FATIGUE CRACK GROWTH AND CLOSURE AT HIGH STRESS RATIOS

1995 ◽  
Vol 18 (4) ◽  
pp. 503-514 ◽  
Author(s):  
H. Tsukuda ◽  
H. Ogiyama ◽  
T. Shiraishi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Stress ◽  
Stress Ratios

Designing Light Alloys for Fatigue Crack Growth Resistance

2011 ◽  
Vol 690 ◽  
pp. 393-396
Author(s):  
Anastasios G. Gavras ◽  
Diana A. Lados
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Stress ◽  
Compact Tension ◽  
Fatigue Crack Growth Resistance ◽  
Reduction Strategies ◽  
Stress Ratios ◽  
And Performance ◽  
Wrought Aluminum

Fatigue crack growthresistance is critical to the design and performance of structural components.This study focuses on understanding the microstructural mechanisms of fatigue crack propagation in commonly used structural materials, cast and wrought aluminum and titanium alloys, with various microstructures resulting from changes in chemistry or heat treatment (A535-F, 6061-T6, and mill- and b-annealed Ti-6Al-4V).Stress ratio effects were evaluated by conducting fatigue crack growth tests on compact tension specimens at low, intermediate, and high stress ratios, R=0.1, 0.5, and 0.7, respectively. Initial flaw size effects were also studied by performing small crack growth tests at R=0.1. Data reduction strategies compensating for closure and Kmax effects on crack growth and design curves will be presented.

Fatigue Performance of Sour Deepwater Riser Welds: Crack Growth vs. Endurance

2011 ◽  
Author(s):  
Colum M. Holtam ◽  
David P. Baxter
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Pipeline Steel ◽  
High Stress ◽  
Fatigue Loading ◽  
Stress Intensity Factor Range ◽  
Valuable Insight ◽  
Stress Ratios ◽  
Fatigue Endurance

Steel catenary risers (SCRs) are increasingly used in deepwater oil and gas developments. SCRs can be subject to low-stress high-cycle fatigue loading, for example from wave and tidal motion, vortex induced vibration (VIV) and operating loads, and corrosive environments (internal and external). When the production fluids are sour, higher fatigue crack growth rates (FCGRs) are expected and therefore shorter overall life compared to performance in air, as a result of the interaction between fatigue crack growth and sulphide stress cracking. Successful design of risers is critically dependent on the availability of appropriate experimental data to quantify the extent to which fatigue lives are reduced and rates of fatigue crack growth are increased. Historically there has been a discrepancy between experimental sour fatigue endurance data and fracture mechanics-based estimates of the corresponding stress-life (S-N) curves. This paper summarises the results of recent sour FCGR tests on C-Mn pipeline steel. Tests were performed under conditions of increasing applied stress intensity factor range (ΔK), on specimens containing shallow initial flaws and at very high stress ratios (R), to obtain data close to threshold. In many cases it is material behaviour at these low values of ΔK that dominate the fatigue life (e.g. VIV loading). The FCGR data are then compared to sour fatigue endurance data, both published and from a TWI Joint Industry Project (JIP). The observed environmental reduction factor (ERF) for endurance tests is compared to that expected from the difference in fatigue crack propagation rates, to examine whether FCGR data might provide an alternative means of predicting ERFs. This paper offers valuable insight into current best practice methods for generating sour FCGR data when qualifying girth welds for sour service, and the relationship between fatigue crack growth and fatigue endurance.

Near-Threshold Fatigue Crack Growth Behavior of ECAPed Ultrafine-Grained Copper

2021 ◽  
Vol 1016 ◽  
pp. 1193-1198
Author(s):  
Shou Dao Qu ◽  
Ze Sheng You
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Threshold ◽  
Coarse Grained ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Resistance ◽  
Ultrafine Grained ◽  
Stress Ratios ◽  
Near Threshold

Fatigue crack growth resistance of ultrafine grained Cu processed by equal channel angular pressing (ECAP) was investigated. Particular emphasis was devoted to the effects of microstructure evolution on fatigue crack growth in the near-threshold regime. The ultrafine grained Cu exhibits a lower fatigue threshold than coarse-grained Cu at stress ratios of 0.1 and 0.7. Fatigue induced coarsening of the UFG structure near the fatigue crack and intergranular fatigue crack growth are observed.

Further Development of a Model for Predicting Corrosion Fatigue Crack Growth in Reactor Pressure Vessel Steels

1987 ◽  
Vol 109 (3) ◽  
pp. 340-346 ◽  
Author(s):  
J. D. Gilman
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Alloy Steel ◽  
High Stress ◽  
Time Dependent ◽  
Crack Advance ◽  
Low Alloy Steel ◽  
Time Rate ◽  
Paris Law

Analysis of fatigue crack growth data for low-alloy steel shows that the influence of cyclic frequency in simulated LWR environments can be interpreted as the superposition of a time-dependent, corrosion-assisted crack growth rate upon an increment predicted by a Paris law. The time-dependent component increases monotonically to a maximum of about 6×10−5 mm/s as stress cycling becomes more aggressive. A useful measure of aggressiveness is the average time rate of crack advance due to the Paris law component alone; i.e., AΔKn × frequency. The result suggests that current ASME Code methods for flaw assessment are highly conservative in some regimes of stress and frequency, but there is a possibility of growth rates well above the ASME XI, Appendix A curves in a very low-frequency, high-stress regime. An upper bound to the time rate of corrosion-assisted crack growth in low-alloy steel is well supported by the data. The threshold conditions for the onset of this high rate are less well defined and require further investigation.

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