Nominal Thickness Research Articles

Microstructure and mechanical properties of thin-walled TA1 titanium pipes fabricated by high-frequency induction welding

High frequency induction welding (HFIW) was effectively employed for the high-speed fabrication of thin-walled TA1 titanium pipes (TWTPs) with a nominal wall thickness of ∼0.6 mm. The microstructure and mechanical properties of TWTPs manufactured under varying welding parameters were investigated. The weld zone (WZ) exhibits a waist shape measuring ∼622 μm in width, and the width of the heat-affected zone (HAZ) spans between 763 and 864 μm. Both the WZ and HAZ are composed of a mixture of coarse serrated α grains with fine acicular and twins, while the BM retains equiaxed grains. This unique microstructure was resulted from the thermal cycling during HFIW, contributing to a notable increase in microhardness within the WZ compared to both the HAZ and the BM. Optimal manufacturing conditions were identified at a welding power of 14.4 kW, a welding speed of 60 m/min, an opening angle of 6°, and a squeeze displacement of 0.2 mm, yielding the TWIP with a tensile strength of ∼307 MPa and tensile elongation of ∼27%. Tensile fracture analysis revealed that failure predominantly occurred within the BM, underlining a ductile fracture mode characterized by pronounced dimple formations. The enhanced mechanical performance of the weld joints can be attributed to the heterogenous microstructure in the WZ, where the presence of large serrated α-grains enhances ductility, and the fine martensite and twins contribute to the high strength.

Compression Molding of Low-Density Polyethylene Matrix/Glass-Fiber-Reinforced Thick Laminates.

Thermoplastic fiberglass was compression molded in the form of thick panels with a nominal thickness of 10 mm and a size of 300 × 300 mm2. A simplified procedure was adopted to speed up the lamination procedure and adapt it to the aim of recycling waste, glass fibers, fabrics, and thermoplastic films. Low density polyethylene was used as a matrix to simplify the laboratory process, but the same procedure can be extended to other thermoplastic film, such as polyamide. The final thermoplastic composite shows unique properties in terms of its repairability, and its performance was improved by increasing the number of repairing repetitions. For this aim, a repairability test was designed in the bending configuration, and three consecutive cycles of bending/repairing/bending were carried out. The static mechanical properties of the final thermoplastic composite were, conversely, low in comparison with traditional fiberglass because of the choice of a polyethylene matrix. The bending tests showed that the maximum strength was lower than 10 MPa and the elastic modulus was less than 1 GPa. Nevertheless, the toughness of the thermoplastic composite was high, and the samples continued to deform under bending without splitting into two halves.

Silk Fibroin Film Decorated with Ultralow FeCo Content by Sputtering Deposition Results in a Flexible and Robust Biomaterial for Magnetic Actuation.

Magnetically responsive soft biomaterials are at the forefront of bioengineering and biorobotics. We have created a magnetic hybrid material by coupling silk fibroin─i.e., a natural biopolymer with an optimal combination of biocompatibility and mechanical robustness─with the FeCo alloy, the ferromagnetic material with the highest saturation magnetization. The material is in the form of a 6 μm-thick silk fibroin film, coated with a FeCo layer (nominal thickness: 10 nm) grown by magnetron sputtering deposition. The sputtering deposition technique is versatile and eco-friendly and proves effective for growing the magnetic layer on the biopolymer substrate, also allowing one to select the area to be decorated. The hybrid material is biocompatible, lightweight, flexible, robust, and water-resistant. Electrical, structural, mechanical, and magnetic characterization of the material, both as-prepared and after being soaked in water, have provided information on the adhesion between the silk fibroin substrate and the FeCo layer and on the state of internal mechanical stresses. The hybrid film exhibits a high magnetic bending response under a magnetic field gradient, thanks to an ultralow fraction of the FeCo component (less than 0.1 vol %, i.e., well below 1 wt %). This reduces the risk of adverse health effects and makes the material suitable for bioactuation applications.

Examination of nonideal film growth in batch atomic layer deposition for plasma-resistant coatings

Atomic layer deposition (ALD) can be used to fabricate protective coatings including moisture barrier layers for organic light emitting diodes, anticorrosion layers for photoelectrodes, and plasma-resistant coating for semiconductor manufacturing equipment, which necessitates the deposition of large and thick ALD films via batch ALD. However, batch ALD for the fabrication of large-area and thick coatings exhibits nonideal film growth, a phenomenon that cannot solely be explained by transient concentration distribution within the deposition chamber. This paper describes the application of precursor “exposure” (in the unit of Langmuir, or Pa s), defined as the integral of concentration over time, as a metric to assess the growth per cycle (GPC) distribution under nonideal ALD conditions, demonstrating that the local GPC correlates well with the cumulative precursor exposure at that site. Consequently, this measure can effectively predict the nonuniformity (NU) distribution of film thickness and facilitate the determination of optimal operating conditions that ensure maximal uniformity of exposure. Under this condition, the intrafilm NU of ALD-grown Al2O3 film (nominal thickness 300 nm) was reduced to 1.2%, and the interfilm NU is diminished to as low as 3.3%. These values represent reductions of 40% and 45%, respectively, compared to the NU levels observed under nonideal conditions (insufficient trimethylaluminum, TMA exposure downstream). The plasma etch rate of ALD-deposited films is merely 4.3 nm/min, representing a reduction of one-half compared to films deposited under nonideal conditions (9.8 nm/min) with overload TMA exposure downstream leading to chemical vapor deposition-like reactions.

Anisotropic piezomagnetic behavior of wire and arc additively manufactured low carbon steel

The objective of this study is to investigate the piezomagnetic behavior corresponding to the mechanical properties of a low-carbon steel fabricated by wire arc additive manufacturing (WAAM) under tensile stress. WAAM rectangular tubes with a nominal thickness of 4 mm were fabricated with ER70S-6 wires using a continuous path with single way stacking between layers. Tests were carried out on WAAM steel specimens with three different orientations relative to the deposition direction extracted from rectangular tubes, and the evolutions of magnetic field around the specimens were recorded. The variation characteristics of piezomagnetic response at different loading stages were analyzed, highlighting the anisotropic nature of the piezomagnetic field evolution. The internal correlation between piezomagnetic field and tensile stress was explored. It is found that the piezomagnetic behavior of WAAM steel during the tensile process corresponds to the mechanical response. The Villari reversal points can be used to predict the yield strength and tensile ultimate strength of WAAM steel, and the area of the magnetic field-stress curve may be a measure of the ductility of WAAM steel. The theory of microscopic magnetic domains and the constitutive relation of ferromagnetic materials considering magnetocrystalline anisotropy were used to explain the experimental results. This study provides new insights into the anisotropic piezomagnetic properties of WAAM steel, offering potential applications in non-destructive evaluation of mechanical performance.

Thermally Active Medium-Density Fiberboard (MDF) with the Addition of Phase Change Materials for Furniture and Interior Design.

No matter where we reside, the issue of greenhouse gas emissions impacts us all. Their influence has a disastrous effect on the earth's climate, producing global warming and many other irreversible environmental impacts, even though it is occasionally invisible to the independent eye. Phase change materials (PCMs) can store and release heat when it is abundant during the day (e.g., from solar radiation), for use at night, or on chilly days when buildings need to be heated. As a consequence, buildings use less energy to heat and cool, which lowers greenhouse gas emissions. Consequently, research on thermally active medium-density fiberboard (MDF) with PCMs is presented in this work. MDF is useful for interior design and furniture manufacturing. The boards were created using pine (Pinus sylvestris L.) and spruce (Picea abies L.) fibers, urea-formaldehyde resin, and PCM powder, with a phase transition temperature of 22 °C, a density of 785 kg m-3, a latent heat capacity of 160 kJ kg-1, a volumetric heat capacity of 126 MJ m-3, a specific heat capacity of 2.2 kJ kgK-1, a thermal conductivity of 0.18 W mK-1, and a maximum operating temperature of 200 °C. Before resination, the wood fibers were divided into two outer layers (16%) and an interior layer (68% by weight). Throughout the resination process, the PCM particles were solely integrated into the inner layer fibers. The mats were created by hand. A hydraulic press (AKE, Mariannelund, Sweden) was used to press the boards, and its operating parameters were 180 °C, 20 s/mm of nominal thickness, and 2.5 MPa for the maximum unit pressing pressure. Five variants of MDF with a PCM additive were developed: 0%, 5%, 10%, 30%, and 50%. According to the study, scores at the MOR, MOE, IB, and screw withdrawal resistance (SWR) tests decreased when PCM content was added, for example, MOE from 3176 to 1057 N mm-2, MOR from 41.2 to 11.5 N mm-2, and IB from 0.78 to 0.27 N mm-2. However, the results of the thickness swelling and water absorption tests indicate that the PCM particles do not exhibit a substantial capacity to absorb water, retaining the dimensional stability of the MDF boards. The thickness swelling positively decreased with the PCM content increase from 15.1 to 7.38% after 24 h of soaking. The panel's thermal characteristics improved with the increasing PCM concentration, according to the data. The density profiles of all the variations under consideration had a somewhat U-shaped appearance; however, the version with a 50% PCM content had a flatter form and no obvious layer compaction on the panel surface. Therefore, certain mechanical and physical characteristics of the manufactured panels can be enhanced by a well-chosen PCM addition.

Investigations of particle-process-part quality relationships in electron beam melting

Electron beam melting is a powder bed fusion process capable of manufacturing parts from a variety of high-temperature alloys. Given that the process relies on feedstock recycling for process economics, understanding process-part quality relationships is critical. This work investigates process-part quality relationships in terms of the internal and external defects and component microstructure relative to a feedstock subjected to 33 build cycles without replacement. To accomplish this, a volume of fluid mesoscale model consisting of three different powder distributions were considered: (1) Monomodal; (2) As-measured; and (3) Irregular. Particle morphology was characterized using shape factors examined via optical microscopy. To approximate the particle shapes in three-dimensions, a method is presented that utilizes a binarized domain to define low frequency, macroscale particle “base” shapes implicitly and is thus not restricted to starlike particles. The discrete element method was also used to investigate velocity distributions and packing densities of the as-measured and irregular particles with respect to deviations in the nominal layer thickness of 50 μm. In general, beam power and scan speed were found to have an appreciable effect on microstructure formation and surface roughness. Finally, correlations were found between specific classifications of irregular particles and lack of fusion defect formation.Graphical abstractOverview of the discrete element method simulation domain for the electron beam melting powder bed fusion process

Perpendicular magnetization switching of RuO2(1 0 0)/[Pt/Co/Pt] multilayers

Current-induced perpendicular magnetization switching holds great potential for high-density magnetic storage technology. We report the growth of perpendicularly magnetized [Pt/Co/Pt] multilayers on a collinear altermagnet RuO2(100) thin films. The current-induced effective magnetic field was determined through anomalous Hall effect loop measurements with current applied along the [010] or [001] direction of RuO2(100). Magnetization switching was successfully achieved with the assistance of an in-plane magnetic field. Furthermore, by adjusting the nominal top Pt thickness of the [Pt/Co/Pt] multilayers, we could change the polarity of the current-induced magnetization switching, demonstrating an effective manipulation of spin polarization direction in RuO2/[Pt/Co/Pt]. These results provide a practical approach to the development of perpendicular magnetic devices based on RuO2 and have advanced the study of spin-splitting altermagnets.

Laser Welding of ARMOX 500T Steel.

The article describes the results of the study on laser welding of armor plates with a nominal thickness of 3.0 mm. The plates were made of Armox 500T steel characterized by a hardness of up to 540 HB, a minimum yield strength of 1250 MPa, an ultimate strength of up to 1750 MPa, and an elongation A5 minimum of 8%. The laser used for the welding tests was a solid state Yb:YAG laser. The influence of basic parameters such as laser output power, welding speed, and focal plane position on the weld geometry was determined during bead-on-plate welding tests. The optimal conditions for butt joint welding were determined, and the test joints were subjected to mechanical and impact tests, metallographic analysis, and hardness measurements. It has been shown that it is possible to laser weld Armox 500T armor plates, and at the same time it is possible to provide high quality butt joints, but this requires precise selection of welding parameters. A decrease in HAZ hardness of about 22-35% in relation to the hardness of the base material, ranging from 470 to 510 HV0.2, was found. The ultimate tensile strength of the test joints was approx. 20% lower than the Armox 500T steel. The bending tests revealed the low plasticity of the tested joints because the bending angle was just 25-35°. The results of Charpy V-notch test revealed that the impact toughness of the weld metal at -20 °C was approx. 30% lower than at room temperature.

Properties of Ti films produced on atomically smooth GaAs substrates by magnetron sputtering

In this study, the morphology and crystallographic properties of thin titanium (Ti) films grown on atomically smooth gallium arsenide (GaAs) substrates are examined. The films were grown by direct current magnetron sputtering in an argon (Ar) flow. The surface is found to be atomically smooth with steps up to 0.1 nm in height and a morphology close to that of the Ti film substrate with nominal thicknesses of 5 and 10 nm. Increasing the film thickness to 60 nm leads to a noticeable surface reconstruction, associated with the formation of clusters up to 16 nm in height. As per X-ray diffraction studies, all films show a crystal structure of the α-Ti phase. In this case, an increase in the crystallite size from 7 to 20 nm and an increase in the film nominal thickness from 5 to 60 nm are also typical. Based on atomic force microscopy analysis, a change is observed in surface morphology. When the film thickness increases from 10 to 60 nm, clusters are formed on the Ti film surface, measuring 1 µm in diameter and 16 nm in height.

Improved Selectivity and Stability in Methane Dry Reforming by Atomic Layer Deposition on Ni-CeO2-ZrO2/Al2O3 Catalysts.

Ni can be used as a catalyst for dry reforming of methane (DRM), replacing more expensive and less abundant noble metal catalysts (Pt, Pd, and Rh) with little sacrifice in activity. Ni catalysts deactivate quickly under realistic DRM conditions. Rare earth oxides such as CeO2, or as CeO2-ZrO2-Al2O3 (CZA), are supports that improve both the activity and stability of Ni DRM systems due to their redox activity. However, redox-active supports can also enhance the undesired reverse water gas shift (RWGS) reaction, reducing the hydrogen selectivity. In this work, Ni on CZA was coated with an ultrathin Al2O3 overlayer using atomic layer deposition (ALD) to study the effects of the overlayer on catalyst activity, stability, and H2/CO ratio. A low-conversion screening method revealed improved DRM activity and lower coking rate upon the addition of the Al2O3 ALD overcoat, and improvements were subsequently confirmed in a high-conversion reactor at long times onstream. The overcoated samples gave an H2/CO ratio of ∼1 at high conversion, much greater than uncoated catalysts, and no evidence of deactivation. Characterization of used (but still active) catalysts using several techniques suggests that active Ni is in formal oxidation state >0, Ni-Ce-Al is most likely present as a mixed oxide at the surface, and a nominal thickness of 0.5 nm for the Al2O3 overcoat is optimal.

Improving the beam quality of the low-energy muon beamline at Paul Scherrer Institute: Characterization of ultrathin carbon foils

The low-energy muon (LEM) beamline at the Paul Scherrer Institute currently stands as the world’s only facility providing a continuous beam of low-energy muons with keV energies for conducting muon spin rotation experiments on a nanometer depth scale in heterostructures and near a sample’s surface. As such, optimizing the beam quality to reach its full potential is of paramount importance. One of the ongoing efforts is dedicated to improving the already applied technique of single muon tagging through the detection of secondary electrons emerging from an ultrathin carbon foil. In this work, we present the results from installing a thinner foil with a nominal thickness of 0.5 μg cm−2 and compare its performance to that of the previously installed foil with a nominal thickness of 2.0 μg cm−2. Our findings indicate improved beam quality, characterized by smaller beam spots, reduced energy loss and straggling of the muons, and enhanced tagging efficiency. Additionally, we introduce a method utilizing blue laser irradiation for cleaning the carbon foil, further improving and maintaining its characteristics. Published by the American Physical Society 2024

Graphite foils as potential skin and epithelium dosimeters at therapeutic photon energies

This work builds upon a prior study, examining the dosimetric utility of pencil lead and thin graphitic sheets, focusing upon the measurement of skin doses within the mammographic regime. In recognizing the near soft-tissue equivalence of graphite and the earlier-observed favourable thermoluminescence yield of thin sheets of graphite, this has led to present study of 50 μm thick graphite for parameters typical of external beam fractionated radiotherapy and skin dose evaluations. The graphite layers were annealed and then stacked to form an assembly of 0.5 mm nominal thickness. Using a 6 MV photon beam and delivering doses from 2- to 60 Gy, irradiations were conducted, the assembly first forming a superficial layer to a solid water phantom and subsequently underlying a 1.5 cm bolus, seeking to circumvent the build-up to electronic equilibrium for skin treatments. Investigations were made of several dosimetric properties arising from the thermoluminescence yield of the 50 μm thick graphite slabs, in particular proportionality and sensitivity to dose. The results show excellent sensitivity within the dose range of interest, the thermoluminescence response varying with increasing depth through the stacked graphite layers, obtaining a coefficient of determination of 90%. Acknowledging there to be considerable challenge in accurately matching skin thickness with dose, the graphite sheets have nevertheless shown considerable promise as dosimeters of skin, sensitive in determination of dose from the surface of the graphite through to sub-dermal depth thicknesses.

Characterizing oxidation, thickness, and composition of metallic glass thin films with combined electron probe microanalysis and X-ray photoelectron spectroscopy

Metallic glass thin films (MGTFs) are a recently developed class of alloy coatings with potential applications ranging from biomedical devices to electrical components. Their tribological performance in service conditions is dictated by MGTF bulk composition but can be limited by the native oxide surface that inevitably forms upon exposure to atmosphere. Surface oxidation, thickness, and composition of ZrCuNiAl MGTFs were characterized using a combination of X-ray photoelectron microscopy (XPS) and electron probe microanalysis (EPMA). MGTF samples with nominal thicknesses of 50, 500, and 1500 nm were sputtered onto Si and SiN wafer substrates within a high vacuum deposition chamber and their amorphicity was confirmed by X-ray diffraction. XPS depth profiling identified the thin film composition and showed that the surface oxide was dominated by a mixed layer of mostly ZrO2, a little oxidized Al, and some metallic Zr. EPMA X-ray intensities were acquired as a function of beam energy to excite characteristic X-rays from different depths of the MGTFs and reconstructed using open-source thin film analysis software BadgerFilm, to determine the composition and thickness of sample layers. EPMA results constrain the composition to be Zr54Cu29Al10Ni7 within 0.7 at. % variation and total thicknesses to be 49, 470, and 1546 nm. Using the oxide composition identified from XPS depth profiling as an input for BadgerFilm analysis, EPMA results indicate the surface oxidation layer on each of the thin film samples was 6.5 ± 1.1 nm thick and uniform across a 0.25 mm region of the film.

Nanometric determination of the thickness of aqueous samples for accurate molar absorption coefficients of water-soluble molecules in the mid-infrared region

Absorption spectra of aqueous samples measured by transmission need to be acquired using very thin cells (5–50 μm) when targeting the mid-infrared (mid-IR) region due to the strong background absorbance of liquid water. The thickness of the cell used controls the pathlength of the light through the sample, a value needed to transform absorption spectra into molar absorption coefficient spectra, or to determine solute concentrations from absorption spectra. The most accurate way to determine the thickness of an empty cell (i.e., filled with air) is from the period of an interference pattern, known as interference fringes, that arises when the cell is placed perpendicular to the path of light in the spectrometer. However, this same approach is not directly applicable to determine the thickness of a cell filled with an aqueous solution, due partially to the smaller amplitude of the interference fringes but fundamentally caused by its complex waveform, with a wavenumber-dependent oscillation period. Here, using Fresnel equations, we derived analytical expressions to model interference fringes in absorption spectra obtained by transmission, which are also valid for aqueous samples. We also present a novel Fourier-based analysis of the interference fringes that, in combination with the derived analytical expressions, allowed us to determine the pathlength of aqueous samples with an error below ∼ 50 nm. We implemented this novel approach to analyze interference fringes as a Live Script running in the software Matlab. As an application, we measured the absorption spectra of a 97 mM solution of MES buffer at pH 3.4 and pH 8.4 using cells of various nominal thicknesses (6, 25 and 50 μm), whose actual thicknesses were determined using the present approach. The derived molar absorption coefficient spectrum for both the acidic and basic forms of MES were virtually identical regardless of the cell, indicating that the determined thicknesses were likely very accurate. These results illustrate the utility of the present methodology in obtaining accurate molar absorption coefficient spectra of water-soluble molecules in the mid-IR region.

The investigation of thickness-dependent mono-fractal, optical and optoelectronics properties of sputtered silver thin film for silicon solar cell

Here we report, the room temperature deposition of silver (Ag) thin films on silicon, glass and silicon solar cell substrates by magnetron sputtering. The effect of thickness on the deposited thin films and their morphological, fractal, optical and solar cell parameters have been extensively investigated. AFM results show that the Ag thin films are composed of different-size of nano-grains and the grain size increases with increasing thickness. Mono-fractal parameters, namely fractal dimension (Df) and Hurst exponent (H), were determined from the power spectral density function. X-ray photoelectron spectroscopy studies indicate that the deposited samples exhibit the presence of oxidation state of Ag (0) in thin films, confirming the stable structure. The optical analysis shows that the transmittance of the deposited thin films decreases with increasing thickness, on the other hand, the silver thin film with thickness of 20 nm shows surface Plasmon resonance (SPR) at 436 nm. Current-voltage (I–V) curves were measured in dark and under illumination mode at standard testing conditions, i.e., 300K, 1000 W/m2 and 1.5 AM global using a solar simulator. These measurement studies indicate that thicknesses are effectively impacts on photovoltaic performance. The calculated values of change in solar efficiency (Δη) are 0.26, −0.20, −0.76 and −6.88 % for thin films with nominal thickness 0.5, 1, 2 and 20 nm respectively.

Reduction of oxygen content in laser powder bed fusion process atmosphere – Effects on stochastic defect formation and mechanical properties

Stochastic defects in materials manufactured via laser powder bed fusion (LPBF) can severely compromise mechanical performance and are challenging to predict and detect, thus motivating the development of defect mitigation strategies. Particle oxidation is a factor well-known to generate defects by disturbing melt pool dynamics. If the particles are spatters, additional disturbances increase the likelihood of defect formation. In this study, restricting oxygen content in the process atmosphere to 50 ppm is investigated to minimize stochastic spatter-induced defects and improve the mechanical properties of Hastelloy X. Specimens were manufactured under this condition at two nominal layer thicknesses, analyzed for internal defects, and mechanically tested. Contrary to expectations, reducing the oxygen content did not prevent spatter-induced defect formation; rather, it could exacerbate the formation of more numerous and larger defects. Nevertheless, this tighter control of the process atmosphere led to significant microstructural refinement, which, when combined with sparse defects, resulted in improved fatigue performance. Despite the inherent ductility of Hastelloy X, the presence of abundant defects significantly larger than the microstructural characteristic size proved detrimental to fatigue performance. Notably, the occurrence of defects exhibited considerable variation across the build area, contributing to scatter in fatigue data. However, quantitative analysis of in-situ monitoring data enabled prediction of variability in defect content and mechanical performance.

THREE-DIMENSIONAL MODEL OF EQUIVALENT ROLL GAP OF CVC MILL UNDER CONDITIONS OF ROLL CROSSING AND NO LOAD

Traditional roll technologies focus solely on the contour of the roll gap at the outlet under ideal conditions. However, upon roll crossing, the three-dimensional distribution of the deformation zone becomes asymmetrical, leading to an adverse impact on the rolling pressure in the deformation zone. To study the screw-down load deviation of plate mills, it is necessary to accurately calculate the equivalent three-dimensional roll gap in the deformation zone under roll-crossing conditions. In this paper a model for calculating the equivalent three-dimensional roll gap under the conditions of roll crossing and no load was established based on the method of the coordinate nonlinear transformation of the spatial rectangular coordinate system. Based on this model, the influences of roll-crossing angles and translation parameters on the symmetry of the equivalent three-dimensional roll gap were analyzed. The distribution of the three-dimensional equivalent roll gap was calculated with different roll lengths, roll radii, and the roll gap’s nominal thickness. The intuitive contour map reveals that under the same condition of crossing angle and translation parameters, the larger the roll length and roll radii and the smaller the roll gap’s nominal thickness are, the greater the influence of the roll crossing on the asymmetrical distribution of roll gap is. It put forward a quantitative calculation method for evaluating the symmetrical distribution of the roll gap, and the calculation results can provide the equivalent roll profile for the roll-deformation model.

Air entrainment by a hydrofoil in a high-speed water flow for design of bubbly drag reduction ships

We have investigated the flow behavior around a hydrofoil bubble generator in a high-speed channel flow up to 10 m/s for the first time to understand the air entrainment characteristics of this hydrofoil device caused purely by the inertia effect of water flow. This study is motivated by our previous success in achieving ship drag reduction for full-scale vessels (Kumagai et al., 2015). Depending on the water flow velocity U and the angle of attack of the hydrofoil α, three different major patterns were identified: continuous generation of dispersed bubbles, intermittent formation of an air cavity, and steady formation of a super air cavity that stretched behind the hydrofoil. The transition from the dispersed bubble state to the air cavity formation regime is explained theoretically using the equation of bubble motion coupled with a potential flow analysis. The air volume flow rate increased linearly with U, and its slope was steeper in the dispersed bubble state than in the air cavity formation regime. The highest air flow rate was realized at U = 9 m/s, which corresponds to the nominal air layer thickness at ta = 4.1 mm, and reaches the feasible range for realization of bubbly drag reduction for a long ship hull.

Asymptotic analysis of elastoplastic bifurcation of cylindrical shells with thickness variation under axial compression

This paper investigates the elastoplastic bifurcation of axially compressed cylindrical shells, featuring three axisymmetric thickness patterns, i.e., periodic, attenuated, and stepped thickness variations. Two asymptotic methods are utilized to derive the analytical solutions for the critical buckling load. The elastoplastic buckling load can be expressed as a function of the Coefficient of Thickness Variation (CTV) and the buckling load of the perfect shell with nominal uniform thickness. It is found that the derived solutions exhibits good agreement with existing elastic buckling solutions when considering solely the elastic scenario. In this work, a total of three thickness patterns are considered, and it is observed that the newly derived solutions using different methods lead to some disparities in the quadratic terms of CTV. In the end, comparative analysis and discussion are conducted to explore the influence of material properties and thickness variations on the bifurcation buckling of shells.