Thin Metal Sheets Research Articles

Investigation of Techniques for Enhancement of Efficiency of a Hybrid Photovoltaic and Solar Thermal System: Literature Review on Applications and its Advancement

Abstract: Over the most recent couple of decades, tremendous consideration is drawn towards photovoltaic–thermal systems because of their advantages over the solar thermal and PV applications. This paper intends to show different electrical and thermal aspects of photovoltaic–thermal systems and the researches in absorber design modification, development, and applications. From the previous review articles, it has been concluded that the heat energy exhausted from the PV module can be further utilized in different ways and helps in achieving better efficiency. Furthermore, the types of photovoltaic–thermal systems such as air collector, water collector, and combi system, coupling with heat pump and their application to buildings are also stated. This paper also discussed certain design aspects like modifications in the flow channel by adding fins, thin metallic sheets, rollbond absorber, and porous media and the effect of these modifications on the hybrid system’s efficiency. Further- more, the use of the latest technologies such as nano fluids, thermoelectric generators, and phase-change materials improves the overall system performance. The role of soft-computing techniques is forecasting the impact of various parameters on the photovoltaic–thermal system is also discussed.

Experiment for Measuring Mechanical Properties of High-Strength Steel Sheets under Cyclic Loading by V-Shaped Double-Shear-Zone Specimens.

The simple shear test shows significant advantages when measuring the hardening and shear properties of thin sheet metal at large strains. However, previous shear tests had an end effect caused by local stress concentration and a boundary effect caused by deformation overflow, resulting in non-uniform strain distribution in the shear zone. Therefore, a unique V-shaped double-shear-zone specimen is proposed to measure the Bauschinger effect under cyclic shear loading conditions in this paper. Simple shear experiments and three different types of cycle shear experiments are conducted to analyze the uniformity of deformation in the shear zone and the effect of pre-strain and the number of cyclic loads on the Bauschinger effect of Q890 high-strength steel sheets. The results indicate that the proposed V-shaped double-shear-zone specimen can still maintain uniform shear deformation in forward/reverse cyclic loading experiments, even at large strains. Q890 high-strength steel exhibits a significant Bauschinger effect, which is more pronounced with the increase in shear pre-strain and loading cycles. The results of this paper provide a new approach for studying the hardening characteristics under large strain and the mechanical properties under cyclic shear loading for metal sheets.

Analysis of hydrogen diffusion in the three stage electro-permeation test

The presence of hydrogen traps within a metallic alloy influences the rate of hydrogen diffusion. The electro-permeation (EP) test can be used to assess this: the permeation of hydrogen through a thin metallic sheet is measured by suitable control of hydrogen concentration on the front face and by recording the flux of hydrogen that exits the rear face. Additional insight is achieved by the more sophisticated three stage EP test: the concentration of free lattice hydrogen on the front face is set to an initial level, is then dropped to a lower intermediate value and is then restored to the initial level. The flux of hydrogen exiting the rear face is measured in all three stages of the test. In the present study, a transient analysis is performed of hydrogen permeation in a three stage EP test, assuming that lattice diffusion is accompanied by trapping and de-trapping. The sensitivity of the three stage EP response to the depth and density of hydrogen traps is quantified. A significant difference in permeation response can exist between the first and third stages of the EP test when the alloy contains a high number density of deep traps.

Morphology, mechanical property, and molten pool dynamics in spot modulated-PLBW of Ti6Al4V alloy sheets with air gap condition

The tailor joining of thin metal sheets frequently suffers from the assembly error of air gap. Herein, an improved laser welding scheme, integrating the pulsed laser power and the modulated beam spot size is developed and applied on 1.5 mm-thick Ti6Al4V sheets with a predetermined air gap range. Weld beads of high continuity and homogeneity are obtained while the tensile property has a nonlinear decrease when increasing the air gap. During the welding, the over-gap metal bridge is obtained due to melt accumulation and periodical keyhole penetration, and the gap bridging capacity, mainly featuring bilateral metal bridges can be weakened as the air gap increases. This evaluation would provide a basis for processing optimization regarding seam appearance and property.

Flexural and sinking stiffnesses investigation of metal, glass fiber reinforced plastic and hybrid laminates through a semi‐experimental method

AbstractThe hybrid metal/GFRP laminate is a kind of typical hybrid structure consisting of thin metal sheets and glass fiber reinforced plastic laminates, which combines the benefits of low cost, high strength, excellent impact resistance, and good corrosion resistance. In this work, a semi‐experimental method based on a nondestructive test and the analytic solution of the thin plate's deflection for the flexural and sinking stiffnesses identification of hybrid metal/GFRP laminates was proposed and validated by corresponding numerical simulations. Then, in total 17 different specimens (including metal, GFRP and hybrid metal/GFRP) were prepared and tested by the proposed semi‐experimental method to investigate their flexural and sinking stiffness performances in multiple perspectives (including stiffness per unit mass/volume/price/surface density). The analytic solutions show that the flexural and sinking stiffnesses are proportional to macro equivalent moduli of laminate specimens and proportional to the third power of thicknesses of specimens. The test results show that the stiffnesses per unit mass/density of the 7‐ply GFRP laminate can be comparable to those of the variable‐thickness rolled blank (VRB) made of steels, but the stiffnesses per volume/price of the 7‐ply GFRP laminate are only one fifth to one quarter of those of VRB. It is also found that though the hybrid metal/GFRP laminate with the combination sequence of aluminum plate/5‐ply GFRP/aluminum plate has the lowest GFRP layers' volume fraction, but has the best performances of stiffnesses per unit mass/density. Besides, the VRB part can significantly improve the stiffnesses per unit volume of hybrid metal/GFRP laminates.

Beam filtration for object-tailored X-ray CT of multi-material cultural heritage objects

Computed tomography (CT) is a powerful non-invasive tool to analyze cultural heritage objects by allowing museum professionals to obtain 3D information about the objects’ interior. These insights can help with the conservation or restoration of the objects, as well as provide contextual information on the objects’ history or making process. Cultural heritage objects exist in a wide variety and have characteristics which present challenges for CT scanning: multi-scale internal features, a diversity of sizes and shapes, and multi-material objects. Because X-ray absorption is related to the density, thickness of the material, and atomic composition, the challenges are greater when the object consists of multiple different materials with varying densities. This is especially true for cases with extreme density contrasts such as that between metals and textiles. An untailored acquisition of CT scans of multi-material objects can lead to reduced image quality and heavy visual errors called image artifacts, which can influence the perception or representation of information. A tailored acquisition can reduce these artifacts and lead to a higher information gain. In this work, we firstly discuss how the X-ray beam properties and the beam-object interaction influence CT image formation and how to use filters to manipulate the emitted X-ray beam to improve image quality for multi-material objects. We showcase that this can be achieved with limited resources in a low-cost DIY fashion with thin sheets of metal as filters, 3D-printed filter frames and a filter holder. Secondly, we give a qualitative analysis of the influence of the CT acquisition parameters illustrated with two case study objects from the textile collection of the Rijksmuseum, Amsterdam, The Netherlands. With this we provide insights and intuitions on tailoring the CT scan to the cultural heritage objects. Thirdly, we extract a general concept of steps for museum professionals to design an object-tailored CT scan for individual cases.

Formed developables - a new class of sheet metal parts

Sheet metal parts are broadly classified as stamped parts versus folded developables. While stamped parts are parts manufactured using conventional sheet metal forming techniques, folded developables are curved developable connections produced by the virtue of the classical theory of folded developables. However, folding is not suitable for parts where material integrity cannot be compromised at the fold lines. In such cases, forming techniques can be used to introduce a distributed curvature and avoid material self-intersection at the curved fold axis. This paper combines the two genres to introduce a third class of parts called the formed developables. A developable shaped, thin sheet metal of very high strength and reasonable inextensibility is formed by flange drawing over a die radius. The die tool establishes the required curved bend axis, and the die radius is small enough to introduce a distributed curvature. A developable connection is successfully formed where the two connected corrugations are mirror images of each other. While no tearing or wrinkling is observed, experimental strain measurements highlight significant surface strains in the transverse direction while marginal stretching strains are observed in the forming direction. A trend of equal and opposite transverse strains strongly suggests that the major deformation in this geometrical process, and in-turn the shape of the final part, is driven by the involved geometrical parameters.

Compression and Fatigue Testing of High-Strength Thin Metal Sheets by Using an Anti-Buckling Device

BackgroundThe modelling of the sheet metal forming operations requires accurate and precise data of the material plastic behaviour along non-proportional strain paths. However, the buckling phenomenon severely limits the compressive strain range that could be used to deform thin metal sheets.ObjectiveThe main aim of this paper was to propose an effective device, that enables to determine of accurate stress-strain characteristics of thin metal sheet specimens subjected to axial deformation without buckling and with a special emphasis on friction correction.MethodsIn this paper, an anti-buckling fixture was proposed to assess the deformation characteristics of X10CrMoVNb9-1 (P91) power engineering steel, and DP500 and DP980 dual-phase steels, under compression loading. The fixture enables monitoring of the friction between the specimen and supporting blocks during the test, and thus the precise stress response of the material could be determined.ResultsThe effectiveness of the fixture was evaluated under tension–compression cyclic loading and during the compression tests in which high-strength thin metal sheets were successfully deformed up to 10% without specimen buckling. Furthermore, the successful determination of a friction force variation between supporting blocks and the specimen during tests enabled to determine an actual force acting on the specimen.ConclusionsThe proposed testing fixture was successfully assessed during the compression and cyclic tension–compression of high-strength thin metal sheets as no buckling was observed. Its advantage lies in adapting to change its length with specimen elongation or shrinkage during a test. The friction force generated from a movement of both parts of the device could be effectively monitored by the special strain gauge system during testing and thus its impact on the stress-strain characteristics could be successfully eliminated.

Thermally Degradable Split-Ring Resonator Made on a Gelatin Substrate with Enhanced Dielectric and Conductive Properties

Ingestible electronics, taken orally for monitoring organs, bacteria, and cells, are innovative wireless diagnostic and therapeutic technologies. Whereas residual in-body devices may require surgical removal, food-based sensors are seen as a way of ensuring safety. This study reports a split-ring resonator (SRR) whose resonance can be observed wirelessly. It is fabricated on a thermoresponsive gelatin substrate with a collaged edible metal leaf. Gelatin is a highly water-absorbing material, which may affect the resonator performance. According to high-frequency structural simulations, this resonator requires a low dielectric loss, <0.05, and high conductivity, >106 S/m. We found that these targets were achieved by completely drying the gelatin film and transferring multiple stacked metal leaves onto the film. Thin metal sheets were glued using an oleogel made of beeswax and olive oil, and the use of a hydrophobic material also aided in the transfer. Thus, we gained insights into the criteria for fabricating transient resonators with thermodegradability. SRRs made with edible materials are a technology that works in harmony with people and the environment and could lead to wireless devices or micromachines for the healthcare, agriculture, and livestock industries.

Investigating the buckling deformation of thin metal sheets during the blanking process

This article describes the effect of the generated stresses due to the cutting process on the possibility of the occurrence of buckling deformation in a thin sheet, which could affect the performance of the cut part, especially for some applications such as the cutting of the thin sheet laminations of motor parts. To achieve the research objectives, an experimental approach was followed. Two different thicknesses and two-grain orientations of silicon steel material were applied to investigate the influence of thickness and grain orientation upon the induced buckling deformation. Blanking dies were designed to cut thin sheets of steel at different cutting speeds. Buckling height was measured optically using a 3D microscope with regard to the cutting parameters. The results showed the appearance of buckling deformation only at low sheet thickness. The maximum buckling height was about 164 µm (82% of the material thickness) in the transverse grain direction at the lower cutting speed. Meanwhile, the results also demonstrated the presence of an elongation in the material of approximately 90 µm (1.8%) on the cutting sides, which played a role in the application of pressure to all sides of the cut plate, resulting in the formation of a plastic buckling deformation prior to the completion of the cutting process, and thus the occurrence of the buckling phenomenon.

Evolution of deformation and stress during necking in uniaxial tension

In this investigation, we study experimentally the evolution of both the deformation and the stress during the necking process of a thin metal sheet subject to uniaxial tension. The deformation over the sample surface is obtained using the optical technique of Digital Image Correlation (DIC), which maps out full-field displacement over a two-dimensional (2D) domain. The stress field associated with the measured deformation is determined using the technique developed by Liu [18], where if the deforming material remains isotropic, the stresses can be computed based on the measured deformation by solving the equation of equilibrium together with appropriate traction boundary conditions. The deformation measurement indicates that after the initiation of the neck the deformation in areas outside the neck is frozen, confirming what Bridgman [2] has speculated, and the deformation within the neck area continues to increase till final failure. There is never a reversal in deformation and, as a result, all material particles in the necking zone only experience softening but not unloading. The results also reveal some unique and interesting patterns of the stress field over the necking zone. Their implications on the analysis and modeling of the necking process are discussed.

Evaluation of limit curves double corrugated profiles of arched roofs

Double corrugated profiles made of thin sheet metal are susceptible to loss of local stability and their shapes exclude the possibility of applying design standards. Arch structures made of these profiles can have a different state of combined axial force and bending moment. Previous scientific research allowed the identification of the load carrying capacity and stability only for selected axial force parameters. The article presents the distribution of the interaction between the bending moment and the axial force, allowing the evaluation of the load-carrying capacity within the entire for static forces. Limit curves were developed using parametrised non-linear numerical analyses. Ansys software and the digital copy of the test model were used for the analysis. Limit curves were generated for two grades of steel and six thicknesses of sheet metal. In addition to the envelope, the limits for the elastic range, the pre-buckling elastoplastic range, and the post-buckling plastic range were estimated. The results are summarised in diagrams and tables.

A New Method to Develop Homogeneous and Heterogeneous Porous Micromodels Applicable to Enhanced Oil Recovery and Flow Visualization Experiments

AbstractIn this paper, a new method to fabricate micromodels having homogeneous and heterogeneous porous structures is reported to gain fundamental insight into the flow through porous media. The technique of microparticle image velocimetry (PIV) is used to map the pore-scale velocity field inside the micromodels. A thin perforated metal sheet composed of uniformly distributed circular holes is used as the master pattern, and the replica of the negative of this perforated sheet is transferred to a polydimethylsiloxane (PDMS) substrate using a method similar to the soft lithography. This method allows an efficient fabrication of micromodels having different porosity by adjusting and selecting the perforated sheets of different hole sizes. The prepared micromodels were tested for its applicability and reliability by carrying out the measurements of pore-scale velocity distribution using the micro-PIV technique. The experiments with micromodels with high porosity but different grain arrangements showed qualitative as well as quantitative differences in the velocity field. The pressure drop across the two ends of micromodel is also measured. The variation of pressure difference with the flowrate is found to be nonlinear with a significant effect on the patterns of micropillars. However, at low porosity, the variation of pressure difference with the flowrate is found linear and there is almost no influence of the micropillar patterns. The flow visualization measurements are also conducted with the dual porosity micromodels, and the flow patterns were examined by analyzing the velocity vector maps.

Dynamic opto-mechanical eye model with peripheral refractions.

Many myopia control methods based on the peripheral defocus theory have emerged towards applications in recent years. However, peripheral aberration is a critical issue, which is still not well-addressed. To validate the aberrometer for peripheral aberration measurement, a dynamic opto-mechanical eye model with a wide visual field is developed in this study. This model consists of a plano-convex lens representing cornea (f' = 30 mm), a double-convex lens representing crystalline lens (f' = 100 mm), and a spherical retinal screen with a radius of 12 mm. To optimize the quality of spot-field images from the Hartman-Shack sensor, the materials and surface topography for the retina are studied. The model has an adjustable retina to achieve Zernike 4th item (Z4 focus) ranging from -6.28 µm to +6.84 µm. As for mean sphere equivalent, it can achieve -10.52 D to +9.16 D at 0° visual field and -6.97 D to +5.88 D at 30° visual field with a pupil size of 3 mm. To realize a changing pupil size, a slot at the back of the cornea mount and a series of thin metal sheets with 2, 3, 4, and 6 mm holes are generated. Both on-axis aberrations and peripheral aberrations of the eye model are verified by a well-used aberrometer and the eye model to mimic a human eye in a peripheral aberration measurement system is illustrated.

Determination of process window for laser peening of thin metal sheets by localized indentation analysis

Determination of process window for laser peening of thin metal sheets by localized indentation analysis

Strain Prediction Using Deep Learning during Solidification Crack Initiation and Growth in Laser Beam Welding of Thin Metal Sheets

The strain field can reflect the initiation time of solidification cracks during the welding process. The traditional strain measurement is to first obtain the displacement field through digital image correlation (DIC) or optical flow and then calculate the strain field. The main disadvantage is that the calculation takes a long time, limiting its suitability to real-time applications. Recently, convolutional neural networks (CNNs) have made impressive achievements in computer vision. To build a good prediction model, the network structure and dataset are two key factors. In this paper, we first create the training and test sets containing welding cracks using the controlled tensile weldability (CTW) test and obtain the real strain fields through the Lucas–Kanade algorithm. Then, two new networks using ResNet and DenseNet as encoders are developed for strain prediction, called StrainNetR and StrainNetD. The results show that the average endpoint error (AEE) of the two networks on our test set is about 0.04, close to the real strain value. The computation time could be reduced to the millisecond level, which would greatly improve efficiency.

Prediction of stress distribution and stiffness degradation in fiber metal laminates containing matrix cracking

Fiber metal laminates (FMLs) are hybrid composite materials in which several thin metal sheets and composite layers are joined. The aim of the present study was to provide an appropriate analytical method to predict damages, including matrix cracks in composite layers and plasticity in metal layers subject to static uniaxial loading. Using the proposed model, the stress distribution in the metal and composite layers in the unit cell enclosed between the two cracks was extracted. Effects of crack spacing, applied stress, and layer thickness on the stress distribution and plasticity of the metal layer were further investigated. Finally, the stiffness reduction due to damage and the energy release rate due to matrix cracking were also extracted. In order to validate the damage model, numerical simulations were performed and the results were in good agreement with the outputs of an analytical model.

On-Body NLoS Radio Channel at Millimeter-Wave Frequencies

This article presents an analysis of on-body radio channels at millimeter-wave frequencies and possible solutions to reduce the path loss, particularly, at non-line of sight (NLoS) locations. We have chosen two specific channels around the wrist and waist, and a comprehensive study has been conducted at the frequency of 94 GHz. It is observed that in the presence of textile, a slow wave mode can be excited tangentially near the surface of human body. Clothing and the thin air between the clothing and the human body surface may attribute to the reduction of path loss at NLoS. Our findings show that the presence of different garment materials is linked to the variation of path loss in on-body radio channels. Moreover, we demonstrate numerically that by attaching thin metallic sheet underneath clothing may further reduce the path loss. In our parametric study, a maximum of 15 dB drop occurs in path loss at only 30 cm distance. A robust theoretical model based on the knife edge diffraction (KED) method has been applied to give physical insights of such a unique radio propagation mechanism, that can lead to abundant applications in 5G communications and beyond.

Relationship between Grain Size and Sample Thickness on the Creep-Rupture Performance of Thin Metallic Sheets of INCONEL Alloy 740H

A study was conducted on INCONEL® alloy 740H® to examine the role of grain size and sheet thickness on the alloy’s creep-rupture behavior. Three different starting sheet thicknesses were utilized and multiple heat-treatment conditions anticipated for compact heat exchanger (CHX) manufacturing were applied to produce a range of grain sizes. Creep-rupture testing was conducted at 750 °C for times up to about 6000 h and the results were compared to wrought databases. The data show that both creep strength and ductility were important factors in the overall creep performance of the sheets. Reductions in performance were observed due either to accelerated creep when grain size was fine or loss of rupture ductility when grain sizes approached the sheet thickness. Some combinations of heat-treatment and thickness were able to produce typical expected wrought creep properties. Historically a ‘rule-of-thumb’ requirement for creep testing suggests 3-5 grains per sample minimum dimension to ensure homogeneous behavior. This research shows that to ensure representative wrought creep performance (i.e. no effect of sample size), the sample minimum cross-section should be 10 times the average ASTM grain size. Statistical analysis of the microstructures suggests the population of larger grains as a controlling feature in creep failure.

Laser Forming of Compliant Mechanisms

AbstractSmall-scale flexible (or compliant) mechanisms are valuable in replacing rigid components while retaining comparable motion and behavior. However, fabricating such mechanisms on this scale (from 0.01 to 10 cm) proves difficult, especially with thin sheet metals. The manufacturing method of laser forming, which uses a laser to cut and bend metal into desired shapes, could facilitate this fabrication. However, specific methods for designing mechanisms formed by lasers need to be developed. This work presents laser forming as a means for creating compliant mechanisms on this scale with thin sheet metal. The unique challenges for designing mechanisms to be laser formed are explored, and new adaptations of existing designs are fabricated and discussed. The design of basic “building-block” features is developed for several mechanisms: a parallel-guided mechanism, a cross-axis flexural pivot, a lamina emergent torsional (LET) joint array, a split-tube flexure, and a bi-stable switch. These mechanisms are shown to perform repeatable behavior and motion comparable to existing nonlaser-formed versions. The further possibilities for fabricating compliant mechanisms with laser forming are explored, as advanced applications can benefit from using lasers to create compliant mechanisms from thin sheet metal.