Fatigue-life prediction by an order statistics treatment of acoustic-emission signals

In fatigue, both the crack-propagation rates and the cumulative acoustic-emission activity are known to be related to the applied stress-intensity range. By considering the energy balance during crack propagation and the relation of strain energy release to the acoustic-emission characteristics, a formal relation between acoustic emission amplitudes and initial fatigue-crack-propagation rates has been derived. Continuous monitoring of acoustic emission during low cycle (tension-tension) fatigue tests has been conducted on aluminum 2024-T3 and 7075-T6 alloys, until fracture. Initial crack sizes and orientations in the fatigue specimens were randomly distributed. Every few hundred cycles, the acoustic signal having the highest peak amplitude was recorded as the extreme acoustic-emission event for the elapsed period. The extreme peak amplitudes, related to extreme crack-propagation rates, were shown, by an order statistics treatment, to be extremally distributed.Statistical, nondeterministic, approach to fatigue considers that only extreme crack-propagation rates are vital to fatigue lives. Knowledge of the distribution function of propagation rates is therefore essential in design for fatigue. Such knowledge can now be obtained in a nondestructive manner, during service in real time, by analyzing the distribution of amplitudes of acoustic-emission signals emitted during cyclic stressing. The statistical treatment enables the prediction of the number of cycles left until failure. Predictions performeda posteriori, based on results gained early in each fatigue test, were in good agreement with actual fatigue lives. The amplitude distribution analysis of the acoustic signals emitted during fatigue tests has been proven to be a feasible nondestructive method for predicting fatigue life.

[1]  J. Baram,et al.  Prediction of low-cycle fatigue-life by acoustic emission—1: 2024-T3 aluminum alloy , 1981 .

[2]  J. Lieblein,et al.  Statistical Investigation of the Fatigue Life of Deep-Groove Ball Bearings , 1956 .

[3]  Karl-Heinz Schwalbe,et al.  Comparison of several fatigue crack propagation laws with experimental results , 1974 .

[4]  Jaap Schijve,et al.  Four lectures on fatigue crack growth , 1977 .

[5]  B. Brookes,et al.  Statistical Theory of Extreme Values and Some Practical Applications , 1955, The Mathematical Gazette.

[6]  Z. Birnbaum,et al.  A new family of life distributions , 1969 .

[7]  J. Baram,et al.  Improved fatigue-life prediction by acoustic emission , 1984 .

[8]  J. Baram,et al.  Prediction of low-cycle fatigue-life by acoustic emission—2: 7075-T6 aluminum alloy , 1981 .

[9]  W. Reuter,et al.  Acoustic emission from low-cycle high-stress-intensity fatigue , 1973 .

[10]  W. Schütz.  The prediction of fatigue life in the crack initiation and propagation stages—a state of the art survey , 1979 .

[11]  Alfred M. Freudenthal,et al.  Fatigue and fracture mechanics , 1973 .

[12]  H. L. Dunegan,et al.  Continuous monitoring of fatigue-crack growth by acoustic-emission techniques , 1974 .

[13]  Alfred M. Freudenthal,et al.  New aspects of fatigue and fracture mechanics , 1974 .

[14]  J. W. Provan.  A Fatigue Reliability Distribution Based on Probabilistic Micromechanics , 1982 .

[15]  J. Schijve,et al.  FATIGUE CRACK GROWTH IN LUGS , 1979 .

[16]  M. Rosen,et al.  Fatigue life prediction by distribution analysis of acoustic emission signals , 1979 .

[17]  Drew V. Nelson,et al.  Review of fatigue-crack-growth prediction methods , 1977 .

[18]  P. M. Besuner,et al.  Probabilistic fracture mechanics , 1977 .

[19]  T. Mackay.  Fatigue crack propagation rate at low ΔK of two aluminum sheet alloys, 2024-T3 and 7075-T6 , 1979 .

[20]  J. W. Provan.  Probabilistic approaches to the material-related reliability of fracture-sensitive structures , 1987 .

[21]  James W. Provan,et al.  Probabilistic fracture mechanics and reliability , 1987 .

[22]  Alfred M. Freudenthal,et al.  Reliability of reactor components and systems subject to fatigue and creep , 1974 .

[23]  I. Palmer,et al.  Acoustic emission — 3: The use of ring-down counting , 1973 .

[24]  A. Teleman,et al.  Detection of fatigue crack growth by acoustic emission techniques , 1971 .

[25]  R. Harrington,et al.  Acoustic emissions of fatigue crack growth , 1973 .