Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen
Abstract
1. Introduction
2. Materials and Methods
3. Experimental Procedure
3.1. Measurement Method for Crack Growth Length
- a = crack length (mm);
- a0 = initial crack length (mm);
- D = diameter of the specimen (mm);
- y = half-distance between the output terminals;
- U = current voltage (;
- U0 = initial voltage (.
3.2. Criteria of Failure Life and Crack Initiation
3.3. Experimental Conditions
4. Experimental Results
4.1. Cycle-Sequential Characteristics of the Nominal Stress Range
4.2. Crack Growth Behavior
4.3. The Load Frequency Characteristics of the Inverse Value of Crack Growth Life
5. Analysis and Discussion
5.1. Relationship Between Crack Length and Stress Reduction Ratio
5.2. Separate Estimation Method for the Cycle-Dependent Mechanism from the Time-Dependent Mechanism for Crack Growth Life
5.3. Representation of the Creep and Fatigue Accumulated Damage Law
5.4. Representation by the Manson–Coffin Law
5.5. Discussion
5.6. Limitations
6. Conclusions
- The cycle-sequential characteristics of the nominal stress range, , was found to monotonously decrease against the applied strain cycles, which verifies the previous result [1] and makes it possible to accurately determine the failure life and crack initiation using the reduction ratio of the nominal stress range, , as proposed in the previous study [1].
- The effect of specimen diameter on the crack growth curve was found to be well-controlled by the initial net section diameter Dnet, and to show good correlation between and η. This result shows that crack growth life is not dominated by the crack length but by the ratio of the crack length to the initial net section diameter of the specimen.
- The crack growth life of the CNS under strain-controlled creep–fatigue conditions for P92 steel was found to be dominated by the cycle-dependent mechanism in a strain range from 0.3% to 0.5%. By contrast, the crack growth life of the CNS under stress-controlled creep–fatigue conditions for P92 steel was mainly dominated by the time-dependent mechanism in the same temperature range.
- A unified cumulative failure law under stress- and strain-controlled conditions was investigated. The results show that, for a sharp notched specimen of P92 steel, the failure life under strain-controlled creep and fatigue conditions exists in the region of the cycle-dependent mechanism; however, the failure life under stress-controlled creep and fatigue conditions exists in the region of the time-dependent mechanism under the same temperature range as that under strain-controlled conditions. These results correspond well to the results in point 3 above.
- Under strain-controlled creep and fatigue conditions for the CNS, since the crack growth life was dominated by the cycle-dependent mechanism in a strain range from 0.3% to 0.5%, the Manson–Coffin law was found to be applicable not only to a smooth specimen under low cycle fatigue but also to the CNS under low cycle fatigue and creep–fatigue conditions with different values of α and C.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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C | Si | Mn | P | S | Cr | Mo | W | Nb | V | N | B |
---|---|---|---|---|---|---|---|---|---|---|---|
0.085 | 0.26 | 0.49 | 0.006 | 0.0012 | 8.85 | 0.50 | 1.80 | 0.06 | 0.20 | 0.0510 | 0.0030 |
0.2YS (MPa) | TS (MPa) | Uniform EL (%) | EL (%) | RA (%) |
---|---|---|---|---|
583 | 731 | 2.68 | 27.6 | 74.6 |
dε/dt [%/s] | Temp. [°C] | Diameter, D [mm] | ∆ε [%] | tH [s] | Nf [-] | |
0.1 | 600 | 10 | 0.3 | 0 | 2980 | |
600 | 1000 | |||||
3600 | 1240 | |||||
630 | ||||||
0 | 1310 | |||||
600 | 1035 | |||||
3600 | 1125 | |||||
630 | 6 | 0.4 | 0 | 372 | ||
600 | 365 | |||||
0.5 | 0 | 168 | ||||
600 | 160 |
σnet [MPa] | Kin [MPa√m] | Temp. [°C] | tR = tD [s] | tH [s] | tf [h] | |
300 | 14 | 600 | 35 | 0 | 172.1 | |
600 | 533 | |||||
3600 | 985.2 | |||||
Creep | 1189 | |||||
615 | 35 | 0 | 88.3 | |||
600 | 279.4 | |||||
3600 | 186.3 | |||||
630 | 35 | 0 | 66.3 | |||
600 | 38.4 | |||||
3600 | 54.8 | |||||
Creep | 31.7 |
Specimen | Temp. [°C] | tH [s] | α [-] | C [-] |
---|---|---|---|---|
CNS | 630 | 0 | 0.594 | 1.8 |
600 | 0.521 | 3.2 | ||
Smooth | 630 | 0 | 0.816 | 1.58 |
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Yokobori, A.T., Jr.; Ozeki, G.; Jinno, K.; Seino, H.; Sugiura, R.; Nonaka, I. Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen. Metals 2025, 15, 737. https://doi.org/10.3390/met15070737
Yokobori AT Jr., Ozeki G, Jinno K, Seino H, Sugiura R, Nonaka I. Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen. Metals. 2025; 15(7):737. https://doi.org/10.3390/met15070737
Chicago/Turabian StyleYokobori, A. Toshimitsu, Jr., Go Ozeki, Kazutaka Jinno, Hiroaki Seino, Ryuji Sugiura, and Isamu Nonaka. 2025. "Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen" Metals 15, no. 7: 737. https://doi.org/10.3390/met15070737
APA StyleYokobori, A. T., Jr., Ozeki, G., Jinno, K., Seino, H., Sugiura, R., & Nonaka, I. (2025). Life Prediction of Crack Growth for P92 Steel Under Strain-Controlled Creep–Fatigue Conditions Using a Sharp Notched Round Bar Specimen. Metals, 15(7), 737. https://doi.org/10.3390/met15070737