Ekaterina Kulikova

This research is aimed to develop the method for damage degree evaluation in metals and alloys during their deformation and destruction based on acoustic emission (AE) technique. Experimental studies were carried out on tensile specimens of high-strength steel with simultaneous registration of AE signals in tested material. It was shown that the time-dependent AE primary parameters, such as the AE signal maximum amplitudes and AE activity, do not have a clear relationship with the material damage degree. This fact makes it difficult to use standard methods for assessing the damage degree of acoustic signal sources, including defects. It was proposed to use the Kolmogorov-Smirnov criterion to differ the processes of metal plastic deformation and crack propagation during the rupture. The possibility of estimating the material damage degree by high-energy AE hits share was shown. Besides, a particular expression was obtained for evaluating the damage degree for the material under study.

The research is devoted to steel structure diagnostics by the acoustic emission (AE) method. The existing regulatory documents for AE diagnostics of metals and alloys do not take into account some critical factors, among which one is the scale factor should be highlighted. As a result, this can lead to an unreliable assessment of the danger degree of defects in structures when using standard AE diagnostic criteria. This paper presents a quantitative assessment of the scale factor impact on the AE data during the static tension test of steel specimens to failure. Experimental studies were carried out on flat specimens of various thicknesses with a side notch made of high-quality alloyed steel 30 KhGSA. It was established that AE data changed (rise in the AE signals amplitudes and AE activity) within the increase of specimen thickness. Growth in the recorded AE signals cumulative energy was registered with a greater specimen thickness. Partial correlation dependences of the mean count frequency and cumulative energy of AE signals on the specimen thickness were obtained. It was shown that such an effect occurred due to both a general increase in the deformed metal volume and greater strain intensity during the tension of thick specimens. The obtained dependences may contribute to the development of AE diagnostics of metallic materials which is invariant to the scale factor impact.

Рассмотрены результаты применения стандартного алгоритма линейной локации источников акустических сигналов, генерируемых широкополосным преобразователем акустической эмиссии (АЭ), установленным на поверхности стальной пластины размером 1000×650×7 мм. Для генерации импульсов АЭ амплитудой u_m = 55—100 дБ разность потенциалов электронного имитатора изменяли в диапазоне 10…300 В. В результате проведения лабораторных исследований проведен расчет приведенной погрешности стандартного алгоритма линейной локации γ. Максимальная погрешность, равная γ = 16,3%, зарегистрирована в координате X = 100 мм при локализации источника акустических сигналов амплитудой менее 60 дБ и базовом размере антенной решетки B = 800 мм. Минимальный уровень погрешности γ = 2,69% зафиксирован при установке электронного имитатора в координате X = 400 мм. Показано, что максимальный уровень погрешности стандартного алгоритма определяется при локализации источников низкоамплитудных сигналов АЭ, расположенных вблизи приемных преобразователей антенной решетки. Приведен расчет вероятности выявления источников АЭ в зависимости от амплитуды регистрируемых импульсов. Для определения вероятности выявления источников АЭ p поток регистрируемых сигналов разделен на три амплитудных диапазона: 1 — 40…60 дБ; 2 — 60…75 дБ; 3 — 75…100 дБ. Для источников акустических сигналов амплитудой менее 60 дБ, расположенных в координатах X = 100, 200, 600 и 700 мм, значение параметра p стремится к нулю. В процессе обработки результатов экспериментальных исследований выявлено, что вероятность выявления источников АЭ повышается при увеличении максимальной амплитуды регистрируемых сигналов. Для импульсов АЭ, амплитуда которых превышает 75 дБ, значение параметра p стремится к 1 независимо от местоположения источника. Установлено, что погрешность стандартного алгоритма линейной локации зависит от удаленности источника АЭ от приемных преобразователей антенной решетки. В качестве численной оценки влияния перечисленных факторов на результаты построения локационной картины продемонстрирована зависимость p(X, u_m).

The one-dimensional (1D) linear location technique has been considered as one of the methods for determining the position of acoustic emission (AE) sources in metallic objects. However, this approach does not take into account the heterogeneity of materials and that leads to poor accuracy of AE sources localization. To estimate the positioning error of the linear location technique which is typically used to determine the AE source location a new approach based on the combination of experimental and simulation methods is proposed. This approach for error estimation contains a finite element model construction of the AE signals localization. The model consists of transmitting and receiving transducers mounted on the test object, the frequency response of which selected close to the characteristics of acoustic emission transducers applied in the preliminary experiments. The application of the approach in current research showed that a reduced positioning error on a flat steel plate reaches 15%. The proposed technique can be used to optimize the number of preliminary tests required to calculate the reduced error of the 1D linear location technique applied for the AE sources localization during the inspection of the structure.