scholarly journals Relationship Between Intrinsic Threshold Stress Intensity And Near-Tip Residual Stress: A Reference Material Property

2021 ◽  
Author(s):  
R Sunder
Keyword(s):  
Residual Stress ◽  
Stress Intensity ◽  
Growth Rates ◽  
Threshold Stress ◽  
Load Shedding ◽  
Threshold Stress Intensity ◽  
Load History ◽  
The Relationship ◽  
Crack Growth Rates ◽  
Near Threshold

The relationship between intrinsic, closure-free threshold stress intensity and near-tip residual stress, characterizes the effect of load magnitude as well as load history on near-threshold fatigue crack growth rates. It serves as a reference against which precise closure data can be extracted from growth rates to calibrate analytical estimates. These possibilities were subjected to rigorous experimental verification involving threshold and near-threshold fatigue response under overloads, underloads with load-shedding on a steel prone to oxide debris formation. The study reveals why conventional load shedding practice to characterize threshold stress intensity is prone to yield unconservative and misleading results.

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.

scholarly journals Near-Threshold Fatigue Crack Propagation in Ultra-High Strength Steel: Influence of Load Ratio and Cyclic Strength

1977 ◽  
Vol 99 (3) ◽  
pp. 195-204 ◽  
Author(s):  
R. O. Ritchie
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Threshold Stress ◽  
Load Ratio ◽  
High Strength ◽  
Threshold Stress Intensity ◽  
Ultra High Strength Steel ◽  
Near Threshold

Fatigue crack propagation behavior of an ultra-high strength steel (300-M) has been investigated in humid air over a very wide spectrum of growth rates from 10−8 to 10−1 mm/cycle. Particular emphasis has been devoted to the influence of mean stress (or load ratio R = Kmin/Kmax) and microstructure on fatigue crack growth near the threshold stress intensity for crack propagation, ΔK0. Increasing the load ratio from R = 0.05 to 0.70 was found to lead to increased near-threshold growth rates, and a decrease in the threshold stress intensity. Similarly, increasing material strength, by varying the microstructure through quench and tempering and isothermal transformation, resulted in higher near-threshold growth rates, and a marked reduction of ΔK0. These effects are contrasted with behavior at higher growth rates. The influence of strength on ΔK0 is rationalized in terms of the cyclic hardening or softening response of the material, and hence it is shown that cyclic softening can be beneficial to fatigue crack propagation resistance at very low growth rates. The results are discussed in the light of crack closure and environmental contributions to fatigue crack growth at low stress intensities.

Effect of Grain Size and Load Ratio on the near Threshold Stress Intensity Factor during Fatigue Crack Propagation of Dual Phase Steel

2012 ◽  
Vol 510-511 ◽  
pp. 67-74 ◽  
Author(s):  
M. Sarwar ◽  
E. Ahmad ◽  
T. Manzoor
Keyword(s):  
Stress Intensity Factor ◽  
Grain Size ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Threshold Stress ◽  
Load Ratio ◽  
Threshold Stress Intensity ◽  
Threshold Stress Intensity Factor ◽  
Near Threshold

Fatigue crack growth near-threshold stress intensity factor is affected by the microstructure of the material. A large portion of microstructural influence is due to the change in grain size of the material. Grain size in the dual phase steel was varied and found that the near-threshold stress intensity factor (rKth) increased as the grain size increased. Influence of load ratio nearthreshold fatigue crack propagation was also studied. It was observed that the near-threshold stress intensity range, rKthfor fatigue growth decreased with increasing load ratio.

Crack Growth in Stainless Steel 304 under Creep-Fatigue Loading

2007 ◽  
Vol 353-358 ◽  
pp. 485-490 ◽  
Author(s):  
Y.M. Baik ◽  
K.S. Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Static Loading ◽  
Fatigue Loading ◽  
Creep Fatigue ◽  
Crack Growth Rates

Crack growth in compact specimens of type 304 stainless steel is studied at 538oC. Loading conditions include pure fatigue loading, static loading and fatigue loading with hold time. Crack growth rates are correlated with the stress intensity factor. A finite element analysis is performed to understand the crack tip field under creep-fatigue loading. It is found that fatigue loading interrupts stress relaxation around the crack tip and cause stress reinstatement, thereby accelerating crack growth compared with pure static loading. An effort is made to model crack growth rates under combined influence of creep and fatigue loading. The correlation with the stress intensity factor is found better when da/dt is used instead of da/dN. Both the linear summation rule and the dominant damage rule overestimate crack growth rates under creep-fatigue loading. A model is proposed to better correlate crack growth rates under creep-fatigue loading: 1 c f da da da dt dt dt Ψ −Ψ     =         , where Ψ is an exponent determined from damage under pure fatigue loading and pure creep loading. This model correlates crack growth rates for relatively small loads and low stress intensity factors. However, correlation becomes poor as the crack growth rate becomes large under a high level of load.

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