The article presents results of the investigation of the quantitative evaluation of the degree of damage, described by the measure of accumulated plastic strain obtained in a static tensile test, using selected non-destructive techniques. Inconel 718 alloy was tested. The tests were conducted using a new type of specimens of variable cross-sectional area of measuring part. This provided a continuous distribution of plastic strain in the gage part of the specimen. The permanent deformation that varies along the sample axis enables an analysis of damage induced by a plastic deformation. The proposed method enables replacing the series of specimens by one sample. Degradation of the alloy corresponds with the changes of the electromagnetic properties of the material—the phase angle of the complex impedance of the eddy current, as well as with acoustics properties of material—acoustic birefringence of ultrasonic waves. It allows to determine the degree of damage of the material using noninvasive, non-destructive methods. Using the damage parameter proposed by Johnson it is possible to obtain the correlation between the non-destructive results and a damage degree of the material. The presented testing method delivers information about changes in the material structure caused by permanent deformation.
We present results of studying the spatial variation of parameters of the electrical response to a weak impact under stepwise loading of concrete beams reinforced with steel rods. It is proposed to use the following diagnostic parameters to characterize the presence of a defective area in reinforced beams: the maximum coefficient of correlation between the spectrum of electrical signal after stepwise loading and the original spectrum; the frequency shift for which the maximum correlation coefficient is observed; the coefficient of correlation between the spectrum of signal at the current loading stage and the signal spectrum at the previous stage; and the center of gravity of the spectrum. The proposed method can be used to locate the defective area in reinforced concrete under bending conditions.
A new Doppler-effect–based method for nondestructive testing of the condition of the inner walls of pipelines using a flowing fluid is considered. An optical method has been used to reveal specific features in the structure of the fluid-medium flow in a circular-section pipeline. A new technique that makes use of laser radiation scattered on flowing-fluid particles has been proposed for determining the coordinates of a flawed zone on the inner pipeline wall. The technique makes it possible to determine the zone coordinates along the length and diameter of the pipeline.
The possibility of detecting subsurface flaws in solids using the scanning high-frequency acoustic-microscopy method was investigated. The influence of a distortion of the focal region and aberrations, which appear during focusing to a subsurface region in a solid, on the formation of the output signal of a microscope is estimated via mathematical simulation of the refraction of focused acoustic beams in a solid and during experiments on a laboratory scanning acoustic microscope at a 400-MHz frequency of probing acoustic waves.
On the basis of analyzed factors that lead to the amplitude variation of an echo signal from identical reflectors in a quality-control sample and a test sample with curved surfaces, the correction factor for the amplitude adjustment is represented as the product of several factors. Calculation methods are proposed for the components of the correction factor for the case of a curved entry surface of an arbitrary shape and a position relative to the transducer.
Equations that are used for the calculation and distributions of the electrical voltage U(t) output from a magnetic-field transducer as it scans a discrete magnetic medium with recorded residual magnetic fields, which were produced in it by acting individual magnetic-field pulses with opposite-polarity surges, are reported. The distributions were obtained via the Delphi programming language. The phenomenon of hysteretic interference (HI) of a magnetic field, which allows one to increase the accuracy of measurements, is used for the inspection of objects made from electrocoductive and magnetic materials.
An algorithm for reconstructing images of reflectors from echo signals that propagate in a test object, which consists of several regions with different acoustic properties, is considered. The ray trajectories are calculated using the method of direct construction of the family of rays that escape from the point where a transmitter is located but not the Fermat variational principle. After the family of rays is constructed, their belonging to a certain acoustic scheme can be analyzed and the approximation of the calculated delays on the spatial mesh of the image reconstruction region (IRR) can be performed. This will allow the reconstruction of both the pulse travel time from the transmitter to any point in the IRR and back to the receiver and the attenuation of the pulse amplitude caused by the divergence, reflection, and refraction effects at the boundaries of the regions that constitute the test object. Numerical and model experiments show the working capacity of the proposed algorithm for reconstructing reflector images.
The principles for the application of methods of optically stimulated luminescence (OSL) in a scanning electron microscope (SEM) were developed in this work. A functional scheme for a diagnostic OSL attachment for the investigation of the local properties and distribution parameters of optically active structure complexes in wide-gap dosimeter materials was proposed. Analysis of the dependencies of OSL on the variation in the size of regions that are irradiated with electrons was conducted with anion-defective α-Al2O3 singlecrystals as an example. The possibility of OSL diagnostics of the surface of solid luminescent media and functional matrices with a microscale spatial resolution was shown.
The results of experimental studies during the eddy-current testing of conducting (including ferromagnetic) objects are considered. A data correcting procedure was suggested; it allows one to decrease the requirements for the phase and frequency stability characteristics of the measuring circuit and to relate experimental results to a theoretic model. Initial and corrected hodographs for a number of materials with different electrophysical properties are reported. The magnetic permeability magnitudes of steel 30X13 were calculated for two electromagnetic-field exciting frequencies (15 kHz and 1 MHz).
Nondestructive microwave and optical methods for contactless local measurements of resistivity, the lifetimes of minority charge carriers in single-crystal and polycrystalline semiconductors, and lifetimes in photoelectric transducers are investigated.
A hardware-software system, which incorporates a scanning unit of a standard magnetographic flaw detector attached to a personal computer and computer programs that allow one to obtain signal records and visualize defect fields that are recorded on a magnetic tape on the screen of a monitor, has been developed for magnetographic nondestructive testing.
A computer model of a weakly magnetic finely dispersed coating is suggested. The magnetic inspection of the thickness of such coatings deposited on nonmagnetic and weakly magnetic bases is substantiated. The effect of the nickel content in the coating on the error of thickness measurement is estimated. It is shown that, at the same average nickel concentration, a nonuniform nickel distribution across the thickness does not affect markedly the informative signal.
-A ДМТП magnetic flaw detector with transverse magnetization of pipes, which was designed at ZAO Spektr is described in brief. It is to be used for inspecting the state of buried gas-main pipelines, detecting mechanical, erosion, and corrosion flaws in them, and estimating their dimensions and location in the tested section. Performance characteristics of the flaw detector are compared with those of earlier designed flaw detectors with longitudinal magnetization of tested pipes.
Dependences of the coercive force, saturation magnetization, residual induction, relaxation magnetization and magnetic susceptibility, maximum magnetic permeability and associated magnetic field, electrical resistivity, and hardness of maraging steel 08X15H5Д2T on the conditions of preliminary heat treatments, hardening, and subsequent aging have been studied. The content of rtained austenite in specially prepared specimens was determined. These specimens were subsequently used to calibrate a differential magnetic instrument. Such an instrument is also used to determine the content of retained austenite in aircraft bolts.
The literature sources devoted to studies and development of flaw detectors based on the EMA method of exciting and receiving ultrasound pulses are analyzed. A new EMA flaw detector with capabilities comparable with those of state-of-the-art contact ultrasonic flaw detectors is developed on the basis of analysis and studies performed.
A computer model for operation of ΠPиз-д11 Π111-2.5-K12-002, Π111-2.5-K20-002) normal probes combined with a Yд2-12 flaw detector was used to consider the effect of the size (radius) of a piezoelectric plate on the amplitude of a detected echo signal. It is shown that the amplitude variation is mainly related to the acoustic part of the electroacoustic channel (a function of signal damping during wave propagation to and from a flaw).
This paper demonstrates the capability of the tangential-radiography technique to detect internal and external pits and to measure their depths on corroded large-diameter insulated and noninsulated carbon-steel and stainless-steel pipes. Tangential-radiography technique, with special care, was successfully applied on specially designed 8-in (219 mm) and 12-in (324 mm) reference steel pipes having inside- and outside-machined steps of different thicknesses and inside and outside artificial pits of different diameters and depths on them. The application of this technique on the two reference pipes, with and without insulation, gave 98% accuracy in the determination of the pits depths when the pits are outside the pipes and their depths are equal to or greater than 10% of the pipe-wall thicknesses, and 96% accuracy when the pits are inside the pipes and their depths are equal to or greater than 15% of the pipe-wall thicknesses.
The field of application, the features of operation, and the main performance characteristics of a ВД-12НФП eddy-current flaw detector are considered. Methods of digital data processing for improving the recognition of flaw-produced signals against the background noise are presented.
A portable contactless EMA thickness gauge for nondestructive testing of the thickness of a wide range of conducting products, in particular, for testing products from ferromagnetic and aluminum alloys, is developed. The results of investigations of the device are given.