Fatigue crack growth behavior was investigated for Ti-62222 titanium alloy under constant amplitude (R=0,1 and 0,5) and miniTWIST flight spectra at 25 deg C and 175 deg C. Based upon nominal stress intensity factor range, delta K, for a given constant R ratio, fatigue crack growth behavior at 25 deg C and 175 deg C were similar. Crack closure levels measured at threshold and near threshold for the low R ratio for both temperatures were found to be similar, resulting in similar delta Kth,eff values. Thus, under constant amplitude loading, there appeared to be very little temperature effect. Scatter in miniTWIST flight spectra duplicate fatigue crack growth life tests for a given mean flight stress and temperature was less than a factor of 1,5 excluding one runout. Fatigue crack growth life using miniTWIST flight spectra at 175 deg C was 2,5-3,5 times longer than at 25 deg C. This increase in life was due to lower miniTWIST fatigue crack growth rates at 175 deg C. NASA/FLAGRO fatigue crack growth life calculations for miniTWIST tests were conservative within a factor of 1,3 at 25 deg C and conservative by factors of 3 and 4 at 175 deg C. The conservatism was due to higher calculated fatigue crack growth rates compared to experimental rates, which is likely attributed to no interaction/retardation effects in the NASA/FLAGRO program. Fatigue crack growth fracture surfaces were flat and trangranular for all conditions. Fatigue crack growth morphology varied under constant R ratio conditions for different delta K values and temperatures: small planar facets intermixed with ductile-like features at near delta Kth, a decrease in facets at intermediate delta K, and significant secondary cracking at 175 deg C. With the miniTWIST flight spectra small facets and no striations were observed at 25 deg C, while striations, secondary cracking and multiple crack paths occured at 175 deg C. Final fracture was ductile tearing for all tests. The experimental and calculated fatigue crack growth results for Ti-62222 provided confidence for using this sheet material in structural aerospace damage tolerant situations for temperatures between 25 deg C and 175 deg C.


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    Title :

    Fatigue crack growth of Ti-62222 titanium alloy under constant amplitude and miniTWIST flight spectra at 25 deg C and 175 deg C


    Additional title:

    Ermüdungsrißwachstum bei konstanter Amplitude und miniTWIST-Flugspektren, bei 25 Grad C und 175 Grad C an der Titanlegierung Ti-62222


    Contributors:

    Published in:

    Publication date :

    1997


    Size :

    8 Seiten, 11 Bilder, 2 Tabellen, 9 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English