Single Metal Sheet Research Articles

Control and optimization of bulge defect in incremental forming of cu-Al bimetal

The bimetal sheets products obtained by the incremental forming are gradually widely used because of the excellent properties of the bimetal sheets. But the forming process of the bimetal sheets is more complicated than that of single metal sheet because this process involves a complicated interface of the bimetal sheets. A three-dimensional model including the tool, the bimetal sheet and the cohesive element between the bimetal sheet has been suggested to discuss the bulge defect affecting the accuracy of incremental forming. And the analysis results have been compared with the experiment results to verify the correctness of the simulation model. The analysis show that the reason of bulge defect is the inconsistent stress state on the upper and lower surfaces of the sheet. Moreover, the results also indicate that the step down size is the most critical factor affecting the bulge height, the height of bulge defect increases by 133% as the step down size increase. In addition, it is found that different parameters also have a great impact on the interface status of the bimetal. Effecting optimization parameter have been proposed to reduce the bulge defect by 53%.

Performance evaluation of CFRP/Al fibre metal laminates with different structural characteristics

FMLs (fibre metal laminates) are a kind of hybrid material consisting of composite material layers alternating to metal sheets, that present high mechanical characteristics. The aim of the present work deals with the flexural behaviour of CARALL (carbon fibre-reinforced aluminium laminates) specimens; in fact, the influence of both the layer thickness and the adhesion interface between CFRP layer and aluminium sheets was analysed. Four different laminates, bonded with structural adhesive or with prepreg resin only and with one or two metal sheets (but maintaining the composite/metal volumetric ratio at a constant value), were tested according to the three points bending scheme. The experimental tests evidenced that the flexural strength increased in absence of the adhesive layer and with a single metal sheet. Moreover, some micrographs of the fractured specimens were taken to determine the failure mechanism.

Deformation of Stacked Metallic Sheets by Shock Wave Loading

The focus of the present work is to develop a deep understanding of deformation of stacked metal sheets with a series of different sequences by using shock wave loading. Here, experimental and numerical investigations of deformation of a single metal sheet of 1.5-mm and the stack of three metal sheets of 0.5-mm thickness of aluminum (Al), copper (Cu) and brass (Br) material were carried out. In the shock wave experiments, helium was used as the driving gas to produce a strong shock wave. Finite elements method (FEM) simulations on 3D-computational models were performed with explicit dynamic analysis, and Johnson-Cook material model was used. The obtained results from experiments of the outer diameter, thickness distribution, and dome height were analyzed and compared with the numerical simulations, and both the results are in excellent agreement. Moreover, for the same pressure load, due to lower inter-metallic friction in the stacked sheets compared to a cohesive property of the single sheet, an excellent deformation of stacked metallic sheets was observed. The results of this work indicated that the shock wave-forming process is a feasible technique for mass production of stacked metallic sheets as well as fabricating a hierarchical composite structure, which provides higher formability and smooth thickness distribution compared to a single material.

Wideband CPW-Fed Flexible Bow-Tie Slot Antenna for WLAN/WiMax Systems

A bow-tie antenna based on a slot configuration in a single metal sheet on top of a very thin flexible substrate is introduced. The antenna is constructed from two slotted right-angle triangles fed by a coplanar waveguide transmission line. The topology is very simple and extremely easy to tune in order to reach the proper characteristics after mounting on a supporting structure. A prototype is designed, fabricated, and characterized experimentally. The tunability is proven by considering both the version in free space and the version for use on a brick wall. Measurements demonstrate good agreement with simulations. Both versions cover the wireless local area network (2.4 and 3.65 GHz) and WiMax (2.3, 2.5, and 3.5 GHz) spectra, with an overall impedance bandwidth of 1.79 GHz (57.7%) and 1.46 GHz (49.7%), respectively. The radiation of the antenna is bidirectional with maximum gains of 6.30 and 5.09 dBi for the free space and brick wall versions, respectively.

Experimental and numerical study of a shunt structure for large dynamic strain measurement

Cost-effective and energy-saving sensor for large dynamic strain measurement is still lacking for wireless sensor networking application. In this paper, a shunt structure is proposed to measure large dynamic strain using metal foil strain gauge without fatigue failure. This shunt structure is made of single metal sheet for convenient installation. The working principle of the strain shunt with one shunt sheet bridging two strain relieving units is illustrated. The strain measured on the shunt sheet surface is proportionally lower than that on the target surface where the strain shunt is attached, and the ratio of strain level reduction is derived analytically from shunt structure dimension. The constancy and stability of the shunt ratio is validated through tensile and bending load tests for both static and dynamic loads. Furthermore, the stress concentration and shunt ratio sensitivity to compound load are investigated numerically.

Dual-Band Integrated Antennas for DVB-T Receivers

An overview on compact Planar Inverted-F Antennas (PIFAs) that are suitable for monitor-equipped devices is presented. In particular, high efficiency PIFAs (without any dielectric layer) with a percentage bandwidth (%BW) greater than 59% (470–862 MHz DVB-T band) are considered. In this context, two PIFA configurations are reviewed, where a dual-band feature has been obtained, in the 3300–3800 MHz (14% percentage bandwidth) WiMAX and 2400–2484 MHz (2.7% percentage bandwidth) WLAN IEEE 802.11b,g frequency bands, respectively, to also guarantee web access to on-demand services. The two PIFAs fill an overall volume of mm3and mm3, respectively. They are composed of a series of branches, properly dimensioned and separated to generate the required resonances. Finally, to show the extreme flexibility of the previous two configurations, a novel dual-band L-shape PIFA has been designed. A reflection coefficient less than −6 dB and −10 dB and an antenna gain of around 2 dBi and 6.3 dBi have been obtained in the 470–862 MHz DVB-T band and the 2400–2484 MHz WLAN band, respectively. The L-shape PIFA prototype can be obtained by properly cutting and folding a single metal sheet, thus resulting in a relatively low-cost and mechanically robust antenna configuration.

A Compact Dual-Band PIFA for DVB-T and WLAN Applications

A compact dual-band Planar Inverted-F Antenna (PIFA) working in both the DVB-T (Digital Video Broadcasting-Terrestrial) and the WLAN (Wireless Local Area Network) IEEE 802.11b,g frequency bands is presented. It is designed to be integrated in a monitor-equipped device, and exhibits reduced electrical size with respect to similar PIFA configurations. A reflection coefficient less than -6 dB and -10 dB was obtained in the 470-862 MHz (59% percentage bandwidth) DVB-T and the 2400-2484 MHz (2.7% percentage bandwidth) WLAN bands, respectively. An antenna gain of almost 3 dBi and 4.5 dBi, with more than 95% radiation efficiency, was obtained in the two frequency bands of interest. The PIFA fills an overall volume of 217 × 12 × 8 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and can be realized by a properly cut and fold single metal sheet. Measurements on prototypes have shown that the proposed layout is robust in terms of the impedance matching detuning that can be caused by the presence of metal parts nearby the antenna.

A Low-Profile Linearly Polarized 3D PIFA for Handheld GPS Terminals

A 3D planar inverted F-antenna (PIFA) is proposed for a Global Positioning System (GPS) receiver. The antenna is designed to be integrated in a portable device and must meet compact size requirements. The 3D PIFA consists of a single metal sheet properly cut and bent in order to minimize costs for realization, materials and series production. The linearly polarized antenna exhibits good impedance matching performance, wide beam radiation patterns and a relatively high gain, which allow the reception from a wide angle toward the satellite constellation. An antenna prototype has been embedded in a commercial GPS receiver and an experimental measurement campaign has been carried out to evaluate the most important performance parameters. Measurements have been performed out by collecting time sweeps signal samples along urban and suburban routes. Time to first fix, carrier to noise ratio distribution and horizontal dilution of precision have been calculated; these parameters are shown and discussed. Comparisons with respect to some reference circularly polarized antennas (a nearly square patch and a quadrifilar helix antenna) and to a simpler inverted-F antenna printed on the receiver PCB have been performed and are shown in the paper.

Response and collapse of foam-supported sheet metal beams and shallow arches

This paper considers the response and failure characteristics of beams and arches constructed by bonding a layer of foam to a single metal sheet, thus creating a “Foam-Supported Sheet Metal,” or FSSM composite. The investigation was conducted from experimental and analytical/numerical perspectives. In the experiments, strips of Rohacell foam were bonded to straight or curved aluminum 2024 strips to construct the composites. The specimens were then supported at the ends and bent under a central load such that the foam was in tension. The results showed that significant increases in stiffness and failure loads could be achieved using this concept with relatively small weight penalty. Catastrophic failure occurred when the foam reached its tensile failure stress. Formulas to predict the bending stiffness and moment at failure of the composite sections were derived from beam theory and are presented. To predict the response of arches, a nonlinear finite element model was developed. The numerical results showed good agreement with the load-deflection responses and failure loads measured experimentally.