Instytut Podstawowych Problemów Techniki

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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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Paper describes the assessment of hoop residual stresses in the rim of monoblock railroad wheels using ultrasonic methods. Dangerous tensile stress builds up during service as a result of heat loads caused by braking with braking blocks/brake shoes. Results of experiments on two types of monoblock wheels are described: on rolled-forged wheels used in Europe and on cast wheels manufactured and used in North America. Stresses in forged wheels are evaluated with birefringence technique. Investigations carried out in various countries, using different ultrasonic equipment, proved that an ultrasonic technique can provide valuable information concerning stress values in wheels during manufacturing and in service. However, they also showed that due to different microstructures in the rim material and differences in wheel plate design, forged and cast wheels present unique problems for ultrasonic stress evaluation. The aim of this paper is to emphasize these differences and to illustrate how they influence ultrasonic readings. The second ultrasonic technique to evaluate stress is proposed to standard cast wheels – technique based on measurements of time of flight of subsurface (surface-skimming) longitudinal waves propagating in hoop direction on both rim faces. Presented data are based on detailed measurements of acoustic properties of monoblock wheel materials and on earlier experiments performed on forged and cast wheels subjected to inductive heating, braking in a test stand or on track.

Słowa kluczowe:

Ultrasonics, Acoustoelasticity, Residual stress, Railroad wheels

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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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W pracy opisano nowy sposób wykonania próbki o określonej anizotropii akustycznej, przydatnej do badania głowic ultradźwiękowych przeznaczonych do pomiarów dwójłomności akustycznej. Do wykonania próbek wykorzystano szklane bryły i podpowierzchniowe grawerowanie laserowe Wymaganą w normach omawiających wzorce do ultradźwiękowych badań naprężeń w kołach kolejowych wartość dwójłomności uzyskano, stosując grawerowanie z podwojonymi, umieszczonymi w linii mikrouszkodzeniami spowodowanymi działaniem lasera. Przedyskutowano również możliwości wykonania wzorca dwójłomności akustycznej ze stali, jak proponują to normy.

Słowa kluczowe:

badania ultradźwiękowe, wady sztuczne, anizotropia

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This paper discusses the development of piezoelectric ultrasonic probeheads for measurements of time of flight of subsurface or surface wave ultrasonic pulses. Sets of such probes found application in ultrasonic stress evaluation. In precise measurements of time of flight using piezoelectric transducers, the main source of time scatter proved to be variation in the condition of liquid couplant layers. The thickness of this couplant layer depends on surface roughness of the sample being evaluated. Paper describes a new configuration of probes, composed of two transmitting and four receiving probes arranged along one line, designed to reduce coupling influence on readings. Presented is comparison of readings obtained with known sets of probes and with a new one. Also presented are results of residual stress evaluation performed with various 6-transducer sets of probes on railroad rails, monoblock railroad wheels and pillars of hydraulic press. All measurements were performed in industrial conditions, without any special surface preparation.

Słowa kluczowe:

Ultrasonic testing, Piezoelectric probes, Evaluation of surface stress

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Słowa kluczowe:

badania ultradźwiękowe, pomiary współczynnika odbicia, ocena powierzchni kontaktu, pomiary chropowatości

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W artykule opisano rozwój głowic ultradźwiękowych do pomiarów dwójłomności akustycznej, budowanych od początku lat 70. ub.w. w Pracowni Badań Ultradźwiękowych prof. Juliana Deputata, a obecnie w Pracowni Badań Nieniszczących Zakładu Wytrzymałości Materiałów IPPT PAN. W pracy omówiono różne zastosowania pomiarów dwójłomności akustycznej, a także przedstawiono historię rozwoju głowic wyposażonych w przetworniki piezoelektryczne. Opisane głowice budowane były głównie z myślą o pomiarach naprężeń własnych w wieńcach monoblokowych kół kolejowych. Przedstawiono różne układy przetworników, w jakie wyposażano kolejno głowice oraz zalety i wady zbudowanych głowic.

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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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Development of creep damage at elevated temperatures and structural degradation due to plastic deformation at room temperature were assessed using destructive and non-destructive methods in steels commonly applied in power plants (40HNMA, 13HMF and P91). As destructive methods the standard tension tests were carried out after every kind of prestraining. Subsequently, an evolution of the selected tension parameters was taken into account for damage identification. In order to assess a damage development during the creep and plastic deformation the tests for the steels were interrupted for a range of the selected strain magnitudes. The ultrasonic and magnetic techniques were used as the non-destructive methods for damage evaluation. The experimental programme also contained microscopic observations.

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This paper describes the application of acoustic birefringence measurement for evaluation of material degradation due to creep. The problem with ultrasonic investigation of the influence of creep-induced voids on ultrasonic wave velocities is the lack of samples containing well-defined voids. The only way to‘‘produce’’ damaged material with numerous voids is accelerated creep laboratory test or long-term service of material in high temperature and stress. To describe voids it is necessary to perform laborious metallographic examination of damaged material. Paper presents glass samples with artificial semi-flat voids created with laser engraving technique. Results of ultrasonic wave velocities and acoustic birefringence measurements in glass samples proved that laser engraving can be helpful for the experimental investigation of voids influence on solid acoustic properties.

Słowa kluczowe:

Ultrasound, Birefringence, Creep, Artificial voids

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Damage development due to creep under uniaxial tension at elevated temperatures is assessed using destructive and non-destructive methods in steels, commonly used in power plants or chemical industry, and in aluminium alloy used in aircrafts for responsible elements. The results obtained using two different destructive methods for assessments of damage development are critically discussed. In the first method the specimens of steel after different amounts of creep prestraining were stretched up to failure and variations of the selected tension parameters were taken into account for damage identification. In the second one, a damage degree was evaluated by studying variations of an initial yield locus position in the stress space and by determination of the yield loci dimensions. The ultrasonic investigations were selected as the non-destructive method for damage development evaluation.

Słowa kluczowe:

Creep, Damage, Mechanical Parameters, Ultrasound (US), Yield Surface

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Various samples with artificial flaws found application in ultrasonic testing of materials. Some of them are used for education, some for calibration of ultrasonic equipment. Possibility of manufacturing of various reflectors in metal blocks are usually limited to simple geometries like cylinders, flat bottom holes, various grooves or notches. There are also limitations to produce small reflectors deep under the surface. All reflectors manufactured using machining present 100% reflectivity of ultrasonic waves. Alternative to steel samples with machined reflectors is optical glass and subsurface laser engraving. Velocities of longitudinal and shear ultrasonic waves in optical glass are almost the same as in carbon steel. Laser engraving allows to produce inside the glass block almost unlimited variety of reflect or shapes, orientations and sizes. Single laser act ion produces a small, about 0,1 mm long, cracking. Such cracks, situated close to each other, can create various surf aces. Separated cracks spread in the volume can modify acoustic properties of naturally isotropic glass and develop acoustic anisotropy, acoustic noise or locally increase attenuation of ultrasonic waves. Paper presents results of measurements performed on laser engraved samples imitating numerous micro-cracks as in steel subjected to creep, regions presenting high acoustic noise and on various artificial flaws reflecting ultrasonic waves

Słowa kluczowe:

Ultrasonic Testing (UT), personnel training and certification

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Słowa kluczowe:

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

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The paper presents results of in-situ investigation of a railway truss bridge in the context of SHM. Three experimental methods are examined. Dynamic responses of the bridge recorded by strain gauges are confronted with alternative ways of acquisition using piezoelectric sensors and ultrasonic probeheads. Numerical model corresponds to experimental data.

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The paper is devoted to an analysis of creep damage at elevated temperatures and structural degradation due to plastic deformation at room temperature of selected steels commonly applied in power plants (40HNMA, 13HMF). The materials were tested in the as-received state, however, in the case of the 13HMF steel also after different periods of exploitation (76000h and 144000h at elevated temperature (813K) under internal pressure (14 bars)). Destructive and non-destructive testing methods were applied to assess material degradation. As destructive methods the standard tension tests were carried out after every kind of prestraining. Subsequently, an evolution of the selected tension parameters were taken into account for damage identification. In order to assess a damage development during the creep and plastic deformation the tests for both steels were interrupted for a range of the selected strain magnitudes. The ultrasonic and magnetic techniques were used as the non-destructive methods for damage evaluation. The last step of the experimental programme contained microscopic observations. A good correlation of mechanical and selected non-destructive parameters identifying damage was achieved for the tested steels. It gives very promising tool for degradation assessments appearing in pipelines at power stations.

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Streszczenie:

Development of damage due to creep at elevated temperatures and fatigue at room temperature was assessed for power engineering steels using destructive and non-destructive methods. The experimental programme contained also microscopic observations to find feedback between macro- and micro-scopic parameters. Three different power engineering steels were tested, i.e. 40HNMA, 13HMF and P91

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Streszczenie:

Development of damage due to creep at elevated temperatures and fatigue at room temperature was assessed for power engineering steels using destructive and nondestructive methods. The experimental programme contained also microscopic observations to find feedback between macro and microscopic parameters

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