Critical Radius Of Curvature Research Articles

New Method for Determining the Machine-Hand Welding Times Using Ultrasonic Welding Machines with Rotary Sonotrode

The paper presents a new method for determining the machine-hand welding times of synthetic polymer materials using ultrasonic welding machines with rotary sonotrode. The method is based on the claims and observations of W. Möller intended for the clothing industry in the 1990s, according to which there is a spontaneous drop in sewing speed when strongly curved seams are joined, which is due to the possibility of human reactions. The method for determining machine-hand sewing times of curved seams was well accepted in garment production processes. It is used to standardize production time. Using ultrasonic welding machines with rotary sonotrode, the problem of determining the time of ultrasonic joining of curved seams on clothing or technical textiles remained unsolved. That is why is completely new and original model was created, which combines eight technical parameters of ultrasonic welds, eight technological parameters of the production process and seven ergonomic parameters depending on the psychophysical conditions of the workers. The systematic development of the mathematical relationship of all 23 parameters mentioned and the corresponding mathematical expressions for determining and calculating these parameters are presented. These results were also verified by experimental measurements, which show a favourable correlation between the calculated and measured machine hand times. The relationships between the recommended welding speeds, the critical radii of curvature and the number of reactions required according to Möller and the new model are also presented. An analysis of the success in the application of Möller’s and the new model was also performed.

Impact of organic inter-layer dielectric for improvement in mechanical flexibility of self-aligned coplanar in-Ga-Zn-O thin-film transistor

A novel device structure has been suggested to introduce organic inter-layer dielectric (ILD) for improving mechanical flexibility of self-aligned (SA) coplanar In-Ga-Zn-O (IGZO) thin-film transistor (TFT). The SA coplanar TFTs fabricated on poly(ethylene naphthalate) (PEN) substrate showed a high saturation mobility of 11.4 cm 2 /V∙s, low threshold voltage of 0.26 V, steep subthreshold swing of 115 mV/dec, and high on/off current ratio (~10 9 ) at flat state. In the proposed structure, all-oxide gate stacks were defined into an island configuration embedded in the organic ILD, and hence, the mechanical stress applied to the active region could be effectively relieved. To investigate the feasibility of a new device concept, the mechanical properties of the fabricated TFTs were characterized. When the PEN thickness was varied 25 and 50 μm, the critical radius of curvature (R C ) values were estimated to be 1 and 3 mm, respectively, which were superior to those for conventional oxide devices. In addition, the mechanical durability during the cyclic bending test at R C of 5 mm was significantly improved from 20,000 to 70,000 cycles when the PEN film thickness was reduced from 50 to 25 μm. The effects of PEN thickness on the mechanical stability of the SA coplanar TFTs were quantitatively discussed from a view point of surface strain. As a result, robust mechanical bendability of proposed device was confirmed even under harsh deformation conditions. • We fabricated flexible SA coplanar IGZO TFTs employing Zeocoat™ ILD on PEN film. • Effects of the island configuration on mechanical flexibility were investigated. • The device structure using organic ILD is favorable design for stress relaxation. • The PEN film thickness has marked impacts on strain induced on device plane. • Reduction of PEN thickness is effective for enhancing the mechanical durability.

Electro-osmotic instability of concentration enrichment in curved geometries for an aqueous electrolyte

We report that an electro-osmotic instability of concentration enrichment in curved geometries for an aqueous electrolyte, as opposed to the well-known one, is initiated exclusively at the enriched interface (anode), rather than at the depleted one (cathode). For this instability, the limitation of unrealistically high material Peclet number in planar geometry is eliminated by the strong electric field arising from the line charge singularity. In a model setup of concentric circular electrodes, we show by stability analysis, numerical simulation, and experimental visualization that instability occurs at the inner anode, below a critical radius of curvature. The stability criterion is also formulated in terms of a critical electric field and extended to arbitrary (2d) geometries by conformal mapping. This discovery suggests that transport may be enhanced in processes limited by salt enrichment, such as reverse osmosis, by triggering this instability with needle-like electrodes.

Numerical Simulation Method for Failure Pressure of Buried Dented Pipeline

In view of the important influence of mechanical damage on the bearing capacity of buried pipelines, the residual strength of dented pipelines has become a hot issue in the pipeline industry. In this paper, X52 steel grade, commonly used in buried pipelines, is taken as the research object. The material properties are obtained by tensile test. The difference of curvature radius at the tip of the dent is accurately considered. Based on finite element method, the limit depth and the failure pressure of the dented pipelines are studied. Results have shown that the ultimate displacement load increases exponentially with the increase in the radius of curvature. When dent depth is small, the dent will not reduce the failure pressure, no matter it is smooth or sharp. As the dent depth increases, the influence of the radius of curvature at the tip of the dent becomes significant. The critical radius of curvature from sharp dent to smooth dent is analyzed. And the corresponding relationship between it and dent depth is obtained. It is found that when the radius of curvature exceeds 50 mm, the dent depth does not affect the failure pressure of the pipeline. An expression about the two parameters is put forward, providing supplementary suggestions for the depth-based evaluation criterion. This paper affords a strong support for better assessment of dented pipelines.

Effect of Plate Curvature on Blast Response of Structural Steel Plates

In the present work an attempt is made, through simulation studies, to determine the effect of plate curvature on the blast response of a door structure made of ASTM A515 grade 50 steel plates. A door structure with dimensions of 5.142 m × 2.56 m × 10 mm having six different radii of curvatures is analyzed which is subjected to blast load. The radii of curvature investigated are infinity (flat plate), 16.63, 10.81, 8.26, 6.61 and 5.56 m. In the present study, a stand-off distance of 11 m is considered for all the cases. Results showed that the door structure with smallest radius of curvature experienced least plastic deformation and yielding when compared to a door with larger radius of curvature with same projected area. From the present Investigation, it is observed that, as the radius of curvature of the plate increases, the deformation mode gradually shifts from indentation mode to flexural mode. The plates with infinity and 16.63 m radius of curvature have undergone flexural mode of deformation and plates with 6.61 and 5.56 m radius of curvature undergo indentation mode of deformation. Whereas, mixed mode of deformation that consists of both flexural and indentation mode of deformations are seen in the plates with radius of curvature 10.81 and 8.26 m. As the radius of curvature of the plate decreases the ability of the plate to mitigate the effect the blast loads increased. It is observed that the plate with smaller radius of curvature deflects most of the blast energy and results in least indentation mode of deformation. The most significant observation made in the present investigation is that the strain energy absorbed by the steel plate gets reduced to 1/3 rd when the radius of curvature is approximately equal to the stand-off distance which could be the critical radius of curvature.

Coating cellulose nanocrystals on polypropylene and its film adhesion and mechanical properties

In this work, we investigated conditions to deposit cellulose nanocrystal (CNC) films onto polypropylene (PP) by spin coating, and studied the adhesion, mechanical property, and oxygen permeability properties of the CNC-coated PP films. It was found that CNC films maintained proper adhesion on UV ozone-treated PP even when deformed, but cracked when bent beyond a critical radius of curvature or scratched with excessive force. We also exposed CNC films to various forms of mechanical strain in order to determine the CNC films’ strength and durability as a coating under different humidity conditions, and found that the film’s scratch resistance increased with longer exposure to humidity. Additional oxygen permeability tests showed that a thin CNC coating film with a thickness of less than 1 μm on UV ozone-treated PP reduced oxygen permeation by 39%. We conclude that CNC films can be coated simply on hydrophobic PP, and the enhanced gas barrier properties of CNC-coated PP could find application in the food packaging industry.

Molecular Dynamics Simulations of Slip on Curved Surfaces

We present Molecular Dynamics (MD) simulations of liquid water confined within nanoscale geometries, including slit-like and cylindrical graphitic pores. These equilibrium results are used for calculating friction coefficients, which in turn can be used to calculate slip lengths. The slip length is a material property independent of the fluid flow rate. It is therefore a better quantity for study than the fluid velocity at the wall, also known as the slip velocity. Once the slip length has been found as a function of surface curvature, it can be used to parameterise Lattice Boltzmann (LB) simulations. These larger scale simulations are able to tell us about how fluid transport is affected by slip in complex geometries; not just limited to single pores. Applications include flow and transport in nano-porous engine valve deposits and gas shales. The friction coefficient is found to be a function of curvature and is higher for fluid on convex surfaces and lower for concave surfaces. Both concave and convex surfaces approach the same value of the friction coefficient, which is constant above some critical radius of curvature, here found to be 7.4 ± 2.9 nm. The constant value of the friction coefficient is 10,000 ± 600 kg m−2 s−1 , which is equivalent to a slip length of approximately 67 ± 4 nm.

Flexible Solar Cells Using Doped Crystalline Si Film Prepared by Self-Biased Sputtering Solid Doping Source in SiCl4/H2 Microwave Plasma.

We developed an innovative approach of self-biased sputtering solid doping source process to synthesize doped crystalline Si film on flexible polyimide (PI) substrate via microwave-plasma-enhanced chemical vapor deposition (MWPECVD) using SiCl4/H2 mixture. In this process, P dopants or B dopants were introduced by sputtering the solid doping target through charged-ion bombardment in situ during high-density microwave plasma deposition. A strong correlation between the number of solid doping targets and the characteristics of doped Si films was investigated in detail. The results show that both P- and B-doped crystalline Si films possessed a dense columnar structure, and the crystallinity of these structures decreased with increasing the number of solid doping targets. The films also exhibited a high growth rate (>4.0 nm/s). Under optimal conditions, the maximum conductivity and corresponding carrier concentration were, respectively, 9.48 S/cm and 1.2 × 10(20) cm(-3) for P-doped Si film and 7.83 S/cm and 1.5 × 10(20) cm(-3) for B-doped Si film. Such high values indicate that the incorporation of dopant with high doping efficiency (around 40%) into the Si films was achieved regardless of solid doping sources used. Furthermore, a flexible crystalline Si film solar cell with substrate configuration was fabricated by using the structure of PI/Mo film/n-type Si film/i-type Si film/p-type Si film/ITO film/Al grid film. The best solar cell performance was obtained with an open-circuit voltage of 0.54 V, short-circuit current density of 19.18 mA/cm(2), fill factor of 0.65, and high energy conversion of 6.75%. According to the results of bending tests, the critical radius of curvature (RC) was 12.4 mm, and the loss of efficiency was less than 1% after the cyclic bending test for 100 cycles at RC, indicating superior flexibility and bending durability. These results represent important steps toward a low-cost approach to high-performance flexible crystalline Si film-based photovoltaic devices.

Quantification of Protein-Induced Membrane Remodeling Kinetics In Vitro with Lipid Multilayer Gratings.

The dynamic self-organization of lipids in biological systems is a highly regulated process that enables the compartmentalization of living systems at micro- and nanoscopic scales. Consequently, quantitative methods for assaying the kinetics of supramolecular remodeling such as vesicle formation from planar lipid bilayers or multilayers are needed to understand cellular self-organization. Here, a new nanotechnology-based method for quantitative measurements of lipid-protein interactions is presented and its suitability for quantifying the membrane binding, inflation, and budding activity of the membrane-remodeling protein Sar1 is demonstrated. Lipid multilayer gratings are printed onto surfaces using nanointaglio and exposed to Sar1, resulting in the inflation of lipid multilayers into unilamellar structures, which can be observed in a label-free manner by monitoring the diffracted light. Local variations in lipid multilayer volume on the surface is used to vary substrate availability in a microarray format. A quantitative model is developed that allows quantification of binding affinity (K D ) and kinetics (kon and koff ). Importantly, this assay is uniquely capable of quantifying membrane remodeling. Upon Sar1-induced inflation of single bilayers from surface supported multilayers, the semicylindrical grating lines are observed to remodel into semispherical buds when a critical radius of curvature is reached.

Anisotropic bending behaviors and bending induced buckling in single-layered black phosphorus

The bending behavior of single-layered black phosphorus was systematically studied using density functional theory. Graphene, containing a single layer of molybdenum disulfide, was studied by considering changes in the bending strain energies as a function of the radius of the curvature. Bending-induced buckling in single-layered black phosphorus and its bent states were found along a zigzag direction as shown by the critical radius of the curvature. Combing the bending strain energies from first-principle calculations of the corresponding single-wall nanotubes of grapheme, single-layered black phosphorus and single-layered molybdenum disulfide with the strain energy densities using pure bending plate theory and by the introduction of a simple equivalent atomic area, the bending stiffnesses of three kinds of two-dimensional crystals were calculated and found to be in good agreement with experimental and empirical results. We also show that the bending stiffness is 5.336 eV under zigzag bending and 1.251 eV under armchair bending in single-layered black phosphorus. Apparent anisotropic bending behavior was found where high bending stiffness under zigzag bending leads to a buckling phenomenon. With insight into the physical mechanism of the anisotropic bending behavior, electron density distributions in the single-layered black phosphorus and the corresponding armchair (11,0) and zigzag (0,15) black phosphorus nanotubes with a similar curvature radius were further analyzed. We show that the anisotropic bending behavior can be attributed to repulsive phosphorus lone pair interactions, which are stronger under zigzag bending compared with armchair bending. When a critical curvature radius is attained, the hybridized sp 3 orbitals in single-layered black phosphorus will be affected by the lone pairs according to Pauli's exclusion principle. The local equilibrium conditions of the electron clouds are thus disrupted and bending-induced buckling finally occurs.

Abstract 321: A Biomimetic Approach to Developing Antithrombotic Small-Caliber Prosthetic Vascular Grafts

Introduction: Prosthetic grafts smaller than 6 mm in diameter are linked with a high incidence of thrombosis and neointimal hyperplasia. We developed a novel graft material that provides controlled release of nitric oxide (NO), an antithrombotic agent that also promotes endothelialization within the lumen. Our very recent study focused on NO release kinetics from a similar composite that demonstrated controlled NO release for up to 200 d with a total release of 1.03 ± 0.09 μmol/mg. Methods: Grafts were fabricated using an electrospinning process that yields a micro-fibrous web composed of poly(ε-caprolactone) (PCL) . These fibers were doped with NO donor diethylenetriamine diazeniumdiolate (DETA/NO) and embedded within a polydimetheylsiloxane (PDMS) elastomer, which was found to regulate water transport and NO release rate. In vitro studies were tested in PBS at 37 C using a Griess assay to compute NO release. The shape memory properties inherent to this composite were used to form kink resistant acute angles through exposure to specific thermal cycles under strain. Results: NO release was proportional to DETA/NO doping and regulated by PDMS. Our present study revealed that the critical radius of curvature, below which kinks form, is a function of graft wall thickness and that a radii of curvature as small as 6 mm can be achieved using our unique process. The accompanying figure shows a 4 mm diameter graft with 0.8 mm wall thickness formed into a kink-free form with a radius of curvature of 6.7 mm. Conclusions: Incorporation of DETA/NO into a PCL/PDMS composite offers tunable long-term NO release and is a candidate for kink-resistant vascular grafts.

Flexibility and electrical stability of polyester-based device electrodes under monotonic and cyclic buckling conditions

The flexibility and electrical stability of highly conductive and transparent amorphous indium tin oxide (a-ITO) films coated on polyethylene terephthalate and polyethylene naphthalate substrates were investigated by buckling tests with in situ monitoring of the electrical resistance. Monotonic and cyclic loading tests of the ITO/polymer systems were conducted. The results show that monotonic buckling in tension is more critical for electromechanical stability of ITO films than in compression (an increase in electrical resistance was observed at a critical radius of curvature, of ~3 and ~1mm, respectively for both cases investigated). In contrast, cyclic loading tests show that the compression mode is more critical than the tensile mode which may be a result of the residual stress present in the film structure. Failure of the ITO film was caused by buckling-driven delamination observed using scanning electron microscopy after the tests. The presence of residual stress could mean that buckling-driven delamination is the dominant failure mode for ITO/polymer systems under repeated flexing. In general, comparable electromechanical stability was observed in both cases. Investigating the electromechanical response of such material systems is important for polymer substrate selection and life-time prediction of flexible polyester-based electronic devices.

Resonant bend loss in leakage channel fibers

Leakage channel fibers, designed to suppress higher-order modes, demonstrate resonant power loss at certain critical radii of curvature. Outside the resonance, the power recovers to the levels offset by the usual mechanism of bend-induced loss. Using C2 imaging, we experimentally characterize this anomaly and identify the corresponding physical mechanism as the radiative decay of the fundamental mode mediated by the resonant coupling to a cladding mode.

Elastic buckling of elliptical tubes subjected to generalised linearly varying stress distributions

The structural behaviour of elliptical hollow sections has been examined in previous studies under several loading conditions, including pure compression, pure bending and combined uniaxial bending and compression. This paper examines the elastic buckling response of elliptical hollow sections under any linearly varying in-plane loading conditions, including the most general case of combined compression and biaxial bending. An analytical method to predict the elastic buckling stress has been derived and validated against finite element results. The predictive model first identifies the location of the initiation of local buckling based on the applied stress distribution and the section geometry. The critical radius of curvature corresponding to this point is then introduced into the classical formula for predicting the elastic local buckling stress of a circular shell. The obtained analytical results are compared with results generated by means of finite element analysis. The comparisons between the analytical and numerical predictions of elastic buckling stress reveal disparities of less than 2.5% for thin shells and, following an approximate allowance for the influence of shear, less than 7.5% for thick shells.

Improvements of Indium Tin Oxide Film Deposited on Poly(ethylene terephthalate) Substrates by Plasma-Polymerized Hydrogenated Silicon–Carbon–Oxide Buffer Layer

A plasma-polymerized hydrogenated silicon–carbon–oxide (Si–C–O:H) buffer layer was interlaid for improving durability of indium tin oxide (ITO) films on poly(ethylene terephthalate) (PET) substrates. It was demonstrated that this buffer layer efficiently improves the durability of specimens under static and dynamic mechanical bending. Experimental results show that the Si–C–O:H buffer layer only negligibly affects the optical transmission and electrical resistivity of coated specimens. The static bending test revealed that the critical radius of curvature (Rc) is 16.0 mm while it is 22.1 mm for the ITO-coated PET with and without buffer layer. The dynamic bending test at curvature radius of 17.7 mm showed that the ITO-coated PET specimen with buffer layer can tolerate more than 2000 cycles, whereas it is less than 200 cycles without buffer layer. The Si–C–O:H buffer layer can significantly reduce the stress in ITO films during bending and therefore improve the bending durability of ITO films.

Durability under mechanical bending of the indium tin oxide films deposited on polymer substrate by thermionically enhanced sputtering

The emerging demand for flexible display panels has created a demand for coating techniques capable of depositing high-quality transparent conductive coatings (TCOs) on polymeric materials. This study demonstrates indium tin oxide (ITO) films deposited on polyethylene terephthalate (PET) substrates using a thermionic emission (TE) enhanced DC magnetron sputtering system to improve electrical and optical properties under static and dynamic mechanical bending. Experimental results show that the ITO-coated PET specimen prepared with TE and without TE presents an average transmittance in the visible region of the spectrum of 83% and 70%, and an electrical resistivity of 4.5 × 10 −4 and 1.7 × 10 −3 Ω cm, respectively. By contrast, the static bending test revealed that the critical radius of curvature ( R c) is 13.9 and 17.0 mm for the ITO-coated PET with and without TE. The dynamic bending test showed that the ITO-coated PET with TE is durable for more than 1200 cycles, while the corresponding number for the ITO-coated PET without TE is smaller than 50 cycles for the ITO-coated PET without TE. These results evidence that the ITO film deposited using the TE approach exhibits a higher degree of crystallinity and film adhesion than that deposited without TE. TE improves optical and electrical properties of the ITO coatings and their longer durability under mechanical bending.

Kink Instability of a Highly Deformable Elastic Cylinder

When a soft elastic cylinder is bent beyond a critical radius of curvature, a sharp fold in the form of a kink appears catastrophically at its compressed side while the tensile side remains smooth. The critical radius increases linearly with the diameter of the cylinder but remains independent of its material properties such as modulus; the maximum deflection at the location of the kink depends on both the material and geometric properties of the cylinder. The catastrophic dynamics of evolution of the kink depicts propagation of a shear wave from the location of the kink towards the edges signifying that kinking is an elastic response of the material which results in extreme localization of curvature. We have rationalized this phenomenon in the light of the classical Euler's buckling instability in slender elastic rods.

Structural and superconducting properties of melt-grown Y–Ba–Cu–O superconductors

YBa2Cu3O7 (123) samples with varying Y2BaCuO5 (211) concentrations (0 mol%, 20 mol%, 28 mol%, and 50 mol%) were synthesized by the melt-growth process. Microstructural characterizations were done using x-ray diffraction (XRD), optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). It was found that 123 platelet width, crack width between the platelets, and 211 particle size decreased systematically with increasing 211 concentration. TEM study showed that there is a critical radius of curvature (rc ≤ 0.2 μm-0.3 μm) of the 123/211 interface where defects/contrasts of strain field start to appear, and these defects are believed to be responsible for pinning the magnetic flux. Microhardness measurements showed that Vickers hardness (VHN) increases with increasing 211 content. Critical current density (Jc) values obtained from magnetization measurements using a SQUID magnetometer were found to increase in melt-grown samples by the addition of 211 content.

On measuring curvature and electrical diffusion coefficients in anisotropic myocardium: comments on "effects of bipolar point and line simulation in anisotropic rabbit epicardium: assessment of the critical radius of curvature for longitudinal block".

Notion of "curvature" and "propagation perpendicular to the activation front" inherited from electrophysiological theory of isotropic reaction-diffusion media do not apply directly to experimental data taken in uniformly anisotropic myocardium. They apply directly only after the concept of "curvature" is normalized and propagation is made to look perpendicular to activation fronts by rescaling distances to achieve isotropy. Without rescaling, the curvature-dependence of longitudinal propagation speed turns out counter-intuitively to measure transverse intercellular electrical coupling.

RELATIVE STABILITY OF SINGLE GRAPHITE SHEETS OF POSITIVE, NEGATIVE AND ZERO CURVATURE

The relative stability of single graphite sheets of zero, positive and negative curvature is investigated through a simple model where both strain and dangling bond energy are taken into account. Although it is found that flat sheets are always more stable than negatively curved ones, calculations show that above a critical radius of curvature there is a crossover from positive to negative curvature as the more stable geometry for a single sheet. A maximum size for a negatively curved sheet is also predicted. Similarly, positive curvature is found to be energetically favored over zero curvature below some value of the curvature radius and above a certain number of atoms of the sheet. These results are discussed in view of available transmission electron microscopy observations of sp2 amorphous carbon.