Published Date
Author
R.Y. Deng
Z.J. Ye
http://www.sciencedirect.com/science/article/pii/016784429190028I
Theoretical and Applied Fracture Mechanics
November 1991, Vol.16(2):109–122, doi:10.1016/0167-8442(91)90028-I
Available online 26 February 2003.
Abstract
An empirical study is made on the fatigue crack growth rate in ferrite-martensite dual-phase (FMDP) steel. Particular attention is given to the effect of ferrite content in the range of 24.2% to 41.5% where good fatigue resistance was found at 33.8%. Variations in ferrite content did not affect the crack growth rate 
when plotted against the effective stress intensity factor range 
which was assumed to follow a linear relation with the crack tip stress intensity factor range 
. A high 
corresponds to uniformly distributed small size ferrite and martensite. No other appreciable correlation could be ralated to the microstructure morphology of the FMDP steel. The closure stress intensity factor 
, however, is affected by the ferrite content with 
reaching a maximum value of 0.7. In general, crack growth followed the interphase between the martensite and ferrite.
when plotted against the effective stress intensity factor range which was assumed to follow a linear relation with the crack tip stress intensity factor range . A high corresponds to uniformly distributed small size ferrite and martensite. No other appreciable correlation could be ralated to the microstructure morphology of the FMDP steel. The closure stress intensity factor , however, is affected by the ferrite content with reaching a maximum value of 0.7. In general, crack growth followed the interphase between the martensite and ferrite.
Dividing the fatigue crack growth process into Stage I and II where the former would be highly sensitive to changes in 
and the latter would increase with 
depending on the 
ratio. The same data when correlated with the strain energy density factor range 
showed negligible dependence on mean stress or 
ratio for Stage I crack growth. A parameter α involving the ratio of ultimate stress to yield stress, percent reduction of area and 
is introduced for Stage II crack growth so that the 
data for different 
would collapse onto a single curve with a narrow scatter band when plotted against 
.
and the latter would increase with depending on the ratio. The same data when correlated with the strain energy density factor range showed negligible dependence on mean stress or ratio for Stage I crack growth. A parameter α involving the ratio of ultimate stress to yield stress, percent reduction of area and is introduced for Stage II crack growth so that the data for different would collapse onto a single curve with a narrow scatter band when plotted against .http://www.sciencedirect.com/science/article/pii/016784429190028I
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