Analysis of Kinetics of Microcracking in Aluminum Alloys by the Method of Acoustic Emission

Investigations of processes of deformation and microcracking in samples of the D16-M aluminum alloy are reported. Matched curves of parameters of acoustic emission and optical signals versus sample elongation have been plotted. Critical parameters of acoustic emission correspond to correct strain values of the elastic-plastic transition and conventional yield strength of the material. A criterion of the prefracture state of the material based on the reported data has been suggested.     

Investigation of the Characteristics of Loop-Type Polymer Fiber-Optic Sensors

An analysis of the applicability of a well-known mathematical model of the process of emission by a bent beam-mode waveguide to loop-type polymer sensors is presented. It is shown that the nonlinear properties of the beam-mode waveguide are not taken into account in this model. Time dependences of the output signal with constant voltage level as well as the relaxation time of the voltage for a beam-mode waveguide made of d-polymethyl methacrylate – polyfluoro-acrylate are obtained.     

Identification of two different vibration modes in the same piezoceramic beam

Amplitude-frequency characteristics (AFC) of piezoceramic elements in the form of a prismatic rectangular beam and a thin rod of piezoceramic TsTBS-3, TsTBS-7, and TsTSS_T-5 polarized along the thickness are investigated. It is shown that, of the four resonance types observed in the investigated spectra, one pertains to the piezoelectric transverse mode L1 and, the other, to the longitudinal mode of vibrations. In this, it is possible to identify these modes under the conditions that the beam length 3.0$$ " align="middle" border="0"> and height of its cross section 3.0$$ " align="middle" border="0"> for TsTSS_T and >4 for TsTBS-7. An improved resonance-antiresonance method for determining the compatible elastic constants in the same specimen is proposed and substantiated. Compared to the known methods, this method facilitates determination of the constants with greater reliability and also simplifies their measurement procedure.Rostov-on-Don. Translated from Problemy Prochnosti, No. 12, pp. 102–105, December, 1989.     

Diagnostics of Multilayered Composite Structures with the Help of a Fiber-Optic System for Strain Measurements

The paper considers a built-in fiber-optic array system for technical diagnostic of composite structures measuring local strains in hazardous cross sections of these structures. The effect of repeated microscopic bends of optical fibers on the transmitted flux in structures strained by a tensile force of up to 1 kN over a temperature range of 20 to 100°C has been investigated. The increase in the tensile stress in components of a composite structure leads to a growth in the optical losses of up to 20–23% of the initial optical flux. The loss function (F) is linear in the region of mechanical forces of up to 1 kN and temperatures up to 40°C. An explanation has been suggested for the nonlinearity of (F) at temperatures above 40°C. The conclusion is that the developed system enables one to estimate the strength of multilayered composite structures and detect their prefracture states using singular points on opto-mechanical characteristics of optical fibers.     

Investigation of Strained States of Materials Using Fiber-Optic and Acoustic-Emission Methods

The paper reports on investigations of strained states and fracture of elements of thin-wall structures using acoustic and fiber-optic methods. A correlation has been found between the parameters of optical and acoustic signals on one side and strength characteristics of tested materials on the other. Combined tests using acoustic-emission and fiber-optic methods yield more reliable information about strained states of structural elements fabricated from various materials. These investigations can be used in developing diagnostic criteria for assessing technical conditions of thin-wall structures with the help of acoustic and fiber-optic methods.     

Technique of Determination of the Piezoelectric Modulus d 33 and Investigation of the Limits of its Use

The classification of the piezoelectric modulus measurement methods for different loading regimes is investigated. It is established that the quasi-static methods make it possible to determine the static piezoelectric constants with the minimum errors. An improved method of measuring the piezoelectric modulus d ₃₃ in the quasi-static regime is developed. The method ensures the minimum effect of changes in the domain orientation and transition processes. Dependences of d ₃₃ on the level of mechanical stresses _n are obtained for TsTS-19, TsTS-23, and TsTBS-3 piezoceramics and it is shown that their nature depends of the ferro-rigidity of the piezoceramics composition. Features of the dependences d ₃₃( _n ) associated with the variation of the contact area of piezoelectric elements in the process of measurements and the effect of changes in the domain orientation are revealed. It is shown that the lower boundary of the compression force amounts to 2 MPa for TsTS-19. It is also established that the optimum dimension of the piezoelectric elements in determining d ₃₃ must satisfy the condition 0:45 < < 1:75. It is calculated that the error in measurements of d ₃₃ in accordance with the method proposed is 4.5% with the confidence probability of 95%.