Probabilistic fatigue life prediction using an equivalent initial flaw size distribution

There has been a large volume of research on structural health monitoring since the 1970s but this research effort has yielded relatively few routine industrial applications. Structural health monitoring can include applications on very different structures with very different requirements; this article splits the subject into four broad categories: rotating machine condition monitoring, global monitoring of large structures (structural identification), large area monitoring where the area covered is part of a larger structure, and local monitoring. The capabilities and potential applications of techniques in each category are discussed. Condition monitoring of rotating machine components is very different to the other categories since it is not strictly concerned with structural health. However, it is often linked with structural health monitoring and is a relatively mature field with many routine applications, so useful lessons can be read across to mainstream structural health monitoring where there ar...

https://journals.sagepub.com/doi/pdf/10.1177/1475921717750047

Structural health monitoring: Closing the gap between research and industrial deployment:

https://apps.dtic.mil/sti/pdfs/ADA525352.pdf

The lead crack fatigue lifing framework

SWCNT-thin-film-enabled fiber sensors for lifelong structural health monitoring of polymeric composites - From manufacturing to utilization to failure

Fatigue crack formation and growth from localized corrosion in Al–Zn–Mg–Cu

This paper summarises a collation of crack growth related data from a significant number of fatigue tests on commercial quality 7050-series aluminium alloy tested under various F/A-18 aircraft spectra. The data presented consist of quantitative fractography measurements of the fracture surfaces including effective initiating defect size and type (mechanical, environmental or chemical). Three different surface conditions were considered: chemically etched, glass bead peened and machined. The purpose of providing these data was to facilitate analyses on the parameters governing the propagation of fatigue cracks in the 7050-series aluminium alloy. Here an investigation to determine whether surface finish or applied stress and spectra have any bearing on the initial defect size or the damage type is summarised. Based on this investigation, it appears that the applied stress and spectra have no correlation to the size of the equivalent initiating flaw; however, the surface finish appears to influence the various crack-initiating mechanisms and to govern the formation of the damage type.

Characterisation of equivalent initial flaw sizes in 7050 aluminium alloy

Fatigue monitoring of airframes has developed over the decades to the stage where it is now incumbent for all fighter type aircraft to be fitted with an airborne fatigue monitoring system. These systems typically collect operational data for the calculation of the safe-life or the inspection interval of the airframe.



This paper presents a state-of-the-art review of fatigue monitoring systems of agile military aircraft. It reviews and comprehensively examines the techniques used in individual aircraft fatigue monitoring programs, and examines current systems and practises. Based on experience from Australian fatigue monitoring programs, it highlights some of the potential pitfalls in the systems and techniques. It also investigates the issues of strain gauge utilization and calibration, collection of flight parameter data, data integrity, comparisons with fatigue test results and fatigue damage models. Some of the problems with current systems are highlighted and requirements for future fatigue monitoring systems are suggested.



This review has determined that there is little uniformity in the fatigue management practices of operators and that many aspects of the fatigue management process have been overlooked by some structural integrity managers. Also, very few of the papers reviewed specified the philosophy or aims of their monitoring systems.

Review of fatigue monitoring of agile military aircraft

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.

L. Molent

Papers

Characterisation of equivalent initial flaw sizes in 7050 aluminium alloy

Review of fatigue monitoring of agile military aircraft

A review of equivalent pre-crack sizes in aluminium alloy 7050-T7451