Instytut Podstawowych Problemów Techniki

Streszczenie:

An experimental and analytical study of the relation between local defect, in a steel structure, and its higher frequencies and higher modes is discussed. The structure is a plane steel frame, assembled of beams, joined together with bolted connections. Removing some bolts from a given connection simulates the damage. In the experiment, an impulse force induced structural vibrations. Effects of vibrations were shown by data from gages, measuring accelerations with a high accuracy. From the data, it could be observed, that mode shapes, for the healthy and damaged structures didn’t show any differences for low frequencies. Only modes around thirteen showed significant gap between picks of Frequency Response Functions, for healthy and damaged frame. Moreover, looking at mode shapes, it could be observed that structural configuration may have some influence on defects to be observable. This aspect is discussed in a separate section. The experiment performed on the whole structure allows finding the place where the defect is localized. However, it can’t give detailed information on the defect itself, here defect of a bolt. For finding it, an ultrasonic measurement of pre-tensioning forces in bolts was applied. It allowed not only to determine stresses in the bolt, but also to verify, if in the process of assembling the structure was not pre-stressed.

Słowa kluczowe:

Detectable damages, Bolted connections, Experimental modal analysis, Ultrasonic measurements, Steel frames, Analytical dynamics

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Thick-walled, main stream pipelines are key elements in many power and chemical plants. Operating for a long time in high temperature and subjected to internal pressure such pipes are subjected to creep resulting in material degradation and strain. The most common method of pipe state evaluation is pipe diameter monitoring. Usually such measurements are performed with micrometer gauge in locations where special “pips” were earlier installed. Other methods are also tested to monitor creep progress like various temperature-resistance strain gauges or eddy current sensors. The paper examines a new ultrasonic technique to evaluate thick-walled pipe diameter changes. Pipe diameter evaluation is based on time of flight of bulk ultrasonic waves propagating in circumferential direction along the polygon, reflecting on the pipe external surface only. Presented are results of experiments performed on 100 mm diameter pipe subjected to internal pressure to generate small diameter changes and on 273 mm diameter and 40 mm wall thickness pipe section. Measurements were performed with longitudinal, shear SV and shear SH waves. Described are advantages and disadvantages of various ultrasonic wave types for pipe diameter evaluation in practice. Discussed is the influence of residual stresses and temperature on accuracy of pipe diameter evaluation with proposed technique. Shear SV wave was chosen as the most easily applicable ultrasonic wave on thick-walled tubes.

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This paper presents results of in situ investigation of a railway truss bridge in the context of structural health monitoring (SHM). Three experimental methods are examined. Dynamic responses of the bridge recorded by strain gauges are confronted with alternative ways of acquisition using piezoelectric patch sensors and ultrasonic probeheads. All types of sensors produce similar output. Also the corresponding responses of the numerical model of the bridge match experimental data.

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W pracy przedstawiono ultradźwiękowe badania naprężeń zmiennych w elementach konstrukcji stalowej. Opisano podstawy ultradźwiękowej metody pomiarów naprężeń, podano zależności z jakich na podstawie pomiarów czasu przejścia impulsów fal ultradźwiękowych obliczane są wartości naprężenia. Opisano wykorzystane w badaniach głowice ultradźwiękowe i układ pomiarowy. Pokazano wyniki badania zmian naprężeń w dwóch elementach kratowego mostu kolejowego – w podłużnicach i w wykrzyżowaniach kratowego dźwigara. Zarejestrowano zmiany naprężeń wywołane przejazdami pojazdów szynowych o różnych masach, poruszających się z różnymi prędkościami, w obu kierunkach. Badania prowadzone dwukanałową aparatur ą równocześnie w dwóch podłużnicach pozwoliły na wykrycie asymetrii obciążenia konstrukcji mostu podczas przejazdu pociągu towarowego. Porównano wyniki pomiarów uzyskanych technik ą ultradźwiękową z wynikami uzyskanymi technik ą tensometrii oporowej.

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This paper presents a new method for evaluating the temperature dependency of ultrasonic shear and longitudinal wave velocities. Results of such measurements allow the determination of elastic properties of solids, such as Young’s and shear moduli, for various temperatures. A short description of well-established techniques of ultrasonic measurements at high temperatures, such as laser and waveguide techniques, is given and their disadvantages listed. The main disadvantage, especially in the case of small samples with low heat capacity, is uneven temperature distribution in the sample volume caused by contact with a waveguide or through heat generated by the laser pulses. The proposed techniques enable velocity measurement of both longitudinal and shear waves in small samples while ensuring constant temperature in the whole sample volume. Measurements were performed using piezoelectric transducers pressed between two samples and generating and detecting ultrasonic waves propagating along the samples. Advantages of this measuring technique are: no need for couplant; the ability to measure small, easily machined samples; and the low cost of the experiment. The main disadvantage of the technique is a limited temperature range. The paper presents results of measurements performed on several samples cut from light alloy castings of various chemical compositions.

Słowa kluczowe:

ultrasonic, velocity, temperature, elastic constants

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The aim of this paper is to present the new method for relative changes measurements of intima-media thickness in the common carotid artery wall. The numerical solver was created for calculation of the fields of ultrasonic beams and scattered fields under different boundary conditions and different angles of penetration of ultrasonic beams with respect to the position of the arterial wall. The cylindrical model of the artery was changing the radius and thickness of the wall under cyclic variation of blood pressure. The presented method was verified on a pipe made of latex. The paper describes also the initial results of examinations of the intima-media thickness. The good agreement for the angle dependence and the perpendicular ultrasonic beam displacement from the longitudinal axis of the artery segment between the numerical calculation and experimental results was obtained for different artery diameters.

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The paper describes the initial results of examinations of the intima-media thickness (IMT) in the common carotid artery wall. The examinations of the IMT enable the assessment of elastic properties of the arterial wall. Ultrasonic examinations were carried out on healthy volunteers with the use the apparatus Vascular Echo Doppler (VED), designed by the authors to measure the elasticity of arteries. Application of the PDA-14 PC-card (Signatec) allowed for the acquisition of ultrasonic RF signal from the output of the apparatus VED and further analysis of dynamic changes of the IMT during a heart cycle. Changing of the IMT in time as a difference between the instantaneous position of the two tracking slopes of RF echoes was obtained. For this purpose, the zero-crossing method for tracking the phase changes of the two rising slopes of the RF ultrasonic echo was used.

Słowa kluczowe:

ultrasound, common carotid artery, elasticity, intima-media thickness

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In this work a structure of a ultrasonic chemical sensor with organic monomolecular layer as well as introductory measurement with the help of a set-up constructed in IFTR PAS are presented. Chemical composition of this layer is an equimolar mixture of 5-[[1,3-dioxo-3- [4-(1-oxooctadecyl) phenyl] propyl] amino] – 1,3 – benzenedicarboxylic acid (DA) and cetylamine (CA). The thickness of this layer is equal to dimension of one molecule. The sensor layer was deposited on one channel of the bi-channel sensor delay line (made from lithium niobiate) by means of the Langmuir–Blodgett method. The chemical sensitivity of this sensor to some mixtures of air with vapor of volatile organic compounds has been investigated

Słowa kluczowe:

ultrasonic chemical sensor, Langmuir–Blodgett layers, air-organic vapor mixtures, volatile organic compounds

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Fatigue tests of AA2124 based metal matrix composites (MMCs) with SiC particles reinforcement were carriedout. The MMCs were manufactured using powder metallurgy. Hysteresis loops were observed during subsequent cycles. Cyclic plasticity and ratcheting were identified as main fatigue damage mechanisms. Inelastic strain amplitude and mean inelastic strain were calculated to be used as fatigue damage indicators. Ultrasonic measurements during fatigue tests were performed but they did not allow to detect damage during fatigue test.

Słowa kluczowe:

metal matrix composites, fatigue, damage

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Słowa kluczowe:

badania ultradźwiękowe, badania degradacji stali, pełzanie, pomiary prędkości fal, pomiary tłumienia fal, dwójłomność akustyczna

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