Acoustic Emission Instrument Research Articles

Analysis on acoustic signal characteristics of the fatigue cracks in anchor structure of cable-stayed bridge tower

The full size model fatigue test on the anchor structure of cable-stayed bridge tower was engaged in laboratory. The acoustic emission instrument was used to monitor the fatigue cracks continuously in the fillet of the anchorage, to investigate the acoustic signal characteristics. Through different ways of loading, the periodic variation of acoustic signals, and crack propagation parameters of the acoustic signals are obtained. By continuously monitoring of the acoustic signal of the fatigue cracks, it can be possible to find the location of the fatigue cracks, and the time it generates. According the active changes of the acoustic signals of the fatigue crack via continuous monitoring, the propagation tendency of the crack in the anchor structure of the cable-stayed bridge tower can be predicted. This method provides support for the crack detection and on-line real-time monitoring by acoustic emission.

On thermo-mechanical reliability of plated-through-hole (PTH)

The mechanical properties of plated copper in plated-through-hole (PTH) were investigated experimentally by a thermo-mechanical analyzer, a nano-indenter, and an acoustic emission instrument. Coefficients of fatigue life prediction models for plated copper have been determined by different failure criteria. Afterwards thermal fatigue test of PTH at three different diameters were performed, and Weibull statistics was employed to evaluate the fatigue life of samples under different failure criteria. Finally, the strain variation of PTH during thermal cycle has been simulated by the finite element analysis (FEA) so as to predict its fatigue life by the selected models. From the comparison of the estimated fatigue life and its experimental results, it is found that the error can be minimized to be within 100%, provided that the drifting of electrical resistance by 20% is used as failure criteria and total strain amplitude is used as control variable in fatigue life prediction model. Based on these findings, design of PTH in printed circuit board (PCB) can be optimized by FEA. It is concluded that fatigue life of PTH will increase with lesser PCB layers, smaller depth-to-diameter ratio, higher PTH density and thicker plated copper.

Discussion on the Relationship between Rockburst Proneness of Rock and its AE b-Value

In order to strengthen the study on rockburst prediction and inquire the relationship between rockburst proneness of rock and its AE b-value, we select three typical rocks of volcanic, sedimentary, and metamorphic to conduct indoor rock mechanics test. Uniaxial compression test are carried to calculate the rockburst proneness of three kinds of rocks, at the meantime we collect the acoustic emission signal during the whole process by acoustic emission instrument. After analyzing the different AE features of all kinds of rocks, we find that the AE b-values of three kinds of rocks both develop in the beginning of two different loading conditions. The AE b-values of marble and sandstone change in a more stable way, and the b-value of granite decline at the 50% of the peak stress. The b-value of granite is the biggest and the sandstone’s is the smallest.

Study on Spectral Characteristics of Acoustic Emission from Pressure Pipe Leakage

Detecting leakage liquid-filled pipe by acoustic emission instrument and researching the acoustic signal that measured with water by experimental medium. Gathering the acoustic signals in different pressures or different diameters of leakage aperture and analyzing the spectrum characteristics by wavelet packets and db5 wavelet basis. The result show that major frequency components contained at about 232KHz-239KHz. The acoustic emission signals’ amplitude and energy enhance as pressure and leakage aperture diameters’ increase.

Acoustic emission measurements and lattice simulations of microfracture events in spruce

Abstract A statistical lattice model was developed to investigate the energy associated with damage and failure of wood. The model incorporates several important morphological aspects of wood such as grain direction, early wood percentage and grain geometry. The model was developed to investigate progressive damage under enforced boundary displacements and has been adapted to predict fracture energy related phenomena. In this particular study, notched specimens were loaded in uniaxial tension while monitored by a passive acoustic emission (AE) measurement system. The energy associated with the mechanical damage was measured by the AE instruments and compared with the energy released by ruptured elements in the lattice model. Cumulative energy release was tracked as a function of specimen load and deformation in both model and experiment. A ratio was established between the cumulative AE energy released at the first drop in load and the cumulative fracture energy released when the model load-deformation relationship becomes significantly non-linear. An additional ratio was established between the total fracture energy measured prior to 50% of peak strain and the total fracture energy measured prior to peak strain. The magnitudes of these energy release ratios vary owing to a change in failure modes between the short model and the larger specimens; however, the shape of the AE energy release curve up to failure coincides well with that predicted by the model simulations.

Acoustic Emission Monitoring of Chemically Bonded Anchors

This paper presents a study on the use of acoustic emission (AE) to assess the structural soundness of concrete reinforced with chemically bonded anchors. The results of an experimental work based on six pullout tests monitored using an AE instrumentation suite are reported below. In every test one rebar was embedded in the hardened concrete by means of polyester resin. The AE was adopted to monitor the onset and progression of any structural damage. The parametric analysis, the intensity analysis and the moment tensor analysis of AE data were used to discriminate among different sources of damage. The technique shows promise for field application and may contribute to fully understand the structural mechanism in the rebar/adhesive/concrete systems.

Investigation of the relationship between internal fluid leakage through a valve and the acoustic emission generated from the leakage

The detection of acoustic emission (AE) signals produced by liquid and gas leakage through valves can be related directly to the qualitative leakage rate. This allows for cost estimation of losses in processes for several industries. However, to find out the relationship between qualitative leakage rate and AE signal large amounts of experimental data is needed. This paper presents a theoretical investigation of the acoustic emission to detect the internal leakage rate through a valve and experimental validation. The AE signals generated by internal liquid and gas leakage through valves were characterised. The effect of the influenced factors of leakage rates, inlet pressure levels, valve sizes and valve types, on AE parameter, AE RMS , were studied and explained. The results of theoretical and experimental showed that AE signal power computed from the power spectral density (PSD) correlated well with influenced factors of leakage rates. Finally, a novel and inexpensive AE instrument has been invented for predicting qualitative leakage rate using a micro processor and derived relationship.

음향방출 기법을 이용한 섬유보강 시멘트 복합체의 정량적 손상평가

Dept. of Civil System Engineering, Konyang University, Chungnam 320-711, KoreaABSTRACT Fiber is an important ingredient in fiber-reinforced cement composite (FRCC) which can control fracture of cementcomposite by bridging action. In compliance with the action of the fiber and the aggregate size, it also showed a different failure mech-anism. For practical application, it is needed to investigate the fracture behavior of the FRCC and to understand the micro-mechanismof cement matrix with reinforcing fiber. In order to evaluate a characteristics of fracture process in the FRCC, acoustic emission (AE)technique was used for the analysis and evaluation of FRCC damage by acoustic emission under flexural and cyclic compressive load-ings. The AE signals were monitored by AMSY4 AE instrument during the entire loading period. The specimens are reinforced with0, 1.0, 1.5 and 2.0% (by volume) Polyvinyl alcohol (PVA) fiber. The test results showed that the damage progress of the FRCC wascharacteristic for the fiber replacement ratio. As a result of analyzing the felicity ratio (FR) values, it is shown that this values can beused for evaluating the degree of FRCC damage. On the whole the felicity ratio values of FRCC are shown between 0.4 and 1.1. And,the AE kaiser effect was shown in the all FRCC specimen. In addition, the damage behavior and the microscopic fracture process ofthe FRCC are evaluated using the AE parameters, such as calm ratio, b-value and felicity ratio. The purpose of this reserch was toadvance the state of knowledge regarding the applicability of acoustic emission as an evaluation method for FRCC.Keywords : fiber-reinforced cement composite, bridging action, Kaiser effect, calm ratio, b-value

EXPERIMENT STUDY ON MECHANICAL PROPERTIES OF GRANITE UNDER REPEATED LOADING AND UNLOADING

Deformation rules and acoustic emission characteristics of granite under repeated loading-unloading are studied using the MTS Mechanics Testing System and Disp. acoustic emission instrument. It's found that the axial stiffness of granite as well as Poisson's ratio increases with the development of the plastic strain while the change trend of lateral stiffness is negative. For brittle rocks, strain is produced by three mechanisms: elastic deformation, axial micro-cracking and compaction. The peak AE rate is increasing with the plastic strain, which indicates that using the axial plastic strain as the internal damage variable to represent rock damage is reasonable.

Acoustic emission sensors for OEM applications

The acoustic emission (AE) technique is concerned with the detection of structure-borne ultrasonic activity that is naturally generated during the operation of all structures, machinery and processes. Most examples of its application involve the purchase and use of commercially available instrumentation by end-users. To satisfy these demands AE instrumentation has evolved into various forms for use by researchers, engineers and craftpersons. The increasing credibility of AE as a robust industrial measurement technique is creating opportunities for AE sensing to be built into machinery by original equipment manufacturers. In this paper, the evolution of AE technology towards an OEM technique is described and illustrated with examples of some of the information AE can provide in the industrial environment.

Structural integrity and remnant life evaluation of pressure equipment from acoustic emission monitoring

It is now in excess of 30 years since modern acoustic emission (AE) techniques have been employed in industry. In that period, great advances have been made in both AE instrumentation development and applications including basic functions such as defect/leak/source detection and location, and some source identification. The industrial community which, in many countries, has been permitted to operate under Self-Regulation Criteria, in some instances has demonstrated a tendency to use economic and convenience constraints to determine their operating scenarios. The desire to make manufacturing plants and structures more productive has resulted in them being operated under conditions which exceed those envisaged during the initial design. While these plants and structures still operate efficiently and safely, the real structural integrity and remnant life evaluation is unknown. AE techniques have been used in a variety of applications in industrial plant, and the techniques described in this paper can provide real-time defect location; identify processes and procedures that are damaging pressurised equipment; provide a structural integrity evaluation and, after a number of tests and analysis operations provide an estimate of remnant life of the structure monitored.

Acoustic Emission from Depressurization to Detect/Evaluate Significance of Impact Damage to Graphite/Epoxy Pressure Vessels

Six aerospace-type, filament-wound graphite/epoxy pressure vessels were studied. Four of these cylindrical vessels had each received a single, controlled impact; four had received thermal exposures including moderate heat and/or cryogenic cold. Acoustic emission (AE) was monitored during a proof test sequence (after the impact/thermal exposure), including the final depressurization from proof pressure (i.e., the second unload cycle). A single set of wideband AE sensors was used to simultaneously record parameter-based AE and waveform-based AE on two independent AE instrumentation systems. Some slight to moderately large differences in AE activity for impacted vs. non-impacted vessels were noted for AE from Felicity ramps and holds at pressure. However, dramatic differences were apparent in quantities of AE from the final depressurization cycle: impacted vessels experienced unload AE activity which was a minimum of an order of magnitude greater in quantity than the unload AE activity for non-impacted vessels. This difference provided a distinctive means of identifying those vessels with impact damage. A newly defined "Shelby ratio" was introduced as a means of quantitatively assessing the unload AE; correlations were obtained between vessels' residual strength and the unload "Shelby ratios." Refinements of the parameter-based data analysis approach were made possible by waveform information. Additionally, examination of the waveform data of the unload cycle revealed a significant quantity of "friction" type waveforms having a repeated, lower frequency character; similar "friction" waveforms were able to be artificially generated by rubbing a pencil lead across a composite vessel surface.

Tensile Properties of Ceramic Matrix Fiber Composites

The mechanical properties of various 2D ceramic matrix fiber composites were characterized by tension testing, using the gripping and alignment techniques development in this work. The woven fabric composites used for the test had the basic combinations of Al2O3 Fabric/Al2O3, SiC fabric/SiC, and SiC minofilament uniweave fabric/SiC. Tension testing was performed with strain gauge and acoustic emission instrumentation to identify the first‐matrix cracking stress and assure a valid alignment. The peak tensile stresses of these laminate composites were about one‐third of the flexural strengts. The SiC monofilament uniweave fabric (14 vol%)/SiC composites showed a relatively high peak stress of 370 MPa in tension testing.

Fatigue Design Model Based on Damage Mechanisms Revealed by Acoustic Emission Measurements

Integration of the microcomputer into acoustic emission instrumentation has brought AE monitoring of fatigue tests into the realm of practicality. On-line processing makes available a selection of software tools, enhancing classical techniques for eliminating the background noise which usually blanked out the desired data. Fatigue tests monitored for acoustic emission were carried out at room temperature on Incoloy 901 material specimens, over a stress-ratio range of −1 ≤ R ≤ .2. Valid AE data were obtained even when the load cycle passed through zero. The AE data permitted specific identification of the various phenomena occurring on the way to final failure. These included initial plasticity, crack nucleation and propagation phases. The AE findings were supported by microscopic examination. Based on the experimental data, a preliminary damage-prediction model was formulated.

Acoustic-emission instrument system for monitoring the heat treatment of polymer composites

Acoustic-emission instrument system for monitoring the heat treatment of polymer composites

Acoustic emission calibration instrumentation

An automatic calibration instrument was developed to improve the calibration accuracy of acoustic emission (AE) instrumentation. The instrument facilitates calibration by automatically displaying the maximum value of the stress used to produce AE calibration pulses and the AE pulse. A repeatable AE signal was generated by breaking a graphite rod on the test assembly. By measuring the breaking load of the rod and the maximum root-mean-square values of the resulting AE signals, a relative calibration of the AE measurement system was achieved. Low-noise amplifiers and filters were developed to improve the sensitivity of AE measurements by more than one order of magnitude over commercially available instruments; thus, the smaller signals obtained in parts testing can be detected. >

Acoustic emission during chromium plating : Todaro, M.E.; Capsimalis, E.S. U.S. Armament research development and engineering center, Waterliet, New York (United States), AD-A180-357, 18 pp. (Mar. 1987)

Abstract : The authors used acoustic emission to study crack formation during the electrodeposition of chromium over a range of temperatures and current densities which characterize the transition from high contraction (HC) to low contraction (LC) chromium. Several characteristics of the acoustic emissions were examined, including the amplitude distribution, signal energy, emission rate, count rate, and frequency spectrum. The acoustic emission technique detected the onset of cracking and yielded useful information regarding the number of cracks. Such information acquired during the actual deposition process can be an invaluable aid in determining the quality of the deposit and in developing improved chromium coatings. Experimental data were acquired and analyzed using commercial acoustic emission instrumentation, including standard piezoelectric transducers. The deposition bath was a standard aqueous solution of 250 gram per liter chromic acid and 2.5 g/l sulfuric acid. The solution temperature and deposition current density were varied to obtain deposits of differing crack content. The substrate was electropolished carbon steel.

Acoustic emission during chromium electrodeposition

The authors used acoustic emission to study crack formation during the electrodeposition of chromium over a range of temperatures and current densities which characterize the transition from high contraction (HC) to low contraction (LC) chromium. Several characteristics of the acoustic emissions were examined, including the amplitude distribution, signal energy, emission rate, count rate, and frequency spectrum. The acoustic emission technique detected the onset of cracking and yielded useful information regarding the number of cracks. Such information acquired during the actual deposition process can be an invaluable aid in determining the quality of the deposit and in developing improved chromium coatings. Experimental data were acquired and analyzed using commercial acoustic emission instrumentation, including standard piezoelectric transducers. The deposition bath was a standard aqueous solution of 250 g/l chromic acid and 2.5 g/l sulfuric acid. The solution temperature and deposition current density were varied to obtain deposits of differing crack content. The substrate was electropolished carbon steel.

Acoustic Emission: Establishing the Fundamentals.

In the mid-1970's a program of fundamental research was initiated at NBS to improve the scientific understanding of acoustic emission. Many individual results of this research have been reported in the literature and are beginning to be incorporated in a new generation of acoustic emission instrumentation, in improved test methodologies, and in the analysis of data. Here, we summarize the problems faced by acoustic emission midway through the last decade, review the accomplishments of the NBS program and related researchs programs, and outline the research that will be required in future years.

The use of acoustic emission instrumentation to monitor powder flows

This paper reviews the use of acoustic emission for powder flow investigations. It then examines the application of the technique to two separate problems of (a) metering metal powder flows; and (b) investigating the velocity profiles inside a fluidised bed.