The influence of cyclic stress intensity threshold on fatigue life scatter

Abstract Understanding factors that contribute to scatter in fatigue lives of metallic structures (particularly airframes) subjected to identical spectrum is critical to maintaining safety and optimising designs. This paper first briefly discusses the sources of scatter, and then concentrates on the effect of variations in the “cyclic stress intensity threshold” (ΔKthr) on fatigue crack growth. It shows that a version of the NASGRO equation can be used to account for the crack growth scatter seen in a number of classical fatigue experiments by accounting for variations in ΔKthr. This is an important outcome for safety and is particularly useful when considering lead cracks for which ΔKthr is small (approaching zero) as these cracks appear to commence growing soon after introduction into service.

[1]  Rhys Jones,et al.  Implications of the lead crack philosophy and the role of short cracks in combat aircraft , 2013 .

[2]  P. Goel,et al.  The Statistical Nature of Fatigue Crack Propagation , 1979 .

[3]  J. Schijve,et al.  The fatigue crack propagation in 2024-T3 Alclad sheet materials from seven different manufacturers , 1966 .

[4]  Lorrie Molent,et al.  The comparison of complex load sequences tested at several stress levels by fractographic examination , 2005 .

[5]  Dietmar Eifler,et al.  An analysis of the growth of short fatigue cracks , 1991 .

[6]  A. Merati.  A study of nucleation and fatigue behavior of an aerospace aluminum alloy 2024-T3 , 2005 .

[7]  Lorrie Molent.  Alternative methods for derivation of safe life limits for a 7050-T7451 aluminium alloy structure , 2015 .

[8]  Wen-Fang Wu,et al.  Statistical aspects of some fatigue crack growth data , 2007 .

[9]  A. J. Mcevily,et al.  Prediction of the behavior of small fatigue cracks , 2007 .

[10]  Lorrie Molent,et al.  Fatigue crack growth in a diverse range of materials , 2012 .

[11]  Russell Wanhill,et al.  The lead crack fatigue lifing framework , 2011 .

[12]  Lorrie Molent,et al.  An experimental evaluation of fatigue crack growth , 2005 .

[13]  Lorrie Molent,et al.  Calculating crack growth from small discontinuities in 7050-T7451 under combat aircraft spectra , 2013 .

[14]  K. J. Miller,et al.  What is fatigue damage? A view point from the observation of low cycle fatigue process , 2005 .

[15]  Rhys Jones,et al.  Fatigue crack growth and damage tolerance , 2014 .

[16]  Bernard Chen,et al.  Prediction of fatigue life in aluminium alloy (AA7050-T7451) structures in the presence of multiple artificial short cracks , 2015 .

[17]  Reji John,et al.  Stress Ratio Effects on Small Fatigue Crack Growth in Ti-6Al-4V (Preprint) , 2008 .

[18]  David Hui,et al.  Application of the Hartman–Schijve equation to represent Mode I and Mode II fatigue delamination growth in composites , 2012 .

[19]  L. Molent,et al.  The equivalence of EPS and EIFS based on the same crack growth life data , 2015 .

[20]  Nam Phan,et al.  Aircraft life management using crack initiation and crack growth models – P-3C Aircraft experience , 2007 .

[21]  R. Ritchie,et al.  Propagation of short fatigue cracks , 1984 .

[22]  N. Iyyer,et al.  A study into the interaction of intergranular cracking and cracking at a fastener hole , 2015 .

[23]  Wenchen Hu,et al.  A convenient way to represent fatigue crack growth in structural adhesives , 2015 .

[24]  R. Ritchie,et al.  Mixed-mode, high-cycle fatigue-crack growth thresholds in Ti–6Al–4V: I. A comparison of large- and short-crack behavior , 2000 .

[25]  A. J. Green,et al.  Characterisation of equivalent initial flaw sizes in 7050 aluminium alloy , 2006 .

[26]  Ding,et al.  Small‐crack growth and fatigue life predictions for high‐strength aluminium alloys. Part II: crack closure and fatigue analyses , 2000 .

[27]  L. Molent,et al.  A review of equivalent pre-crack sizes in aluminium alloy 7050-T7451 , 2014 .

[28]  Lorrie Molent,et al.  A comparison of crack growth behaviour in several full-scale airframe fatigue tests , 2007 .

[29]  Y. Kondo,et al.  Short Crack Growth Behavior and Its Relation to Notch Sensitivity and VHCF , 2013 .

[30]  Y. Macheret,et al.  Improved Estimation of Aircraft Probability of Failure , 2008, 2008 IEEE Aerospace Conference.

[31]  Adam Bowler,et al.  Fatigue crack growth from environmentally induced damage in 7075 alloy , 2015 .

[32]  Simon Barter,et al.  Interpreting fatigue test results using a probabilistic fracture approach , 2005 .

[33]  Lorrie Molent,et al.  Experimentally derived crack growth models for different stress concentration factors , 2008 .

[34]  Steffen Stelzer,et al.  Thoughts on accounting for the scatter seen in delamination growth , 2015 .

[35]  David Hui,et al.  Fatigue crack growth in nano-composites , 2013 .

[36]  Robert O. Ritchie,et al.  AN ANALYSIS OF CRACK TIP SHIELDING IN ALUMINUM ALLOY 2124: A COMPARISON OF LARGE, SMALL, THROUGH‐THICKNESS AND SURFACE FATIGUE CRACKS , 1987 .

[37]  B. Aktepe,et al.  Review of fatigue monitoring of agile military aircraft , 2000 .

[38]  Pu Huang,et al.  Crack Growth from Naturally Occurring Material Discontinuities in Operational Aircraft , 2015 .

[39]  Steffen Stelzer,et al.  Mode I, II and Mixed Mode I/II delamination growth in composites , 2014 .

[40]  J. P. Gallagher,et al.  Estimating the statistical properties of crack growth for small cracks , 1983 .