Room Temperature Creep and its Effect on Fatigue Crack Growth in a X70 Steel with Various Microstructures

2007 ◽  
Vol 353-358 ◽  
pp. 138-141 ◽  
Author(s):  
De Fu Nie ◽  
Jie Zhao
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Room Temperature ◽  
Pipeline Steel ◽  
Threshold Region ◽  
Single Wave ◽  
Temperature Creep ◽  
Crack Tips ◽  
Room Temperature Creep

Fatigue crack growth (FCG) tests have been performed in an X70 steel with various microstructures (respectively in the as-received and the normalized condition). The effect of room temperature creep (RTC) on FCG behavior has been investigated by comparing with single wave overloads (SWOL). The as-received X70 pipeline steel has high FCG rate at the near-threshold region. While at the Paris region, FCG rate seems insensitive to the microstructure. In both conditions, time-dependent deformation is observed at crack tips (i.e., RTC), which increases with increasing stress-intensity-factor. And this deformation has a high value in the normalized state, under identical testing conditions. Both RTC and SWOL can bring subsequent fatigue crack growth a very short initial acceleration before deceleration, whereas the former induces more serious deceleration and retardation, which attributes to more significant crack closures.

Room Temperature Creep and Its Influence on Fatigue Crack Growth in a 304 Stainless Steel

2005 ◽  
Vol 297-300 ◽  
pp. 1083-1088 ◽  
Author(s):  
Jie Zhao ◽  
Tao Mo ◽  
Weixing Chen ◽  
Fu Gang Wang
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Room Temperature ◽  
304 Stainless Steel ◽  
Propagation Mode ◽  
Temperature Creep ◽  
Room Temperature Creep

The current paper investigated the phenomena of room temperature creep at the crack tip and its influence on fatigue crack growth behavior of a 304 stainless steel. From the experiments, a time-dependent deformation is obviously observed under various stress intensity factors. The deformation depends on stress intensity factor as well as load history. Both acceleration and retardation of fatigue crack growth are found after room temperature creep, which rest on load patterns. A distinct marking line was seen on the fracture surface following the holding period. It is proposed that the crack propagation mode changed after the hold time.

Threshold and Low-Rate Fatigue Crack Growth of a NiMoV Rotor Steel

1981 ◽  
Vol 103 (2) ◽  
pp. 104-111 ◽  
Author(s):  
T. T. Shih ◽  
J. K. Donald
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Room Temperature ◽  
Stress Ratio ◽  
Threshold Region ◽  
Rotor Steel ◽  
Low Rate

An automated, computer-controlled K-decreasing technique was used to determine the threshold, ΔKth, and low-rate fatigue crack growth of a NiMoV rotor steel. A more conventional K-increasing technique was also used. Excellent agreement between results obtained from both techniques was observed. For the material and environment studied, no crack arrest was observed for crack growth rate down to 2.5 × 10−8 mm/cycle (10−9 in./cycle). As such, an operational definition of ΔKth was defined as the stress intensity factor range corresponding to a crack growth rate of 2.5 × 10−8 mm/cycle (10−9 in./cycle). In room temperature air environment, ΔKth was found to be 6.2 and 4.0 MPam (5.6 and 3.6 ksiin.) for R = 0.1 and R = 0.5, respectively. At the same ΔK level, crack growth rate was found to increase with increasing stress ratio. The influence of stress ratio on crack growth rate, however, decreases with increasing ΔK. By raising temperature to 93° C (200°F), ΔKth was found to be suppressed to 4.4 and 2.9 MPam (4.0 and 2.6 ksiin.) for R = 0.1 and R = 0.5, respectively. Stress ratio effect on crack growth rate is the same as at room temperature, but is less significant. Temperature was found to influence crack growth rate in the threshold region for both stress ratio studied, with higher crack growth rate at 93°C (200°F) than at room temperature. Temperature sensitivity was found to be less for R = 0.5 than R = 0.1. The existence of hydrogen was found to have little effect on ΔKth and low-rate fatigue crack growth behavior of this NiMoV rotor steel.

Corrosion-Fatigue Crack Growth in Age-Hardened Al Alloys: Examples of Failures and Explanations for Fractographic Observations

2014 ◽  
Vol 891-892 ◽  
pp. 248-253 ◽  
Author(s):  
Rohan Byrnes ◽  
Noel Goldsmith ◽  
Mark Knop ◽  
Stan Lynch
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Compact Tension ◽  
Al Alloys ◽  
Corrosion Fatigue Crack ◽  
Crack Tips ◽  
Corrosion Fatigue Crack Growth ◽  
Additional Support

The characteristics of corrosion-fatigue in age-hardened Al alloys, e.g. brittle striations on cleavage-like facets, are described, with reference to two examples of component failure. Mechanisms of corrosion fatigue (and explanations for fracture-surface features) are then reviewed. New observations of corrosion-fatigue crack growth for 7050-T7451 alloy compact-tension specimens tested in aqueous environments using a constant (intermediate) ΔK value but different cycle frequencies are then described and discussed. These observations provide additional support for a hydrogen-embrittlement process involving adsorption-induced dislocation-emission from crack tips.

Fatigue Crack Growth in SA508-CL2 Steel in a High Temperature, High Purity Water Environment

1974 ◽  
Vol 96 (4) ◽  
pp. 255-260 ◽  
Author(s):  
T. L. Gerber ◽  
J. D. Heald ◽  
E. Kiss
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
High Purity ◽  
Room Temperature ◽  
Water Environment ◽  
Cyclic Frequency ◽  
Asme Code ◽  
Temperature Rate

Fatigue crack growth tests were conducted with 1 in. (25.4 mm) plate specimens of SA508-CL2 steel in room temperature air, 550 deg F (288 deg C) air and in a 550 deg F (288 deg C), high purity, water environment. Zero-tension load controlled tests were run at cyclic frequencies as low as 0.037 CPM. Results show that growth rates in the simulated Boiling Water Reactor (BWR) water environment are 4 to 8 times faster than growth rates observed in 550 deg F (288 deg C) air and these rates are 8 to 15 times faster than the room temperature rate. In the BWR water environment, lowering the cyclic frequency from 0.37 CPM to 0.037 CPM caused only a slight increase in the fatigue crack growth rate. All growth rates measured in these tests were below the upper bound design curve presented in Section XI of the ASME Code.

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