Principal Regularities of Pochhammer-Wave Interaction with Defects

Nedzvetskaya²,

Russ J Nondestruct Test

et al. 2004

Self Cite

A procedure of the pulse echo-mirror method for testing rods by Pochhammer waves that uses multiple reflections of the transmitted pulse from flaws and free end faces of these rods is presented. It is shown that the sensitivity of the method can be increased considerably. The experimental studies of multiple reflections from an artificial flaw are confirmed theoretically.It is known [1] that the sonication of articles with plane-parallel surfaces in the form of plates results in a series of multiply reflected echo pulses that follow each other at distances equal to the plate thickness on the flaw detector's display. The echo-signal amplitude decreases with an increase in the number of reflections for several reasons: damping of the ultrasound in the plate material in accordance with the exponential law, divergence of the ultrasonic beam, and losses upon reflection at the test object-transducer boundary.Losses caused by divergence can prevail when testing thick-walled objects and low-damping materials. During contact with metal, reflection losses are high for piezoelectric probes with an acoustically hard protector, slightly smaller for piezoelectric transducers with an acoustically soft protector, and almost absent for the contact-free excitation method, for example, using electromagnetic-acoustic transducers.If a plate contains one minor flaw that only slightly distorts the echo pulse from the back wall, for instance, a layer with some finite permeability, the reflection from this flaw will be observed after each of the multiple reflections from the back wall. The amplitude of the echo signal from the flaw changes in a different manner than the amplitude of the reflection from the back wall. It was noted in [1] that the location with the highest sensitivity to a flaw is located at the end of the near-field zone, while in the long-field zone, the amplitude of the echo pulse decreases inversely to the square of the distance.Despite some increase in the sensitivity to flaws in the zone of multiple reflections, this fact has not found any practical use.It was shown in [2] that Pochhammer waves propagate along a rod with minimal losses. Pochhammer waves propagate only in one direction (along a rod); they are planar and are attenuated only due to damping in the material of the test object. Damping of the S 0 mode of a Pochhammer wave in the region of the minimum velocity dispersion (at a low frequency) caused by internal losses is low, which makes it possible to observe a series of multiple reflections in sufficiently long rods. Figure 1 shows the functional diagram of the experimental setup for observing the pattern of multiple reflections in a rod. Short acoustic pulses of symmetric mode S 0 are excited in a rod ( 1 ) of length L from one of its ends using an electromagnetic-acoustic (EMA) transmitter ( 3 ). After passing through the rod, the pulses are detected by an EMA receiver ( 4 ), which converts the acoustic oscillations into electrical pulses that are displayed on an electronic oscilloscope ( 6 ). The genera...

Section: Acoustic Methodsmentioning

confidence: 99%

Acoustic nondestructive testing of rods using multiple reflections

Nedzvetskaya²,

Russ J Nondestruct Test

et al. 2004

Self Cite

Instrumentation Engineering, Electronics and Telecommunications

“…In the simplest case, when moving from a section with a mechanical impedance Z 1 to a section with a mechanical impedance Z 2 the reflection coefficient R is defined by formula: R = (Z 2 -Z 1 ) / (Z 2 + Z 1 ). If the material properties of the waveguide do not change (C = const), and only its cross section changes (surface defects leading to the loss or addition of some part of the metal), R is defined by formula: R = (S 2 -S 1 ) / (S 2 + S 1 ) [19][20]. This makes it possible to evaluate the interaction of acoustic waves with defects that weaken the cross-section of the object: captives, weights, inclusions, rubs, delaminations, etc.…”

Section: Defectoscopy Of Composite Fiberglass Fittingsmentioning

confidence: 99%

Defectoscopy of composite fiberglass fittings by the acoustic waveguide technique

Strizhak¹,

Mkrtchyan²,

Khasanov³

et al. 2018

In this paper we propose the procedure of non-destructive testing of composite fiberglass reinforcements by using the acoustic waveguide technique. Experiments on defectoscopy of the composite armature with rod waves were conducted. More than 1000 composite fiberglass reinforcements with length of 6 meters were tested according to the developed procedure. The experimental results shown that rejection level of 2 % allows to detect, confirm and identify flaws by type. Furthermore, we derived the dependence between signal amplitude and discontinuities or changes in the crosssection of the composite reinforcement body. The simulation of flaw as an element with a crosssectional difference was performed. A graphical dependence of the signal amplitude from the flaw and from the defect zone cross-sectional area value was obtained. The photographs of typical defects and the corresponding echograms are given in this paper.

Vestn. IžGTU im. M.T. Kalašnikova

“…В условиях незначительного затухания, отсутствующей или низкой дисперсии скорости импульс отражается от противоположного торца объекта и возвращается в зону излучения, затем вновь проходит по телу объекта до противоположного торца и обратно. Сигнал, отраженный от дефектной области, возникает на участках с измененным сечением и пропорционален изменению площади сечения [16,17]. По резуль-К татам измерения амплитуды сигнала от противоположного торца и сигнала от участка с измененным сечением дается заключение о величине изменения сечения.…”

Section: Introductionunclassified

Artificial Reflector for Setting up a Flaw Detector that Implements an Acoustic Waveguide Method for Monitoring Composite Reinforcement

Strizhak

2020

Предложен способ нанесения искусственного отражателя на длинномерный объект без разрушения его тела, что позволяет разработать настроечный образец для волноводного метода контроля при упрощении способа нанесения искусственного отражателя. На основании существующих методик оценки спектральных свойств сигналов, отраженных и прошедших через участки с перепадом сечения, разработана расчетная модель. Модель позволяет оценить амплитуды эхосигналов в зависимости от высоты и длины искусственного отражателя. Приведены результаты моделирования и экспериментальных исследований влияния габаритных размеров искусственного отражателя на эхосигнал. Показано, что максимум эхосигнала достигается при длине искусственного отражателя на 19 % меньше значения, соответствующего критерию четверти волнового резонанса. Амплитуда от искусственного отражателя в 1,2…1,3 раза меньше процента прироста площади, и с увеличением площади в зоне отражателя различия растут в силу уменьшения коэффициента его прозрачности.Полученные зависимости позволяют по амплитуде эхосигнала и видимой длине дефекта оценить его внутренний размер. Предлагаемая методика характеризуется высокой точностью, оперативностью и позволяет повысить достоверность волноводного метода контроля длинномерных объектов из полимерных композитных материалов (пруток, труба, арматура).