An investigation into the location of crack initiation sites in alumina, polycarbonate and mild steel

The effects of notch root radius on fracture toughness and crack initiation sites have been investigated in this paper using three different classes of materials. Data on alumina which represent ceramics, mild steel from the metals ffeily and polycarbonate representing plastics were obtained and analysed. The locations of crack initiation sites have been pinpointed by scanning electron microscopy. These identified sites more or less are located within the critical process zone or the theoretical plastic zone. The critical process zone size ( D _c ) or the theoretical plastic zone size ( R _YF ) are independent of the notch root radius unlike the plain-strain fracture toughness of notched specimens [ K _{IC (ρ)].} The authors emphasize why the parameters D _c and R _YF are useful for a quantitative evaluation of the reliability of structural materials.     

Numerical analysis of integrated acoustooptic tunable filters withweighted coupling

A numerical approach based on the finite element method (FEM) and the beam propagation method (BPM) is newly formulated for design and modeling of integrated acoustooptic tunable filters (AOTF's) with weighted coupling on a piezoelectric substrate. First, acoustical field profiles in the substrate region and on the substrate surface are separately calculated with FEM and BPM, respectively. These two-dimensional (2-D) profiles are used for constructing three-dimensional (3-D) strain and electric field profiles. Then, from the strains and electric fields the refractive index changes due to acoustooptic (AO) and electrooptic (EO) effects are derived. Finally, by analyzing modified optical waveguides with AO8- and EO-induced changes in refractive indexes using again BPM, optical filter characteristics of AOTF's can be evaluated. Numerical examples are shown for AOTF's with a tapered acoustical directional coupler on a LiNbO₃ substrate     

Stress analysis method for elastically anisotropic material basedoptical waveguides and its application to strain-induced opticalwaveguides

A numerical approach for the stress analysis of elastically anisotropic material-based optical waveguides is newly formulated with the finite element method (FEM). The stress analysis method developed here is linked to the guided mode analysis method to produce a two-step analysis of acoustooptic modulation of optical waveguides. Numerical examples are shown for strain-induced optical waveguides on LiNbO₃ substrates     

Noncontact impedance control for redundant manipulators

Proposes an impedance control method that can regulate a virtual impedance between a robot manipulator and external objects using visual information. The conventional impedance control method is not useful in some cases where no interaction force between the arm and its environment exists, although it is one of the most effective control methods for manipulators in contact with the environment. Using the proposed method, we can control the manipulator motion based on the virtual impedance before contact with the objects. The validity of the proposed method is verified through computer simulations and experiments using a direct-drive robot     

Guided-mode and leaky-mode analysis by imaginary distance beampropagation method based on finite element scheme

As a simple analysis method to solve eigenmodes of optical waveguides, we present an imaginary distance beam propagation method (BPM) based on finite element scheme. The matrices used in the beam propagation analysis are essentially complex, so lossy optical waveguides can be easily treated. Moreover, employing the transparent boundary condition or perfectly matched layer boundary condition, the validity of a which has been already confirmed in the real distance BPM, we can easily treat not only guided modes but leaky ones. To show the validity and usefulness of this approach, eigenmodes of twoand three-dimensional leaky waveguides, and optical fibers are calculated     

Terminal sliding mode control of second-order nonlinear uncertain systems

In this paper, a terminal sliding mode control scheme is proposed for second-order nonlinear uncertain systems. By using a function augmented sliding hyperplane, it is guaranteed that the output tracking error converges to zero in finite time which can be set arbitrarily. In addition, the proposed scheme eliminates the reaching phase problem so that the closed-loop system always shows the invariance property to parameter uncertainties. Copyright © 1999 John Wiley & Sons, Ltd.     

Blends of aliphatic polyesters. II. Hydrolysis of solution-cast blends from poly(L-lactide) and poly(E-caprolactone) in phosphate-buffered solution

Blend films were prepared from poly(L -lactide) (PLLA) and poly(E-caprolactone) (PCL) with different PLLA contents [X_PLLA (w/w) = PLLA/(PCL + PLLA)] by the solution-casting method and their hydrolysis behaviors were investigated up to 20 months in a phosphate-buffered solution of pH 7.4 at 37°C by gel permeation chromatography, tensile testing, differential scanning calorimetry, and gravimetry. Polarizing microscopic observation and dynamic mechanical analysis revealed that PCL and PLLA were phase-separated in blend films before hydrolysis. The mass remaining, molecular weight, and tensile strength of the blend films with X_PLLA of 0.5 and 0.75 decreased more rapidly by hydrolysis than those of the nonblended PLLA, while the elongation at break of the blend film of X_PLLA = 0.25 decreased the slowest. The rate constant for hydrolysis (k) calculated from the M_n change during hydrolysis was higher for blend films of X_PLLA = 0.5 and 0.75 than those expected from k of nonblended PLLA and PCL. The melting temperature (T_m) of PLLA in the blend and nonblended films of X_PLLA = 0.5, 0.75, and 1 decreased from 179 to 161, 160, and 175°C upon hydrolysis for 20 months, respectively, while that for X_PLLA = 0.25 slightly increased from 176 to 177°C. On the other hand, T_m and the crystallinity of PCL was significantly increased by hydrolysis for 20 months, irrespective of X_PLLA. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 405–415, 1998     

Servo motor adaptive speed control under angle-dependent disturbances using an RBF network

It is well known that the angle-dependent disturbance in a servo motor caused by nonuniformity of field windings, armature cogging, rotor imbalance, nonuniform load and so on, may influence the speed control performance greatly. This often leads to large speed fluctuations which are undesired in practical situations. Therefore speed fluctuation reduction techniques in the presence of angle-dependent disturbances are strongly required and have been studied by many researchers. In this paper, the authors propose a new approach to this problem via adaptive control with the aid of a radial basis function (RBF) network composed of Gaussian basis functions. The angle-dependent disturbance, viewed as a periodic non-linear function with a period of 2π radians in the angular domain, is approximated by an RBF network in (0, 2π) radians. Then an adaptive linearization control system employing the RBF network which compensates for the disturbance is proposed. The RBF network has the advantage that it is linear in the parameters and hence parameter adaption is very fast and easy to implement. It is proved through theoretical analysis that the stability of adaptive control is guaranteed by Lyapunov stability theory. Finally, simulation and experimental results are included in the paper to show the excellent performance of the proposed method. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(4): 77–86, 1997     

Observation of lightning effect on power distribution lines by still cameras

In order to clarify the cause of lightning outages of a distribution line, simultaneous observation of lightning discharge channels and types of damage on distribution lines were carried out with still cameras from July 1993 through July 1995. High-voltage lines located in the observation area did not suffer from induced voltages due to indirect lightning strikes, even if such lightning strikes were nearby. One instance of a direct lightning strike on a distribution line was observed. The striking point was the span center of the overhead ground wire, and only a transformer fuse was blown on the high-voltage line. Damage to surge arresters was observed in the case of a lightning strike on a building located near a distribution line. The cause is thought to have been lightning current which flowed into the nearby distribution line through the damaged arresters. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(1): 17–23, 1997