Wide Sheet Research Articles

Bauschinger-Like Effect of AZ31 Magnesium Alloy Wide Sheet During the Straightening Process

The Bauschinger-like effect, which showed up in the straightening process of the AZ31 magnesium alloy wide sheet, was investigated through the multi-pass discrete three-point bending–unloading–bending (BUB) experiments. The stress variable, anisotropy, and asymmetry of tension and compression on the straightening process were corresponding to the Bauschinger-like effect. The Bauschinger-like effect in the initial, intermediate, and end of the straightening process was dominated by the twinning, detwinning, and dislocation induced by pyramidal slip, respectively. Also, they were responsible for the transformation of the Bauschinger stress parameter (BSP) and Bauschinger energy parameter (BEP). Later, the anisotropic nonlinear kinematic hardening model (ANK model) to describe the Bauschinger-like effect was optimized and simplified.

Ultra‐Low Molecular Weight Photoswitchable Hydrogelators

AbstractTwo photoswitchable arylazopyrozoles form hydrogels at a concentration of 1.2 % (w/v). With a molecular weight of 258.28 g mol−1, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Photoswitching of the E‐ to the Z‐form by exposure to 365 nm light results in a macroscopic gel→sol transition; nearly an order of magnitude reduction in the measured elastic and loss moduli. In the case of the meta‐arylazopyrozole, cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E‐gel state narrow to 13±2 nm upon photoswitching to the predominantly Z‐solution state. Photoswitching for meta‐arylazopyrozole is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a rhodamine B dye encapsulated in gels formed by the arylazopyrozoles is accelerated more than 20‐fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light‐controlled cargo release.

Ultra-Low Molecular Weight Photoswitchable Hydrogelators.

Two photoswitchable arylazopyrozoles form hydrogels at a concentration of 1.2 % (w/v). With a molecular weight of 258.28 g mol-1 , these are the lowest known molecular weight hydrogelators that respond reversibly to light. Photoswitching of the E- to the Z-form by exposure to 365 nm light results in a macroscopic gel→sol transition; nearly an order of magnitude reduction in the measured elastic and loss moduli. In the case of the meta-arylazopyrozole, cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-solution state. Photoswitching for meta-arylazopyrozole is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a rhodamine B dye encapsulated in gels formed by the arylazopyrozoles is accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.

Laser processing over a large area by wavefront-controlled scanning

In the processing of laser materials, the scanning area is limited by the extent to which the laser focus can be maintained within a plane. In order to increase the processing area, one has to enlarge the size of the laser focal spot, and, therefore, reduce the peak intensity and spatial resolution. In this paper, the authors report on a method that extends the processing area by controlling the wavefront of a laser beam using adaptive optics. By adding Zernike modes to the laser beam wavefront, the axial (along the beam propagation direction) location of the focal spot can be tuned within a range larger than the confocal length (two times the Rayleigh length), while the lateral spot size (and, thus, peak intensity and resolution) is maintained throughout the tuning range. A wave propagation model that simulates the propagation of a wavefront-controlled beam is used to compare with the experimental results, which are also confirmed by Zemax calculation. Laser trepanning of circular holes with consistent size on a wide polypropylene sheet is demonstrated. This work shows the potential of tailoring the phase of a laser beam for improving the accuracy and throughput in large-area laser processing of materials.

Energy Transfer by Turbulent Dissipation in Glacial Conduits

Water flow within and beneath glaciers and ice sheets influences ice dynamics and is relevant for practical applications such as modeling outburst floods from mountain glaciers. The most general models for glacial hydrologic conduits include an energy equation, wherein a heat transfer coefficient controls the rate at which heat generated by mechanical energy dissipation is transferred to conduit walls, producing melt. Previous models employ heat transfer coefficients derived for engineering heat transfer problems, where heat is transferred between the walls of a conduit and a flowing fluid that enters the conduit at a temperature different from the wall temperature. These heat transfer coefficients may not be appropriate for glacial hydrologic conduits in temperate ice, where the water and conduit walls (ice) are at almost the same temperature. We revisit the energy transport equations that provide a basis for the derivation of heat transfer coefficients and highlight the distinctions between the heated walls and dissipated energy heat transfer cases. We present computational results for both cases across a wide range of Reynolds numbers in circular conduit and sheet geometries. We show that the heat transfer coefficients for transfer of heat generated by mechanical energy dissipation to circular conduit walls are smaller than calculated using the Dittus‐Boelter correlation by approximately a factor of 2. However, heat transfer coefficients are higher for flow through a wide sheet at , highlighting the influence of noncircular geometries on heat transfer in englacial conduits and subglacial drainage systems.

Experimental Analysis of Limited Distance Effects on Self Induced Blow Off and Heat Transfer in Upward Flame Spread Over Thin Fabric Fuels

Most previous work concentrated on the one-sided upward flame spread under limited conditions. However, few investigations have studied the effects of limited distance between wall and fuel surface on two-sided upward flame spreading. In this paper, a series of upward flame spread experiments were conducted using 0.65 mm thick, 130 cm tall and 4.0 cm wide flax fabric sheets with various limited distance of 1.0 cm–3.5 cm. The flame shape, flame length, flame standoff distance, pyrolysis spread rate and surface temperature were measured and analyzed. An unexpected but interesting behavior of one-sided flame blow off was observed in upward flame spread. When limited distance is no more than 1.5 cm, the one-sided flame blow off behavior occurs on unlimited side, whereas this behavior occurs on limited side for 2.0 cm–3.5 cm limited distance. This result could be qualitatively explained by Damkohler number Da, which could be characterized by two parameters of induced flow velocity and heat flux received by virgin surface. Moreover, the maximum flame length, steady flame length, maximum spread rate and steady spread rate first increase and then decrease as the limited distance. This non-monotonicity trend is determined by heat flux profiles in the preheating zone, which is due to the combined limited distance effects of restricting oxygen supply, chimney effect and wall radiation. The surface temperature profile ahead of pyrolysis front is used to qualitatively describe the heat flux received by virgin surface. The results in this paper are essential for better understanding of self induced flame blow off mechanism and upward flame spread under limited distance conditions.

Theoretical research on branch-guide energy coupler for wide bandwidth terahertz relativistic sheet electron beam TWTs

Branch-guide energy couplers can be used in the terahertz relativistic sheet electron beam traveling wave tubes (THz-RSBTWT) for high and high frequency microwave radiations. To analyze this type of coupler, a new method based on the phase superposition principle was put forward in this paper. A physical model was developed, which is applicable no matter the coupler width is large or small. The general distance relationship between the branches was derived and a rapid design formula was obtained, which can help design energy coupler with arbitrary coupling coefficient.

Quantification of the Severity of Ridging in Ferritic Stainless Steel Sheets Using a Profilometric Technique

A new method to quantify the ridging phenomenon in ferritic stainless steels has been developed based on the evaluation of surface profiles after the tensile elongation of 100 mm wide sheet specimens. The ridging components of the surface profiles are extracted by a tailored spline filtering procedure. A ridging index is proposed to quantify the severity of the surface defect based on surface profile height and spacing parameters. The procedure is independent of the type of profilometer used as long as unfiltered raw profiles can be recorded. The reproducibility of the measurement method and its correlation with the visual assessment of strained specimens is discussed.

Study of the Structure and Properties of Long-Length Wide Sheets of Aluminum Alloy V95pchT2

A comprehensive research was conducted to study long-length (> 10 m), wide (> 2 m), 7 mm thick sheets of high-strength aluminum alloy V95pch after quenching and “softening” aging according to T2 temper conditions. It is shown that a homogeneous (length- and widthwise) structure, typical for such type of semi-finished products made of alloy V95pch, temper T2, can be sustained in wide, long-length sheets measuring 7 × 2300 × 12,000 mm, produced using advanced equipment installed at the JSC “AMR.” This results in achieving a level of mechanical, corrosion, and long-term performance characteristics necessary for manufacturing the components of the internal airframe structure of future advanced aircraft.

Self-Assembly of Minimal Peptoid Sequences.

Peptoids are biofunctional N-substituted glycine peptidomimics. Their self-assembly is of fundamental interest because they demonstrate alternatives to conventional peptide structures based on backbone chirality and beta-sheet hydrogen bonding. The search for self-assembling, water-soluble “minimal” sequences, be they peptide or peptidomimic, is a further challenge. Such sequences are highly desired for their compatibility with biomacromolecules and convenient synthesis for broader application. We report the self-assembly of a set of trimeric, water-soluble α-peptoids that exhibit a relatively low critical aggregation concentration (CAC ∼ 0.3 wt %). Cryo-EM and angle-resolved DLS show different sequence-dependent morphologies, namely uniform ca. 6 nm wide nanofibers, sheets, and clusters of globular assemblies. Absorbance and fluorescence spectroscopies indicate unique phenyl environments for π-interactions in the highly ordered nanofibers. Assembly of our peptoids takes place when the sequences are fully ionized, representing a departure from superficially similar amyloid-type hydrogen-bonded peptide nanostructures and expanding the horizons of assembly for sequence-specific bio- and biomimetic macromolecules.

Pulsed Magnet Design and Fabrication for Generating Background Magnetic Field in Discharge Current-Based Forming

Discharge current-based forming (DCF) is a forming method that directly loads a pulse current into two parallel placed metal sheets connected in series, and the mutually exclusive electromagnetic force between them causes the sheets to be deformed. Compared with the electromagnetic forming (EMF), this method can improve the current density for the low-conductivity sheets. However, the forming height of the sheets is extremely poor due to the weak magnetic field generated by the pulsed current. In order to solve this problem, a new DCF approach adopted a pulsed magnet for wide sheets forming is proposed, which can provide a background magnetic field (BMF) with high uniformity and strength during the forming process. The influence of magnet parameters (shape, size, wire size, number of turns, etc.) on the magnetic field uniformity and strength at the forming region is analyzed by the finite element method, and the design scheme is listed. After that, the magnet is fabricated based upon the manufacturing technique of pulsed magnets, and the DCF and EMF experiments of AA1060 and SS304 sheets with 100 mm widths are carried out. The testing results show that the magnet can provide a 2.8 T BMF with more than 93% uniformity for the forming region. The forming results show that the forming height of sheets in DCF under BMF can be increased by 300% compared with that without BMF, and DCF has a huge advantage in comparison with EMF in forming low conductivity materials.

Thermal behavior of functionalized conventional polyaniline with hydrothermally synthesized graphene/carbon nanotubes

Conventional polyaniline (PANI) was mixed as a binder polymer matrix with carbonous materials. Hydrothermal technique was utilized to fabricate a nanocomposite of graphene (G)/carbon nanotubes (CNTs). The morphological features and quality of the synthesized PANI, G/CNTs, and their mixtures were investigated. Scanning electron microscopy (SEM) images confirm the formation of wide area graphene sheets with folds around the edges. In addition, the hydrothermally fabricated G/CNTs exhibited a uniform distribution with partial agglomeration. However, adding their mixture to PANI generated a mesh like porous morphology which demonstrates an enhancement in surface area and providing 3D conduction network. Moreover, Raman spectra confirm the quality of the synthesized samples. The generated disorder and defects within the structure, and the ratio of quinoid ring (Q) to benzenoid (B) ring in the fabricated samples were depicted. In addition, the enhancement in thermal parameters and reversing the thermo-electric carrier type into N-type after doping were attributed to the generated facile conduction paths of G/CNTs.

Influence of multiple anchor arrangement in the behaviour of FRP-to-concrete anchored joints

The effectiveness of fibre-reinforced polymers (FRP) external reinforcements is limited by premature delamination from concrete. In recent years, various anchoring systems were developed for FRP sheets. Among these, FRP anchors stand out for their effectiveness. When the unit strength of a connector is insufficient, multiple anchors may be employed. This paper presents an experimental campaign consisting of single shear tests on CFRP anchored narrow (100 mm width) and wide (200 mm width) sheets in concrete substrates. One anchor was installed in narrow sheets for comparison with wide sheets. Wide sheets were tested with one anchor and with two anchors transversally distributed to evaluate the influence of multiple anchors. Results from both literature and tests show that an optimal arrangement of one anchor in narrow FRP sheets or two transversally distributed anchors in wide sheets can be equivalent, which allows the anchored joints to develop more than twice the bond strength.

3D hierarchical graphene/CNT with interfacial polymerized polyaniline nano-fibers.

In this work Polyaniline (PANI) fiber has been synthetized by the interfacial polymerization method. The thermal behavior of graphene - multiwall carbon nanotubes (MWCNs) composite material (C-Mix) blended with PANI fiber was investigated. Graphene was prepared by thermal reduction of the fabricated graphene oxide (GO) using modified Hummers' method. SEM measurement reveals that MWCNTs were well organized within 2D large surface area graphene nano-sheets to form 3D carbon-base hierarchical structure, and PANI was mixed as a binder polymer matrix. Structural measurements confirm the formation of wide area graphene sheets with crumples, wrinkles, and folds around the edges. Transmission electron microscopy (TEM) images agreed with the well distribution of CNTs within graphene nano-sheets. Also, the surface morphology of the synthesized composites has a spherical regular agglomeration of PANI granular structure on wide area graphene nano sheets with CNT embedded. The change in the existed phonon modes of the fabricated nano-composite was analyzed using Raman spectroscopy. Moreover, Seebeck coefficient changes from+132.4μV/K to-10.3μV/K after adding carbon-based materials which reflects the reverse of predominate carriers by doping PANI with carbon-based material. It has been noticed that there is an enhancement of thermal conductivity of the fabricated composite with respect to neat polymer. Hence, we propose that 3D carbon structure with PANI construct a stable N-Type thermoelectric material.

A Flow in a Thin Plastic Layer: Generalizations of the Prandtl’s Problem

The analytical solutions of various generalizations of the classical L.Prandtl’s problem are of great interest in studying the problem of straightening plates using uniaxial stretching beyond the elastic limit. The straightening by stretching allows obtaining a high degree of flatness of thin wide strips and sheets of high-strength steels and special alloys, while the straightening by other methods does not provide satisfactory results. Based on Ilyushin’s theory of flow in a thin plastic layer, generalizations of the classical Prandtl’s problem on plastic strip compression were studied and their solutions were obtained. The planar problem of compression of a plastic strip between two parallel rough planes with accounting for the asymmetry of the conditions on the spreading ends has been solved and the upper estimate of the total compression force of the face-end areas of the plastically stretched strip has been obtained.

Extension of the span and optimization of the optical "magic carpet": generation of a wide quasi-nondiffracting light sheet.

Light sheet illumination is the basis in developing light sheet microscopy (LSM), a technique with significant advantages compared with other classical techniques. Most proposed optical systems to generate light sheets for LSM use many optical elements, which require extensive adjustments and are costly; moreover, they generate a nonuniform or semiuniform light sheet or have a short depth of field (DOF). A simple scheme using a pair of double slits and a cylindrical lens for generating a quasi-nondiffracting 2D light sheet was reported in Opt. Lett.40, 5121 (2015)OPLEDP0146-959210.1364/OL.40.005121. In the present investigation, we elaborate on the optimization of the mask used. As the separation between the two slits increases, the light sheet becomes thinner and the DOF smaller and vice versa. The slits' width does not affect the light sheet thickness, but it does affect the intensity of the side lobes. For convergence angles of the inner slits from 0.75° to 8°, an optimum ratio of the slits' separation/width of 2.182 is recommended. The obtained light sheet is quasi-diffraction-free, namely, while its DOF is comparable with that of a Gaussian beam, its diffraction broadening is substantially smaller. We also add to the previously developed configuration a Powell lens in order to expand the beam in the spanwise direction while keeping nearly constant intensity in this dimension. We perform scalar diffraction theory calculations and conduct measurements showing the nearly constant intensity in the significantly broadened span of the light sheet. Potential applications for the augmented width include imaging of certain large embryos, laser micromachining, and microparticle image velocimetry.

Experimental Analysis of Critical Acceleration Condition for Two-Sided Upward Flame Spread Over Inclined Thin Fuel Surfaces

Most of previous work focused on the one-sided upward flame spread over inclined surfaces. However, few investigations have systematically addressed the dependence of spread rate on the inclination angle for two-sided upward flame spreading. The present paper investigates the two-sided upward flame behaviors over inclined surfaces by performing experiments using 0.255 mm thick, 100 cm tall and 5 cm wide cotton sample sheets with various inclination angles varying 0° to 90° from the horizontal. The pyrolysis spread rate, pyrolysis length, preheating length, ignition time, flame tilt angle and standoff distance are obtained and analyzed. The corresponding results are as follows: As the inclination angle increases, the pyrolysis spread rate, pyrolysis length and preheating length increase, but the ignition time decreases. One transition zone is observed around 10° to 15° for flame spread rate, pyrolysis length and preheating length, which is an external manifestation of the change of flame spread from steady state to acceleration. Two parameters of tilt angle and standoff distance are used to qualitatively modify the heat flux profiles ahead of the flame front, which control the flame spread rate. Generally, the tilt angle and standoff distance of upper flame decrease as a function of inclination angle. On the contrary, the standoff distance shows an opposite trend with inclination angle. The combined effects of radiation and convection of upper and lower flames result in a sharp increase in net heat flux, and correspondingly a transition zone occurs around 10° to 15°. The results of this study have implications concerning designs for fire safety and may help advance understanding of two-sided flame spread over inclined surfaces.

The Effect of Morphologicat Changes in Urban Fabric on its Syntactical properties

urban centers had been grew and expanded gradually with a littre renewalof their parts . In the past, this process was veryilowly i'ue to limited dereropment inneeds .Most renewal works occurred as a response to destruction cas"a ry naturJdisasters or wars This was true until the industrial revolution which wasaccompanied with a dramatic changes in transportation systems and the necessity to erect wide sheets in most historic centerc .ln many cases ,these works did not take inconsideration the importance of spatial attributes of such centers .

The Effect of Morphologicat Changes in Urban Fabric on its Syntactical properties

urban centers had been grew and expanded gradually with a littre renewalof their parts . In the past, this process was veryilowly i'ue to limited dereropment inneeds .Most renewal works occurred as a response to destruction cas"a ry naturJdisasters or wars This was true until the industrial revolution which wasaccompanied with a dramatic changes in transportation systems and the necessity to erect wide sheets in most historic centerc .ln many cases ,these works did not take inconsideration the importance of spatial attributes of such centers .

Structure of Current Sheets with Quasi-Adiabatic Dynamics of Particles in the Solar Wind

Within the self-consistent hybrid model based on the quasi-adiabatic approximation of the proton dynamics, a fine structure of strong current sheets (SCSs) in the solar wind has been investigated, including the heliospheric current sheet. The motion of electrons is fast and considered in the Boltzmann approximation. The simulation results have been shown that the SCS profiles have a multiscale enclosed structure with a narrow central current sheet that is enclosed in a wider sheet, similar to the heliospheric current sheet surrounded by the plasma sheet. The features of the SCS structure are determined by the relative contributions of the current of demagnetized protons in serpentine orbits and drift currents of electrons. The model predicts and describes the properties of SCSs observed by spacecraft. It has been shown that the multiscale structure of current sheets is an inherent intrinsic property of current sheets in the solar wind.