Papers by Keyword: Sandwich Structure

Abstract: Sandwich structures consist of one light core layer and two top layers, which form the load-bearing structure. These layers have to be stiff and strong and have to protect the structure against indentations. The main task of the core layer is to keep the top layers in place and to generate a high shear stiffness. In order to obtain the required space between the top layers, the core layer has to have a high specific volume. Different sandwich materials with aluminium or steel top layers and cores of aluminium combs, corrugated aluminium sheets or aluminium foams are already known. In order to obtain better properties in terms of strength fibre-reinforced plastics (FRP) are utilised as top layers; this is the focus of numerous of the current research studies. The sole use of these materials leads to negative effects regarding the damage and impact behaviour. New top layers with high strength and high stiffness characteristics as well as good damage tolerances are to be expected by utilising metal layers in combination with endless fibre-reinforced plastics, so called hybrid laminates. These hybrid laminates combine the positive properties of metals (e.g. ductility) and fibre-reinforced plastics (e.g. tensile strength). The focus of this investigation lies on the production and characterisation of sandwich structures with aluminium foam core layers and hybrid laminate top layers. The foam cores consist of closed pore aluminium foams produced by utilising ingot and powder metallurgical techniques. The top layers consist of glass fibre-reinforced thermoplastics and aluminium layers. The production of the sandwich materials is realised by means of thermal pressing.

Abstract: Sandwich structures with metal foams core are widely used in various engineering applications due to their special properties of high-strength and high-stiffness to weight ratio when compared to the properties of pure material systems. Sandwich structures have the capability to resist impact loads which make them favorable for energy absorber application. The aim of this research is to investigate the impact properties of aluminium foam sandwiched with glass fibre reinforced plastic (GFRP). Drop weight impact test was conducted using hemispherical impactor tip at velocity of 6.7 m/s by striking the samples with and without face-sheets. The result showed that the GFRP and aluminium foam core sandwich panel exhibited promising energy absorption properties, corresponding to the highest specific energy absorption value observed.

Abstract: The paper applies composite technology into the field of hydraulic metal structures and hydropower construction mechanical equipment design, and presents the method of optimum design of hydraulic steel gate metal sandwich construction and simulation analysis. According to characteristics of the structure of the flat hydraulic steel gate and selecting the appropriate metal sandwich construction, this paper optimize the design of a hydraulic steel gate of metal sandwich construction from the perspective of light-weight purpose of structure. Considering the overall mechanical behavior of steel gate structures and using technology of three-dimensional modeling and numerical simulation, this paper has a numerical simulation analysis on the optimum hydraulic steel gate. Numerical simulation analysis and theoretical calculation results show the optimum structure of hydraulic steel gate is reasonably practicable.

Abstract: This research paper deals with an investigation of the mechanical properties of sandwich structures consisting of High Pressure Laminate facing layers (HPL) and various types of cores that are produced by vacuum bagging technology. These materials are connected with different adhesive layers and quality of connection to individual materials is evaluated. Moreover, prepared sandwich structures are tested in three-point bend. Based on the results, suitable combinations of individual materials are proposed for sandwich structures with regard to the quality of the adhesive bonding.

Abstract: The behavior of foam sandwich composites subjected to the quasi-static load has been investigated. The results revealed that the indenter tip shapes have an influence on the indentation behavior of the specimens. Failure modes were studied by sectioning the samples at the damage location and observing under an optical microscope. The primary damage mode was found to be the fiber breakage, delamination and foam crack. Knowledge of the damage resistance properties of a sandwich panel is useful for product development and material selection.

Abstract: In order to get a stable heat preserved property of temperature control textile, the sandwich structure of thermochromic phase change nanofibers/ woven composite materials was made by electrospinning, weaving and simple suture. In this material, the thermochromic powder acted as a temperature indicator, lauric acid is selected as phase change material. The morphologies and heat preserved property were characterized by SEM, a digital single lens camera and an increase-decreased temperature system test, respectively. The results showed that such composite materials exhibited an obviously heat preserved property; it took 17mins to decrease the temperature from 50 °C to 30 °C, which was 4 mins longer than the weaves.

Abstract: The dynamic characteristics of the Polypropylene honeycomb (PPHC) sandwich composites have been investigated under various temperatures (30°,35°,40°,45°,50°,55°,60°, 65°,70°,75° and 80°C) and different orientations (0° and 90°) of the glass fibers in the composites. Since the thermal properties of the constituent materials (glass fiber, epoxy resin and PPHC core) of the PPHC sandwich composites are different and the in-plane effect of the composites varies with the two different orientations (0° and 90°) of the fibers, the variation of the loss factor under the various temperatures are also different for these orientations. A two stage layup technique has been used to fabricate the sandwich composite specimens. Impulse technique associated with the half power bandwidth method, has been used to evaluate the natural frequency and damping values of the sandwich composite under different temperatures.

Abstract: The fracture properties of a series of metal foam sandwich structures based on glass fiber-reinforced polyamide 6,6 composite (GF/PA6,6) skins have been investigated. The open cell core materials were manufactured using the Lost Carbonate Sintering (LCS) process, a recently-developed technique for manufacturing metal foams. Initially, the effect of varying the compaction pressure used in producing the metal foams as well as the density of the samples were investigated through a series of compression tests. Here, it was shown that the compressive strength and the elastic modulus of the foams varied with density and compaction pressure, in spite of the fact that the average size of the cells in these foams were insensitive to either of these two parameters. The resistance of sandwich structures to localized loading was investigated through a series of indentation tests. Here, it was shown that the indentation response of sandwich structures could be characterized using a simple indentation law, the parameters of which did not exhibit any clear dependency on the density of the foam. Finally, three point bend tests on the sandwich structures have shown that their loading-bearing properties were sensitive to foam density.

Abstract: In order to broaden the absorbing bandwidth of radar-absorbing materials (RAMs), a type of sandwich-structure RAMs (SSRAMs) derived from a Salisbury absorber and comprising two dielectric layers and one resistive sheet was investigated. In this paper, the impedance characteristics of the SSRAMs were analysed and the mechanisms of broadening microwave-absorbing bandwidth were interpreted using a Smith chart. In order to realise the study’s SSRAMs, plain-woven glass fibre fabric and silicon carbide (SiC) fibre fabric with low electrical resistivity were employed as reinforcements of the dielectric layers and lossy layer, respectively. The microwave-absorbing properties of the SSRAMs were measured and compared with simulated results. The results showed that the experimental and simulated results were in good agreement, that the SSRAMs had better wideband microwave-absorbing properties and that the microwave-absorbing bandwidth at reflectivity below −10 dB can reach 11.6 GHz.

Abstract: The dynamic characteristics of fiber reinforced polymer skins with the alternate arrangement of continuous and chopped fibers on the polypropylene honeycomb core are investigated. It is envisaged that the damping could be improved by splitting the length of fiber into different short lengths so that more energy can be dissipated. The dynamic characteristics of FRP specimens with different forms of fibers were studied. The fibers were considered in the following five groups:, all continuous fibers, alternate arrangement of continuous and two chopped fibers, the same with three chopped fibers, four chopped fibers, and the five chopped fibers in. The natural frequencies and damping loss factors were evaluated by using the impulse technique with the half power band width method. The results revealed that for a given fiber volume fraction the damping could be improved by reducing the length of fibers.