Plane Problem for Layered Composites with Periodic Array of Interfacial Cracks Under Compressive Static Loading

The current paper addresses the problem of 2-D modelling of the onset of failure process in a layered composite with periodic array of interfacial cracks under static compression along layers. The statement of the problem is based on the most accurate approach, the model of piecewise-homogenous medium. The condition of plane strain state is considered. The shear and the extensional buckling modes are examined. The laminae are modelled by transversally isotropic material (a matrix reinforced by continuous parallel fibres). The complex non-classical failure mechanics problem is solved utilizing finite element analysis. It is found that the 0°-plies volume fraction, the crack length and the mutual position of cracks influence the critical strain in the composite.     

Effect of the green noise on the phase-locked-loop frequency-control system

The operation of the phase-locked-loop frequency-control system under the action of low-passfiltered broadband stationary noise (green noise) is considered. In order to analyze such systems, an averaging method that takes into account the external noise in a zeroth-order approximation has been constructed. Notions of an effective potential and correction process have been introduced and their role in the development of the dynamics of the system has been determined. A numerical experiment has been performed, which confirms the theoretical conclusions.     

Control of attendance applied in higher education through mobile NFC technologies

This paper presents an improved attendance control system, required for continuous evaluation which has become compulsory following the Bologna Process. It provides a solution based on NFC technology and is based on a real project developed and pilot tested at the “Universidad Pontificia de Salamanca, Campus Madrid”.     

Characteristics of the fracture surface of gray magnesium cast irons after dynamic fracture

Conclusions Modification of gray test iron with as much as 0.08% Mg leads to globularization of graphite and greatly changes the average rate of fracture. The fracture of the pearlitic matrix is brittle in character. The fracture of the pearlitic matrix is brittle in character. Thus, the discrete pattern of crack propagation observed is due mainly to the presence of graphite inclusions, which are areas of scattering of the elastic energy of the crack — relaxation areas. Comparison of the electron fractographs of cast and heat-treated samples (alloy with 0.08% Mg) revealed new elements of brittle fracture in the latter. Crack propagation in the ferritic cast iron is a ccompanied by intensive twinning (Fig. 3g, positive replica). It should be noted that ferritizing annealing has a negligible effect on the average rate of crack propagation (350 m/sec).The presence of ferrite in castings of alloys modified with 0.15 and 0.23% Mg has a negligible effect on the fracture, since the ferrite contains silicon and is therefore not a ductile phase. Comparison of the type of fracture leads to the conclusion that fracture can be regarded as brittle for all the cast irons tested. The change in the fine structure of the fracture surface with increasing magnesium concentrations first manifest in increasing signs of brittle fracture (up to 0.08% Mg) and then in weakening of these signs, is due to the change in the rate of crack propagation, which in turn depends on the shape and distribution of graphite, depending on the structural condition of the cast iron.Institute of Problems of Machine Construction, Academy of Sciences of the Ukrainian SSR. V. I. Lenin Kharkov Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 26–28, August, 1979.     

Elastodynamic Problem for Two Penny-Shaped Cracks: The Effect of Cracks’ Closure

The paper is devoted to the solution of the three-dimensional elastodynamic problem for linearly elastic, homogeneous and isotropic solid with two penny-shaped in-plane cracks under normally incident harmonic tension-compression wave with allowance for the contact interaction of crack faces. The effect of the distance between cracks on the stress intensity factor (opening mode) is studied for different wave numbers. The results are compared with those obtained neglecting the cracks’ closure.     

Computation scheduling in multiprocessor real-time automatic control systems with constrained processor memory

For the automatic control systems with tight real time, construction of feasible schedules under the given job execution deadlines was considered, and in addition the constraints on processor memory were taken into consideration. Two methods were developed to solve this problem. The first method is based on reducing the original problem to the search of a multi-commodity flow in a special network. The second method offers a fast algorithm to determine a feasible schedule for the uniprocessor case.Translated from Avtomatika i Telemekhanika, No. 2, 2005, pp. 138–147.Original Russian Text Copyright © 2005 by Guz, Furugyan.     

Contact problem for flat crack under two normally incident tension–compression waves with wave mode-shifting

The frictionless contact interaction of the finite crack edges in an infinite plane is studied for the case of normal incidence of two harmonic tension–compression waves with multiple mode-shifted frequencies. Boundary integral equation method and constrained optimization algorithm are used for the problem solution. Distribution of the forces of contact interaction and displacement discontinuity in space and time are analyzed. Influence of the wave frequencies on the stress intensity factor for different normalized wave numbers is considered here.     

An automated system for PAA control and adjustment

The paper presents a classification of contemporary methods for measurement of PAA characteristics, potentialities of their development and hardware implementation. The emphasis is made on diagnostic of PAA technical state, on determination of amplitude-phase distribution (APD) over the aperture, and on PAA adjustment procedures. The paper considers technical characteristics of automated measurement systems (AMS) and of the relevant equipment. Examples of AMS application for PAA parameter determination are included.     

3D Model and Estimation of Fiber Interaction Effects During Internal Instability in Non-Linear Composites

A 3D model and an estimation of fiber interaction effects during internal instability n non-linear composites are presented Results are based on a micrornechanies solution for a series of fibers embedded in an infinite non-linear incompressible matrix. An ideal bonding between the fibers and the matrix is assumed. Comparison with a limiting case in which the distance bet’ween the neighboring fibers tends to infinity is carried out. It shows the significance of the fiber interaction effects in the considered problem.