Molecular Dynamics Simulation of the Effect of Large Angle and Small Angle Grain Boundaries on the Near-Threshold Fatigue Crack Growth in Iron

2004 ◽  
Author(s):  
Shiro Kubo ◽  
Masaki Misaki
Keyword(s):  
Molecular Dynamics ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Crack Growth ◽  
Small Angle ◽  
Large Angle ◽  
Atomic Scale ◽  
Near Threshold

In the near-threshold region of the fatigue crack growth in metals, the amount of crack growth per cycle is in the order of the atomic scale. This may suggest that the near-threshold fatigue crack growth is controlled by atomic scale events. In previous papers the present authors applied the molecular dynamics to the simulation of near-threshold fatigue crack growth. In this study, the molecular dynamics method was applied to investigate the influence of inclined grain boundary on the near-threshold mode I fatigue crack growth behavior in BCC iron. Large angle grain boundaries served as an obstacle to the fatigue crack growth. Small angle grain boundaries had the effect of decreasing crack growth when the crack approached the grain boundary. When the crack reached the grain boundary it was trapped by the grain boundary.

Improvement of Fatigue Crack Growth Resistance by Serrated Grain Boundary at High Temperature

1991 ◽  
Vol 113 (1) ◽  
pp. 9-14 ◽  
Author(s):  
Hiroshi lizuka ◽  
Manabu Tanaka ◽  
Fumio Ashihara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Crack Growth Resistance ◽  
Fatigue Crack Growth Resistance ◽  
Crack Growth Rates

Effects of serrated grain boundaries on the improvement of fatigue-crack growth resistance were investigated using austenitic 21Cr-4Ni-9Mn heat-resisting steel at 973K in air. Grain boundaries were serrated by grain-boundary reaction precipitates. The crack-growth rates were considerably decreased in the specimens with the serrated grain boundaries. The fatigue cracks were largely deflected by the serrated grain boundaries, and brittle intergranular fracture was retarded. The improvement of the crack-growth resistance was obtained especially under the conditions of low crack-growth rates of less than 30 μm/cycle. The widths and the heights of the deflected portions of the cracks were in the range from about a few μm to 30 μm.

Evaluation of Fatigue Crack Growth Curves in Existing Codes and a Proposed Modification Based on Experimental Data of Cr-Ni-Mo-V Steel Welded Joints

2016 ◽  
Author(s):  
Yan-Nan Du ◽  
Ming-Liang Zhu ◽  
Fu-Zhen Xuan ◽  
Shan-Tung Tu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Welded Joints ◽  
Growth Curves ◽  
Crack Growth Behavior ◽  
Fatigue Assessment ◽  
Crack Growth Model ◽  
Threshold Regime ◽  
Near Threshold

A comparison of currently available codes for assessment of fatigue crack growth, including ASME (America Society of Mechanical Engineers) SEC. XI, FKM (Forchungskuratorium Maschinenbau) guideline, WES (Japan Welding Engineering Society) 2805, BS7910 and JSME (The Japan Society of Mechanical Engineers), was carried out by paying attention to the suitability of application and the easiness to obtain the parameters, based on fatigue crack growth data of Cr-Ni-Mo-V steel welded joints. Results showed that fatigue crack growth curves provided by the FKM or WES were good choice when few inputs were at hand while the curves in the BS7910, JSME and ASME were recommended for precise estimation. It was indicated that the assessment of welded joints solely by fatigue crack growth behavior at base metal part and the assessment of fatigue crack growth for the aged condition by as-received one both resulted in non-conservativeness, albeit dependent on the range of stress ratios, R. A new bilinear form of fatigue crack growth model independent of R was developed based on transition point occurred in the near-threshold regime. This constituted the bilinear approach to fatigue assessment, and thus contributed to the optimization of fatigue assessment in the near-threshold regime.

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