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The closing of micropipes during sublimation epitaxy has been studied. Shallow trenches are formed along the direction of the step-flow growth in the vicinity of closed micropipes. The trenches are related to a serious disturbance of the flowing steps and the formation of stacking faults in the (0001) basal plane as well as in the (1100) plane. A micropipe closes when the speed of the growth steps is higher than the spiral growth around the micropipe. This mechanism is related to a bending of the micropipe along the trench and the progressive emission of elementary screw dislocations along the trench. The morphology of the disturbed steps at the trenches and the related defects have been studied by transmission electron microscopy and atomic force microscopy. Supporting evidences are presented with optical micrographs from etched epilayers. Image forces, which are developed by the growth steps, stabilize the bending of the micropipes. The limitation of the bending is also discussed. [ABSTRACT FROM AUTHOR]

In this study, a suitable method to simulate pipe-manufacturing processes (i.e., bending, unbending, and flattening) was developed to reproduce the process and the mechanical properties of the pipe. To verify the reliability of the strain distribution and plastic deformation behavior predicted by the proposed method, experimentally-derived strain by digital image correlation (DIC) and finite element analyses were employed. Hardness and tensile tests were performed on bent-flattened specimens. The finite element method confirmed that the proposed method can predict the yield strength of pipes. [ABSTRACT FROM AUTHOR]

An analytical nonlinear solution was provided for unbalanced composite single-lap joint (CSLJ) using an improved one-dimensional beam model, which incorporated the effect of bending–tension coupling. The bending–tension coupling stiffness was introduced to characterize the coupling bending and tension behavior induced by the un-symmetric stacking sequence of composite laminates. The governing differential equations captured the bending–tension coupling behavior and the geometrically nonlinear features were constructed based on the displacement compatibility conditions of flexible interface. The transverse deformation in overlap region, edge moment factors and adhesive stress distributions for the unbalanced CSLJ with inflexible, intermediate flexibility and flexible adhesive can be determined by the present one-dimensional beam model. The accuracy of the present model was validated by the comparison with nonlinear finite element model. The effect of bending–tension coupling on edge moment factors and peak values of adhesive stresses was shed light on with the present model. [ABSTRACT FROM PUBLISHER]

In order to investigate the influence of mandrel on the forming quality of bending L-shaped hollow parts, three types of mandrels, which are polyurethane rubber mandrel, low-melting-point mandrel, and ball bearing mandrel. Polyurethane rubber mandrel and low-melting-point mandrel, which supposed as elastic-plastic deformable part in the numerical simulation. The effect of different forms of mandrel on the forming quality of L-shaped hollow parts, such as section deformation and wall thickness variation, were compared with push bending without a mandrel. The results show that the low-melting-alloy mandrel leads to a better formability and a more uniform tube thickness distribution compared with the polyurethane rubber mandrel and ball bearing mandrel, for the low-point-melting mandrel brings about smaller stress in the bending process. Cold push-bending trials of rectangular cross-section tubes were conducted successfully based on the finite element simulation results. The experimental results showed that the formability and quality of L-shaped tubes greatly improved compared to no mandrel, ball bearing mandrel, and rubber mandrel when the low-melting-point-alloy mandrel was used as the flexible mandrel. [ABSTRACT FROM AUTHOR]

Three-point bending test is a common test for the pipes produced according to ASTM 335. This standard defines the bending test only for certain geometries of pipe. Due to the fact that this test is more and more required and also for 'not' in standard defined sizes, and only few practical, industrial experiences exist in this field, the aim of this work is to correlate some simulations with experimental results. Systematic investigations of the influence of mechanical properties and geometry of the seamless pipe are performed. The influence of the testing parameters during the bending is investigated as well and presented in this paper. It is found that strength level, that is, yield strength to tensile strength ratio, has a strong influence on the evolution of stresses during the bending. Geometry of the pipe, in the range of investigated sizes, has not a crucial influence but defines the outside/inside area, in other words a sensitivity of tested samples. [ABSTRACT FROM AUTHOR]

The combined effect of ovality and variable wall thickness on collapse load of pipe bends under in-plane opening bending moment with internal pressure was investigated using finite element limit analysis considering large geometric change effect. The material was assumed to be elastic–perfectly plastic. The collapse moments were obtained from moment-rotation curves drawn for each bend using twice-elastic-slope method. Thickening/thinning effect on collapse load is very minimal and can be neglected. The effect of ovality is significant with the reduction of collapse load by a maximum of 39.1% for the maximum internal pressure and ovality considered. Based on the finite element results, a mathematical expression is proposed to determine collapse load of the pipe bends with ovality and this equation has been verified with experimental collapse loads. [ABSTRACT FROM AUTHOR]

We report measurements of the splay and bend elastic constants of 4′-butyl-4-heptyl-bicyclohexyl-4-carbononitrile (CCN47). We find K11 to be largely constant across the nematic range, with a value of ∼10 pN. K33 has a slightly lower value with K33/K11 ∼ 0.9 pN far from the transition to the SmA. In the vicinity of the SmA phase, K33 diverges with critical exponent γ = –0.6, with K33/K11 exceeding 5 close to the transition. [ABSTRACT FROM AUTHOR]

In automobile parts manufacturing, the fuel, exhaust pipes are specialized equipment that requires highly skilled, heavy machine and high problems arise when parts are not qualifying in the assembly line at long distance from manufacturer's location or in overseas. This paper describes a project to develop the computer numerically controlled (CNC) pipe bending process that for a pipe manufacturer that achieve final dimensions and have right fitting at assembly line . The company has been using traditional methods of machine assisted manual pipe bending techniques. In a drive of continuous improvement, the company has acquired a pre-owned CNC bending machine capable of bending pipes automatically up to 15 bends. However, due to process mismatch, pipe does not qualify in the fixture or some time fixture is not make according to specification of pipes and take very long time due to either not referencing of pipe fixture or pipe bending process this take a very long time for developing new automobile pipe having large number of bends this paper help in developing new products sand reduce fitting problems and save cost and time. [ABSTRACT FROM AUTHOR]

Abstract: The estimation of the flexural stiffness and bending capacity of composite slim beams is rather complicated, because the influence of many factors should be taken into account. These factors include variable section dimensions, development of cracks and non-linear characteristics of concrete. This is especially true for the composite slim frame beam, in which the sagging moment region and the hogging moment region should both be considered. In this paper, experimental investigations have been conducted to investigate the flexural behavior of two specimens of composite slim frame beam with deep deck under monotonic loading. Based on the experimental results, formulas of calculating the bending capacity and flexural stiffness in the hogging moment region of the slim beam with deep deck has been proposed. Combining these formulas with existing formulas of sagging moment, formulas for the equivalent stiffness and the design method of the frame slim beam have been developed. The feasibility of the proposed formulas and design method has been verified by the test results. [Copyright &y& Elsevier]

Abstract: A cyclic bending experiment is designed to investigate the interface fracture behaviour of a hard chromium coating on a ductile substrate with periodic surface hardened regions. The unique deflection pattern of the vertical cracks after they run through the coating and impinge at the interface is revealed experimentally. A simple double-layer elastic beam model is adopted to investigate the interfacial shear stresses analytically. A FE model is employed to compute the stresses of the tri-phase structure under a single round of bending, and to investigate the effect of the loading conditions on the deflection pattern of the vertical cracks at the interface. [Copyright &y& Elsevier]

Abstract: The whole process of thin-walled tube NC bending includes three processes: bending tube, retracting mandrel and springback. Based on the numerical simulation of the whole process, the springback mechanism and rule of thin-walled tube NC bending are revealed. During springback, the angle of the bending portion decreases and the radius of the bending portion increases. The springback of the two straight portions is similar to the bending deformation of a projecting beam. The total springback angle considering retracting mandrel is much smaller than that not considering retracting mandrel and the maximum difference between them in the paper is 107.34%. The process of retracting mandrel must be considered to predict accurately the springback of thin-walled tube NC bending. The total springback angle increases linearly with the increase of the bending angle when the bending angle is big. The springback radius can be obtained based on that the length of the neutral layer keeps unchangeable during springback. The length change of the bending portion during springback is usually very small so that it can be neglected when the springback radius is computed. And then the springback radius is independent on the bending angle and the linearly increasing rate of the total springback angle with the increase of the bending angle can be used to compute the springback radius. [Copyright &y& Elsevier]

Abstract: There are more than 10 kinds of bending, for example press bending, stretch bending, stretch draw bending and others. There are many studies about characteristics of tube bending. But there is no study about the effects of tubular material property on bending. Therefore, we try to examine the effect of material property about hardening exponent on tube bending. Bending radius, strain distribution, springback and flatness of tube are examined on press bending by FEM (finite element method) and experimental results. The results are about the effects of tubular material property such as hardening exponent n. The effect of hardening exponent is clear in the tube bending in the study. The hardening exponent n does not have an effect on springback, thickness strain distributions and flatness ratio at the same bending radius of same tube dimension. [Copyright &y& Elsevier]

Abstract: The present work aims at studying the combined effect of tangential bending and stretching stress (quite common in the stamping process, e.g. in the pinch or die shoulder regions) on thin magnesium (Mg) sheets when working at elevated temperature. An experimental/numerical approach was adopted using specific equipment able to heat the sheet only in the bending region and to stretch the sheet after the wiping process. Stretch-bending tests were aimed at understanding the process parameters really affecting the stretch-bending process at elevated temperature using the design of experiment (DOE) technique. In particular the temperature, the punch speed, the bending radius and the rolling direction were considered in the screening analysis. Beside the maximum stretching load, also the springback phenomenon was measured, in order to quantify the amount of plastic strain in the bending section when changing the process parameters. The finite element (FE) analysis was focused on the process parameters which resulted to play a key role: the bending radius and the temperature. Plastic strain distributions in the bending area and the critical condition occurrence in the stretching step were evaluated using 2D fully coupled thermo-mechanical models. [Copyright &y& Elsevier]

Abstract: A bending system was proposed in order to realize high precision V-bending. This system can calculate the appropriate bending condition during work progress and its calculation algorithm is satisfactorily time-efficient for a practical use. The essential point of this system is that the work-piece is released once just before the punch reaches the final target position. Using this method the system can collect the data, calculate material properties and predict the final target position. This position is determined by considering the spring-back after release. However, the spring-back is not constant due to the differences of material properties between each work-piece. In the proposed system, the material properties: flow stress, Young''s modulus and hardening ratio were calculated based on information of load, tilt angle of plate and spring-back at the pre-release phase for determination of appropriate bending conditions. The proposed bending system can realize high-precision bending and has successfully been adopted in actual operation. [Copyright &y& Elsevier]

In the present study, the bending collapse of an elastoplastic cylindrical tube subjected to static pure bending is investigated using the finite element method (FEM). The moment of the elastoplastic cylindrical tube is controlled by the flattening rate of the tube cross-section. For a long tube, the flattening rate can be expressed in terms of the axial and circumferential stresses that, in turn, depend on the material and geometrical properties and the curvature of the tube. On the other hand, for a short tube, the boundary condition of the fixed walls prevents the flattening rate. In order to account for the length effect of tubes, we propose a new method in which flattening is considered as a deflection problem of a fixed curved beam. The proposed method was able to predict the change in the flattening rate as the curvature was increased. A rational prediction method is proposed for estimating the maximum bending moment of cylindrical tubes that accounts for the length effect. Its validity is demonstrated by comparing it predictions with numerical results obtained using the finite element method. [ABSTRACT FROM AUTHOR]

Abstract: Almost universally, the effective stimulus for mammalian 9+0 primary cilia has been taken to be bending. In this article I point out that in several physiological contexts there is great advantage in detecting pressure differences across the cell wall, i.e. axially directed forces pushing fluid to and fro through the hollow cilium and its basal body beneath. The form of the cilium – a fluid-filled pipe that connects to an intricate pinwheel-shaped basal body – is well configured for detecting fluid flow. Pressure-detection calls for compressible elements within the cell, but it effectively matches form and function in a range of cases. The “pipe and pinwheel” scheme suggests that the bulbous swellings commonly found near the tip of some primary cilia are compliant, pressure-sensitive elements which act like the bulb of an eye-dropper. In looking exclusively at the bending of cilia, we might be missing aspects of a dual-stimulus system. [Copyright &y& Elsevier]

Abstract: Comb-drive structures consisting of two opposing parallel arrays of microcantilevers are commonly adopted in many designs of MEMS. This work studies pull-in instability of comb-drive structures in which two opposing arrays have different bending rigidities. Based on a simplified spring model, it is verified that equilibrium deflections of all intermediate microcantilevers in the arrays are negligibly small prior to the onset of instability, and non-negligible deflections of the end microcantilevers cause a significant end-effect on pull-in instability of the comb-drive array. With this concept, the critical value for instability of the comb-drive arrays is estimated, with or without the end-effect, for varying bending rigidity ratios. Compared to the results without the end-effect, the end-effect is found to lower the critical interaction coefficient for instability, and the reduction in the critical value for instability increases with decreasing bending rigidities of the end microcantilevers. These results for varying bending rigidity ratios indicate the significance of the end design on the instability of comb-drive structures. In particular, the results obtained by the present method are in good agreement with some known experimental data available in the literature and the exact results obtained by iteration numerical method for the spring model. [Copyright &y& Elsevier]

This paper provides plastic limit and TES (twice-elastic-slope) plastic load solutions for 90° pipe bends under combined pressure and out-of-plane bending, via three-dimensional non-linear FE analyses using elastic-perfectly plastic materials. Without internal pressure, a closed-form approximation is given. For combined pressure and out-of-plane bending, tabulated data are given, from which TES plastic loads can be interpolated. It is found that TES plastic loads for pipe bends under out-of-plane bending are lower than those under in-plane opening bending, but are higher than those under in-plane closing bending. It suggests that the in-plane closing bending mode is the most critical loading mode for 90° pipe bends, which is fully consistent to existing findings. [ABSTRACT FROM AUTHOR]

Summary: Potassium channels fluctuate between closed and open states. The detailed mechanism of the conformational changes opening the intracellular pore in the K+ channel from Streptomyces lividans (KcsA) is unknown. Applying Monte Carlo normal mode following, we find that gating involves rotation and unwinding of the TM2 bundle, lateral movement of the TM2 helices away from the channel axis, and disappearance of the TM2 bundle. The open-state conformation of KcsA exhibits a very wide inner vestibule, with a radius ∼5–7 Å and inner helices bent at the A98–G99 hinge. Computed conformational changes demonstrate that spin labeling and X-ray experiments illuminate different stages in gating: transition begins with clockwise rotation of the TM2 helices ending at a final state with the TM2 bend hinged near residues A98–G99. The concordance between the computational and experimental results provides atomic-level insights into the structural rearrangements of the channel''s inner pore. [Copyright &y& Elsevier]

Abstract: Local and overall transport critical current I C and n-value at 77K of multifilamentary Bi2223-composite tape were studied under applied tensile and bending strains. The I C and n-value of the local elements constituting of the overall sample and those of the overall sample were measured for the voltage probe distances 10 and 60mm, respectively. The local I C as well as n-value varied along the sample length under both tensile and bending strains, while the critical current reduction process under the tensile strain was quite different from that under bending one; a big difference in damage among the local elements was found under tensile strain but not under bending one. While the damage process was different between the tensile and bending strains, the relation of overall I C and n-value to the local ones was described comprehensively by the voltage summation model. From the analysis of the experimentally observed critical current–applied strain relation of the local elements, the variation of the critical current determining factor “fracture strain–residual strain” along the sample length was revealed. [Copyright &y& Elsevier]

Abstract: Three-point bending tests on specimens cut from Dy123 bulks with X wt.% Ag (X =5, 7.5 and 10) were carried out at room temperature. Bending test specimens with 2.8×2.1×24mm3 were cut from the bulk samples and then annealed in O2 atmosphere at 723K for 100h. The Young’s modulus decreased with increase of the Ag content, 136, 128 and 124GPa for X =5, 7.5 and 10, respectively. On the other hand, the fracture strength increased, 86, 89 and 91MPa. The Ag content dependences of the Young’s modulus and the fracture strength are analyzed through the area fraction of the pores and Ag particles in each bending test specimen. [Copyright &y& Elsevier]

Abstract: An experimental investigation was conducted to compare the crush characteristics and energy absorption capacity of AA6061-T6 aluminum alloy extrusions with centrally located through-hole discontinuities. Three different types of geometrical discontinuities, namely, circular, slotted and elliptical holes were fabricated into AA6061-T6 extrusions which had a length of 200mm, nominal side width of 38.1mm and wall thickness of 3.15mm. Furthermore, three different major axis lengths (7.14, 10.72, and 14.29mm) and three different aspect ratios (1.33, 2.0, and 3.0) of the slotted and elliptical discontinuities were considered. It was found that by introducing crush initiators into the structural members, a splitting and cutting deformation mode was generated rather than global bending deformation which was observed for specimens without any discontinuities. The peak crush load was reduced by incorporating the through-hole crush initiators within a range of 5.2–18.7%, and total energy absorption was increased within a range of 26.6–74.6%. The most significant improvement was noted in the crush force efficiency, which was increased within the range of 54.5–95.8%. For specimens with discontinuities which had a major axis length of 7.14mm the peak crush load and total energy absorption was independent of initiator geometry and aspect ratio. However, for specimens which had discontinuities with a major axis length of 10.72 and 14.29mm and an aspect ratio of 3, a geometrical influence on the peak crush load and total energy absorption was apparent. [Copyright &y& Elsevier]

This article describes the theoretical principles behind the design and reconfiguration of continuous casters with radial molds into continuous casters with a vertical molds. Two variants for such reconstruction are examined: retention of the base radius and retention of the original height of the caster. Mathematical relations are presented for increasing caster height while preserving the base radius and changing the latter while keeping the height unchanged. The choice of approach depends on such parameters as the height of the vertical section, the height of the bending section (for casters with a vertical mold), and the distance from the axis of oscillation of the mold to the top of the copper sleeve (for casters with a radial mold). [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure in p-type δ-doping GaAs is calculated self-consistently by including the contribution of the photogenerated carrier. The theoretical results indicate that the band bending around the δ-doping region is induced by the injection of photogenerated holes into the potential well of the δ-doping GaAs. Moreover the band bending results in two photogenerated carrier-induced wells for electrons. The potential of the two wells is deepened with the increase of the photogenerated carrier density. The photoluminescence (PL) properties are explained in terms of the dependence of the confined electronic states and the Fermi level of the two-dimensional hole gas (2DHG) on the concentration of photogenerated carrier, which is in good agreement with experimental observation of the variation of peak position and intensity with the excitation light intensity. [Copyright &y& Elsevier]

In order to clarify the significant parameters to control the deformability of high-grade induction bend pipes, finite element analyses simulating the deformation behavior subjected to an internal pressure and bending moment were carried out. Parametric studies were conducted using the finite element models with various mechanical properties and geometric imperfections. The change in the integrity of the buried pipeline due to the quality of the induction bend pipe was then quantitatively examined. Consequently, this study indicated that the mechanical properties, the dimensions and tolerance and the properties of the "should be appropriately designed in proportion to the ground deformation. [ABSTRACT FROM AUTHOR]

To comprehensively investigate the tensile properties of cold bends, full-scale cold bending experiments, tensile tests using prestrained small-scale specimens, and finite element (FE) analyses of the cold bending processes were conducted on API 5L X60 and X80 grade line pipes. The tensile tests revealed that the tensile properties of the cold bends were comparable to the uniaxially prestrained specimens machined from the straight part of the pipes. A FE model simulating the cold bending process was verified with the full-scale experimental results in terms of the distributions of residual strains. These results supported a procedure for estimating the tensile properties of the cold bends with a combination of the FE model and the tensile tests using the prestrained specimens; the residual strains obtained from the FE model are transformed into the tensile properties based on the relationship between the residual strains and the tensile properties. This study clarified that the tensile properties come close to being uniformly distributed by reducing the distance between the bending locations; the distance between the bending locations has a significant influence on the overlap of adjacent deformed areas, which governs the distribution of the tensile properties of the cold bends. [ABSTRACT FROM AUTHOR]