scholarly journals Investigation of the Enhancement Interactions between Double Parallel Cracks on Fatigue Growth Behaviors

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2952
Author(s):  
Zhichao Han ◽  
Caifu Qian ◽  
Huifang Li
Keyword(s):  
Stress Intensity ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Growth Rates ◽  
Shielding Effect ◽  
Enhancement Effect ◽  
Intensity Factors ◽  
Single Crack ◽  
Parallel Cracks ◽  
Crack Growth Rates

In this paper, interactions of double parallel cracks were studied by performing experiments and numerical simulations. Fatigue crack propagation tests were carried out to measure crack growth rates in the specimens with double parallel cracks or a single crack. Finite element method was adopted to calculate stress intensity factors at the crack tips. Results show that the double parallel cracks at different positions present a shielding effect or enhancement effect on crack growth rates and stress intensity factors. When the double parallel cracks are offset, crack interactions mostly behave as enhancement effects. Empirical formulas were obtained to calculate the stress intensity factor at the “dangerous” crack tip of the double parallel cracks. By modifying the material parameters in Paris equation of the single crack, the double parallel cracks are simplified into a single crack with the same crack growth rates.

scholarly journals Study of the Shielding Interactions between Double Cracks on Crack Growth Behaviors under Fatigue Loading

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 202
Author(s):  
Zhichao Han ◽  
Caifu Qian ◽  
Huifang Li
Keyword(s):  
Stress Intensity ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Growth Rates ◽  
Fatigue Loading ◽  
Intensity Factors ◽  
Single Crack ◽  
Finite Element Calculations ◽  
Crack Tips ◽  
Crack Growth Rates

In this paper, the interactions between double cracks with a co-bisector-line were investigated theoretically and experimentally. Fatigue crack growth tests of specimens with a single crack or double cracks were carried out to measure the crack growth rates, and finite element calculations were performed to obtain the stress intensity factors at crack tips. It was found that when the double cracks are in co-bisector-line, they present shielding interactions which reduce the stress intensity factors at crack tips as well as the crack growth rates. By modifying the stress intensity factors and the Paris equation considering the shielding interactions, a new simplification method was proposed to simplify the double cracks into a single crack with the same crack growth rates.

Fatigue Crack Growth in Steels 42CrV and IR3Mo

2004 ◽  
Vol 261-263 ◽  
pp. 1179-1184 ◽  
Author(s):  
Qin Zhi Fang
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Measurement System ◽  
Growth Rates ◽  
Fatigue Tests ◽  
Intensity Factors ◽  
Growth Measurement ◽  
Crack Growth Rates

An automatic fatigue crack growth measurement system was developed, in which a special four-channel A-D acquisition board that could collect data in phase was used. The data collecting frequency is in the range of 4×(2~25600)Hz. The system is suitable for fatigue tests with the frequencies not higher than 250Hz. Eddy current transducers and standard load cell were used to measure displacement and load, respectively. The system can instantly calculate fatigue crack lengths, stress intensity factors and fatigue crack growth rates. As an application of the system, fatigue crack growth rates (FCG) and the thresholds of steels 42CrV and IR3Mo were presented.

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 Determination of the Enhancement or Shielding Interaction between Two Parallel Cracks under Fatigue Loading

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1331 ◽  
Author(s):  
Zhichao Han ◽  
Caifu Qian ◽  
Lanqing Tang ◽  
Huifang Li
Keyword(s):  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Fatigue Loading ◽  
304 Stainless Steel ◽  
Shielding Effect ◽  
Stress Distributions ◽  
Intensity Factors ◽  
Parallel Cracks ◽  
Two Parallel Cracks

In this paper, the interactions between two parallel cracks are investigated experimentally and numerically. Finite element models have been established to obtain the stress intensity factors and stress distributions of the parallel cracks with different positions and sizes. Fatigue crack growth tests of 304 stainless steel specimens with the single crack and two parallel cracks have been conducted to confirm the numerical results. The numerical analysis results indicate that the interactions between the two parallel cracks have an enhancement or shielding effect on the stress intensity factors, depending on the relative positions of the cracks. The criterion diagram to determine the enhancement or shielding effect between two parallel cracks is obtained. The changes of the stress fields around the cracks have been studied to explain the mechanism of crack interactions.

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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