Method for determination of threshold stress intensity factors and fatigue crack growth rates in metallic materials

1991 ◽  
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Stress Intensity Factors ◽  
Threshold Stress ◽  
Threshold Stress Intensity ◽  
Metallic Materials ◽  
Intensity Factors ◽  
Crack Growth Rates

Experimental Study and Numerical Simulation on Fatigue Crack Growth Behavior of GH4133B Superalloy

2012 ◽  
Vol 512-515 ◽  
pp. 980-988
Author(s):  
Rong Guo Zhao ◽  
Xiu Juan Li ◽  
Yong Zhou Jiang ◽  
Xi Yan Luo ◽  
Jun Fei Li ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Threshold Stress ◽  
Threshold Stress Intensity ◽  
Intensity Factors

The fatigue crack growth tests for nickel-based GH4133B superalloy used in turbine disk of a type of aero-engine are carried out at room temperature. The stress intensity factor ranges and the fatigue crack growth rates at various stress ratios are measured, and the corresponding threshold stress intensity factor ranges are determined. Using the Paris formula, the experiment data of fatigue crack growth are analyzed. It is shown that the fatigue crack growth rate increasing with increasing stress intensity factor range and stress ratio, and a modified Paris formula considering threshold stress intensity factor range can describe the fatigue crack growth behavior precisely. The fracture surface morphologies are investigated using a scanning electron microscope. It is shown that in the crack initiation region, steady growth region and rapid growth region, the fracture surface exhibits a cleavage fracture mode, fatigue striations and an intergranular fracture mode, respectively. Finally, the von Mises stresses and stress intensity factors at the crack tip of specimen of GH4133B superalloy at various external loads and crack lengths are simulated using the finite element method, and the threshold stress intensity factors under different maximal external loads at a certain crack length are calculated. The comparison between test and simulation indicates that the stress intensity factors at the crack tip calculated by the finite element method agree well with experimental data.

Fatigue Crack Propagation of Short Cracks

1979 ◽  
Vol 101 (1) ◽  
pp. 42-46 ◽  
Author(s):  
M. H. El Haddad ◽  
K. N. Smith ◽  
T. H. Topper
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Length ◽  
Crack Growth ◽  
Growth Rates ◽  
Threshold Stress ◽  
Threshold Stress Intensity ◽  
Intensity Factors ◽  
Short Cracks ◽  
Crack Growth Rates

Previous studies have shown that both threshold stress intensity factors and fatigue crack growth rates are dependent on crack size. The average growth rates for very short cracks considerably exceed those given by conventional stress intensity-crack growth laws fitted to long crack data. Elastic and elastic plastic fracture mechanics solutions are modified to predict this behavior of short cracks by introducing an effective crack length l0 into the solutions for intensity factors and the J integral method of analysis. The threshold stress at a very short crack length approaches the fatigue limit of the material, and therefore the value of l0 can be obtained once the threshold stress intensity factor and the fatigue limit are known. The accuracy of the term l0 in predicting crack growth rates for short cracks is found to be independent of the applied strain level. It varies linearly with the grain size of the material and can be considered at the surface as a measure of the reduced flow resistance of surface grains due to their lack of constraint.

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