Acoustic Emission Investigation Research Articles

A comparative investigation of electrical resistance and acoustic emission during cyclic loading of CFRP laminates

This paper reports on simultaneous monitoring of electrical resistance and acoustic emission (AE) during cyclic tensile loading of cross-ply carbon-fibre-reinforced plastics (CFRP). The detection of the AE allows further insight into the damage mechanisms causing the electrical response. During loading and unloading the samples the electrical measurements show a hysteresis in the corresponding resistance vs strain plot. When the previous load maximum is exceeded in the subsequent load cycle a characteristic increase in the measured slope of the resistance vs strain curve appears to combined with a sudden rise in the AE (Kaiser effect). After unloading the resistance relaxes to a new equilibrium value. This behaviour is consistent with the formation, opening and closing of cracks in the CFRP samples. The observed time dependence in the resistance hysteresis and relaxation can be attributed to the influence of the stressed polymeric matrix. Thus, the reported in situ observation of the electrical resistance allows virgin and damaged CFRP samples to be identified and the previous load maximum to be determined by the characteristic change in the resistance-strain slope.

Determination of the Bulk Damage of Aluminum Alloys by Signals of Acoustic Emission

We present the results of acoustic-emission investigations of the bulk damage of D16-T and 1201-T aluminum alloys in a plastically deformed volume. Cylindrical specimens of aluminum alloys 4 mm in diameter were tested by stretching. For both alloys, constants are established which allow one to perform quantitative estimates of the bulk damage in the plastically deformed volume of a structural material by signals of acoustic emission in the process of nondestructive testing and technical diagnostics. On the basis of the results of investigations, we obtained a criterion for determination of the onset of macrofracture and showed that the dependence of bulk damage on the true tensile deformation is well approximated by a linear function.

Acoustic-Emission Criteria for Rapid Analysis of Internal Defects in Composite Materials

We present the results of acoustic-emission investigation of volume damage of composite materials with various types of stacking of carbon fibers. All 16 layers of fibers placed in the same matrix give different contributions to the strength properties of the material with varying acoustic-emission activity in the process of loading. We established criteria for the quantitative estimation of volume damage of composite materials with regard for the specific character of changes in amplitudes of acoustic-emission signals at various stages of loading. The analysis of spectral characteristics of acoustic-emission pulses passed through original and damaged materials of the specimen confirms the efficiency of the proposed criteria. We give values of criterional parameters for the investigated types of specimens of composite materials.

Investigation of acoustic emission due to deformation of titanium alloy and some results of acoustic-emission diagnostics of its predestruction states

The paper presents acoustic-emission (AE) characteristics of the Ti-Al-Mo-Si alloy. The energy of one AE event has been estimated over the entire frequency band under investigation. AnS-shaped curve of the logarithm of the frequency of AE events plotted against the strain has been obtained, and the physical interpretation of such a dependence has been given. A tentative explanation of the delay of AE events on the initial stage of the material deformation with a stress concentrator has been suggested. On the base of the correlation between the service-life expectancy and the frequency of AE events, which has been established in our experiments, the degree of confidence in the diagnostic data concerning the predestruction state of gas-turbine blades in turbojet aircraft engines has been estimated.

Acoustic emission monitoring of sheet metal forming: characterization of the transducer, the work material and the process

A systematic investigation of acoustic emission (AE) in cup-drawing was conducted. The AE transducer was characterized by subjecting it to known excitations both directly and through a plastically-deforming material. The AE activity in well-controlled tensile tests was characterized using root-mean-square (RMS) AE measurement. A model of RMS AE based on dislocation generation, motion and annihilation was formulated. Model parameter values were determined using tensile-test results. Finite element calculations of the strain distributions in the cup-drawing process using experimentally determined friction boundary conditions were performed. The calculated strain and strain rate were used in the RMS AE model to predict AE activity in cup-drawing. The RMS of AE signals was measured in cup-drawing, and predicted and measured results were compared. Transducer and signal transmission path characteristics have significant effects on measured AE signals. If only correlations between process variables and RMS AE is sought, the combined transducer, signal path and AE effects can be used. The RMS AE model developed using experimental tensile-test results was capable of predicting RMS AE measurements in cup-drawing. The large AE activity in the initial stages of plastic deformation in cup-drawing makes AE measurements easy and meaningful, but the small signal after this part of the process makes the monitoring of subtle changes in this part of the process doubtful.

Acoustic-emission investigation of the sensitivity of spring steel to hydrogen degradation

By using the results of tensile tests of cylindrical and flat specimens, we determined the sensitivity of spring steel to hydrogen embrittlement. As criteria, we use the moment of the beginning of generation of acoustic-emission signals and the sum of their amplitudes. We have shown that, in the course of deformation of specimens of nonhydrogenated steel, the acoustic emission signals are characterized by low values of the sum of amplitudes and a total count of pulses exceeding the discrimination level. The maximal amplitudes, fixed at the output of a primary transducer of acoustic-emission signals, are some-what higher with a smaller number of events for nonhydrogenated specimens than for hydrogenated ones. It is possible to determine the tendency of a material to hydrogen degradation through violation of the Kaiser effect. Additional information on hydrogen degradation can also be obtained by spectral characteristics of acoustic-emission signals.

Acoustic emission investigations of the ductility of L12Al3Ti+Cr under high hydrostatic pressure

Compression and tension tests were carried out on the L1 2 Cr-modified Al 3 Ti intermetallic under high hydrostatic pressures ranging from atmospheric to 1 GPa pressure. Both encapsulated and non-capsulated specimens were tested. There was a significant increase of deformability of the material both in compression and tension tests under pressure in the case of encapsulated specimens. Nearly the same effect was observed in the case of non-capsulated samples in compression tests but it was insignificant in tension tests. The in-situ acoustic emission (AE) investigations carried out under pressure and microscopic studies conducted on the deformed material afterwards showed that the deformation process of the material under pressure is controlled by two mechanisms of deformation, plastic and cataclastic ones. The difference in the compressive and tensile properties of the material under pressure was explained by the influence of pressure on the cataclastic mechanism which is strongly affected by pressure because the pressure delays both the process of microcracks growth from nuclei and the process of their propagation. AE monitoring allowed to determine both transformations from pure plastic to cataclastic deformations and from stable cataclastic deformation to catastrophic fracture of the material. Analysis of the amplitude distribution of AE signals showed that the pressure also diminishes the failure process of the material.

Acoustic emission investigation of phase transitions in antiferromagnetic PbZrO3 and PbHfO3 crystals

Acoustic emission investigation of phase transitions in antiferromagnetic PbZrO3 and PbHfO3 crystals

Mechanical properties of carbon fiber reinforced plastics and their response to a radiation environment

“TORAYCA T300 3K” is a two and a half dimensional woven carbon fiber reinforced epoxy which was developed for various applications including cryogenics. “Scaling” experiments in tension, in the shear-mode (mode II) and in the crack-opening-mode (mode I) were made at room and low temperature, in order to establish suitable sample geometries for irradiation experiments. Moreover, the interlaminar and the intralaminar shear strength as well as the ultimate tensile strength were investigated after irradiation at 340 K with a reactor spectrum up to a fast neutron fluence of 5 × 10 22 m −2 ( E > 0.1 MeV). The irradiated material was measured at 77 K and acoustic emission (AE) investigations were made for the tensile and the mode II samples.

Acoustic Emission and Anisotropic Expansion when Heating Marble

Types of failure such as bowing, increased surface absorption, and loss of strength can frequently be observed on facades even a few years after installation of crystalline calcite marble is used. The investigation discussed evaluated the process taking place in the structure of marble that lead to such damage. By means of a dilatometer the anisotropic thermal expansion of a coarse-grained marble type was measured systematically under temperatures between 20 and 200°C. The thermal expansion coefficient α amounted to between 15±2·10\u–\u6 K\u–¹ and 0±2·10\u–\u6 K\u–¹, depending on the orientation of the specimens, thus showing an extremely pronounced anisotropy. Special attention was paid to residual dilatation in the marble specimens that remained after the first heating-cooling cycle of the individual specimen (hysteresis). The dilatometric measurements were compared with investigations of acoustic emission (AE), which were carried out during the dilatometric measurements. These AE measurements provided information about the phase in the heating-cooling cycle during which the marble structure was damaged most by microcracks at the grain boundaries. The results proved that measuring AE signals is a suitable method of determining and analyzing thermal microfracturing of marble.

Acoustic emission investigation and signal discrimination in steel highway bridge application : Hariri, R. Dissertation Abstracts International, Vol. 51, No. 3, pp. 1399 (Sep. 1990)

Acoustic emission investigation and signal discrimination in steel highway bridge application : Hariri, R. Dissertation Abstracts International, Vol. 51, No. 3, pp. 1399 (Sep. 1990)

Fracture behaviour of plastic-copper interfaces in the crack opening mode (mode I) after neutron and gamma irradiation

We report on the mechanical properties of interfaces between fibre reinforced plastics and copper in the crack opening mode (mode I) at room temperature and at 77 K. In addition, neutron and gamma irradiations were performed in the TRIGA reactor (Vienna, Austria) up to a fluence of 1 × 10 22 m −2 ( E > 0.1 MeV) prior to testing. The mechanical tests were made on two-dimensionally reinforced epoxy (ISOVAL10)-copper interfaces at room temperature and at 77 K with a newly developed and experimentally simple splitting method. Details of the testing technique as well as influences of different treatments of the copper surface and of irradiation on the mechanical behaviour of the interfaces are presented and discussed, together with results of acoustic emission and fractographic investigations of the fracture surfaces.

Acoustic emission investigations of the work hardening of cerium under multiple high pressure isomorphic phase transitions

Generally, high hydrostatic pressurization at constant temperature can cause a permanent change in the microstructure of a polycrystalline material only in two cases: (1) when the material consists of not less than two phases with different compressibilities (pores should be taken as a phase of infinite high compressibility), or (2) when the single phase material has an anisotropic compressibility, i.e. non-cubic structure. In such materials there are conditions for generating the local non-hydrostatic stresses which can produce irreversible changes in the defect structure. Isomorphic high pressure {gamma} {Leftrightarrow} {alpha} transitions in cerium cause work hardening effects in the material at room temperature. The microstructure changes have asymptotic character versus number of these transitions. The approximate stabilization of the defect structure can be determined by the acoustic emission method.

An investigation of acoustic emission from an irradiated nuclear graphite

Acoustic emission (AE) responses from unirradiated nuclear graphites subject to cyclic loading have been shown to exhibit the Felicity effect, i.e., AE is detected at stresses below the previous peak stress. This has been attributed to time dependent recovery processes which occur upon unloading and at zero stress [1]. This paper describes work comparing similar unirradiated and irradiated nuclear sleeve graphites. The number of AE event counts from irradiated graphite was shown to be greater than that from unirradiated graphite, subjected to similar stresses. This effect was attributed to the increase in porosity caused by radiolytic oxidation. A Felicity effect was observed on cyclic loading of irradiated graphite, but no evidence for a Kaiser effect was found for irradiated graphite loaded monotonically to failure. The absence of a Kaiser effect can be attributed to relaxation and recovery processes that occur in the considerable time interval between removing the irradiated graphite from the reactor and post-irradiation examination. Therefore, it was concluded that AE monitoring is not a suitable technique for measuring internal stresses in irradiated graphites.

An investigation of acoustic emission in sliding fraction and wear of metals : Wear, Vol. 130, No. 2, pp. 367–379 (Apr. 1989)

An investigation of acoustic emission in sliding fraction and wear of metals : Wear, Vol. 130, No. 2, pp. 367–379 (Apr. 1989)

Effect of the rate of cooling the materials of a petroleum hydrocracking reactor on crack formation

Acoustic-emission investigations of the effect of the rate of cooling the materials of petroleum hydrocracking reactor heated in a hydrogen atmosphere are carried out. It is established that crack formation and lamination processes are slowed down with a decrease in the cooling rate of the specimens.

An experimental investigation of the AE source location and magnitude on 2-D frame structures using intelligent signal processing

The results of experimental investigation of acoustic emission (AE) source characterization in 2-D frames is reported in this paper. Determination of the AE source location and magnitude from the displacement field is an inverse problem. It is known that humans have remarkable sensory abilities to undo a large number of demanding inverse problems with little effort. Here, nature is modeled by implementing intelligent signal processing algorithms to solve the problems of the AE source location and magnitude determination. The signal processing algorithms implemented are; FFNN trained by a modified back-propagation algorithm, and a linear system called an auto-associative processor (AAP). The standard feature of these algorithms is the use of a set of pre-processed, measured signals to form a system memory. The pre-processed signals used by the AAP algorithm are tutor augmented, while in the case of the FFNN the pre-processed signals are nonlinearly mapped to the training vectors provided by the tutor. The system memory is consequently utilized to process experimental signals to determine some of the AE source properties. [Work partially supported by NSF and ONR.]

Acoustic emission investigation and signal discrimination in steel highway bridge application

Acoustic emission investigation and signal discrimination in steel highway bridge application

Acoustic-emission investigations of structural changes in tungsten-carbide metal-ceramics during thermal and radiation treatment and hydrogenation

Acoustic-emission investigations of structural changes in tungsten-carbide metal-ceramics during thermal and radiation treatment and hydrogenation

Acoustic emission investigation into some concrete construction problems

Acoustic emission investigation into some concrete construction problems