AE Data Research Articles

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.

Properties of AE data and bicolored noise

A detailed analysis has been made of 13 periods of 20 days of the AE data. The average correlation dimension is found to be 3.4, and the calculated dimension is found to depend on the magnetospheric activity such that more active periods have smaller dimensions. This apparent correlation dimension does not, however, imply that the magnetospheric system behind the AE data is low‐dimensional. On the contrary, bicolored noise is shown to share many properties with the AE data. The AE time series is also found to be self‐affine such that the scaling exponent changes at the time scale of about 2 hours. This same time scale is suggested to appear as a spectral break at about 1/(5 hours) in the power spectrum of the AE data.

Characteristic time scale of auroral electrojet data

The structure function of the AE time series shows that the AE time series is self‐affine such that the scaling exponent changes at the time scale of approximately 113 (±9) minutes. Autocorrelation function is shown to have scaling properties similar to those of the structure function. From this result it can be deduced that the time scale at which the scaling properties of the AE data change should equal the typical autocorrelation time of these data. We find the typical autocorrelation time of the AE data is 118 (±9) minutes. The characteristic time scale of the AE data appears as a spectral break in their power spectrum at a period of about twice the autocorrelation time.

AE monitoring and data analysis for large spherical tanks

Abstract The successful assessment of structural integrity by means of AE depends on the quality of the recorded AE data and on correct post-test data analysis. AE monitoring and signal analysis of tests on two large, spherical tanks were carried out using a 32-channel AE system (Spartan, from PAC, USA). Water pressurization was used on one, whilst the other was tested on-line. The effects of both the residual and loading stresses on the surface-opening cracks produced by multiple welding passes were assessed by means of AE. AE measurements generally take a rather long time and background noise cannot always be restricted during the test period (a major problem with on-line testing). It is possible to improve the detection of AE in the field by varying the pressure of the operating medium by 10% P ( P = operating pressure of tank). The relationship between the source (a crack growing with load changes) and its associated AE parameters is also discussed.

Correlation dimension and affinity of AE data and bicolored noise

We have made a detailed analysis of several periods of the AE time series and find that the average correlation dimension is 3.4. We have generated bicolored noise and shown that it shares many properties with the AE data. We also find that the AE time series is self‐affine such that the affinity exponent changes on a time scale of about two hours, which is a typical length of magnetospheric substorms. We suggest that this same time scale appears as a spectral break at about 5.6 × 10−5Hz (5‐hour period) in the power spectrum of the AE data.

ＦＲＰの破壊とＡＥ計測 ＡＥセンサの周波数感度特性およびしきい値が計測結果に及ぼす影響

This paper presents how the frequency characteristics of AE sensors and threshold affect acoustic emission measurement. Static and fatigue tests of FRP reinforced by plain woven glass fabric were conducted. Three different types of AE sensors having different sensitivities with respect to frequency were used simultaneously to distinguish the difference of observed AE data. Following results are obtained from the test. 1. Threshold of AE system strongly affects observed AE data. Namely, observed AE under a certain threshold condition is different from that under another condition. This threshold dependence is due to the dead time and resolution time of AE measuring system. Total AE events and rate do not always increase as the threshold becomes lower. AE observation at a different threshold condition might derive different conclusions. 2. The frequency characteristics of AE sensors strongly affect the observed AE data as well as the threshold under a static loading while a rough tendency of total AE count record agrees with each other under a fatigue loading. The above results attract a strong attention that AE sensors must be carefully selected according to material AE nature taking the machine characteristics (i.e., dead time and so on) into consideration. It is quite difficult to compare the AE data obtained at a certain condition with the data obtained using different AE sensors or different condition.

Relative bioavailability of olsalazine from tablets and capsules: A drug targeted for local effect in the colon

The aim of this investigation was to compare two formulations of the prodrug olsalazine (OLZ) with regard to local bioavailability of 5-aminosalicylic acid (5-ASA) in the colon. Since 5-ASA can not be measured directly in the colon, the bioavailability was evaluated by studying the plasma concentration and cumulative urinary excretion (Ae) of its main metabolite N-acetyl-5-aminosalicylic acid (ac-5-ASA). The absorption of OLZ was also studied. A single dose of 1g OLZ tablets and capsules was given to nine healthy fasting volunteers in two repeated two-period cross-over studies. Blood and urine samples were collected for 72 and 96 h, respectively. AUC, Cmax and Ae data from both studies were combined for statistical analysis. Ninety per cent confidence limits for differences in mean AUC for ac-5-ASA (tablet-capsule) compared to that of capsules were -0.31 per cent and 30.8 per cent. This indicates bioequivalence if a more relaxed criterion than the conventional +/- 20 per cent is applied, which is justified in this situation. The 90 per cent confidence limits for Cmax were -10.5 per cent and 36.9 per cent while for Ae the values were -20.5 per cent and 23.7 per cent. Within and between subject variability estimates for AUC of ac-5-ASA were 24 per cent and 46 per cent, respectively.

Chaotic appearance of the AE index

A typical time sequence of AE shows no obvious regularities which suggests either that the magnetosphere is a random (stochastic) system or displays deterministic chaos. To find out whether the magnetosphere is random or chaotic, AE data have been studied by the embedding dimension method to find the correlation dimension of the magnetosphere. The autocorrelation (AC) time scale τ[AC(τ) = ½ AC(0)] is about 50 minutes for all the cases we have investigated. This time scale may represent the time over which the magnetosphere adjusts to sudden changes. The frequency spectrum of the AE data is broadband with a universal form P(ω) ∼ ω−β, where β is about 2 for the frequencies, f = ω/2π between 0.04 mHz and 4 mHz. The correlation dimension for the AE data using a 1 minute delay to construct a time series of m dimensional vectors is between 3 and 4. With the proper time delay τ ⋍ 50min, which is the autocorrelation time, the correlation dimension is around 2.4. The variation of the correlation dimension with different time delays is shown. But because colored noise with β = 2 has a correlation dimension near 2.1, it is not yet possible to determine whether AE index is a signal resulting from colored noise or from deterministic chaos.

Interaction of borazine with a Re(0001) surface, studied by LEED, TDS, AES and ELS

The interaction of borazine (N 3B 3H 6) with a Re(0001) surface has been studied by low energy electron diffraction (LEED), thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS). Two LEED patterns have been observed following borazine adsorption and annealing. One is the 2 × 2 structure, assigned to arise from atomic nitrogen. The other is the 3 1 2 × 21 1 2 pattern and is related to boron. The appearance of the two patterns indicates that bo dissociates at 570 K. With a high exposure ( #62; 6 L) of borazine and a subsequent annealing, only the well-formed 3 1 2 × 21 1 2 pattern is observed. Completion of this boron structure depends on both the surface boron coverage and the annealing temperature. Thermal desorption spectra show three states for borazine (α, β 1 and β 2) and three states for hydrogen (α, β 1, β 1). The a state in desorption spectrum is due to desorption of multilayers of borazine. The β state hydrogen is shown to correspond primarily to decomposition of borazine on Re(0001). Two desorption states of nitrogen are observed at T #62; 1300 K and also arise from the decomposition of borazine. AE data show that borazine decomposes to a boron-nitrogen compound when irradiated with a 2 keV e −-beam. Chemisorbed borazine, on the other hand, without e −-beam irradiation, dissociates into atomic nitrogen and boron upon annealing to T #62; 450 K. ELS results corroborate the LEED, TDS, and AES data that borazine adsorbs on Re(0001) non-dissociatively at 115 K and dissociates into N and B upon annealing to ~ 600 K.

Cross correlation of high‐latitude upper mesospheric neutral winds with AE and Kp

High‐latitude upper mesospheric neutral winds are investigated for evidence of a response to changes in the level of geomagnetic activity through a cross‐correlation analysis using AE and Kp. A consistent and significant causal response within several days of intervals of increased activity is not evident in the neutral wind data from 80 to 90 km altitude. Instead, through cross correlation with the neutral wind data set, the low‐frequency components of the AE and Kp data sets have been identified. These results, in conjunction with other recent studies, indicate that it is above 90 km, in the lower thermosphere, that magnetospheric forcing first becomes significant for affecting neutral dynamics at high latitudes.

The acoustic emission measurement of cleavage initiation near the ductile brittle transition temperature in steel

By use of the AE technique, the microcleavage fracture process in HSLA steel has been studied near the ductile-brittle transition temperature. Upon loading, several AE events were detected before final instability. Multiple origins of the cleavage were evident ahead of the fatigue crack front. It was concluded that weakest link hypotheses were not applicable near the ductile-brittle transition temperature. Good correlations were found between AE data and cleavage facets as a function of stress intensity factor.

Acoustic emission measurement of geothermal reservoir cracks in Takinoue (Kakkonda) field, Japan

Crack extension caused by a shut-down operation in production wells (build-up test) in Takinoue (Kakkonda) geothermal power plant, Iwate Prefecture, Japan, has been successfully measured by an acceleration-sensitive long-distance acoustic emission measurement technique. The distribution and activity of subsurface cracks in a geothermal reservoir can be determined by the combined procedure of the pressure build-up test and AE measurements. The feasibility and importance of the measurements are demonstrated by AE data and their interpretation.

Event study on pre-substorm phases and their relation to the energy coupling between solar wind and magnetosphere

On 11 November 1976, after a magnetically quiet period with the interplanetary magnetic field (IMF) directed northward, a sudden southward turning of the IMF immediately led to a world-wide intensification of convection which was observed to start almost simultaneously at stations within the auroral zone and polar cap. The two-dimensional equivalent current system over the northern hemisphere had a typical two-cell convection pattern with a maximum disturbance of ΔH = −300 nT observed on the morningside in the westward electrojet region. This enhancement of activity ended after 35 min in a localized substorm onset in the midnight sector over Scandinavia. The recordings made in this area indicate large fluctuations of various ionospheric parameters starting several minutes before the substorm onset. Two subsequent stages can be resolved: (1) high-energy particle precipitation recorded by balloon X-ray detectors and maximum ionospheric current density increase, while the electrojet halfwidth shrinks and the total electrojet current becomes weaker; (2) the maximum ionospheric current density stays constant and the high-energy particle precipitation decreases, while the auroral brightness increases and the total electrojet current and its half-width show a growing trend prior to the final breakup. A suggestion is made that the time interval of these two stages should be called “trigger phase”. A short discussion explains the trigger phase observations in a magnetospheric scale. The energy coupling between solar wind and magnetosphere during the pre-substorm phases is discussed by utilizing the energy coupling function ϵ defined by Perreault and Akasofu ( Geophys. J. R. Astr. Soc. 54, 547, 1978). The ϵ values appear to be on substorm level during the period of enhanced convection. A good correlation between ϵ and the growth of the Joule heating rate (estimated from the AE data) is found in the beginning, but during the last 20 min before substorm triggering ϵ is high while the Joule heating rate decreases. The behaviour of ϵ during the two stages of the trigger phase suggests that the start of the trigger phase is purely internally controlled while the length of the trigger phase and the final substorm onset may be influenced by the variation in ϵ.

Molecular dynamics of hydrated proteins

This contribution presents the first results of an application of high-resolution quasi-elastic neutron scattering to the dynamics of protein hydration. Using two samples (film stacks and 'fluffy’ powders) of biosynthetically fully deuterated C-phycocyanin extracted from blue-green algae, we have studied the Doppler-like broadening of the quasi-elastic line as a function of scattering angle 20 at several sub-monolayer H 2 O hydration levels. The backscattering spectrometer IN 10 at the Institut Laue-Langevin (I.L.L.), Grenoble, was employed to measure wet-minus-dry difference broadenings A E of up to 5 x 10 -3 cm -1 , or 0.4 geV, for momentum transfers k = (4tt/A0) sin 0 between 0.15 and 1.7 Å-1 (incident wavelength A 0 = 6 Å). The results show that A E ( k ) possesses an oscillatory structure with a first maximum between k max = 0.4 and 0.8 Å-1. The position of this maximum shifts to higher k with increasing hydration, while its intensity increases and the following minimum at k max = 0.7-1.3 Å -1 becomes progressively more shallow. Structure factor measurements indicate that line narrowing due to structure in S ( k ) is not the dominant mechanism in determining this oscillatory behaviour of A E ( k ).A Chudley-Elliott jump diffusion model was adopted as a working hypothesis to extract a characteristic length (water migration distance a ) and a characteristic time (residence time t 0 at a hydration site) from the A E ( k ) data. Values of a = 6-9 Å and r 0 = 5-30 ns were obtained for the powder sample and are shown to agree well with the average jump distances derived from topographical considerations in conjunction with hydration number estimates.

An experimental and theoretical study of the mean diurnal variation of O+, NO+, O2+, and N2+ ions in the mid‐latitude F1 layer of the ionosphere

Over the past decade, several models have been developed which describe the diurnal behavior of molecular and atomic ions in the altitude range where the atomic and molecular densities are comparable. However, no complete set of diurnal measurements has been available in the past with which to compare these theoretical results, because the altitude regime (130–220 km) lies below the reach of conventional satellites and rocket results give only a transient picture. The Atmosphere Explorer C, D, and E satellites have been taking measurements of ion concentrations together with related aeronomic parameters in the thermosphere for over 4 years. These data have been analyzed to extract the average diurnal variation (i.e., for solar zenith angles less than 105°) of the ion species NO+, O2+, N2+, and O+ as functions of altitude. The AE data have been used in a number of separate studies which have reduced the uncertainties associated with key reaction rate coefficients. As a test of the overall consistency of the photochemistry of the F1 layer we compare the measured ion concentrations with those calculated by using a model which incorporates our latest understanding of the chemistry and which uses, as input parameters, the measured neutral concentrations and temperature, the solar extreme ultraviolet flux, and electron and ion temperatures. The results show that a fairly simple model, in which the free parameters are minimized, reproduces the measurements to a satisfactory degree.

Evening sector auroral oval dynamics from DMSP photographs

Expansions and contractions of the auroral oval and substorm activity over a 10‐day period were studied. Changes in latitude of the equatorward boundary of the diffuse aurora, scaled at 2000 CGT from DMSP photographs, reflect expansions and contractions of the oval. Hourly average and 5‐min average IMF Bz component data and AE (11) data are examined relative to the expansions and contractions of the oval and to auroral substorm activity as seen in the photographs. The minimum‐size oval occurs near 73° CGL at 2000 CGT. Over the range of Bz values examined, the oval expands or contracts by less than 2.5° within 102 min, which is the temporal resolution limit imposed by the DMSP satellite orbital period. As was previously reported, Bz appears to control both the expansion and the contraction of the oval. Substorm activity accompanies both the expansion and the contraction. Substorms which occur during the oval expansion are more intense than the substorms which occur during the ensuing contraction. Also, the oval appears to be able to expand more rapidly than it can contract.

AE monitoring of rapid crack growth in a production-size wing fatigue test article

Acoustic emission source location techniques were successfully used on a production-size aircraft wing fatigue test article to monitor crack growths in the range from 0.25 mm to 1.6 mm per load cycle. The AE data showed good correlation with the crack length data. Analyses of these correlations show that AE monitoring has the potential for being used to determine crack length over this range of crack growth rates. The fatigue test article was constructed of 7075-T6511 aluminum alloy. The test period lasted 14 days and the results demonstrated that AE has application to aircraft structures.