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Molent L.,Defence Science and Technology Organisation, Australia
Fatigue and Fracture of Engineering Materials and Structures | Year: 2014

This paper reviews some analyses of quantitative fractography measurements of the fatigue fracture surfaces of 7050 aluminium alloy specimens along with relevant fatigue crack information including crack initiating discontinuity size and type. These data were used to assess whether surface finish or applied stress level has any effect on the estimated effective crack initiating discontinuity size, namely the equivalent pre-crack size (EPS). The statistical distributions for the EPSs of the following initiating discontinuity types were examined: chemically etched pits, glass bead peening damage, mechanical damage, inclusions and porosity. The EPSs at various percentile levels for these types were determined on the basis of the samples considered. Finally, the correlation between measured initiating discontinuity depth and EPS was investigated, and good correlation was found in the case of mechanical damage. The purpose of conducting these analyses was to gain a better understanding of the parameters governing the fatigue crack-like effect of discontinuities to facilitate the better prediction of fatigue lives. © 2014 Wiley Publishing Ltd. Source


Lynch S.,Defence Science and Technology Organisation, Australia
Corrosion Reviews | Year: 2012

Mechanisms of hydrogen embrittlement in steels and other materials are described, and the evidence supporting various hypotheses, such as those based on hydride formation, hydrogen-enhanced decohesion, hydrogen-enhanced localized plasticity, adsorption-induced dislocation emission, and hydrogen-vacancy interactions, are summarised. The relative importance of these mechanisms for different fracture modes and materials are discussed based on detailed fractographic observations and critical experiments. © 2012 by Walter de Gruyter. Source


Foster S.,Defence Science and Technology Organisation, Australia
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Thermodynamic phase fluctuations in optical fiber cavities are analyzed in detail, with an emphasis on asymptotic behavior in the low-frequency regime. Both exact series solutions and closed-form approximations are derived for thermal noise under a range of different boundary conditions. These results clarify theoretical limits to strain resolution in optical fiber sensors at low frequency, enabling correct interpretation of recent experiments. © 2012 the American Physical Society. Source


Molent L.,Defence Science and Technology Organisation, Australia
International Journal of Fatigue | Year: 2010

The 1969 in-flight failure of an F-111 wing due to the presence of a rogue manufacturing flaw precipitated the adoption of the damage tolerance aircraft design philosophy by the United States Air Force. This article compares this flaw to several flaws or initiating discontinuities that led to unexpected failures in combat-type aircraft operated by the RAAF and found these to be in general an order of magnitude smaller. Failure in the RAAF examples considered here were also dependent upon several other design and production factors in-addition to the initial discontinuity size. Crown Copyright © 2009. Source


Dong Y.,Defence Science and Technology Organisation, Australia
IET Radar, Sonar and Navigation | Year: 2012

An optimal detector in the sense of generalised likelihood ratio test (GLRT) for coherent radar detection in a compound K-distributed clutter environment is re-studied in detail. A few properties of the detector are derived showing potential of its implementation in radar systems. To the optimal detector, sea spikes (abnormally high radar returns from the sea surface) are unlikely to trigger false alarms, leading to a significant improvement in target detection. Two suboptimal detectors, aiming at saving computational cost, are proposed, and their performance is compared with the GLRT detector. The detector is assessed using true radar sea clutter data, and the problem of sea spikes causing excessive false alarms is identified and discussed. © 2012 Published with permission Commonwealth of Australia. Source

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