Effect of Loading Frequency on Fatigue Crack Growth Behaviour and Microstructural Damage in P92 HAZ

2007 ◽  
Vol 120 ◽  
pp. 21-24
Author(s):  
Bum Joon Kim ◽  
Byeong Soo Lim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Frequency ◽  
Growth Behavior ◽  
Frequency Effect ◽  
Crack Growth Behavior ◽  
Loading Frequency ◽  
Crack Growth Behaviour ◽  
Microstructural Damage

Various hold periods in a cyclic wave of fatigue load were introduced to investigate loading frequency effects on crack growth behavior and microstructural damage. The crack growth path and microstructural damage characteristics at 600°C in tempered martensitic 9Cr-2W (P92) HAZ of welded steel were studied. Generally, low frequency effect with increasing hold periods affects microstructural damage with microvoids/cavities nucleation due to the effect of creep. Results showed that the fatigue crack growth behavior was sensitive to the loading frequency. As frequency decreased, the fatigue crack growth rate increased and the crack path mode changed from transgranular to intergranular in terms of microstructural damage. As the loading frequency decreased, it was found that the microvoids /cavities and microcracks that formed along the prior austenite grain boundaries ahead of the main crack contributed to the intergranular crack growth.

scholarly journals Modeling of environmentally assisted fatigue crack growth behavior

2015 ◽  
Vol 33 (6) ◽  
pp. 351-359
Author(s):  
Daniel Kujawski ◽  
Phani C.R. Sree
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Extension ◽  
Crack Tip ◽  
Load Cycle ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Loading Frequency ◽  
Crack Tip Opening

AbstractIt is well recognized that environment has a significant role on the failure of mechanically loaded structures. In most cases of cyclic loading, fatigue crack growth (FCG) behavior exhibits lower threshold and faster growth rate in air than in vacuum. It is well documented that the effect of loading frequency on FCG behavior can be more pronounced in aggressive environment/material systems. This is seen in the Kmax term of the FCG. On the other hand, a weak dependence of FCG behavior with R ratio in inert environment indicates that a crack extension is governed mainly by ΔK. Existing experimental data indicate that the actual crack extension per cycle is associated with the rising part of the load cycle than the unloading part. In this paper, the synergetic role of environment and mechanical loading on crack growth behavior is considered to see their roles on FCG. In this article, we attempt to model how crack extension interplays between a crack-tip opening and crack-tip blunting angle associated with the applied load and environment, respectively. To support such a model for discussion, we have selected limited FCG data taken from literature corresponding to different environments ranging from vacuum to air and NaCl solution for a number of alloys and with different specimens geometries. We are also not discussing innate mechanisms for each alloy, due to space concerns.

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