The influence of mean stress on fatigue crack propagation in a quenched and tempered alloy steel

1977 ◽  
Vol 12 (2) ◽  
pp. 81-88 ◽  
Author(s):  
E H R Wade ◽  
G M C Lee
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Crack Front ◽  
Mean Stress ◽  
Free Surfaces ◽  
Front Profile ◽  
Crack Growth Rates

A series of tests are reported which support the proposal that fatigue crack growth rates are retarded by crack closure at low values of applied mean stress intensity. In particular, the evidence presented indicates that closure occurs most readily at the specimen's free surfaces. This leads to dramatic changes in crack front profile under certain loading conditions.

A Superposition Approach for Time-Dependent Fatigue Crack Growth

2012 ◽  
Author(s):  
Fashang Ma
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Time Dependent ◽  
Crack Growth Rates ◽  
Time Dependent Crack Growth

High temperature fatigue crack growth is a combination of fatigue, creep and environmental attack, which greatly enhance fatigue crack growth. In order to understand the damage mechanisms and develop a physically based crack growth model, systematic experimental research has been conducted under various loading conditions for different specimen geometries made from a high strength nickel alloy. Test results from this work showed that time-dependent fatigue crack growth rates differ significantly from those observed in conventional fatigue crack growth tests. Crack geometry and loading history significantly affect fatigue crack growth rate. These results suggest the need for a change in the K based superposition approach for time-dependent crack growth modeling. A phenomenological model has been developed to predict time-dependent crack growth under various loading histories and crack geometries. In this model an effective stress intensity factor is defined to account for the effects of constraint loss of fracture mechanics due to crack-tip plasticity, and the creep stress relaxation on stress intensity factor. It is found the model can accurately predict the dwell crack growth rates for different crack geometries under various loading conditions.

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 Growth of Stainless Steel Piping in a Pressurized Water Reactor Environment

1979 ◽  
Vol 101 (1) ◽  
pp. 73-79 ◽  
Author(s):  
W. H. Bamford
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Pressurized Water ◽  
Crack Growth Rates

Fatigue crack-growth behavior was investigated for types 304 and 316 stainless steel exposed to a pressurized water reactor environment. The effects of test frequency, stress ratio, specimen orientation, heat to heat variables and weld versus base metal performance were evaluated. Crack-growth rates were correlated with the range of crack-tip stress intensity factor, as well as the “effective stress intensity factor” proposed by Walker to account for R ratio effects. Results of the study showed that fatigue crack-growth rates in the water environment were not significantly different from results at the same stress ratio in an air environment at the same temperature. The most important parameter found to affect the crack-growth rate was the stress ratio R, and increasing values of R produced increased crack-growth rates at any given value of stress intensity factor range ΔK. The stress ratio effects were successfully accounted for by employment of the Walker model.

Modelling Fatigue Crack Growth Rates in Aluminium Plates Reinforced by Bonded Fibre-Metal Laminates for Fatigue Life Extension

2014 ◽  
Vol 891-892 ◽  
pp. 1803-1809
Author(s):  
Jeremy Doucet ◽  
Xiang Zhang ◽  
Philip E. Irving
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Damage Tolerance ◽  
Element Model ◽  
Bond Line ◽  
Life Extension ◽  
Crack Growth Rates

Aircraft structural design and manufacture is moving towards lighter structures that have extended lives and improved damage tolerance. Hybrid structures are a possible solution to improve damage tolerance. They are a combination of metallic structure locally reinforced with adhesively bonded damage tolerant straps. In the present study a 3D finite element model has been developed with a bond line delamination growing under a fatigue law. A series of fatigue delamination tests on bonded aluminium were performed to provide input data. An iterative model for crack and debonding growth was developed to describe how debonding influence crack stress intensity and crack profile, which in turn influence debonding. The model predicts decrease in stress intensity on the bonded face and an overall retardation of fatigue crack growth rates. The stress intensity factor was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the reinforcing strap.

Corrosion Fatigue Crack-Growth Behavior of HY-130 Steel and Weldments

1981 ◽  
Vol 103 (4) ◽  
pp. 314-321 ◽  
Author(s):  
D. A. Davis ◽  
E. J. Czyryca
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Weld Metal ◽  
Crack Growth ◽  
Growth Rates ◽  
Hold Time ◽  
Base Plate ◽  
Weld Metals ◽  
Crack Growth Rates

Fatigue crack propagation was studied in HY-130 steel base plate, as-deposited shielded metal-arc weld metal, and gas metal-arc weld metal using compact specimens. The effects of seawater, cathodic protection, frequency and hold time were investigated. The results indicated that saltwater increased crack-growth rates in HY-130 base plate at stress intensity factors below 60 ksi in. No significant effects of cyclic load-wave pattern or of frequency (0.10 to 10 cycles per min.) were evident. Cathodic potentials from zinc (−1.05 V) and magnesium couples (−1.40 V) increased fatigue crack-growth rates in seawater. Fatigue crack growth in the weld metals showed different characteristics than in wrought materials in that higher stress intensities were required to initiate crack growth, and growth rates increased over a narrow range of stress intensity. Results of the environmental effects of weld metals indicated that, even under the most severe conditions of cathodic potential in seawater, fatigue crack-growth rates in weld metal were lower than those observed with base plate in air.

Environmentally Assisted Fatigue Crack Growth Rates in SAE 4340 Steel

1969 ◽  
Vol 91 (4) ◽  
pp. 598-602 ◽  
Author(s):  
J. P. Gallagher ◽  
G. M. Sinclair
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Growth Rates ◽  
Corrosion Fatigue Crack ◽  
4340 Steel ◽  
Corrosion Fatigue Crack Growth ◽  
Crack Growth Rates

Corrosion fatigue crack growth rates for SAE 4340 steel in distilled water environments were investigated utilizing fracture mechanics techniques. Crack growth rates, resulting from various forms of repeated loading, were compared to those induced by static load using small sample statistical theory. These comparisons indicate that corrosion fatigue crack growth may be either time or cycle dependent depending on the load profile, loading frequency, and temperature. Data are presented suggesting that whenever the maximum cyclic stress intensity in the fatigue cycle is below the static threshold stress intensity (KIscc), the environment no longer plays a major part in assisting the crack growth rate.

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