Showing papers on "Acoustic emission published in 1980"

Acoustic emission for physical examination of metals

Abstract: Acoustic-emission techniques are beginning to be frequently used as a means of detecting and locating deformation and fracture processes in both metallic and non-metallic engineering structures This has happened despite a relatively poor understanding of the basic physical processes involved in the generation, propagation, and detection of acoustic-emission signals, and of the influence in metals of factors such as composition and microstructure, upon the acoustic emission from different types of deformation and fracture processes The measurement of acoustic emission, potentially, could yield much information about dynamic aspects of these processes However, it is shown that the limitations of existing acoustic-emission recording instrumentation have enabled only qualitative information to be obtained to date Even this data, however, has demonstrated that metallurgical variables greatly affect the acousticemission response of metals, and simple models to account for this are discussed

New method of detecting contact between floating-head and disk

Abstract: Acoustic Emission (AE) technique is applied to the detection of slider-to-disk contact. The type of slider-to-disk contact is identified by detecting the AE caused by contact. Advantages of this method are simplicity of measurement and the ability to detect contact between slider and disk fabricated from any material. In addition, this method can be used to measure the projection height distribution over an entire disk surface, which is one of the most important factors governing the reliability of disk files.

Elastic wave emission from damage processes

Abstract: The theory of elastic wave emission (i.e., acoustic emission; AE) from damage processes such as slip and microcracking is discussed. Analogous developments in the literature on earth-quake seismology and dynamic dislocation theory are noted and utilized. A general representation of the displacement field of an AE event is given in terms of the double-couple response to a distribution of “moment density tensor” in the source region. Results are specialized to a point source model and to a general far-field analysis of outgoing elastic waves, and conditions for validity of such representations and their low-frequency specializations are noted. Emitted wave fields are compared for tensile opening and slip events, and procedures which might enable the approximate determination of the size or area increase of tensile microcracks are discussed.

Hertzian indentation of thorium dioxide, ThO2

Abstract: The Hertzian indentation technique was used to study the fracture properties of ThO2 and to measure the fracture surface energy, γ, of sintered ThO2 Optical microscopy and acoustic emission were employed to detect ring crack formation Perfect cracks were always formed and no indication of permanent plastic deformation was observed From the observed crack behaviour, a fracture surface energy, γ, of 25±02 J m−2 at room temperature and a fracture toughness, KIc, of 107 MN m−3/2 were deduced

Acoustic emission and electron emission during deformation of anodized aluminium

Abstract: Tribostimulated exoelectron emission provides a sensitive way to characterize anodic films on aluminium. This paper describes the detection of acoustic emission (AE) and electron emission (EE) during the tensile deformation of anodized aluminum. It is shown that the observed bursts of AE are associated with cracking of the oxide, that AE and EE count rates vs strain are closely related, and that most EE occurs very soon after AE events. Evidence is also presented for a component of EE unrelated to AE which is attributed to chemi‐emission.

Acoustic detection of tool wear and fracture

Abstract: For detecting brittle fracture and wear of a tip of a cutting tool an acoustic emission monitoring system has a converter for converting acoustic emission into an electric signal, a filter for rejecting frequency components in the signal below a frequency between 50 kHz and 300 kHz, a detector to detect the amplitude of the signal after the rejection of those frequency components, and a comparator for comparing that amplitude to a predetermined reference amplitude.

Acoustic emission studies of damage in GRP

Abstract: A study has been made of the amplitude distributions of acoustic emissions from glass reinforced plastics of several different kinds during tensile loading of test coupons. It is shown that the structure of a GRP laminate exerts a dominating effect on the AE patterns observed, and that direct correlations between microfailure events in the composite and the amplitude distributions of the emissions cannot be made. Understanding of AE patterns from any given GRP material (or structure) may only be possible if there is already a substantial background knowledge of the behaviour of similar materials or structures under known conditions.

A theory for optimization in the use of acoustic emission transducers

Abstract: We postulate that measurement precision and the magnitude of acoustic emission signals will be affected by the type and thickness of the couplant used to couple the transducer to a structure. A theoretical solution is provided to determine the transmission coefficient of a multilayer system of n layers. A longitudinal wave is assumed to be normally incident on the system. Theoretical transmission coefficients are obtained for waves transmitted through three, four, and five layers. Specific calculations are carried out for a particular five‐layer system which is applicable to an acoustic emission transducer. Conclusions are drawn concerning the measurement precision likely to be obtained from this type of transducer used in this configuration.

The acoustic emission response of snow

Abstract: In this work a model of the ultrasonic acoustic emission response in snow is developed. The model derived considers the acoustic emission response in snow as a function of stress and strain. It is suggested that the acoustic emission activity in snow is a quantitative indicat ion of the creep rupture taking place in the material. The governing differential equation is developed; an example is then presented that considers the applicability of this equation to the release of certain types of avalanche. REsuME. L'emission acollstique de la neige. D ans ce travail on develop pe un modele de l'emission acoustique ultrasonore dans la neige. Le modeJe considere l'emission acoustique comme une fonction de la contrainte et de la deformation. On suggere que I'act ivite emissive acoustique dans la neige est une indication quantitative des ruptures dues a la fluage qui se produisent dans le materiau. On developpe I'equation differentielle qui regit le phenomene: on presente alors un exemple qui envisage I'applicabilite de cette equation au declenchement de certains types d'avalanches. ZUSAMMENFASSUNG. Die Schallemission von Sclmee. In dieser Arbeit wird ein Modell fur die Emission von Dberschallwellen aus Schnee entwickelt. Das Modell betrachtet diese akustische Emission als eine Funktion von Spannung und Verformung. Es wird angenommen, dass die Schallemission von Schneeeine quantitative Anzeige fur die Kriechbruche sind, die in dem Material stattfinden. Die massgebliche Differentialgleichung wird hergeleitet; an einem Beispiel wird dann die Anwendbarkeit dieser Gleichung auf den Abgang bestimmter Lawinentypen untersucht.

A feasibility study of detecting reinforcing-bar debonding by acoustic-emission technique

Abstract: Acoustic emissions (AE) detected by two transducers mounted on a reinforcing bar in a reinforced-concrete block, which is subjected to cyclic tension-compression loading, are used to assess the locations of re-bar debonding. Preliminary uniaxial-tension tests of the re-bar were conducted to establish the proper level of AE sensitivity which was then verified by uniaxial-tension tests of re-bar embedded in a concrete block. The main tests consist of simulated beamcolumn connection with a 90-deg hooked No. 8 Grade 60 rebar subjected to various cyclic-loading histories. Reasonably good correlations were established between the debonding regions indicated by the AE signals and those detached by dye injected into the cracked concrete.

Acoustic emission warning system for a fiberglass member

Abstract: An apparatus is provided for use as an onboard monitor and warning system attached to a fiberglas boom to detect potentially hazardous loads by detecting and counting acoustic emissions produced in the boom by the breakage of glass fibers. The monitor and warning system produce a warning signal when the number of acoustic emissions detected in a selected period of time indicates the existence of a potentially hazardous load. The apparatus includes a piezoelectric transducer which may be placed in contact with the surface of the fiberglas to produce electrical signals corresponding to pressure waves detected in the fiberglas. Apparatus is provided for distinguishing by the electrical signals those pressure waves which are acoustic emissions associated with the breakage of glass fibers from all other pressure waves. Further apparatus is provided for counting each electrical signal associated with fiber breakage, for selecting a period of time during which the electrical signals associated with fiber breakage will be accumulated, and for producing a warning signal when the number of electrical signals associated with fiber breakage during the selected time period indicates the existence of a potentially hazardous load.

Material Reaction of Diaphyseal Bone Under Torsion: An Experimental Study on Dogs

Abstract: The formation of microcracks in entire canine diaphyseal bones under torsional loads was studied. the acoustic emission technique was used to register the stress waves which were generated in the bones by crack formation and/or growth. Acoustic emission signals, characteristic of crack formation and/or growth, were recorded exclusively during the non-linear deformation. This is a strong indication of the elastic behaviour of diaphyseal canine bone material.

Ae monitor unit

Abstract: PURPOSE:To make it possible to change arbitrarily a monitor section without change of the arrangement interval of sensors, by delaying one of detection outputs of two sets of acoustic emission (AE) sensors by a prescribed time and by deciding the phase difference between this output and the other by comparison CONSTITUTION:The phase difference between the receiving detection output of AE sensor 11b and the receiving detection output of AE sensor 11a which is delayed in delay circuit 13 of phase deciding part 15 by prescribed time T1 is decided by deciding circuit 14, and circuit 14 generates a decision pulse only when the phase of the delayed detection output advances, and generation position P of the AE wave signal is detected by signal processing circuit 16 to monitor the AE wave signal Consequently, only when distance D1 from sensor 11a to detection point P is shorter than distance D1 from sensor 11b, the position of detection point P is detected, and the monitor region is limited to prevent the influence of noise and so on In this case, detection points different in distances D1 and D2 can be determined on the basis of expressions I and II by changing time T1, and the monitor section can be changed arbitrarily without change of the arrangement position of sensors Here, V is the AE wave propagation speed, and L is the delay equivalent distance

Basic Wave Analysis of Acoustic Emission

Abstract: Acoustic emission or stress wave emission is the phenomenon of transient elastic wave generation due to a rapid release of strain energy caused by a structural alteration in a solid material. Generally these structural alterations are a result of either internally or externally applied mechanical or thermal stress. Depending on the source mechanism, acoustic emission signals may occur with frequencies ranging from several hertz up to tens of megahertz. Often the observed acoustic emission signals are classified as one of two types: burst and continuous. As shown in Fig. 1, the burst type emission resembles a damped oscillation, while the continuous type emission appears to consist of an overlapping sequence of individual bursts. The importance of acoustic emission monitoring lies in the fact that proper detection and analysis of acoustic emission signals can permit remote identification of source mechanisms and the associated structural alteration of solid materials. This information in turn can augment understanding of material behavior, can be used as a quality control method during materials processing and fabrication, and as a nondestructive evaluation technique for assessing the structural integrity of materials under service conditions.

Effective noise discriminator for use in acoustic emission studies

Abstract: Both coherent and random short duration electromagnetic noise source pose serious problems to meaningful acoustic emission studies. A simple but effective discriminator is described which makes acoustic emission studies possible in severe noise environments. Additional circuitry is presented which permits one to eliminate coherent noise sources from the acoustic emission data.

Experimental assessment of static and fatigue damage of graphite/epoxy laminates

Abstract: This paper is concerned with the damage due to transverse cracking, loss of stiffness, and delamination under static and fatigue loading. Knowledge about this type of damage formation may be useful in providing data for establishing a reliable fatigue life prediction scheme. To accomplish this, the cracks developed in the angle plies during the various stages of loading were observed on the free edge of the specimen using a microscope. Acoustic emission was employed to detect the first ply failure and onset of delamination under static loading. The stiffness change for the [0/90/±45]s laminate at two fatigue stress levels was measured using strain gages. The observed cracks in each angle ply were presented vs. applied stress and fatigue life. The effect of stacking sequence, ply thickness, and delamination on the transverse crack formation was also considered. An attempt was made to correlate the damage in terms of crack density and stiffness loss to fatigue life.

Acoustic emission source characterization

Abstract: The source function for glissile dislocation loops and microcracks have been modeled in terms of time dependent force dipoles and the acoustic emission waveforms, at the epicentre, evaluated for an isotropic elastic half‐space. A specimen geometry has been designed that allows microcracking to occur under the influence of an applied stress but which also approximates to a half‐space for a short period of time after operation of an event. The epicentre waveforms of such a specimen have been measured, quantitatively, with a broad band capacitance transducer and the waveforms recorded by Biomation transient recorders and stored on computer disk. The inverse transfer function for the experimental configuration has been calculated and used to determine the source function of carefully characterized brittle cleavage and intergranular microcracking in mild steel and electrolytic iron at 77K. The microcrack lengths deduced from acoustic emission measurements were consistent with fractographic observations. The ve...

Ultrasonic and Acoustic Emission Detection of Fatigue Damage.

Abstract: : The primary purpose of the research was to optimize existing ultrasonic and acoustic emission techniques and to investigate new ones for early detection of fatigue damage in aluminum alloys used in aircraft construction. Ultrasonic attenuation measurements made simultaneously with fatigue tests on aluminum alloy bar, and sheet specimens gave warning of crack formation and imminent fracture much earlier than conventional ultrasonic methods. An ultrasonic pulse-echo system was used during fatigue cycling to record conventional A-scan waveforms as well as to monitor ultrasonic attenuation. In addition, acoustic emission signals were recorded simultaneously with the ultrasonic measurements on each test specimen using two different acoustic emission systems. The correlation of evidence of cumulative fatigue damage and acoustic emission data was approached by the use of long term true-rms averaging of the system output and frequency domain analysis of acoustic emission signals recorded at selected intervals throughout the test. The integrity of the data was verified by independent electronic testing of the instrumentation. Visual and in situ eddy current inspection, and optical and scanning electron microscopy were used to correlate acoustic emission and ultrasonic attenuation data to the physically deformed microstructure.

Acoustic emission analysis using pattern recognition

Abstract: Three different pattern recognition techniques were applied to a data set consisting of acoustic emissions (AE) caused by crack growth and acoustic signals caused by extraneous noise sources. The purpose was to test the techniques for prescreening acoustic events and filtering out those that are produced by extraneous sources. The results were surprisingly good. Most of the noise waveforms used in this study cannot be distinguished from valid AE by visual examination; however, we were able to correctly classify 90% of the waveforms as either valid AE or noise using the least squares decision rule. Since the current application of AE data in nondestructive evaluation rely primarily on counting acoustic events, the waveforms caused by noise in the environment must be filtered out to avoid misinterpretation. The results of this investigation have convinced us that pattern recognition concepts can be used to design such a filter.

Clinical Application of Acoustic Emission Techniques to Bone Abnormalities

Abstract: Based on previous '!conventional" acoustic emis- sion (AE) studies on fresh animal bones, a new AE technique has been developed for application to hu- mans and animals both noninvasively and non-trauma- tically. Applying loads to the bone under test as in conventional AE applications would introduce ad- ditional trauma to the live subject. Therefore, simulated low-intensity ultrasonic pulses are in- jected into the bone through an AE transducer, while another receiving AE transducer is used to collect five types of useful AE data: per-event-distribu- tions of counts, peak amplitude, energy and pulse duration, and cumulative counts vs. time. These AE data have been found to be very sensitive to most of the simulated bone abnormalities introduced into animal bones by pre-loading, saw cutting and drill- ing, as well as by cutting the surrounding soft tissues to varying depths with a scapel. In the human study involving fourteen volunteers (mostly runners with histories of stress fractures in their tibiae), their AE data have been found to provide a consistent picture of normal vs. injured bones. Also, reasonablv consistent AE results were obtained from the animal study where a surgical defect was introduced in the right mid-tibia of a beagle, while the left leg served as the contralateral control; subsequently healing processes were monitored both with x-rays and AE for