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.

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 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.

Definition of Fatigue Crack Growth Thresholds for Ferritic Steels in Fitness-for-Service Codes

2018 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Tests ◽  
Ferritic Steels ◽  
Stress Ratios ◽  
Definition Of ◽  
Crack Growth Rates

Fatigue crack growth rates are expressed as a function of the stress intensity factor ranges. The fatigue crack growth thresholds are important characteristics of fatigue crack growth assessment for the integrity of structural components. Almost all materials used in these fatigue tests are ferritic steels. As a result, the reference fatigue crack growth rates and the fatigue crack growth thresholds for ferritic steels were established as rules and they were provided by many fitness-for-service (FFS) codes. However, the thresholds are not well defined in the range of negative stress ratio. There are two types of thresholds under the negative stress ratio. That is, constant thresholds and increment of thresholds with decreasing stress ratios. The objective of this paper is to introduce the thresholds provided by FFS codes and to analyze the thresholds using crack closure. In addition, based on the experimental data, definition of the threshold is discussed to apply to FFS codes. Finally, threshold for ferritic steels under the entirely condition of stress ratio is proposed to the ASME Code Section XI.

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.

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.

Fatigue Crack Growth Rates of S235 and S355 Steels after Friction Stir Processing

2012 ◽  
Vol 726 ◽  
pp. 203-210 ◽  
Author(s):  
Dorota Kocańda ◽  
Volodymyr Hutsaylyuk ◽  
Tomasz Ślęzak ◽  
Janusz Torzewski ◽  
Hryhoriy Nykyforchyn ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Friction Stir Processing ◽  
Growth Rates ◽  
Fatigue Tests ◽  
Carbon Steels ◽  
Internal Stresses ◽  
Friction Stir ◽  
Crack Growth Rates

Abstract. In the study, there were investigated the effects of friction stir processing (FSP) which was applied in order to improve the surfaces of notched specimens made of S235JR and S355J2 carbon steels, on their fatigue crack growth rates in the air. There were presented the results of comparative fatigue tests conducted at asymmetric tension (R= -0.2) for these steels treated by means of FSP and for the ones in the delivery state. The method of successive etched material layers used revealed the presence of internal tensile stresses in the surface layers of treated specimens. Crack growth rates were described on the basis of non-linear fracture mechanics, taking the effects of internal stresses into account.

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