The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform

Raj N. Singh - One of the best experts on this subject based on the ideXlab platform.

  • Effect of the mechanical boundary condition at the crack Surfaces on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1998
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    Abstract A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the combined mechanical and electrical loads. For high electrical to mechanical load ratios, the assumption of crack Surfaces to be free of Surface Traction as the mechanical boundary condition is not valid for two cases of combined electrical and mechanical loadings—(i) applied stress and negative applied electric field (electric field opposite to the direction of poling) and (ii) applied strain and positive applied electric field. The stress distributions at the crack tip for these loading conditions under the assumption of closed crack mechanical boundary condition are found to be different from those under the assumption of crack Surfaces to be free of Surface Traction.

  • Influence of applied electric field and mechanical boundary condition on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1997
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic subject to the applied electric fields. Under a negative applied electric field (electric field opposite to the direction of poling), the assumption of crack Surfaces to be free of Surface Traction as the mechanical boundary condition is found to be invalid. It is shown that the stress distributions at the crack tip under the negative applied electric field are different for the closed crack mechanical boundary condition than those for the Traction-free crack Surface mechanical boundary condition.

Kazumi Matsui - One of the best experts on this subject based on the ideXlab platform.

  • A quadrilateral shell element with degree of freedom to represent thickness–stretch
    Computational Mechanics, 2017
    Co-Authors: Takeki Yamamoto, Takahiro Yamada, Kazumi Matsui
    Abstract:

    This paper presents a quadrilateral shell element incorporating thickness–stretch, and demonstrates its performance in small and large deformation analyses for hyperelastic material and elastoplastic models. In terms of geometry, the proposed shell element is based on the formulation of the MITC4 shell element, with additional degrees of freedom to represent thickness–stretch. To consider the change in thickness, we introduce a displacement variation to the MITC4 shell element, in the thickness direction. After the thickness direction is expressed in terms of the director vectors that are defined at each midSurface node, additional nodes are placed along the thickness direction from the bottom Surface to the top Surface. The thickness–stretch is described by the movement of these additional nodes. The additional degrees of freedom are used to compute the transverse normal strain without assuming the plane stress condition. Hence, the three dimensional constitutive equation can be employed in the proposed formulation without any modification. By virtue of not imposing the plane stress condition, the Surface Traction is evaluated at the Surface where the Traction is applied, whereas it is assessed at the midSurface for conventional shell elements. Several numerical examples are presented to examine the fundamental performance of the proposed shell element. In particular, the proposed approach is capable of evaluating the change in thickness and the stress distribution when the effect of the Surface Traction is included. The behavior of the proposed shell element is compared with that of solid elements.

  • A quadrilateral shell element with degree of freedom to represent thickness---stretch
    Computational Mechanics, 2016
    Co-Authors: Takeki Yamamoto, Takahiro Yamada, Kazumi Matsui
    Abstract:

    This paper presents a quadrilateral shell element incorporating thickness---stretch, and demonstrates its performance in small and large deformation analyses for hyperelastic material and elastoplastic models. In terms of geometry, the proposed shell element is based on the formulation of the MITC4 shell element, with additional degrees of freedom to represent thickness---stretch. To consider the change in thickness, we introduce a displacement variation to the MITC4 shell element, in the thickness direction. After the thickness direction is expressed in terms of the director vectors that are defined at each midSurface node, additional nodes are placed along the thickness direction from the bottom Surface to the top Surface. The thickness---stretch is described by the movement of these additional nodes. The additional degrees of freedom are used to compute the transverse normal strain without assuming the plane stress condition. Hence, the three dimensional constitutive equation can be employed in the proposed formulation without any modification. By virtue of not imposing the plane stress condition, the Surface Traction is evaluated at the Surface where the Traction is applied, whereas it is assessed at the midSurface for conventional shell elements. Several numerical examples are presented to examine the fundamental performance of the proposed shell element. In particular, the proposed approach is capable of evaluating the change in thickness and the stress distribution when the effect of the Surface Traction is included. The behavior of the proposed shell element is compared with that of solid elements.

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

  • influence of Surface Traction on soft robot undulation
    The International Journal of Robotics Research, 2013
    Co-Authors: Carmel Majidi, Robert F Shepherd, Rebecca K Kramer, George M Whitesides, Robert J Wood
    Abstract:

    A pneumatically-driven robot traverses Surfaces with different Traction by adopting an undulatory mode of locomotion. The robot is composed of soft elastomer (elastic modulus ~100 kPa), an inextensible but flexible neutral plane, and embedded pneumatic channels. In contrast to conventional robots and wheeled vehicles, the robot deforms elastically to make ground contact over a relatively large area, where interfacial Tractions have a unique role in controlling both the speed and direction of locomotion. Here, we demonstrate that for the same undulatory gait, the robot will either move forward or backward depending on the ground composition. Building on mathematical principles of elasticity and friction, we introduce a theoretical model that identifies the tribological properties that determine the direction of locomotion. Though overlooked in the past, this tribology-controlled phenomenon represents a central feature of undulation on smooth, soft, and slippery Surfaces. These insights provide a starting point for identifying locomotion strategies that allow soft robots, like their natural invertebrate counterparts, to navigate a broad range of Surfaces and terrains.

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

  • Hypersingular integral formulation of elastic wave scattering
    Engineering Analysis With Boundary Elements, 1992
    Co-Authors: L J Gray, S J Chang
    Abstract:

    Abstract A hypersingular boundary integral formulation for calculating two dimensional elastic wave scattering from thin bodies and cracks is described. The boundary integral equation for Surface displacement is combined with the hypersingular equation for Surface Traction. The difficult part in employing the Traction equation, the derivation of analytical formulas for the hypersingular integral by means of a limit to the boundary, is easily handled by means of symbolic computation. In addition, the terms containing an integrable logarithmic singularity are treated by a straightforward numerical method, bypassing the use of Taylor series expansions. Example wave scattering calculations for cracks and thin ellipses are presented.

Susmit Kumar - One of the best experts on this subject based on the ideXlab platform.

  • Effect of the mechanical boundary condition at the crack Surfaces on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1998
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    Abstract A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the combined mechanical and electrical loads. For high electrical to mechanical load ratios, the assumption of crack Surfaces to be free of Surface Traction as the mechanical boundary condition is not valid for two cases of combined electrical and mechanical loadings—(i) applied stress and negative applied electric field (electric field opposite to the direction of poling) and (ii) applied strain and positive applied electric field. The stress distributions at the crack tip for these loading conditions under the assumption of closed crack mechanical boundary condition are found to be different from those under the assumption of crack Surfaces to be free of Surface Traction.

  • Influence of applied electric field and mechanical boundary condition on the stress distribution at the crack tip in piezoelectric materials
    Materials Science and Engineering: A, 1997
    Co-Authors: Susmit Kumar, Raj N. Singh
    Abstract:

    A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic subject to the applied electric fields. Under a negative applied electric field (electric field opposite to the direction of poling), the assumption of crack Surfaces to be free of Surface Traction as the mechanical boundary condition is found to be invalid. It is shown that the stress distributions at the crack tip under the negative applied electric field are different for the closed crack mechanical boundary condition than those for the Traction-free crack Surface mechanical boundary condition.