The Experts below are selected from a list of 102 Experts worldwide ranked by ideXlab platform

Valery I Levitas - One of the best experts on this subject based on the ideXlab platform.

  • plastic flows and Strain induced alpha to omega phase transformation in zirconium during compression in a diamond anvil cell finite element simulations
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Biao Feng, Valery I Levitas
    Abstract:

    Abstract Coupled plastic flows and the Strain-induced α → ω phase transformation (PT) in a zirconium sample under compression in a diamond anvil cell are investigated using finite element method (FEM). The PT is treated as Strain-induced rather than pressure-induced and the previously developed model for Strain-induced PTs is utilized. Very heterogeneous fields of stress tensor, accumulated plastic Strain, and concentration of the ω phase are obtained for different applied loads. The PT starts at the center of a sample when pressure exceeds the minimum pressure p e d = 1.7 G P a , below which a Direct Strain-induced PT to a high pressure phase cannot occur, and it propagates from the center to the periphery with an increasing load. Even at the maximum pressure of 7 GPa, the PT is not completed everywhere. With an increasing load, the pressure and pressure gradient along the radial Direction significantly increase in the two-phase region due to the much larger yield strength of the ω phase. This in turn promotes transformation and produces a positive mechanochemical feedback. Obtained results are utilized for the interpretation of published experimental data on pressure-, stress-, and Strain-induced α → ω PTs in Zr and Titanium (Ti) and α → β and ω → β PTs in Zr under compression and high pressure torsion. This includes correcting the reported minimum pressures for these transformations by a factor of 3–6 due to the stress heterogeneity, the effect of transmitting media, the pressure hysteresis, and the reversibility of the transformation.

  • plastic flows and Strain induced alpha to omega phase transformation in zirconium during compression in a diamond anvil cell finite element simulations
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Biao Feng, Valery I Levitas
    Abstract:

    Abstract Coupled plastic flows and the Strain-induced α → ω phase transformation (PT) in a zirconium sample under compression in a diamond anvil cell are investigated using finite element method (FEM). The PT is treated as Strain-induced rather than pressure-induced and the previously developed model for Strain-induced PTs is utilized. Very heterogeneous fields of stress tensor, accumulated plastic Strain, and concentration of the ω phase are obtained for different applied loads. The PT starts at the center of a sample when pressure exceeds the minimum pressure p e d = 1.7 G P a , below which a Direct Strain-induced PT to a high pressure phase cannot occur, and it propagates from the center to the periphery with an increasing load. Even at the maximum pressure of 7 GPa, the PT is not completed everywhere. With an increasing load, the pressure and pressure gradient along the radial Direction significantly increase in the two-phase region due to the much larger yield strength of the ω phase. This in turn promotes transformation and produces a positive mechanochemical feedback. Obtained results are utilized for the interpretation of published experimental data on pressure-, stress-, and Strain-induced α → ω PTs in Zr and Titanium (Ti) and α → β and ω → β PTs in Zr under compression and high pressure torsion. This includes correcting the reported minimum pressures for these transformations by a factor of 3–6 due to the stress heterogeneity, the effect of transmitting media, the pressure hysteresis, and the reversibility of the transformation.

Biao Feng - One of the best experts on this subject based on the ideXlab platform.

  • plastic flows and Strain induced alpha to omega phase transformation in zirconium during compression in a diamond anvil cell finite element simulations
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Biao Feng, Valery I Levitas
    Abstract:

    Abstract Coupled plastic flows and the Strain-induced α → ω phase transformation (PT) in a zirconium sample under compression in a diamond anvil cell are investigated using finite element method (FEM). The PT is treated as Strain-induced rather than pressure-induced and the previously developed model for Strain-induced PTs is utilized. Very heterogeneous fields of stress tensor, accumulated plastic Strain, and concentration of the ω phase are obtained for different applied loads. The PT starts at the center of a sample when pressure exceeds the minimum pressure p e d = 1.7 G P a , below which a Direct Strain-induced PT to a high pressure phase cannot occur, and it propagates from the center to the periphery with an increasing load. Even at the maximum pressure of 7 GPa, the PT is not completed everywhere. With an increasing load, the pressure and pressure gradient along the radial Direction significantly increase in the two-phase region due to the much larger yield strength of the ω phase. This in turn promotes transformation and produces a positive mechanochemical feedback. Obtained results are utilized for the interpretation of published experimental data on pressure-, stress-, and Strain-induced α → ω PTs in Zr and Titanium (Ti) and α → β and ω → β PTs in Zr under compression and high pressure torsion. This includes correcting the reported minimum pressures for these transformations by a factor of 3–6 due to the stress heterogeneity, the effect of transmitting media, the pressure hysteresis, and the reversibility of the transformation.

  • plastic flows and Strain induced alpha to omega phase transformation in zirconium during compression in a diamond anvil cell finite element simulations
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Biao Feng, Valery I Levitas
    Abstract:

    Abstract Coupled plastic flows and the Strain-induced α → ω phase transformation (PT) in a zirconium sample under compression in a diamond anvil cell are investigated using finite element method (FEM). The PT is treated as Strain-induced rather than pressure-induced and the previously developed model for Strain-induced PTs is utilized. Very heterogeneous fields of stress tensor, accumulated plastic Strain, and concentration of the ω phase are obtained for different applied loads. The PT starts at the center of a sample when pressure exceeds the minimum pressure p e d = 1.7 G P a , below which a Direct Strain-induced PT to a high pressure phase cannot occur, and it propagates from the center to the periphery with an increasing load. Even at the maximum pressure of 7 GPa, the PT is not completed everywhere. With an increasing load, the pressure and pressure gradient along the radial Direction significantly increase in the two-phase region due to the much larger yield strength of the ω phase. This in turn promotes transformation and produces a positive mechanochemical feedback. Obtained results are utilized for the interpretation of published experimental data on pressure-, stress-, and Strain-induced α → ω PTs in Zr and Titanium (Ti) and α → β and ω → β PTs in Zr under compression and high pressure torsion. This includes correcting the reported minimum pressures for these transformations by a factor of 3–6 due to the stress heterogeneity, the effect of transmitting media, the pressure hysteresis, and the reversibility of the transformation.

Zhenghua Luo - One of the best experts on this subject based on the ideXlab platform.

  • shear force feedback control of flexible robot arms
    International Conference on Robotics and Automation, 1995
    Co-Authors: Zhenghua Luo, N Kitamura, Baozhu Guo
    Abstract:

    For flexible robots with rotational joints it has been shown previously by Luo (1993), that Direct Strain feedback can damp out vibrations very satisfactorily. In this paper, a simple sensor-based output feedback control law, called shear force feedback, is newly proposed to control vibrations arising from structural flexibility of robots of Cartesian or SCARA types. Closed-loop exponential stability of such shear force feedback system is proved. Experimental results on set point control and trajectory tracking control are reported. It is found that the simple PI+shear force feedback can yield good performance for both robot motion and vibration suppression. >

  • Direct Strain feedback control of flexible robot arms new theoretical and experimental results
    IEEE Transactions on Automatic Control, 1993
    Co-Authors: Zhenghua Luo
    Abstract:

    This paper addresses control problems for flexible robot arms by using Direct Strain feedback. The purpose is to make clear why Direct Strain feedback can damp out vibration of flexible arms satisfactorily. We concentrate on one-link flexible robot arms whose dynamic models can be represented by linear partial differential equations with appropriate boundary conditions which have been well examined in a number of papers. A key contribution of this paper is the introduction of the concept of (strict) A-dependent operators, which allows us to prove rigorously the closed loop stability of Direct Strain feedback and the existence and uniqueness of nonstandard second order abstract differential equations in Hilbert spaces. Several control experiments are performed, verifying the main theoretical points of this paper, demonstrating satisfactory control results of Direct Strain feedback, and leading to potential application of this simple control method for flexible robot control. >

Donald E Ingber - One of the best experts on this subject based on the ideXlab platform.

  • ultra rapid activation of trpv4 ion channels by mechanical forces applied to cell surface β1 integrins
    Integrative Biology, 2010
    Co-Authors: Benjamin D Matthews, Charles K Thodeti, Jessica D Tytell, Akiko Mammoto, Darryl R Overby, Donald E Ingber
    Abstract:

    Integrins are ubiquitous transmembrane mechanoreceptors that elicit changes in intracellular biochemistry in response to mechanical force application, but these alterations generally proceed over seconds to minutes. Stress-sensitive ion channels represent another class of mechanoreceptors that are activated much more rapidly (within msec), and recent findings suggest that calcium influx through Transient Receptor Potential Vanilloid-4 (TRPV4) channels expressed in the plasma membrane of bovine capillary endothelial cells is required for mechanical Strain-induced changes in focal adhesion assembly, cell orientation and Directional migration. However, whether mechanically stretching a cell's extracellular matrix (ECM) adhesions might Directly activate cell surface ion channels remains unknown. Here we show that forces applied to β1 integrins result in ultra-rapid (within 4 msec) activation of calcium influx through TRPV4 channels. The TRPV4 channels were specifically activated by mechanical Strain in the cytoskeletal backbone of the focal adhesion, and not by deformation of the lipid bilayer or submembranous cortical cytoskeleton alone. This early-immediate calcium signaling response required the distal region of the β1 integrin cytoplasmic tail that contains a binding site for the integrin-associated transmembrane CD98 protein, and external force application to CD98 within focal adhesions activated the same ultra-rapid calcium signaling response. Local Direct Strain-dependent activation of TRPV4 channels mediated by force transfer from integrins and CD98 may therefore enable compartmentalization of calcium signaling within focal adhesions that is critical for mechanical control of many cell behaviors that underlie cell and tissue development.

Baozhu Guo - One of the best experts on this subject based on the ideXlab platform.

  • shear force feedback control of flexible robot arms
    International Conference on Robotics and Automation, 1995
    Co-Authors: Zhenghua Luo, N Kitamura, Baozhu Guo
    Abstract:

    For flexible robots with rotational joints it has been shown previously by Luo (1993), that Direct Strain feedback can damp out vibrations very satisfactorily. In this paper, a simple sensor-based output feedback control law, called shear force feedback, is newly proposed to control vibrations arising from structural flexibility of robots of Cartesian or SCARA types. Closed-loop exponential stability of such shear force feedback system is proved. Experimental results on set point control and trajectory tracking control are reported. It is found that the simple PI+shear force feedback can yield good performance for both robot motion and vibration suppression. >