The Experts below are selected from a list of 2439 Experts worldwide ranked by ideXlab platform

Heng Li - One of the best experts on this subject based on the ideXlab platform.

  • global sensitivity analysis and coupling effects of forming parameters on wall thinning and cross sectional distortion of rotary draw Bending of thin walled rectangular tube with Small Bending Radius
    The International Journal of Advanced Manufacturing Technology, 2014
    Co-Authors: Heng Li, H. Yang
    Abstract:

    To research the coupling effects of forming parameters on wall thinning and cross-sectional distortion, the global sensitivity analysis model of rotary draw Bending of thin-walled rectangular tube is established based on ABAQUS/Explicit platform and Morris’ global sensitivity analysis method. By using the model, the 15 groups with different parameter combinations are selected, and their sensitivities to wall thinning and cross-sectional distortion are analyzed. Results show that (1) wall thinning is influenced significantly by the coupling interactions of the clearance of cores–tube and the booster velocity, while cross-sectional distortion is influenced significantly by the coupling interactions of the clearance of pressure die–tube, the core number, and the booster velocity. (2) The groups with higher sensitivity to wall thinning all include the variable parameter of clearance of pressure die–tube, while the ones with higher sensitivity to cross-sectional distortion all include the parameter combination of booster velocity and core number. (3) Compared with other groups, the group including all of the parameters has lower sensitivity to wall thinning and section distortion, due to the coupling effects of all the parameters. The global sensitivity analysis evaluates the coupling effects of forming parameters on wall thinning and section distortion quantitatively by means of sensitivity degree, which is helpful to get rid of nonsensitive parameter and guide further optimization.

  • FE-Based Analysis of Heat Bending of Thin-Walled Ti-Alloy Tube with Large Diameter and Small Bending Radius
    Advanced Materials Research, 2012
    Co-Authors: Heng Li, Dan Wang, He Yang, Zhiyong Zhang
    Abstract:

    The numerical control (NC) heat Bending of thin-walled Ti-alloy tube with large diameter and Small Bending Radius with Ф50×1×R75mm (diameter OD Bending Radius CLR) is explored by 3D-FE thermal-mechanical coupling simulation of heat conducting and NC Bending. The results show that: (1) The heating of both pressure die and mandrel is proved to be appropriate to obtain the required temperature field. (2) In terms of wall thickness variation, wrinkling and cross-section deformation, the optimum span of the key parameters are obtained: the Bending velocity of 0.4rad/s, the matched pressure die speed of 80%-110%, and temperature of 600-800°C.

  • Numerical study on deformation behaviors of thin-walled tube NC Bending with large diameter and Small Bending Radius
    Computational Materials Science, 2009
    Co-Authors: Heng Li, H.-k. Yang, J Yan
    Abstract:

    With respect to wrinkling, wall thinning and cross section deformation, combined with analytical description, the deformation behaviors of thin-walled tube NC Bending with large diameter D/t (50.0-87.0) and Small Bending Radius Rd/D (1.0-2.0) are explored via a series of reliable 3D-FE models under ABAQUS platform. The results show that: (1) The segmentation feature is observed for the deformation fields such as effective compressive/tensile regions τc / τt, stress/strain distributions, wrinkling tendency, wall thinning and cross section deformation. With Smaller Rd/D, the tangent stress increases and becomes more inhomogenous. The maximum tangent stress σφ at the intrados increases by 46% with Rd/D from 2.0 to 1.2. While the distributions of σφ are nearly similar with larger D/t. With Smaller Rd/D and larger D/t, the velocity variation of tube materials becomes more obvious. (2) The wrinkling tendency and cross section deformation degree Δ D increase with Smaller Rd/D and larger D/t; With Smaller Rd/D, both the wall thinning and thickening degrees increase. The maximum wall thinning and thickening degrees increase by 24.0% and 52.5%, respectively. However, with larger D/t, the wall thinning degree increases, while the thickening degree decreases significantly. The maximum wall thinning degree increases by 31.3%, while the maximum thickening one decreases by 58.9%. Crown Copyright © 2009.

  • Forming characteristics of thin-walled tube Bending process with Small Bending Radius
    Transactions of Nonferrous Metals Society of China (English Edition), 2006
    Co-Authors: Heng Li, H.-k. Yang, R. J. Gu
    Abstract:

    Currently requirements of thin-walled tube with Small Bending Radius cause the defects such as wrinkling, overthinning and cross-section distortion more prone to occur in Bending process. Based on the analysis of the forming characteristics by analytical and experimental methods, a complete 3D elastic-plastic FEM model of the process was developed using ABAQUS/Explicit code, including Bending process, balls retracting and unloading process, and thus the plastic deformation characteristics with Small Bending Radius were investigated. The main results show that: 1) The utmost deformation feature of the NC Bending process is its continuous progressive deformation. 2) The occurring conditions of the defects such as wrinkling and tension instability in the process are obtained. The wrinkling is traditional on the double compressive stresses state and the tension instability is on the double tension stresses state. 3) The enhanced non-uniform deformation in thin-walled tube with Small Bending Radius is demonstrated by comparing the stress/strains distributions under the 1.5D and 1D Bending conditions. 4) For 1D Small Bending process, a new method-'stepped mandrel retraction' is proposed to improve the Bending quality in experiment according to the FE simulation. The simulation results are verified by experiment.

He Yang - One of the best experts on this subject based on the ideXlab platform.

  • FE-Based Analysis of Heat Bending of Thin-Walled Ti-Alloy Tube with Large Diameter and Small Bending Radius
    Advanced Materials Research, 2012
    Co-Authors: Heng Li, Dan Wang, He Yang, Zhiyong Zhang
    Abstract:

    The numerical control (NC) heat Bending of thin-walled Ti-alloy tube with large diameter and Small Bending Radius with Ф50×1×R75mm (diameter OD Bending Radius CLR) is explored by 3D-FE thermal-mechanical coupling simulation of heat conducting and NC Bending. The results show that: (1) The heating of both pressure die and mandrel is proved to be appropriate to obtain the required temperature field. (2) In terms of wall thickness variation, wrinkling and cross-section deformation, the optimum span of the key parameters are obtained: the Bending velocity of 0.4rad/s, the matched pressure die speed of 80%-110%, and temperature of 600-800°C.

  • significance based optimization of processing parameters for thin walled aluminum alloy tube nc Bending with Small Bending Radius
    Transactions of Nonferrous Metals Society of China, 2012
    Co-Authors: He Yang, Li Heng-tai
    Abstract:

    Abstract Thin-walled aluminum alloy tube numerical control (NC) Bending with Small Bending Radius is a complex process with multi-factor coupling effects and multi-die constraints. A significance-based optimization method of the parameters was proposed based on the finite element (FE) simulation, and the significance analysis of the processing parameters on the forming quality in terms of the maximum wall thinning ratio and the maximum cross section distortion degree was implemented using the fractional factorial design. The optimum value of the significant parameter, the clearance between the tube and the wiper die, was obtained, and the values of the other parameters, including the friction coefficients and the clearances between the tube and the dies, the mandrel extension length and the boost velocity were estimated. The results are applied to aluminum alloy tube NC Bending d 50 mm×1 mm ×75 mm and d 70 mm×1.5 mm×105 mm (initial tube outside diameter D 0 ×initial tube wall thickness t 0 ×Bending Radius R ), and qualified tubes are produced.

  • Deformation Behavior of Medium-strength TA18 High-pressure Tubes During NC Bending with Different Bending Radii
    Chinese Journal of Aeronautics, 2011
    Co-Authors: Zhiqiang Jiang, Mei Zhan, He Yang
    Abstract:

    To improve the forming quality and forming limit of the numerical control (NC) Bending of high-pressure titanium alloy tubes, in this study, using three-dimensional (3D) finite element method, deformation behavior of medium-strength TA18 high-pressure tubes during NC Bending with different Bending radii is investigated. The results show that the cross-sectional deformation and the wall thickness variation during NC Bending of TA18 tubes using a Small Bending Radius (less than 2 times of tube outside diameter) are clearly different from that using a normal Bending Radius (between 2 and 4 times of tube outside diameter). For Bending with a normal Bending Radius, with or without a mandrel, the distribution of the flattening in the Bending area resembles a platform and an asymmetric parabola, respectively. For Bending with a Small Bending Radius, with or without a mandrel, the flattening both distributes like a parabola, but the former has a stable peak which deflects toward the initial Bending section, and the latter has a more pronounced peak with a Bending angle and deflects slightly toward the Bending section. The wall thickness variations with a normal Bending Radius, with and without a mandrel, both resemble a platform when the Bending angle exceeds a certain angle. For the Bending with a Small Radius, the distribution of the wall thickness variation without a mandrel follows an approximate parabola which increases in value as the Bending angle increases. If a mandrel is used, the thickening ratio increases from the initial Bending section to the Bending section.

  • Cross-sectional distortion behaviors of thin-walled rectangular tube in rotary-draw Bending process
    Transactions of Nonferrous Metals Society of China, 2010
    Co-Authors: Gangyao Zhao, Yuli Liu, He Yang
    Abstract:

    Abstract The cross-sectional distortion usually appears during rotary-draw Bending process of thin-walled rectangular tube with Small Bending Radius. To study the cross-sectional distortion of the tube, a three-dimensional finite-element model of the process was developed based on ABAQUS/Explicit code and its reliability was validated by experiment. Then, the cross-sectional distortion behaviors of the tube were investigated. The results show that a zone of larger circumferential stress appears on the tube when Bending angle reaches 30°. And in the larger circumferential stress zone, the sagging phenomenon is produced obviously. The maximum cross-sectional distortion is located in the larger circumferential stress zone and the angle between the plane of maximum cross-sectional distortion and the Bending reference plane is about 50°. The position of the maximum cross-sectional distortion keeps almost unchanged with the variation of the clearances between dies and tube.

  • Application of ductile fracture criteria in spin-forming and tube-Bending processes
    Computational Materials Science, 2009
    Co-Authors: Mei Zhan, Zhiqiang Jiang, He Yang
    Abstract:

    Abstract As one of the principal failures that occur in metal spin-forming and tube-Bending processes, ductile fracturing restricts the process of metal forming. It is difficult to predict the rupture and forming limit for the complex processes of spin forming and tube Bending. Thus, in this paper we aim to choose reasonable ductile fracture criteria to accurately predict the time, position and distribution of the damage that occurs in these processes. By embedding the Lemaitre and Cockcroft–Latham (C&L) criteria into VUMAT (user material subroutine of the ABAQUS/explicit finite element method (FEM) code), finite element models are built and validated for predicting rupture failure and forming limit in the shear spin-forming, splitting spin-forming and tube-Bending processes. The results show that the Lemaitre criterion is better than the C&L criterion at accurately predicting the position at which damage will occur and its distribution for both spin forming and tube Bending. The maximum feed ratio varies within a Small range with the splitting angle of the roller. There is an obvious difference between the distribution, variation and level of the damage that can occur for a normal Bending Radius without rupturing, and that for a very Small Bending Radius, where there is a greater risk of rupturing. For tube Bending using a very Small Bending Radius and without a mandrel in the tube, the pressure die velocity increases, so the flattening of the Bending area increases to some extent, which makes it opposite of normal tube Bending.

J Yan - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study on deformation behaviors of thin-walled tube NC Bending with large diameter and Small Bending Radius
    Computational Materials Science, 2009
    Co-Authors: Heng Li, H.-k. Yang, J Yan
    Abstract:

    With respect to wrinkling, wall thinning and cross section deformation, combined with analytical description, the deformation behaviors of thin-walled tube NC Bending with large diameter D/t (50.0-87.0) and Small Bending Radius Rd/D (1.0-2.0) are explored via a series of reliable 3D-FE models under ABAQUS platform. The results show that: (1) The segmentation feature is observed for the deformation fields such as effective compressive/tensile regions τc / τt, stress/strain distributions, wrinkling tendency, wall thinning and cross section deformation. With Smaller Rd/D, the tangent stress increases and becomes more inhomogenous. The maximum tangent stress σφ at the intrados increases by 46% with Rd/D from 2.0 to 1.2. While the distributions of σφ are nearly similar with larger D/t. With Smaller Rd/D and larger D/t, the velocity variation of tube materials becomes more obvious. (2) The wrinkling tendency and cross section deformation degree Δ D increase with Smaller Rd/D and larger D/t; With Smaller Rd/D, both the wall thinning and thickening degrees increase. The maximum wall thinning and thickening degrees increase by 24.0% and 52.5%, respectively. However, with larger D/t, the wall thinning degree increases, while the thickening degree decreases significantly. The maximum wall thinning degree increases by 31.3%, while the maximum thickening one decreases by 58.9%. Crown Copyright © 2009.

Daoxin Dai - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Demonstration of Deeply-Etched SiO $_{2}$ Ridge Optical Waveguides and Devices
    IEEE Journal of Quantum Electronics, 2010
    Co-Authors: Zhen Sheng, Bo Yang, Liu Yang, Daoxin Dai
    Abstract:

    Deeply-etched SiO2 optical ridge waveguides are fabricated and characterized. A detailed discussion of the fabrication process (especially for the deep etching process) is presented. The measured propagation losses for the fabricated waveguides with different core widths range from 0.33 ~ 0.81 dB/mm. The loss is mainly caused by the scattering due to the sidewall roughness. The losses in Bending sections are also characterized, which show the possibility of realizing a Small Bending Radius (several tens of microns). 1 × N (N = 2, 4, 8) multimode interference couplers based on the deeply-etched SiO2 ridge waveguide are also fabricated and show fairly good performances.

  • Compact Microracetrack Resonator Devices Based on Small SU-8 Polymer Strip Waveguides
    IEEE Photonics Technology Letters, 2009
    Co-Authors: Daoxin Dai, Bo Yang, Liu Yang, Zhen Sheng
    Abstract:

    Compact microracetrack resonator (MRR) devices are presented with Small SU-8 polymer strip waveguides. The SU-8 strip waveguide has an SU-8 polymer core (n~1.573) , a SiO2 buffer (n~1.445), and an air cladding. The fabricated straight waveguide has a low propagation loss of about 0.1 dB/mm. With such a high index-contrast optical waveguide, a compact MRR with a Small Bending Radius (~150 mum) are designed and fabricated. The measured spectral responses of the through/drop ports show a Q-factor of 8000.

  • Compact Microring Resonator With 2 $\,\times\,$ 2 Tapered Multimode Interference Couplers
    Journal of Lightwave Technology, 2009
    Co-Authors: Daoxin Dai, Zhen Sheng, Liu Yang, Bo Yang
    Abstract:

    Compact microring resonator devices are realized by using a Small SU-8 polymer strip waveguide that has an SU-8 polymer core (n ~ 1.573), an SiO2 buffer (n ~ 1.445), and an air cladding. Due to the high index contrast of the optical waveguide, a Small Bending Radius ( ~ 150 mum) is used for the MRR. To enhance the coupling between the access optical waveguides and the microring, 2 times 2 multimode interference couplers are used. The measured spectral response of the through port shows a high extinction ratio of over 15 dB and a 3-dB bandwidth of about 0.38 nm (corresponding to a moderate Q-value of ~ 4500).

  • Numerical analysis of silicon-on-insulator ridge nanowires by using a full-vectorial finite-difference method mode solver
    Journal of the Optical Society of America B, 2007
    Co-Authors: Daoxin Dai, Zhen Sheng
    Abstract:

    The characteristics of silicon-on-insulator (SOI) ridge waveguides are analyzed by using a cylindrical full-vectorial finite-difference method mode solver with a perfectly-matched layer treatment. First, the single-mode condition for an SOI ridge nanowire with different Si core thicknesses is obtained. The obtained single-mode condition is different from that for the conventional micrometrical SOI ridge waveguides with a large cross section. By adjusting the cross section (the core width and the etching depth), one can have a nonbirefringent SOI ridge nanowire. The analysis on the Bending loss of SOI ridge nanowires shows that one can have a relatively Small Bending Radius even with a shallow etching (i.e., a Small ratio γ between the etching depth and the total thickness). For example, even when one chooses a Small ratio γ=0.4, one still has a low Bending loss with a Small Bending Radius of 15 μm for an SOI nanowire with a thin core hco=250 nm, which is very different from a conventional large SOI ridge waveguide.

  • Deeply Etched $\hbox{SiO}_{2}$ Ridge Waveguide for Sharp Bends
    Journal of Lightwave Technology, 2006
    Co-Authors: Daoxin Dai, Yaocheng Shi
    Abstract:

    A deeply etched SiO2 ridge waveguide including the buffer, core, and cladding is presented for realizing sharp bends. The present SiO2 ridge waveguide has a strong confinement at the lateral direction, while it has a weak confinement at the vertical direction. Due to the strong confinement, a sharp bend (with a very Small Bending Radius of about 10 mum) is obtained for an acceptable Bending loss. A detailed analysis of the loss in a bent waveguide is given by using a finite-difference method. In order to reduce the transition loss, a narrow Bending section with an optimal lateral offset is used. A low leakage loss is obtained by using wide straight waveguides, and linear tapers are used to connect the wide straight section and narrow bent sections

H.-k. Yang - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study on deformation behaviors of thin-walled tube NC Bending with large diameter and Small Bending Radius
    Computational Materials Science, 2009
    Co-Authors: Heng Li, H.-k. Yang, J Yan
    Abstract:

    With respect to wrinkling, wall thinning and cross section deformation, combined with analytical description, the deformation behaviors of thin-walled tube NC Bending with large diameter D/t (50.0-87.0) and Small Bending Radius Rd/D (1.0-2.0) are explored via a series of reliable 3D-FE models under ABAQUS platform. The results show that: (1) The segmentation feature is observed for the deformation fields such as effective compressive/tensile regions τc / τt, stress/strain distributions, wrinkling tendency, wall thinning and cross section deformation. With Smaller Rd/D, the tangent stress increases and becomes more inhomogenous. The maximum tangent stress σφ at the intrados increases by 46% with Rd/D from 2.0 to 1.2. While the distributions of σφ are nearly similar with larger D/t. With Smaller Rd/D and larger D/t, the velocity variation of tube materials becomes more obvious. (2) The wrinkling tendency and cross section deformation degree Δ D increase with Smaller Rd/D and larger D/t; With Smaller Rd/D, both the wall thinning and thickening degrees increase. The maximum wall thinning and thickening degrees increase by 24.0% and 52.5%, respectively. However, with larger D/t, the wall thinning degree increases, while the thickening degree decreases significantly. The maximum wall thinning degree increases by 31.3%, while the maximum thickening one decreases by 58.9%. Crown Copyright © 2009.

  • Forming characteristics of thin-walled tube Bending process with Small Bending Radius
    Transactions of Nonferrous Metals Society of China (English Edition), 2006
    Co-Authors: Heng Li, H.-k. Yang, R. J. Gu
    Abstract:

    Currently requirements of thin-walled tube with Small Bending Radius cause the defects such as wrinkling, overthinning and cross-section distortion more prone to occur in Bending process. Based on the analysis of the forming characteristics by analytical and experimental methods, a complete 3D elastic-plastic FEM model of the process was developed using ABAQUS/Explicit code, including Bending process, balls retracting and unloading process, and thus the plastic deformation characteristics with Small Bending Radius were investigated. The main results show that: 1) The utmost deformation feature of the NC Bending process is its continuous progressive deformation. 2) The occurring conditions of the defects such as wrinkling and tension instability in the process are obtained. The wrinkling is traditional on the double compressive stresses state and the tension instability is on the double tension stresses state. 3) The enhanced non-uniform deformation in thin-walled tube with Small Bending Radius is demonstrated by comparing the stress/strains distributions under the 1.5D and 1D Bending conditions. 4) For 1D Small Bending process, a new method-'stepped mandrel retraction' is proposed to improve the Bending quality in experiment according to the FE simulation. The simulation results are verified by experiment.