Acoustic Emission Equipment Research Articles

Cold Cracking in Weldments of Steel S 690 QT

The cold cracking process in shielded metal arc and gas metal arc welding of steel S 690 QT is investigated by Tekken test. The conditions for cold cracking are varied by changing the specimens’ thickness, heat input, initial weld metal hydrogen concentration and preheating temperature. The kinetics of initiation and propagation of cracking is monitored by acoustic emission equipment. It is found out that the crack’s propagation path shifts from weld metal to fusion line and HAZ with decreasing initial weld metal hydrogen concentration and increasing hardness of HAZ. In the investigated range of cold cracking conditions the magnitude of cracking is mainly controlled by the preheating temperature and heat input. The acoustic emission signal provides valuable information about the factors controlling the kinetics of crack initiation and propagation and the intensity of cold cracking. The initial hydrogen concentration in weld metal controls the incubation period’s duration and affects the cracking intensity at higher heat inputs. The preheating temperature does not influence the incubation period, but significantly affects the kinetics of crack propagation. The heat input has a complex influence on the cracking kinetics and intensity. This is related to the contradictive effects of heat input on the initial hydrogen concentration per unit length of weld metal and on the behaviour of hydrogen during cooling. The obtained results provide a basis for combined experimental — modelling investigations on the cold cracking phenomenon in weldments of higher strength structural steels, aiming at quantitative evaluation of the influence of the main controlling factors.

Sirolimus-eluting vs. uncoated stents for prevention of restenosis in small coronary arteries: A randomized trial

Acoustic emission (AE) monitoring is a powerful procedure used to detect and locate damage in mechanically loaded structures, materials, and components. This chapter presents the capability of a new data processing system based on wireless AE equipment that is very useful for long-term monitoring of concrete and masonry structures. Systems based on wireless transmission should be cost-efficient, easy to install, and adaptive to different types of structures and infrastructures. To this purpose, computer-based procedures are implemented. These procedures are performed by automatic AE data processing and used to evaluate the AE data in laboratory tests and in situ monitoring. The final output of the code returns a description, as complete as possible, of damage patterns and their evolution of the monitored structure. In the most critical cases, or in some cases requiring in situ, long observation periods, the AE monitoring method is fine-tuned for a telematics processing procedure of AE data clouds. Finally, to increase the safety of structures and infrastructural networks, the proposed AE monitoring system could also be used to determine the seismic risk of civil constructions and monuments subjected to earthquakes.

Plasma surfactant protein-B: A novel biomarker in chronic heart failure (HF)

Acoustic emission (AE) monitoring is a powerful procedure used to detect and locate damage in mechanically loaded structures, materials and components. This chapter shows the capability of a new data processing system based on wireless AE equipment that is very useful for long-term monitoring of concrete and masonry structures. Systems based on wireless transmission should be cost efficient, easy to install and adaptive to different types of structures and infrastructures. To this purpose, computer-based procedures are implemented. These procedures are performed by automatic AE data processing and used to evaluate the AE data in laboratory tests and in situ monitoring. The final output of the code returns a description, as complete as possible, of damage patterns and their evolution of the monitored structure. In the most critical cases, or in some cases requiring in situ, long observation periods, the AE monitoring method is fine-tuned for a telematics processing procedure of AE data clouds. Finally, in order to increase the safety of structures and infrastructural networks, the proposed AE monitoring system could also be used to determine the seismic risk of civil constructions and monuments subjected to earthquakes.

Electrocardiographic features of arrhythmogenic right ventricular dysplasia/cardiomyopathy according to disease severity. A need to broaden diagnostic criteria

Acoustic emission (AE) monitoring is a powerful procedure used to detect and locate damage in mechanically loaded structures, materials and components. This chapter shows the capability of a new data processing system based on wireless AE equipment that is very useful for long-term monitoring of concrete and masonry structures. Systems based on wireless transmission should be cost efficient, easy to install and adaptive to different types of structures and infrastructures. To this purpose, computer-based procedures are implemented. These procedures are performed by automatic AE data processing and used to evaluate the AE data in laboratory tests and in situ monitoring. The final output of the code returns a description, as complete as possible, of damage patterns and their evolution of the monitored structure. In the most critical cases, or in some cases requiring in situ, long observation periods, the AE monitoring method is fine-tuned for a telematics processing procedure of AE data clouds. Finally, in order to increase the safety of structures and infrastructural networks, the proposed AE monitoring system could also be used to determine the seismic risk of civil constructions and monuments subjected to earthquakes.

Initiation of stress-corrosion cracking in unidirectional glass/polymer composite materials

The purpose of this research is to determine the resistance to stress-corrosion cracking (SCC) of three unidirectional (pultruded) E-glass/polymer composites based on modified polyester, epoxy and vinyl ester resins. The composites have been subjected to a nitric acid solution of pH 1.2 in a newly designed four-point bend fixture. The stress-corrosion process was initiated on the as-supplied surfaces of the composites. The process has been monitored for acoustic emissions and the stress-corrosion surface damage in the specimens was investigated by the use of scanning electron microscopy. Experimental results indicate that the stress-corrosion cracks originate predominantly from exposed glass fibers on the surfaces of the composites. The process can be successfully monitored by means of acoustic emission equipment. Three stages of SCC, crack initiation, sub-critical crack extension and stable crack propagation, can be distinguished by carefully examining the curves of acoustic emission (number of events) versus time. For the first and second stages of SCC, the acoustic emission outputs are linear functions of time. The slopes of the first and second stages of the curves of acoustic emission versus time have been used to determine quantitatively both the resistance of the composites to crack initiation and sub-critical crack extension, respectively. It has been shown in this research that the resistance to the initiation of SCC in nitric acid of the E-glass/vinyl ester composite is approximately 10 times greater than the E-glass/epoxy composite. Furthermore, the E-glass/epoxy system exhibits approximately 5 times higher resistance to the initiation of SCC than the E-glass/modified polyester system. The sub-critical crack extension process is also significantly more rapid in the E-glass/modified polyester than in the E-glass/epoxy composite.

Application of ultrasound to the inspection of insulation

Ultrasonic methods have been employed for the inspection of electrical insulation, using both the NDT approach (pulse-echo techniques) and by acoustic emission. The NDT approach used a commercial ultrasonic flaw detector to produce A-scans of the insulation system under investigation. A PC scanner system has been developed so that the insulation could be mapped according to the signal depth or amplitude. The acoustic emission equipment was also a standard commercial system with a 1 MHz probe. A fibre-optic link was built to isolate the probe and its pre-amp from the rest of the equipment. Fast Fourier transformation of the signals into the frequency domain allowed the use of neural networks for signal recognition. The systems have been utilised to inspect bushings, transformers, switchgear and cables for internal flaws, dimensional integrity, partial discharges and water trees.

Acoustic emission detection and monitoring of highway bridge components : Azimi, M. Dissertation Abstracts International, Vol. 50 No. 7, p. 3050-B (Jan. 1990)

Fatigue cracking is the most common problem in steel highways bridges. Early detection of cracks requires simple, inexpensive repairs, whereas late detection of cracks may cause catastrophic accidents. Currently, the bridges are inspected by visual examination, dye penetrant, magnetic particles, ultrasonics, and radiography. Low reliability and high inspection costs require a more efficient inspection system to be developed. Acoustic emission (AE) seems to be the solution to these problems. It has developed over the past two decades as a nondestructive testing technique with high sensitivity to detect progressive microscopic events in the material. Development of portable AE equipment has made it an even more practical method for bridge inspections. In a prior study, acoustic emission was applied to A588 weathering steel beams (rolled and welded sections), and the effective frequency range for monitoring highway bridges was established. In this study, research characterizing the parameters of cracks versus noise was conducted. A total of 18 beams made of A588 steel including welded, rolled and coverplated beams, were monitored. Half of the beams were exposed to severe atmospheric environments to investigate the effect of rusting on the AE signals. Also, a total of twelve small specimens made from the same material were monitored to establish a relationship between the AE signals and stress intensity factors. In addition, three small welded specimens were monitored for comparison to the coverplated beams. As a result of this study, a statistical range of variation of the AE parameters at various stages of crack growth has been established. This range can be used as a reference for bridge inspection. A model for predicting the stage of crack growth versus AE parameters has been discussed, and a systematic inspection procedure by AE has been recommended.

Acoustic emission detection and monitoring of highway bridge components

Fatigue cracking is the most common problem in steel highways bridges. Early detection of cracks requires simple, inexpensive repairs, whereas late detection of cracks may cause catastrophic accidents. Currently, the bridges are inspected by visual examination, dye penetrant, magnetic particles, ultrasonics, and radiography. Low reliability and high inspection costs require a more efficient inspection system to be developed. Acoustic emission (AE) seems to be the solution to these problems. It has developed over the past two decades as a nondestructive testing technique with high sensitivity to detect progressive microscopic events in the material. Development of portable AE equipment has made it an even more practical method for bridge inspections. In a prior study, acoustic emission was applied to A588 weathering steel beams (rolled and welded sections), and the effective frequency range for monitoring highway bridges was established. In this study, research characterizing the parameters of cracks versus noise was conducted. A total of 18 beams made of A588 steel including welded, rolled and coverplated beams, were monitored. Half of the beams were exposed to severe atmospheric environments to investigate the effect of rusting on the AE signals. Also, a total of twelve small specimens made from the same material were monitored to establish a relationship between the AE signals and stress intensity factors. In addition, three small welded specimens were monitored for comparison to the coverplated beams. As a result of this study, a statistical range of variation of the AE parameters at various stages of crack growth has been established. This range can be used as a reference for bridge inspection. A model for predicting the stage of crack growth versus AE parameters has been discussed, and a systematic inspection procedure by AE has been recommended.

A Multi-Purpose Sensor for Composite Laminates Based on a Piezo-Electric Film

In this study, a multi-purpose sensor for composite laminates is devel oped. The sensor is based on a piezo-electric film. A specialty charge amplifier was devel oped for signal conditioning for long time duration measurements. Experiments were con ducted to show the utility of the sensor for static and dynamic strain measurement. By effectively isolating the piezo film for unidirectional strain, a method was developed to utilize the piezo sensor for general, in-plane strain sensing, regardless of the constitutive properties of the laminate. Non-destructive evaluation in through-transmission and pulse- echo modes were shown to be effective for measuring and quantifying damage in lami nated structures. Using the piezo film as a sensor to detect impact, it was shown that an "event" as well as the onset of damage can be accurately measured. With standard acoustic emission equipment, the piezo film proved to be an effective direct substitution for typical piezo-crystals at a fraction of the cost and weight for acoustic emission monitoring in ad vanced composite laminates. The onset of damage, as well as damage location were ac curately measured. The preliminary results indicate that the sensor is quite versatile, inex pensive and sensitive for a variety of sensing applications in advanced composite laminates. In particular, the electronics needed for signal conditioning are much less elab orate than typical sensors such as strain gages, piezoceramic sensors, thermocouples, etc.

ＣＦＲＰロケットモーターノズルホルダーのＡＥ特性

The present paper reports the possibility of the acoustic emission (AE) application from the results of the testing performed at NASDA (National Space Development Agency of Japan) on H-I rocket motor nozzle holders (Graphite/Epoxy composites), such as materials tests, the burst test and the hydroproof test. Amplitude distribution during tests shows three types of the fracture mechanism, such as fiber breakage (over 70 dB), delamination (between 60 and 70 dB) and matrix cracking (under 60 dB). After the middle stage of the burst test, AE event rate is shown a saturated behavior, and a large scale delamination is observed in the fracture surface. The upper limit speed for data acquisition (40 events/s) of AE equipment (3000/3104: PAC) underestimated the number for middle amplitude events of the delamination. During the hydroproof test, both large amplitude events and large number of AE events are detected in spite of the higher threshold (+20 dB) than that of the burst test. The strain gages on the hydroproof sample indicate higher strain than that of the burst test. Both AE and strain results show that the hydroproof test sample would have bigger damage than the burst test sample.

A study of crack initiation and propagation in Ni-Cr thermally sprayed coatings using acoustic emission techniques

Many metallurgical coatings applied by thermal spraying tend to exfoliate or spall through the growth of cracks, presumably initiated at the metal-coating interface or at the substrate. The present study was undertaken to determine whether such cracks are at the substrate-coating interface or within the coating or the substrate themselves. An AISI 1045 steel overlayed with a nickel-chrome alloy was used and the samples were subjected to a positive stress and fatigued using sinusoidal oscillations. In order to obtain a continuous record of crack initiation and propagation, acoustic emission equipment was used. The variation of the events and count rates and energy liberated per event made it possible to determine crack initiation and to follow crack growth. Scanning electron microscopy was used to examine sections of the specimens at different stages of the real-time graphs of acoustic emission. It was found that the cracks initiated in the coating near the interface and not at the substrate or interface as suggested elsewhere. The conditions promoting crack initiation were also determined.

General review of developments in Acoustic Emission methods

The ability of Acoustic Emission (AE) to detect, with high sensitivity, the mechanical energy released by flow evolution, may be used to get information about crack growth, onset of new defects and their dynamic behaviour, during the first hydrotest and later requalification testing of nuclear components and continuous monitoring of power plant operation. In this review, the most recent developments in AE for nuclear component monitoring are examined. Suitable AE equipment for logging high rates of AE data, real-time source location and parametric analysis are here discussed. In recent years many AE processes (deformation, slow crack growth, fatigue processes, intergranular stress corrosion cracking, leak monitoring) have been studied and considerable effort has been made in preparing guidelines, recommended practices and standard procedures based on AE. In this paper all these aspects are considered and the main results are reported.

Monitoring of thermal shock induced crack growth in a feed water nozzle corner of a reactor pressure vessel by acoustic emission

In the framework of a reactor safety research programme, thermal shocking of a clad feed water nozzle has been carried out during simulated operating conditions (temperature = 300°C, pressure = 11 MPa). The objective of these trials is to contribute to the understanding of crack initation and propagation under realistic thermal shock conditions, and to monitor crack initiation and growth by NDT on-line as well as off-line. Up to now the nozzle corner has been shocked 5200 times. The shocked area was monitored by acoustic emission (AE). During the last 800 thermal shocks new AE equipment with optimized capabilities for detection, location of AE sources and interpretation of AE signals has been used. This AE system and the results obtained during the last 800 shocks will be described. One important result is that it is possible to separate crack-growth signals from friction noise of the cracks by signal analysis when the AE signals are received with broad-band transducers.

Analysis of the effect of using two different strain rates on the acoustic emission in bone

To study the effect of strain rate on the acoustic emission amplitude signature of bone, bovine cortical bone was milled into standard tensile specimens which were tested at two different strain rates while being monitored with acoustic emission equipment. It was demonstrated that the amplitude distribution of the acoustic events in bone is dependent on strain rate. Greater numbers of events occurred with the slower strain rate (0.0001 s −1), but these events were of lower amplitude than those emitted during the more rapid strain rate (0.01 s −1). The plot of the cumulative event amplitude distribution followed the power-law model, and the slope of this output, the b-value, represented a signature of the amplitude distribution. The mechanical test results were consistent with the behavior of a viscoelastic multi-phase composite material.

Further responses of the bond in reinforced concrete to high temperatures

Synopsis Tests were carried out to examine the effects of heat treatment upon the bond between concrete and steel by using direct displacement measurements and monitoring acoustic emission. A description of the experimental set-up has been given previously and, as before, it was used to test cylindrical pull-out specimens with an actual embedment length of 32 mm. The variables considered were type of bar (plain anddeformed bars of 16 mm diameter) and the effect of load cycling (for the deformed bar only) upon the bond after it has been subjected to heat treatment. The acoustic emission equipment was incorporated into the system to assess its validity in this type of testing and was used in all three of the different test situations investigated.