Thin Stainless Steel Foil Research Articles

Ultrarelativistic Fe plasma with GJ/cm3 energy density created by femtosecond laser pulses

The generation of a plasma with an ultrahigh energy density of 1.2 GJ/cm3 (which corresponds to about 12 Gbar pressure) is investigated by irradiating thin stainless-steel foils with high-contrast femtosecond laser pulses with relativistic intensities of up to 1022 W/cm2. The plasma parameters are determined by X-ray spectroscopy. The results show that most of the laser energy is absorbed by the plasma at solid density, indicating that no pre-plasma is generated in the current experimental setup.

Damage failure prediction study of carbon fiber metal laminates in hot stamping process

In addressing the difficulty of forming Fiber Metal Laminates (FMLs), a laminate composed of a 0.1 mm-thick 304 Stainless Steel Foil (SSF) and Carbon Fiber Reinforced Plastics (CFRP) as the base material is prepared using a specific process. Subsequently, forming limit diagrams are obtained through hemispherical bulge forming experiments to investigate the forming performance of FMLs laminates. The damage phenomena of various forming specimens during the thermal stamping process are analyzed. Based on different damage forms, corresponding theoretical models are established to simulate and predict the forming damage modes of FMLs through simulation. The research results indicate that the stamping formability of FMLs is influenced by the damage tolerance of the thin stainless steel foil. During the thermal stamping process, FMLs may experience delamination, fracture/crack of the thin stainless steel foil, and rupture/tearing/wrinkling of the prepreg. To address these issues, cohesive elements, GTN-M-K damage, and Hashin damage models are established, providing a reasonable simulation prediction of the stamping damage phenomena of FMLs.

Evaluation of surface pretreatment methods on thin austenitic stainless steel foils for adhesive bonding applications

ABSTRACT Stainless steel is used across all industries, from the chemical or construction sector to household appliances. To produce load bearing joints, a surface treatment of the passive surface of austenitic stainless steel is generally necessary. However, the treatment of thin-walled foil materials inhibits challenges concerning the deformation under thermal loads. This work investigates the effectiveness and mechanisms of different surface treatments on 50 µm thin AISI 316 L steel foil. Basic cleaning, surface finishing with an aluminum oxide abrasive, flame-pyrolytic deposition of silicon dioxide and application of a primer, etching with hydrochloric acid, treatment by atmospheric plasma, ns-pulsed laser surface cleaning, and fs-laser structuring are investigated. The effects of these treatments are analyzed in surface energy investigations by contact angle measurement, roughness measurements, and SEM-EDX. The bonding strength is tested with epoxy adhesives and a methyl methacrylate adhesive under 90° peel load. The failure mechanisms are further investigated by FTIR spectroscopy and SEM-EDX. The results show that the used coating with primer produces the strongest bonds, followed by the fs-laser treatment. In particular, sub-microscopic surface structures induced by fs-laser show promising results. SEM images show a full wetting of the capillary structures, providing the possibility of mechanical interlocking on a sub-microscopic level.

IMPACT OF MEASUREMENTS TECHNIQUES ON HEAT TRANSFER CHARACTERISTICS IN AIR JET ARRAYS

Air impact processes have diverse applications in engineering, including backflow welding, textile drying, and gas turbine blade and combustion liner cooling. This research examines the influence of experimental methodologies and measurement tools on convective heat transfer in adjustable air jet assemblies. The experiment involves the use of heated targets made of thin stainless steel foil with constant heat flux boundary conditions. Thermography measures target surface temperatures by analyzing how internal passage cross-flow affects convective heat transfer via outflow adjustments. The experiments involve two arrays of jet nozzles: inline and staggering, each comprising 44 impingement jet nozzles arranged in 4 rows with 11 jet holes in each row. The study presents unsteady time average local and spatial Nusselt numbers as functions of jet Reynolds number (4630-14000) and explores their dependence on the jet nozzle diameter. Cross-flow levels significantly affect spatial and local Nusselt numbers in both local and span-wise averaged values, regardless of the Reynolds number. Strong cross-flow (single configuration) distributes flow causing turbulence and uneven heat distribution, reducing Nusselt numbers. In contrast, moderate cross-flow (double configuration) improves heat transfer and increases Nusselt numbers. The study emphasizes the crucial role of experimental techniques in heat transfer evaluation and demonstrates agreement with prior studies within a standard error below 5%.

Effect of metal foam thickness on the conduction and convection heat transfer for a flat plate with metal foam impinged by multiple jets

ABSTRACT The influence of metal foam thickness on the convection and conduction heat transfer is studied by measuring the local heat transfer of a smooth flat plate, attached and detached metal foamed flat plate under multiple jet impingement conditions. 27 jets of 3 mm diameter are introduced from a jet plate. These jets impinge on a thin stainless steel foil that serves as a targeted plate. The pitch of the jets is 4d in both the spanwise and streamwise directions. The spent fluid is exiting in all directions. The influence of metal foam thickness is investigated for an open-cell aluminum foam with 4, 8, and 12 mm thickness. The porosity of aluminum metal foam is 0.92. The pore density (pores per inch) is 20 PPI. The local heat transfer is measured using infrared thermography and a thin metal foil technique. A smooth flat plate impinged by multiple jets serves as a reference case. The evaluation of the convection and conduction heat transfer offered by the metal foamed flat plate is obtained with the help of the detached foam configuration. The jet diameter-based Reynolds number ranges from 2500 to 15000. The range of the jet to plate spacing covered is 3d to 6d. Depending on the metal foam thickness, the metal foamed flat plate offers additional hydraulic resistance to the jet flow and conduction effect. The additional hydraulic resistance attenuates the convective heat transfer and is represented by attenuation factor (α). For metal foam having 4, 8, and 12 mm thickness, the attenuation factor is around 1.11, 0.99, and 0.64, respectively. The conduction effect offered by metal foam is responsible for the enhancement of the heat transfer. The conduction effect is represented as an enhancement factor (E). For metal foam having 4, 8, and 12 mm thickness, the enhancement factor is around 1.51, 1.58, and 2.32, respectively. The conduction effect presented in the metal foamed flat plate dominates over the attenuation in the convective heat transfer. The overall enhancement offered by 4, 8, and 12 mm metal foamed flat plate is around 1.67, 1.56, and 1.48, respectively.

Fabrication and thermal tests of SS/Cu bimetal plate for the use in the concept of flowing liquid lithium layer in tokamak limiters and divertors

A prospective technology for manufacture of the tokamak divertor target based on the concept of flowing liquid lithium layer is described. A small-size bimetal plate was produced by the hot isostatic pressing diffusion bonding of a thick solid copper base, which serves as a thermal sink, and a thin (0.2 mm) stainless-steel foil, which serves as a corrosion-resistance coating. The mock-up with cooling channels in the copper sink was tested by loading the stainless-steel surface by a high heat flux in two loading modes. First, the absorbed heat flux density was increased step-by step from 0.5 MW/m2 to 11.9 MW/m2. Second, thermocycling (1000 cycles) at an absorbed heat-flux density of about 8 MW/m2 was performed. The mock-up demonstrated acceptable uniformity of the temperature on the surface without spot overheating and good stability in thermal cycling in the range of RT-500 °C. No defects were observed after the tests performed.

Heat transfer characteristics of jet impingement onto the concave surface of a cone

ABSTRACT Heat transfer coefficient measurements for jet impingement onto the concave surface of a cone with apex angles equal to 30° and 70° are reported in this study. Static pressure measurements along the cone surface are also reported which aid in explaining the results from the heat transfer measurements. The conical geometry finds application for the heating of aircraft gas turbine engine nose bullet region which could experience ice formation whenever aircraft operates at higher altitudes. The concave surface of the cone is heated by impinging hot air tapped from the compressor. The heat transfer coefficients, which are significantly different compared to flat surface impingement, and are scarcely available, are reported in this study. The influence of the jet axis coincident with the cone axis and impinging into apex region was studied first. The methodology where a thin stainless-steel foil is heated with a known heat flux by passing electric current through it and then measuring the detailed surface temperature using an infrared thermal camera, was used to compute the wall Nusselt distribution. The Nusselt number variation is presented as a function of nondimensional apex to nozzle spacing (L/D) and the nondimensional axis displacement (O/D). Three different diameter (D equal to 10 mm,14 mm and 20 mm) pipes were used for the concentric impingement case and the Nusselt number distribution was observed not depend on the injection diameter. The jet Reynolds number was varied between 25000 and 82000. The peak Nusselt number values are similar to those for flat plate impingement and do not occur at the cone apex, but at a nondimensional distance between 3.2 and 3.9 for 4.25 < L/D < 10.25 for the 30° cone. The peak Nusselt number values increase by almost 30% with decrease in the L/D from 10.2 to 3.0. Wall static pressure measurements indicated that the peak Nusselt number values occur in regions where the interaction between the incoming and outgoing streams is strongest – these regions occur at distances downstream from the stagnation region toward cone exit. The peak heat transfer coefficient location could not be obtained for the 70° cone, but the measured maximum values are higher by 30–50% compared to those for the 30° case. The jet is able to penetrate further toward the apex of the cone for 70° cone compared to 30° cone shifting the peak heat transfer locations closer to the apex for larger apex angle case. There is insignificant influence of jet diameter on Nusselt number variation for the three diameter values investigated in this study. The influence of displacing the jet axis by a distance equal to half the jet diameter in a direction perpendicular to the cone axis was also studied but detailed measurements were possible only for the 30° cone. Two semi-circular regions, one close to the impingement tube and the other away from the tube, displaying similar heat transfer coefficient behavior were observed. A peak in the Nusselt number occurs in each semi-circular region and the magnitude of the peaks are nearly same and they lie on either side of the peak location observed for the concentric impingement case when the flow geometric parameters are similar for the two cases. The measurements for the 70° cone exhibited all features of the 30° cone but the maximum values were higher by nearly 40% for this case.

Effect of Grain Misorientation and Martensitic Transformation on Surface Roughening Behavior in Thin Austenitic Stainless Steel Foils

Stainless steel thin foils have unlimited applications in the field of microforming industries, making them attractive for use in industrial society. The problem hindering their use is the different mechanical properties that exist between thick

Multiwalled carbon nanotubes synthesis from methane using a stainless steel foils as a catalyst

In this study, a thin stainless-steel foil was used as a catalyst for carbon nanotubes (CNTs) using methane as a carbon source via the chemical vapor deposition (CVD) method. Our results revealed that pre-treatment step of the catalyst plays an important role in CNT formation. In our experiments, a catalyst pre-treatment temperature of 850 oC have been found to facilitate the surface roughness and provide more active nucleation sites for CNTs formation. Multiwalled CNTs with 6 layers, their diameters of 10 – 20 nm and their length of app. 300 nm were grown. This finding might lead to a process for improving the quality of MWCNTs grown on steel foil as catalyst.

Effects of Catalyst Pretreatment on Carbon Nanotube Synthesis from Methane Using Thin Stainless-Steel Foil as Catalyst by Chemical Vapor Deposition Method.

Synthesis of carbon nanotubes (CNTs) was carried out using methane as a carbon source via the chemical vapor deposition (CVD) method. A thin stainless-steel foil was used as catalyst for CNT growth. Our results revealed that pretreatment step of the stainless-steel foil as a catalyst plays an important role in CNT formation. In our experiments, a catalyst pretreatment temperature of 850 °C or 950 °C was found to facilitate the creation of Fe- and Cr-rich particles are active sites on the foil surface, leading to CNT formation. It is noted that the size of metallic particles after pretreatment is closely related to the diameter of the synthesized CNTs. It is interesting that a shorter catalyst pretreatment brings the growth of semiconducting typed CNTs while a longer pretreatment creates metallic CNTs. This finding might lead to a process for improving the quality of CNTs grown on steel foil as catalyst.

Multiwalled carbon nanotubes synthesis from methane using a stainless steel foils as a catalyst

In this study, a thin stainless-steel foil was used as a catalyst for carbon nanotubes (CNTs) using methane as a carbon source via the chemical vapor deposition (CVD) method. Our results revealed that pre-treatment step of the catalyst plays an important role in CNT formation. In our experiments, a catalyst pre-treatment temperature of 850 oC have been found to facilitate the surface roughness and provide more active nucleation sites for CNTs formation. Multiwalled CNTs with 6 layers, their diameters of 10 – 20 nm and their length of app. 300 nm were grown. This finding might lead to a process for improving the quality of MWCNTs grown on steel foil as catalyst.

Uniaxial Tensile Behaviour of 75μm Thick Stainless-Steel Foils

Accurate knowledge about tensile behavior of thin stainless-steel foils at micro/meso scale is of great importance for potential industrial applications. In this work, two 75μm thick AISI 304L and 439 stainless-steel foils were tested under uniaxial tension. Digital image correlation (DIC) based strain measurement method was applied to characterize the plastic deformation of foil specimen. The stress-strain relations of foil specimens were identified from DIC-based strain measurement and compared with the results derived from crosshead displacement. It is found that the applied DIC method can more precisely characterize the mechanical behaviors of foil materials at small size scale. Fracture surface of foil specimens were also characterized. The material microstructures are found have predominant effect on tensile behaviors of foil materials.

A new strain-based method to determine GTN parameters for thin stainless steel foil

In this work, tensile tests were carried out on the 316L foil with a thickness of 0.1mm to calibrate the Gurson–Tvergaard–Needleman (GTN) model. Two calibration methods were compared for calibrating the same test data. The common approach is to use iterative finite element simulations to fit the experimental load-displacement curve. A new strain-based approach, which uses strain data obtained by a Digital Image Correlation (DIC) system, is presented here. It uses a stress-return-mapping algorithm to reconstruct the fracture related state variable, i.e., the accumulated void volume fraction. Fracture is predicted when the critical void fraction is reached at the measured fracture moment. The study shows that the new approach gives similar fracture model parameters compared to the common method, but with significantly higher computational efficiency.

High resolution X-ray spectra of stainless steel foils irradiated by femtosecond laser pulses with ultra-relativistic intensities

We report on the spectra of x-rays emitted from dense plasma generated via irradiation of thin stainless steel foils by ultra-relativistic femtosecond laser pulses (intensities ~3 × 1021 W/cm2). Kinetic modelling was used to estimate electron plasma density and temperature, demonstrating Te ~2.1 keV for Ne ~5 × 1022 cm−3 in the hottest emission region. Thus, it is experimentally demonstrated for the first time that the laser pulse of over 1021 W/cm2 intensity is absorbed neither in the solid density plasma nor in a pre-plasma of a common critical density, but in the matter of so called relativistic critical density.

Optimization of pulsed laser welding process parameters in order to attain minimum underfill and undercut defects in thin 316L stainless steel foils

In this study, the optimization of pulsed Nd:YAG laser welding parameters was done on the lap-joint of a 316L stainless steel foil with the aim of reducing weld defects through response surface methodology. For this purpose, the effects of peak power, pulse-duration, and frequency were investigated. The most important weld defects seen in this method include underfill and undercut. By presenting a second-order polynomial, the above-mentioned statistical method was managed to be well employed to balance the welding parameters. The results showed that underfill increased with the increased power and reduced frequency, it first increased and then decreased with the increased pulse-duration; and the most important parameter affecting it was the power, whose effect was 65%. The undercut increased with the increased power, pulse-duration, and frequency; and the most important parameter affecting it was the power, whose effect was 64%. Finally, by superimposing different responses, improved conditions were presented to attain a weld with no defects.

Deformation in Micro Roll Forming of Bipolar Plate

Micro roll forming is a new processing technology to produce bipolar plates for Proton Exchange Membrane Fuel Cells (PEMFC) from thin stainless steel foil. To gain a better understanding of the deformation of the material in this process, numerical studies are necessary before experimental implementation. In general, solid elements with several layers through the material thickness are required to analyse material thinning in processes where the deformation mode is that of bending combined with tension, but this results in high computational costs. This pure solid element approach is especially time-consuming when analysing roll forming processes which generally involves feeding a long strip through a number of successive roll stands. In an attempt to develop a more efficient modelling approach without sacrificing accuracy, two solutions are numerically analysed with ABAQUS/Explicit in this paper. In the first, a small patch of solid elements over the strip width and in the centre of the “pre-cut” sheet is coupled with shell elements while in the second approach pure shell elements are used to discretize the full sheet. In the first approach, the shell element enables accounting for the effect of material being held in the roll stands on material flow while solid elements can be applied to analyse material thinning in a small discrete area of the sheet. Experimental micro roll forming trials are performed to prove that the coupling of solid and shell elements can give acceptable model accuracy while using shell elements alone is shown to result in major deviations between numerical and experimental results.

Airflow energy harvester of piezoelectric thin-film bimorph using self-excited vibration

The airflow energy harvesters (AFEHs) of piezoelectric Pb(Zr,Ti)O3 (PZT) thin films were developed. Electric power was generated by self-excited vibration of the piezoelectric bimorph cantilevers induced by a continuous airflow. To enhance the vibration in low wind speed, we used very thin stainless-steel (SS) foils with thickness of 20μm as base substrates, and the PZT thin films were deposited on both surface of SS foils by radio-frequency (rf) magnetron sputtering. When the angle of attack (AOA) was 20° and above, stable self-excited vibration was generated at wind speeds larger than 4.5m/s. When the wind speed was 8m/s, the maximum output power reached 36.4μW at the AOA of 20°. From the evaluation of the thickness effect of the base cantilevers, it was confirmed that the thinner substrate reduced not only cut-in wind speed but also maximum output voltage.

Effects of Process Parameters on the Tensile-Shear Strength of Pulsed Laser Welded Thin 316L Stainless Steel Foils

In this research, the parameters of pulsed Nd:YAG laser welding on the lap-joint of a 316L stainless steel foil were optimized through the response surface methodology with the aim of enhancing the tensile-shear strength. For this purpose, the effects of peak power, pulse-width, and frequency were investigated. The results showed that the analysis of welding parameters in the form of a simple combination of pulse energy could not completely predict welding properties, and the above-mentioned statistical method could appropriately be employed to balance the parameters by modeling and presenting a second-order polynomial. In this model, with the increased power and pulse-width, the strength first increased and then it decreased, and its maxima occurred at a power of 260 W and a pulse-width of 3 ms. The most important parameters affecting this model have been found to be power and pulse-width with impacts of 65 and 25%, respectively. In addition, microscopic studies showed that decrease in strength was because of the undercut and lack of penetration.

Influence of turn geometry on turbulent fluid flow and heat transfer in a stationary two-pass square duct

The turbulent flow and heat transfer in a two-pass smooth square duct were studied experimentally and numerically. Four different turn configurations (cases-1, 2, 3, and 4) having various divider and outer turn geometries were considered in this study. A thin stainless steel foil is used as heater and infra-red thermography (IR) technique has been employed to obtain the local temperature distribution on the heated surface for three different Reynolds numbers namely, 25,000, 35,000, and 45,000. In addition, all four cases were investigated numerically using CFD commercial code FLUENT®. A realizable k–ε model with a two-layer near-wall formulation is employed to simulate the turbulent flow and heat transfer field. The numerical result shows that the bend induced secondary flow structure and its effect on local heat transfer distribution varies significantly with different turn configurations. Comparison of averaged Nusselt number and friction factors of various turn configurations reveals that the numerical simulations follows the similar behavior as experimentally observed but the selected turbulence model underpredict the heat transfer augmentation in the bend region. The overall thermal performance of case-3 (sharp 180° bend with circular divider) is better than that of other three cases.

Completion of TF Strand Production and Progress of TF Conductor Manufacture for JT-60SA Project

In the framework of the JT-60SA project, aiming at upgrading the present JT-60U tokamak, Europe, as part of its in-kind contribution within the Broader Approach agreement, will provide the toroidal field (TF) magnet system. For this purpose, Fusion for Energy is committed to procure about 29 km of TF conductor. The TF conductor is cable-in-conduit type and includes 486 strands (2/3 NbTi-1/3 copper) wrapped with a thin stainless steel foil and compacted into a rectangular stainless steel jacket. The procurement is split into two main contracts: one for TF strand manufacturing and the other for TF conductor cabling and jacketing. TF strand manufacture was completed while the TF conductor one is being finished. In the present paper, we draw an overview of both productions emphasizing on the quality control (QC) approaches and on aspects relevant to risk management of the JT-60SA tokamak operation. For the NbTi strand, the complete production overview is provided including extensive statistical considerations on NbTi strand critical performances ( IC, TCS). For the TF conductor, the overview also deals with collected results from acceptance tests and peripheral tests led for consolidating the QC (hydraulic tests, nondestructive examination, full-size sample cold tests in SULTAN facility).