Yotsugi Shibuya

Mechanical environment of the supraspinatus tendon: A two-dimensional finite element model analysis

We performed 2-dimensional finite element model analysis to estimate the mechanical environment of the supraspinatus tendon. The geometric shape of the finite element model was determined by magnetic resonance imaging of a normal human shoulder obtained at 0 degrees, 30 degrees, and 60 degrees of abduction, whereas the histologic location of noncalcified and calcified fibrocartilage was determined from a cadaveric specimen. The supraspinatus tendon was pulled proximally with the force of 10 N at 0 degrees, 53 N at 30 degrees, and 115 N at 60 degrees of abduction. The area of high principal stress maximum was observed on the articular side of the supraspinatus tendon, which shifted toward the insertion as the arm was abducted. High stress concentration on the articular side of the supraspinatus tendon near its insertion during arm elevation may explain the frequent occurrence of rotator cuff tears at this site.

Mechanical environment of the supraspinatus tendon: three-dimensional finite element model analysis

BackgroundWe analyzed the mechanical environment of the supraspinatus tendon using a three-dimensional finite element model with the software programs MENTAT and MARC.MethodsThe supraspinatus tendon that attaches to the superior facet was extracted and modeled. The geometric shape of the humeral head was determined from computed tomography images, and the shape of the supraspinatus tendon was determined from magnetic resonance images of the shoulder at 0° of abduction in a healthy 27-year-old man. The distal portion of the humeral head was fixed, and 10 N of tensile force was applied to the proximal end of the tendon. The tensile stress was calculated.ResultsThe tensile stress was 1.8 MPa for the bursal side and 15.0 MPa for the articular side of the anterior portion of the supraspinatus tendon. The intensity was 0 MPa for the bursal side and 4.5 MPa for the articular side of the middle portion of the tendon. The intensity was 0.1 MPa for the bursal side and 5.2 MPa for the posterior edge of the tendon.ConclusionsBased on the three-dimensional finite element method, the maximal tensile stress was observed on the articular side of the anterior edge of the supraspinatus tendon. Our result may explain the frequent occurrence of rotator cuff tears at this site.

THERMOELASTIC ANALYSIS OF INTERFACIAL STRESS AND STRESS SINGULARITY BETWEEN A THIN FILM AND ITS SUBSTRATE

From advances in microelectronics and microelectromechanics, the area of applications for thin-film devices has been widely expanding. The thermal environment is severe in an increasing number of locations for thin-film devices. Thin-film devices are subjected to thermoelastic load due to a thermal expansion mismatch between a thin film and a substrate. In this study, interfacial stress between a thin film and its substrate and the behavior of singular stress at the edge are discussed on the basis of thermoelasticity. A boundary element method using fundamental solutions for dissimilar materials is extended to the thermoelastic problem. This method uses the solution that satisfies boundary conditions at the interface. Analytical treatment of the singular integral along the interface is used to evaluate the derivative of displacement. The method does not require discretization along the interface in the boundary element analysis. The interfacial stress is shown in detail, and the behavior of singular stress at the edge of the film is discussed from the results of the interfacial stress.

High Precise Positioning Control for Block Spring Motor

Nanotechnology is based on a combination of many technologies such as high precise positioning and force control, especially magnetic recording, biotechnology and semiconductor industry require the utilization of nanotechnology. To date, various actuator systems have been proposed, but their structural models show working distances of either less than a millimeter or over ten millimeters. Structural models with working distances of several millimeters are rare. Therefore, we propose a new structural design of an actuator that would enable construction of actuator systems with such working distances. This new actuator consists of a voice coil motor (VCM) and a new guide with an elastic support mechanism (ESM). The ESM consists of a special spring which is restricted to moving in only one direction. This new ESM engenders no lost motion, mechanical play, or friction with motion. Because, characteristically, the VCM thrusts and displaces the ESM linearly, highly precise positioning and force control can be realized using a simple controller. This paper presents basic data for developing future nano-actuator systems.

Force Feedback Control for Block Spring Motor

High precise positioning and force control are based on nanotechnology. Nanotechnology, especially nanometer positioning technology with high speed and robust force feedback control requires the utilization of a variety of technical fields including magnetic recording, biotechnology and the semiconductor industry. Until now there have been various actuator systems proposed, but the structure models have only working distances of either under a millimeter or over ten millimeters. A structural model with working distances ranging several millimeters has not yet been designed. Therefore we are proposing a new structure design of actuator that would allow us to build actuator systems with working distances between those parameters. This new actuator consists of a voice coil motor and a new guide with an elastic support mechanism. The elastic support mechanism consists of a special spring which is restricted to moving only one-way. This new ESM does not cause any lose motion, mechanical play or friction with motion. Since characteristically voice coil motor thrusts and displaces the elastic support mechanism linearly, highly precise positioning and force control can be realized using a simple controller. This paper will provide basic data for developing future nano-actuator systems.

Micro-Structural Model of Magneto-Rheological Composites With Magnetically Induced Stress for Harmonic Shear Deformation

Magneto-rheological composites with magnetic particles are prepared. The magnetic particle is Fe-Si-B-Cr system and the average diameter is 10μm. Matrix of the composite is silicon gel. We characterized dynamic response of the material by shear test in magnetic field where intensities are 0 mT, 105 mT and 211 mT. The stiffness and damping capacity of the composite increase with increasing of the magnetic field. To understand mechanism of behavior of magneto-rheological composites, we make a model of the composite with periodical micro structure. The magneto-rheological composite undergoes magnetically induced internal stress field by applied magnetic field. The analysis model involved effect of the applied magnetic field as initial stress in the material. Particles and the magnetically induced stress make locally large strain field in the gel material. A large deformation analysis with the Ogden model using finite element method is made to demonstrate behavior of magneto-rheological composites. The simulation results are compared with experiment results and verified the effectiveness of the model.© 2014 ASME

Shear Vibration Property of Magnetically-Responsive Gels in Magnetically Open Looped System

This paper deals with dynamic shear deformation characteristics of magnetically-responsive (MR) gels under inhomogeneous magnetic fields. Magnetic particles as Fe-Si-Ni type which is generally known as permalloy, were dispersed in silicone gel to prepare the MR composite. An external magnetic field is applied only to one side of the MR gel by using magnetically open-looped circuit, and different excitation frequencies with constant shear strain amplitude is also applied to MR gels with each different thickness. The shear displacement-force relation of MR gel in open-looped circuit were observed, and mechanical properties such as storage and loss moduli were evaluated from experimental data. As a result, it is found that the characteristics change to a large extent depending on the applied magnetic field and the thickness of the MR gel.Copyright

Evaluation of Nonlinear Damping Properties of Magnetorheological Gels Under Shear Loading

Rheological properties of magnetorheological gels can be changed reversibly by applied magnetic fields. Magnetorheological gels with different material system are characterized the dynamic response of the material by shearing test in magnetic field. Nonlinear behavior is observed in the dynamic response of the material. To understand mechanism of the behavior, dynamic properties of magnetorheological gels are evaluated by experiment and nonlinear viscoelastic model. Magnetorheological gels used in this study consist of three types of paramagnetic particles and a cyclic-poly-siloxane gel matrix. Three material systems of magnetic particles are chosen: Fe-Si-Ni, Si-Fe and Fe-Si-B-Cr types. Shear testing is conducted in magnetic field 0mT, 105mT and 211mT. The stress-strain response under shear deformation is characterized by non-ellipsoidal hysteresis loop due to nonlinearity of the response. To identify the nonlinear properties, analysis in frequency domain is applied to identify the dynamic response of the material. Nonlinear viscoelastic model with high order components is made and phenomenon of the non-ellipsoidal hysteresis loop in the stress-strain relation and damping properties are illustrated.Copyright

Viscoelastic Homogenization Approach for Damping Properties of Polymer Composites Using Fractional Calculus

Polymer composites are attractive material system with damping ability to reduce vibration of mechanical structures and improve controllability of mechanical system. To understand effect of constituents and microstructure on damping properties of polymer composites, a detailed micromechanical study is needed to develop the method of analysis for microscopic viscoelastic deformation and macroscopic damping properties. Viscoelastic homogenization approach with fractional calculus is developed to evaluate effective damping properties of polymer composites. The microstructure of the composite is supposed to be periodic and polymer matrix is viscoelastic medium. Damping properties of the composite are evaluated from the stress strain diagram and associated energy dissipation during cyclic loading. Viscoelastic properties of the polymer matrix are identified using a generalized fractional Maxwell model with spring and fractional elements. Coefficients of elements in the generalized fractional Maxwell model are determined to be fitting into experimental data in frequency domain. The homogenized stress strain relation in time domain given by inverse Laplace transform is derived and numerical calculations are carried out.Copyright

Evaluation of Internal Friction of Viscoelastic Composites with Meso-Scale Structures for Vibration Damping of Mechanical Structures

Viscoelastic analysis of polymer composites is focused to understand effect of meso-scale structure of composite on the internal friction for application of vibration damping in precision instruments. In this paper, the meso-scale structure of the composite is supposed to be periodically clustered hexagonal array of fibers. Internal damping of the composite is evaluated by energy dissipation in cyclic response. Interaction of fibers and viscoelasticity of the matrix cause the energy dissipation in the composite. To evaluate the damping capacity of the composite in details, a homogenization theory with multi-scale asymptotic expansion is used to analyze meso- and macro-scale behavior of the composite