Function Of Bending Angle Research Articles

Mechanically Flexible and Optically Tunable Organic Crystal Resonator

AbstractAn organic single‐crystal optical resonator that maintains its optical performance even upon mechanical bending remains a challenging target. Here, the first flexible organic crystal (FOC) that works as a tunable optical resonator as a function of bending angle is developed. A fluorescent π‐conjugated molecule, cyano‐substituted oligo(phenylenevinylene)s, is allowed to crystallize slowly, yielding a discrete rod‐shape microcrystal (FOCCOPV). FOCCOPV not only works as an efficient optical waveguide along its longitudinal direction with the optical loss coefficient of 0.249 dB µm−1 but also works as a Fabry‐Pérot type optical resonator along its lateral direction. The resonance wavelength is finely tunable toward the shorter wavelength region by the mechanical bending of FOCCOPV plausibly due to the Poisson effect, namely, the contraction of the lateral dimension of the crystal by the longitudinal strain, along with the change in the refractive index. The mechanical bending and associated spectral shift is repeated for many cycles without deterioration in their mechanical and optical properties.

The effect of substrate curvature on capacitance and current–voltage characteristics in thin-film transistors on flexible substrates

Mechanically flexible electronics are devices designed to operate under significant physical deformations such as bending, twisting, and stretching. While the materials systems and devices compatible with flexible substrates have been extensively studied, the mathematical framework for analysis remains identical to that of traditional planar silicon-based electronics. However, the non-planar and dynamic form factors desired from flexible electronics invalidate assumptions made in these models. For electronic devices to be predictable and ultimately commercially viable, they must be understood in any physical form. Here we employ the method of moments to calculate the capacitance between two electrical conductors of arbitrary shape. Combined with a model for source–drain current in thin-film transistors (TFTs) on the surface of a cylinder, we are able to calculate the current–voltage characteristics in curved TFTs as a function of bending angle. We demonstrate how deformations to device geometry are expected to lead to non-negligible changes in current–voltage characteristics. This work represents the first step towards a new framework for understanding and characterizing electronics with any physical form factor, ultimately bringing flexible electronics closer to commercial viability.

Design, modelling and validation of a novel extra slender continuum robot for in-situ inspection and repair in aeroengine

In-situ aeroengine maintenance works are highly beneficial as it can significantly reduce the current maintenance cycle which is extensive and costly due to the disassembly requirement of engines from aircraft. However, navigating in/out via inspection ports and performing multi-axis movements with end-effectors in constrained environments (e.g. combustion chamber) is fairly challenging. A novel extra-slender (diameter-to-length ratio < 0.02) dual-stage continuum robot (16 degree-of-freedom) is proposed to navigate in and out confined environments and perform required configuration shapes for repair operations. Firstly, the robot design presents several innovative mechatronic solutions: (i) dual-stage tendon-driven structure with bevelled disks to perform required shapes and to provide selective stiffness for carrying high payloads; (ii) various rigid-compliant combined joints to enable different flexibility and stiffness in each stage; (iii) three commanding cables for each 2-DoF section to minimise the number of actuators with precise actuation. Secondly, a segment-scaled piecewise-constant-curvature-theory based kinematic model and a Kirchhoff-elastic-rod-theory based static model are established by considering the applied forces/moments (friction, actuation, gravity and external load), where the friction coefficient is modelled as a function of bending angle. Finally, experiments were carried out to validate the proposed static modelling and to evaluate the robot capabilities of performing the predefined shape and stiffness.

Ultrasoft slip-mediated bending in few-layer graphene.

Continuum scaling laws often break down when materials approach atomic length scales, reflecting changes in their underlying physics and the opportunities to access unconventional properties. These continuum limits are evident in two-dimensional materials, where there is no consensus on their bending stiffnesses or how they scale with thickness. Through combined computational and electron microscopy experiments, we measure the bending stiffness of graphene, obtaining 1.2-1.7 eV for a monolayer. Moreover, we find that the bending stiffness of few-layer graphene decreases sharply as a function of bending angle, tuning by almost 400% for trilayer graphene. This softening results from shear, slip and the onset of superlubricity between the atomic layers and corresponds with a gradual change in scaling power from cubic to linear. Our results provide a unified model for bending in two-dimensional materials and show that their multilayers can be orders of magnitude softer than previously thought, among the most flexible electronic materials currently known.

Bending deformation and fracture characterisation in quenching and partitioning steel

ABSTRACTThe bending deformation recorded and fracture characterisation seen during the process of quenching and partitioning (Q&P) steel are investigated as a function of bending angle. According to experimental results, the mechanically induced martensitic transformation of the retained austenite occurred heterogeneously in the direction of thickness. Results from electron backscattered diffraction and finite element analysis confirmed that the heterogeneous phase transformation was caused by the stress difference in the direction of thickness. The results prove fracture behaviour is dominated by martensite cracking. The results provide a new insight into deformation characterisation of the Q&P steel under bending, which allows the design and optimisation of mechanical properties.

Mechanical Robustness of Graphene on Flexible Transparent Substrates.

This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend-relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium-tin oxide on PET. After 10(4) bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.

Optimization Efficiency of Monte Carlo Simulation Tool for Evanescent Wave Spectroscopy Fiber-Optic Probe

In a previous work, we described the simulation tool (FOPS 3D) (Khankin et al., 2001) which can simulate the full three-dimensional geometrical structure of a fiber and the propagation of a light beam sent through it. In this paper we are focusing on three major points: the first concerns the improvements made with respect to the simulation tool and the second, optimizations implemented with respect to the calculations' efficiency. Finally, the major research improvement from our previous works is the simulation results of the optimal absorbance value, as a function of bending angle for a given uncladded part diameter, that are presented; it is suggested that fiber-bending may improve the efficiency of recording the relevant measurements. This is the third iteration of the FOPS development process (Mann et al., 2009) which was significantly optimized by decreasing memory usage and increasing CPU utilization.

Crack initiation and propagation of galvanized coatings hot-dipped at 450 °C under bending loads

Crack initiation and propagation behaviors in the intermetallic layers of galvanized coatings subjected to bending loads are characterized and numerically simulated. Coating structure of galvanized steel prepared by hot dipping at 450°C is a laminate composite consisting of δ, ζ, and η phases, with an infinitesimal layer between the coating and steel article speculatively representing a Γ phase. The specimens were deformed in a four-point bending configuration, and the evolution of cracks was investigated as a function of bending angles. Through-cracks were found to develop in the δ layer of the coatings after thermal cooling due to thermal stresses and propagate toward the outer surface under increments of bending loads. Finite element simulations of galvanized steels were subsequently developed with an initial crack tip located in the δ layer to determine the controlling parameters of the crack propagation and to assess the coatings' fracture parameter, critical far field stress, and stress distributions. The analysis highlights the enhancement of fracture resistance of the galvanized coatings owing to the presence of the ζ layer.

Discrete microfluidics: Reorganizing droplet arrays at a bend

Microfluidic manipulation of densely packed droplet arrangements (i.e., gel emulsions) using sharp microchannel bends was studied as a function of bend angle, droplet volume fraction, droplet size, and flow velocity. Emulsion reorganization was found to be specifically dependent on the pathlength that the droplets are forced to travel as they navigate the bend under spatial confinement. We describe how bend-induced droplet displacements might be exploited in complex, droplet-based microfluidics.

Shear bands evolution in bulk metallic glass with extended plasticity

Shear band development and evolution of their spacing under bending in a Zr-based bulk metallic glass with extended plasticity has been monitored as a function of bending angle from the onset of plastic deformation to fracture. We find that sliding of existing shear bands is an important mechanism accounting for the plastic deformation of the plastic bulk metallic glass. The results are beneficial to understanding deformation in metallic glasses.

Shrink Flanging with Surface Contours

Experimental and analytical studies on shrink flanging with surface curvatures are presented in this paper. An analytical model is proposed to predict the circumferential strain along the flange edge as a function of bending angle under a given geometry condition. A semi-empirical failure criterion to capture the occurrence of wrinkling is also developed. Both the strain model and the wrinkling model are well supported by experiments. These models can be used as a practical design tool for shrink flanging process analysis.

Emittance growth of bunched beams in bends.

Talman [Phys. Rev. Lett. 56, 1429 (1986)] has proposed a novel relativistic effect that occurs when a charged particle beam is bent in the magnetic field from an external dipole. The consequence of this effect is that the space-charge forces from the particles do not exhibit the usual inverse-square energy dependence and some part of them are, in fact, independent of energy. This led to speculation that this effect could introduce significant emittance growth for a bending electron beam. Subsequently, it was shown that this effect's influence on the beam's transverse motion is canceled for a dc beam by a potential depression within the beam (to first order in the beam radius divided by the bend radius). In this paper, we extend the analysis to include short bunch lengths (as compared to the beam pipe dimensions) and find that there is no longer the cancellation for forces both transverse to and in the direction of motion. We provide an estimate for the emittance growth as a function of bend angle, beam radius, and current, and for magnetic compression of an electron bunch.

Electronic states and potential energy surfaces of ScH 2

Complete active space MC SCF (CAS SCF) followed by second-order configuration interaction (SOCI) calculations are carried out for the three lowest-lying states of ScH 2. The potential energy surface of the 2A 1 state is investigated as a function of bending angle. A barrier (< 36 kcal mole ) is found for the insertion of Sc into H 2 to form the linear 2Σ + g state. The ScH 2 2Σ + g state is found to be only 5 kcal mole more stable than Sc+H 2.