Fatigue Microcracks in a Low Carbon Steel

Suh, Chang‐Min; Yuuki, Ryoji; Kitagawa, Hideo

doi:10.1111/j.1460-2695.1985.tb01203.x

Cited by 73 publications

(28 citation statements)

References 7 publications

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“…The data obtained by Orbtlik et al 43 for Type 316L SS in air at 25°C and ª0.2% strain range were used to estimate the crack growth in air at 0.75% strain range. Studies on carbon and low-alloy steels 41,42,49 indicate that the fatigue crack size at various life fractions is independent of strain range, strain rate, and temperature; consequently, the depth of the The results show that at the same number of cycles, the crack length is longer in low-DO water (PWR) than in air, e.g., after 1500 cycles the crack length in air, high-DO water (BWR), and PWR water is ª40, 300, and 1100 mm, respectively. The growth of cracks during the initiation stage, i.e., growth of MSCs, is enhanced in water; fatigue cycles needed to form a 500-mm crack are a factor of ª12 lower in low-DO water than in air.…”

Section: Growth Of Small Cracks In Lwr Environmentsmentioning

confidence: 99%

Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

Chopra¹

2002

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The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life (e-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of fatigue crack initiation in austenitic stainless steels in LWR coolant environments. The existing fatigue e-N data have been evaluated to establish the effects of key material, loading, and environmental parameters (such as steel type, strain range, strain rate, temperature, dissolved-oxygen level in water, and flow rate) on the fatigue lives of these steels. Statistical models are presented for estimating the fatigue e-N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. The influence of reactor environments on the mechanism of fatigue crack initiation in these steels is also discussed. Executive SummarySection III, Subsection NB, of the ASME Boiler and Pressure Vessel Code contains rules for the design of Class 1 components of nuclear power plants. Figures I-9.1 through I-9.6 of Appendix I to Section III specify the Code design fatigue curves for applicable structural materials. However, Section III, Subsection NB-3121, of the Code states that effects of the coolant environment on fatigue resistance of a material were not intended to be addressed in these design curves. Therefore, the effects of environment on fatigue resistance of materials used in operating pressurized water reactor (PWR) and boiling water reactor (BWR) plants, whose primary-coolant pressure boundary components were designed in accordance with the Code, are uncertain.The current Section-III design fatigue curves of the ASME Code were based primarily on strain-controlled fatigue tests of small polished specimens at room temperature in air. Best-fit curves to the experimental test data were first adjusted to account for the effects of mean stress and then lowered by a factor of 2 on stress and 20 on cycles (whichever was more conservative) to obtain the design fatigue curves. These factors are not safety margins but rather adjustment factors that must be applied to experimental data to obtain estimates of the lives of components. They were not intended to address the effects of the coolant environment on fatigue life. Recent fatigue-strain-vs.-life (e-N) data obtained in the U.S. and Japan demonstrate that light water reactor (LWR) environments can have potentially significant effects on the fatigue resistance of materials. Specimen lives obtained from tests in simulated LWR environments can be much shorte...

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Section: Growth Of Small Cracks In Lwr Environmentsmentioning

confidence: 99%

Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

Chopra¹

2002

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“…When the crack length was small (e.g., l < 0.2 mm), a crack tended to propagate with shear mode. For the crack length in excess of 0.2 mm, the propagation mechanism was principally dominant by tensile mode, and dl/dN is nearly proportional to l. Since a shear microcrack is strongly influenced by the inhomogeneity of its microstructure [11][12][13][14][15], the fluctuation of dl/dN is relatively larger than that of large crack propagating with tensile mode. In addition, the growth rate of SMCG is higher than that of a tensile-mode crack with corresponding crack length, evaluated from the relation holds for l > 0.3 mm.…”

Section: Crack Initiation and Growth Behaviourmentioning

confidence: 90%

Effect of Zr addition on the fatigue strength of Cu-6Ni-2Mn-2Sn-2Al alloy

Goto¹,

Han²,

Kim³

et al. 2007

WIT Transactions on Modelling and Simulation, Vol 46

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Fatigue tests of Cu-6Ni-2Mn-2Sn-2Al alloy smooth specimens were carried out to clarify the effect of trace Zr on the fatigue strength. The growth behaviour of a major crack, which led to the final fracture of the specimen, was monitored to study the physical basis of fatigue damage. When stress amplitude was less than σ a = 350 MPa, the fatigue life of Zr-containing alloys was about two times larger than that of alloys without Zr. When σ a > 350 MPa, increments of fatigue life due to Zr decrease with an increase in σ a and the increments were negligible at σ a = 400 MPa. Increased fatigue life due to Zr addition resulted from an increase in crack initiation life and microcrack growth life. The growth rate of a small crack was determined by a term, σ a n l, independent of Zr addition. The effects of trace Zr on fatigue strength were discussed with relation to the initiation and propagation behaviour of a major crack.

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“…The surface cracks combined with other adjacent small cracks and grow into larger crack as shown as dotted area. The cracking phenomena were commonly observed for "after SP" specimens [14][15][16][17].…”

Section: S-n Curves Of Ultrasonic Fatigue Tester (Uft 20 Khz)mentioning

confidence: 99%

VHCF Properties of A7075-T651 Al Alloy Depending on Shot Peening and Fatigue Testing Methods

Suh

Nahm

et al. 2014

Advances in Mechanical Engineering

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Fatigue characteristics of A7075-T651 aluminum material were studied with surface treatment of shot peening. The fatigue life was characterized by two fatigue testing methods, ultrasonic fatigue test (UFT, 20 kHz) and the rotary-bending fatigue test (RFT, 53 Hz). The fatigue life improvement was confirmed by rotary bending fatigue tester. However, the surface modification effects were hardly observed by UFT method. The RFT results validate that the fatigue properties of RFT show a fine congruence regardless of the test machine types. The results of hardness, compressive residual stress, fatigue strength, and mechanical properties of specimen were improved by shot peening.

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Fatigue Microcracks in a Low Carbon Steel

Cited by 73 publications

References 7 publications

Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

Effect of Zr addition on the fatigue strength of Cu-6Ni-2Mn-2Sn-2Al alloy

VHCF Properties of A7075-T651 Al Alloy Depending on Shot Peening and Fatigue Testing Methods

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