Showing papers on "Acoustic emission published in 1972"

Elastic surface waves

Abstract: Devices that exploit the properties of elastic surface waves can perform very complex signal‐processing functions, identical to those carried out by conventional electromagnetic devices. The great advantage to using surface waves instead of electromagnetic waves is the tremendous reduction in size of surface‐wave devices compared to their electromagnetic counterparts. This great reduction in size is the result of the great difference between the elastic and electromagnetic velocities. Surface waves propagate at velocities approximately 105 times slower than electromagnetic velocities; thus, at the same frequency, the elastic wavelength is 105 times shorter than the electromagnetic wavelength. A further advantage is that the energy in the elastic surface wave can readily be sensed anywhere along its path.

The fracture energy and acoustic emission of a boron-epoxy composite

Abstract: The fracture surface energy (γ) of a boron fibre-epoxy resin composite has been measured by three different techniques: work of fracture, linear elastic fracture mechanics, and compliance variation. Significant differences were obtained by the different methods. The compliance data were analysed to giveγ at different stages of crack propagation. It was observed thatγ decreased as the crack entered the material and that this variation ofγ could be correlated with the pull-out length of fibres and acoustic emission generated during fracture. The fracture surface energy is explained in terms of a debonding model.

Acoustic Methods For Monitoring Failure In Rock

Abstract: Monitoring elastic wave velocity variation and the acoustic emission in rock in the process of fracturing affords a method of assessing the structural quality of rock, detecting the onset and progress of fracturing, and providing information on the attitude of fractures and the mode of failure. The technique used in the present investigation, referred to as BVM (biaxial velocity monitoring), monitors longitudinal (compressional) wave velocity in the directions of greatest and least principal stresses. Velocity data are concurrently obtained with stress-strain characteristics during unconfined and conventional triaxial compression tests to permit the interpretation of velocity variation in terms of the deformational and fracture characteristics of the rock. The combined acoustic data are used to infer the stress level and deformation characteristics in rock under stress. Deformation conditions that can be recognized are (1) crack closure, (2) linear elasticity, (3) fracture initiation and development, (4) accelerated fracture development, and (5) gross failure and post peak behavior. (60 refs.)

Detection of fiber cracking by acoustic emission.

Abstract: A theoretical model is presented that relates acoustic emission to fiber cracking which occurs during a rising load tension test on a fiber reinforced composite. The percentage of broken fibers in an Al3Ni fiber reinforced aluminum was measured as a function of tensile strain by optical inspection of the polished surface of strained specimens. This information was used in conjunction with the proposed model to predict the acoustic emission response of the composite material. These predictions were compared with experimental observations, and a good agreement was obtained between the two sets of results. These results indicate that it is possible to relate acoustic emission quantitatively to the micromechanics of the deformation processes occurring within fiber reinforced composites, thereby demonstrating the applicability of acoustic emission to materials studies and also to nondestructive evaluation of the integrity of composite materials.

The propagation and growth of acceleration waves in heat-conducting elastic materials

Abstract: In the thermo-mechanical theory of continua an acceleration wave may be defined as a propagating singular surface on which the strain, velocity, temperature and entropy are continuous and on which discontinuities in acceleration, strain rate and strain gradient occur. We study here basic properties of such waves in homogeneous heat-conducting elastic bodies, placing no restriction on the symmetry of the material. In a paper which has strongly influenced the course of recent research in the theory of non-linear elastic waves TRUESDELL [1961] has discussed the propagation of acceleration waves through a finitely strained material according to the purely mechanical theory of elasticity. The central result in this analysis is the FRESNEL-HADAMARD theorem, requiring the acceleration amplitude of a wave travelling in a given direction to be a right proper vector of a certain tensor, called the acoustical tensor, which depends upon the direction of propagation and the state of deformation at the location of the wave. The wave speed is determined by the proper number of the acoustical tensor associated with the acceleration amplitude, and thus in a given direction there are up to three speeds with which an acceleration wave can propagate, different speeds corresponding to distinct amplitudes. The FRES~,mL-HADAMARO theorem determines the direction of the acceleration amplitude but places no restriction on its magnitude. For plane acceleration waves propagating through a homogeneously deformed isotropic elastic material GREEN [1964, 1965] has shown that the magnitude of the acceleration amplitude either increases without bound over a finite interval of the time t, decays towards zero as t ~ ~ , or remains constant. These results have been extended to acceleration waves of arbitrary form by CHEN [1968, 1, 2] and JtrNEJA & NARiBOLI [1970], and to general elastic materials by CrrEN [1970, 1, 2] (in respect of longitudinal and transverse waves*) and CHADWICK & OGDEN [1971, 1]. An analysis of the growth of acceleration waves in hyperelastic materials embracing both of these generalizations has been given by SUI-IVBI [1970], and BOWEN & WANG [1970] have studied.

Fracture behavior of stainless steel

Abstract: An experimental program has been carried out to characterize the fracture properties of austenitic stainless steel piping and plate material. Characterization was in terms of the J-integral, and several specimen types were tested, including compact specimens, center-cracked panels, and three-point bend specimens. Several methods of monitoring crack extension were used in the program, including unloading compliance, electrical potential, and acoustic emission in addition to the multiple-specimen heat tinting method used for baseline data. These methods are compared and evaluated in detail. In addition to determining J I c values for the material, Paris's proposed tearing modulus is evaluated, and various proposed specimen size requirements are discussed.

Acoustic emission damage measurement

Abstract: A precracked gage element is attached to a structural member to be monitored for damage and is continuously or periodically monitored to determine acoustic emission therefrom as a measure of fatigue damage of a structural member

Some Observations on Acoustic Emission during Continuous Tensile Cycling of a Carbon Fibre/Epoxy Composite

Abstract: HERE we report preliminary experiments on the acoustic emission from a composite when subjected to sequential cycles of tensile stressing. Two different conditions of cycling were followed; in the first (A) the maximum cycling stress was gradually increased with successive cycles and in the other (B) all cycles were of the same stress amplitude.

Application of Correlation Analysis to Acoustic Emission

Abstract: : Correlation analysis techniques have been used in order to characterize acoustic emission pulses from metals. A brief description of correlation functions and the method of their determination is presented. The time varying spectra of a magnesium sample has been obtained using the present techniques, and then compared with the more common methods of measuring acoustic emission. Other uses of correlation analysis in acoustic emission studies are included. (Author)

Acoustic emission weld monitoring of nuclear components

Abstract: Acoustic emission monitoring augments other nondestructive testing methods and is sometimes applicable when other tests cannot be applied. This is, in part, due to the high sensitivity of acoustic emission monitoring. Acoustic emission monitoring is only sensitive to active flaw-growth, however, and will not detect a flaw in equilibrium. This paper describes the application of acoustic emission monitoring to nuclear reactor fuel pin end closure welds and other weldments of the reactor piping.

Energy Propagation in a Deformed Elastic Material

Abstract: Resultant material and spatial energy propagation vectors are defined for waves of small amplitude superposed on large static deformations in elastic materials of arbitrary symmetry. It is shown that the resultant material energy propagation vector is in the direction of the normal to the slowness surface and hence in that of the bicharacteristics.

Use of Acoustic Emission in Nondestructive Testing

Abstract: : A model based on the activation of dislocation sources was developed for predicting the effect of microstructure on acoustic emission The model predicts a minimum dislocation source length and slip distance below which no emission will be detected Experimental results obtained on various metals and alloys having different microstructures substantiate the model The effect of grain size on the acoustic emission from 9999% aluminum and 999% copper suggests that macroscopic yielding in these metals occurs with the help of dislocation pile-ups that have been held up by grain boundaries and that the emission results from the activation of dislocation sources near the grain boundaries Experimental results obtained under conditions of very low background noise level show that some metals produce acoustic emission when the applied load is removed The amount of emission that is observed correlates with the magnitude of the Bauschinger effect in the metal In those metals that show an 'unload' acoustic emission effect there is the possibility of using it to investigate the magnitude of the residual stress in a specimen Creep and fatigue phenomena can also be studied by the use of acoustic emission