卷 55, 编号 10 (2019)

The standards of evaluating welded joints based on the results of nondestructive ultrasonic testing are described. The results of calculating the optimum sensitivity of ultrasonic testing that implements the specified evaluation standards are presented. Samples of welded joints based are investigated in nondestructive tests by the ultrasonic echo technique. The results of these tests are compared with data from a metallographic analysis of the samples in which defects such as wormholes, root lack of penetration, and pitting corrosion were revealed. Recommendations are given on optimizing the sensitivity of ultrasonic testing in order to objectively assess detected discontinuities in welded joints, taking the existing criteria for assessing quality based on testing results into account.

In metallic plate structures, a lamination defect is a type of internal defect that is commonly generated in the manufacturing process, which is mostly parallel to the surface of the plate. This study presents a technique of imaging a lamination defect in a metallic plate by using Lamb waves based on the local wavenumber domain analysis method. Owing to the processing technique, an aluminum beam structure is utilized to represent the metallic plate for the detection of the lamination defect. A three-dimensional finite-element model of an aluminum beam with a rectangular lamination defect is constructed with MatLab and ABAQUS commercial software. The propagation characteristics of Lamb waves are discussed by analyzing the simulated wavefield. A complicated wave-propagation phenomenon of multiple reflection and transmission is observed between the interaction of Lamb waves and the lamination. By performing local wavenumber domain analysis on the wavefield, the wavenumber distribution is obtained, from which the location and profile of the lamination defect are identified. An experimental study is carried out to verify the numerical result. A fully non-contact detection system consisting of an electromagnetic acoustic transducer and laser ultrasonic inspection system is established to inspect the artificial machined beam structure. The experimental result is in good agreement with the numerical result.

An algorithm has been developed for numerical solution of the direct linear problem of magnetostatics on calculating the field of a finite cylinder with constant magnetic permeability μ. Sampling parameters for the system of equations have been established in numerical experiments. The solution has been checked for compliance with the results of problems with exact solutions. The limits of applicability of the infinite cylinder model have been indicated. Prospects for further use of the numerical algorithm and computer program have been outlined.

It has been experimentally established that a change in the temperature of samples made of steels widely used in engineering in the range of –10 to +40°C leads to a considerable change in the magnetic properties of these steels. With increasing temperature, the area of the hysteresis loop increases. The coercive force and remanence increase with the saturation magnetization value remaining practically constant. The value of maximum magnetic susceptibility also grows. The greatest change in properties is observed in steel 10 880, which is close in composition to technical ferrum. The established changes in the magnetic properties should be taken into account when conducting magnetic testing under climatic (natural) conditions.

A \(\gamma \)-introscopy method and an installation using “electronic focusing” of \(\gamma \)-quanta transmitted through the studied object are proposed. The apparatus contains a powerful ⁶⁰Co-source; a device for positioning the studied object; and a measuring facility, including a thin scintillation coordinate detector-scatterer with 64 silicon photomultipliers (SiPMs) and digital detector pulse processors (PDPs), a total absorption scintillation detector with analog-digital PDP, a unit for coincidence and energy event selection and on-line coordinate calculation, and a communication interface to a PC. The spatial resolution achieved for thick objects is \( \approx \)400 μm. The theoretical limit is \( \approx {\kern 1pt} 50\) μm.

Non-destructive testing (NDT) is one of the best alternatives to perform inspections and maintenance operations in aerospace and aeronautics industries. In Lock-in Thermal Tests (LTT) the stimulation is modulated in a sinusoidal wave using mechanical loads, ultrasounds, microwaves or, as in this work, visible light through halogen lamps. This work assesses the influence of the parameters of LTT, such as defect geometry, cycle period, and number of cycles, interpolation method, and the type of image to identify the sensitivity of the LTT (parameter c). Several samples were manufactured with precise notches to simulate defects (slots). And performed several LTT in a controlled environment and with a custom jig to secure the samples. The performed tests permitted the analysis of various results for numerous types of controlled situations and defects, such as the slot width, depth, and cycle period. This work compared the number of cycles used during the test (1–15), the interpolation method (Harmonic or DFT) and the type of analysis (phase or amplitude). The cycle period indirectly defines the amount of energy applied during the test; therefore, it was expected to have a great impact in the results. Shorter cycles produced lower thermal differences, while longer cycles resulted in blurred images. The type of image was also found to be one of the most important setting, with the phase delay analysis presenting a higher differentiation of defects and its boundaries. The results from the variation of the number of cycles revealed these should be kept between three and nine. Additionally, the optical stimulation may also be a decisive setting, depending the defect geometry. As a major conclusion, the current LTT can detect defects with a width to depth ratio of 1.25, far less than 2.0, as is stated by the current literature.

In this work, we conducted an experimental research to verify a developed analytical model based on the magnetic sensing of thermoelectric currents produced by ellipsoidal inclusions embedded in an inhomogeneous matrix under the influence of an external temperature gradient. By changing the aspect ratios b/a designated by e of the ellipsoidal inclusions, a wide range of real situations can be simulated. The aspect ratio of the ellipsoidal inclusions varied from 0.33 to 4. An external 1.8°C/cm temperature gradient in the bio-metallic specimen produced magnetic flux densities ranging from 2 to 150 μT at 1.5 mm lift-off distance between the tip of the magnetometer probe and the bio-metallic specimen. Due to the difference in the thermoelectric properties of the host (matrix) and the inclusion (imperfection), the temperature and electric field distributions will be distorted accordingly to the geometry of the inclusion; therefore, the magnetic signal produced by an inclusion will depend not only on its material properties and size, but also on its shape. The experimental magnetic field distribution illustrated the potential for the proposed thermoelectric coupling technique to detect and characterize metallic inclusions of different geometries based on their magnetic signature.