Cracks fatigue cracking

Keywords Environmental stress cracking Fatigue crack growth Molecular variables... 

Luty W. Modem views on nucleation of fatigue micro-cracks in roiling bearings MOC IMP No 6, 1973,... 

Lafarie-Frenot, M.C. and Henaff-Gardin, C., Formation and Growth of 90° Ply Fatigue Cracks in Carbon/Epoxy Laminates , Composites Science and Technology Vol. 40, p. 307-324, 1991... 

YOSHIOKA,T. Detection of Rolling Contact Sub-Surftice Fatigue Cracks Using Acoustic Emission Technique. Lubrication Engineering, Vol.49, No.4, 1993, p.303-308. 

In the near future the technique will be further evaluated using ultrasonic signals from natural defects, e.g., fatigue cracks. The performance measure and the parameter optimization procedure wilt also be refined in order to obtain a computationally efficient implementation, easy to use for a trained operator. 

Inspection of frame equipment and pipe - lines for the presence of the fatigue, hardening, and other cracks, corrosion. 

Safe fatigue life testing for crack resistance. 

Measurement of the fatigue fractures depth during bench tests for crack resistance. 

Shear Horizontal (SH) waves generated by Electromagnetic Acoustic Transducer (EMAT) have been used for sizing fatigue cracks and machined notches in steels by Time-of-Flight Diffraction (TOED) method. The used EMATs have been Phased Array-Probes and have been operated by State-of-the-art PC based phased array systems. Test and system parameters have been optimised to maximise defect detection and signal processing methods have been applied to improve accuracy in the transit time measurements. 

Fig. 2. Typical rf signal from a 28 mm deep fatigue crack in 56 mm thick carbon steel sample...

Prompted by the success, TOFD measurements were conducted on a fatigue crack in a stainless steel compact tension specimen. Test and system parameters were optimised following the same procedure used for carbon steel specimens. A clear diffracted signal was observed with relatively good SNR and its depth as measured from the time-of-flight measurements matched exactly with the actual depth. 

H.Toda Quantiative evaluation of fretting fatigue cracks on the surface of the railroad axles by grazing SH Wave ultrasonic method. Journal of JSNDI, Vol. 40, March, pl58-164, (1991)... 

There are no classification requirements for routine NDE beyond thickness testing and visual inspection except for repairs, modifications or where service history has identified a specific problem in which case the Surveyors will request NDE at the same locations in similar ships. Under circumstances where visual inspection has found evidence of fatigue cracking the Surveyor can also call for NDE to assess the full extent... 

The cyclic loading applied to hull structure will eventually lead to fatigue cracking. 

For existing ships the only NDE method nominated by classification for the detection of fatigue cracks is close-up visual inspection - although all Surveyors have the option of requesting additional NDE when warranted. The sensitivity of visual inspection is influenced by the degree of surface preparation and the level of lighting at the inspected surface - which may not always meet the level of 500 lux nominated by some NDE specifications. 

Doyle, J. L., Wood, G. R., and Bondurant, P. D. Using Laser-Based Profilometry to Locate and Measure Corrosion Fatigue Cracking in Boiler Tubes, Materials Evaluation, D The American Society of Nondestructive Testing, Inc., Vol. 51, No. 5, pp. 556-560 (1993). 

Corrosion fatigue is a type of failure (cracking) which occurs when a metal component is subjected to cyclic stress in a corrosive medium. In many cases, relatively mild environments (e.g., atmospheric moisture) can greatly enhance fatigue cracking without producing visible corrosion. 

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