a sandwich composite in an economic production process presents a major challenge. Thus, a method has been developed that prevents excessive penetration of the resin into the pores of the aluminum foam. A high volume fraction of the resin in the foamed sandwich core would increase density and negatively influence damping properties. The implementation of a barrier layer will avoid this penetration. A DoE was developed and RTM process parameters were varied with the objective of achieving the highest specific bending stiffness. In preliminary experiments the appropriate range of injection pressure, mold temperature, and pressure force was determined. Tests with a nonwoven fabric could prevent the resin from infiltrating into the aluminum foam. Mechanical properties of the sandwich composite are only marginally affected.A model was developed to calculate the obtainable sandwich composite properties. The calculation method considers both the characteristics of the aluminum foam and the CFRP anisotropy. Based on this model a reliable calculation of the applied load could be accomplished. The design of the sandwich composite was targeting at high stiffness and determination of the natural frequency. Parallel to calculations, tests on specimen were performed and the obtained results were included into the calculation as part of the material model.

Abstract: The necessary thermal insulation for buildings was provided for years optimally by polymer foams. Generally the foam is based on petrochemical resources. It is used for external wall insulation and not employed for additional functions. A Sandwich build of rigid laminates and a quite shear resistant polymer foam core results in an extraordinary stiff element. This provides thermal insulation and forms an independent load carrying structure. The sustainability of the sandwich structure can be raised by combining materials from renewable resources. The sandwich system currently developed, in cooperation with our partner from industries C3 Technologies, consists of lignin based foams of varying density and natural fibre reinforced laminates. The lignin is produced from beech-wood via the organosolv-process. Afterwards it is chemically integrated into the phenolic resin. The proportion of lignin in the resin can be varied from 10% up to 40%. This poses a quite prospective idea since using lignin means using nature’s own synthesis instead of artificial petrochemical processes for resin production and thus reducing the energy needed for resin production

Abstract: Lightweight solutions and functional integration become more and more important in different fields of industry. In order to achieve a sensor and actuator functionality of shaped sheet metal parts, today a generally manual application step of the piezomodule is necessary. This subsequent process is time consuming and leads to high costs. In earlier studies a method was presented allowing the fabrication of a formable compound with an integrated sensor and actuator functionality. The formability of the compound is achieved using a viscous adhesive, surrounding the piezomodule during the forming operation. The low viscosity of the adhesive allows a relative movement between the piezomodule and the sheet metals and drastically reduces the transfer of critical strains to the piezomodule. Curing of adhesive takes place after the forming operation. To improve the efficiency of the process chain an advanced adhesive system with robust application properties has to be used. Furthermore, the productivity of several fabrication steps and their sequence in the process chain have to be verified and improved. The paper presents the process chain designed for automated production of formable sandwich sheets with integrated piezomodules, including the production steps for the fabrication of the semi-finished part as well as the forming operation. Aiming on a good formability during the shaping operation and on a stiff connection between the piezomodule and the sheet metal in the finished sandwich part, one focus is set on the adhesive properties required during the different process steps.

Abstract: Polyurethane (PU)/multiwalled carbon nanotubes (MWCNTs) foam composites were produced by reaction of based palm oil polyol (POP) with methylene diphenyl diisocyanate (MDI). The MWCNTs were added into PU foam with the percentages varied from 0 wt.% to 3 wt.%. Sandwich composites were prepared using hand lay-up method where Aluminium (Al) sheet as skin were stacked onto PU foam using Araldite adhesives. The PU/MWCNTs foam composites (PMFC) and PU/MWCNTs foam sandwich composites (PMFSC) were characterized using flexural test analysis. Observation showed higher value of flexural strength for PMFC and PMFSC at 0.5% incorporation of MWCNTs. The flexural strength of sandwich PU foam is higher with an average value of 159.38% than control PU foam, due to Al sheet act as ductile skin and prevents samples from rupture rapidly. The modeling using finite element analysis (NX Software-version 8.5) showed the displacement nodal magnitude for 0.5% PMFC (2.537 mm) are higher than 0.5% PMFSC (0.288 mm).

Abstract: Thick composites are increasingly used in the design of mechanical structures. Combined with low weight, they are generally resistant structures, which can support importante loads. In addition, depending on the number and nature of the materials used, it is possible to adapt properties for specific applications (damping structures).This work proposes the establishment of a new theoretical model of multilayer beam. The model, which is simple and easy handling, is intended for the subsequent establishment of a finite element. The goals are:improve the refinement of the transverse displacement and transverse shear, avoiding the calculation of transverse shear, the use of correction factors,keep only the usual displacement,test the accuracy of the model compared with models from the literature (for an equivalent single-layer approach).The proposed approach is of the kinematics, the form adopted for the displacement field is justified from a dimensional point of view, by the equations of elasticity. The equations of motion and boundary conditions are obtained by applying the principle of virtual power.The validity of the model is tested on problems for which solutions (obtained by previous theories) exist.

Abstract: This paper describes the design verification process of a new bus roof. The aim was to obtain a roof with comparable or better mechanical properties and likely dropped weight. The sandwich roof is developed in the framework of the project when properties matching real roof were compared to test samples. Different core materials and faces have been investigated. The experimental results serve to verify the suitability of the proposed FEM modelling for the future use on global structure roof numerical model.

Abstract: The main objective of the present paper is the characterization of the mixed-mode delamination in sandwich plates. To this purpose a mixed-mode delamination failure model is proposed. Then, the failure model is implemented in ANSYS code to calculate the damage propagation parameters. The analysis is based on the Finite Element Method and interface techniques. Within the interface finite element modeling there are calculated the individual components of spring reaction force, relative displacement and energy rate release along the lamination front.

Abstract: The numerical modeling of lightweight sandwich beam in four-point bending, using combination of finite elements by help of two modeling approaches 2-D and 3-D models is presented. The mechanical results of hot-dipped zinc steel face layers and polyurethane foam core, obtained from comprehensive material testing program, were used as input data in order to implement the finite element analysis by the commercial ANSYS code. The material nonlinearities, most pronounced in the core, as well as geometric nonlinearities are included in the models. As was shown an advantage of plane stress condition can be applied in numerical models in one-way bending.

Abstract: Heat conductive materials, which widely used in the field like electronic information, electrical engineering and aerospace, are required high thermal conductivity, excellent electrical insulation, corrosive resistance, chemical stability and so on. In this paper, metal/unsaturated polyester (UP) sandwich composite is prepared to use as heat conductive material. Hollow and solid model are prepared to study their capacity of thermal transmission by software ANSYS and experiment. The results showed that capacity of solid model thermal transmission increased with increasing the number of wires. Equivalent thermal conductivity of solid composite model is 3 times more than that of pure UP. Heat transfer effect of hollow composite model is better than that of solid composite model, even though the latter has two layers of wires more than the former.

Abstract: In this work, we prepared the sandwich-like carbon@SnO₂@carbon hollow spheres by templating against polystyrene spheres. The hollow spheres are characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). The electrochemical performance as the anodes of lithium-ions batteries are studied by the cyclic voltammogram (CV) and galvanostatic discharge-charge voltage tests. Because of the interesting structure, the as prepared carbon@SnO₂@carbon hollow spheres deliver a reversible capacity of 492 mA h g^-1 after 50 cycles at a high current density of 400 mA g^-1.