Evaluation for fracture resistance curves of nuclear real pipes using curved equivalent stress gradient (curved ESG) specimens

Shen, Tao; Park, Keontae; Choi, Jae Boong; Moon, Byungwoo; Koo, Jae-Mean; Seok, Chang-Sung

doi:10.1016/j.engfracmech.2016.11.008

Cited by 7 publications

(4 citation statements)

References 12 publications

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Section: Fracture Morphologysupporting

confidence: 59%

“…The fracture morphology was observed using a scanning electron microscope (SEM) as shown in Figure 9 for the sample tested with the novel ultrasonic bending fatigue. It shows a similar feature of fractography taken from the flexural fatigue sample studied in the literature [ 33 , 34 , 35 , 36 ]; i.e., due to the stress gradient, single or multiple crack initiation sources nucleate on the surface, which expands from the outside to the inside. Moreover, the crack is a river-like shape during the expansion, and the expansion direction is about 45° inclined.…”

Section: Resultsmentioning

confidence: 55%

See 1 more Smart Citation

A Novel Model of Ultrasonic Fatigue Test in Pure Bending

Yang

Tang

et al. 2022

Materials

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The very high cycle fatigue (VHCF) failure of in-service components is mainly caused by the vibration of thin-wall elements at a high frequency. In this work, a novel model of ultrasonic fatigue test was developed to test thin-wall material in bending up to VHCF with an accelerated frequency. The theoretical principle and finite element analysis were introduced for designing a sample that resonated at the frequency of 20 kHz in flexural vibration. In the advantage of the second-order flexural vibration, the gauge section of the sample was in the pure bending condition which prevented the intricate stress condition for thin-wall material as in the root of cantilever or the contact point of three points bending. Moreover, combining the constraint and the loading contact in one small section significantly reduced heating that originated from the friction at an ultrasonic frequency. Both strain gauge and deflection angle methods were applied to verify the controlling of stress amplitude. The fractography observation on Ti6Al4V samples indicated that the characterized fracture obtained from the novel model was the same as that from the conventional bending test.

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Section: Fracture Morphologysupporting

confidence: 59%

Section: Resultsmentioning

confidence: 55%

A Novel Model of Ultrasonic Fatigue Test in Pure Bending

Yang

Tang

et al. 2022

Materials

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“…In addition, Figure 2b shows that the J-R curves obtained from the fracture resistance tests of the curved ESG specimen are similar to those of the real piping but different from that of the CT specimen. Thus, we can conclude that, in applying the LBB concept to the design of NPP, ESG specimens demonstrate identical constraint effects as real piping, thus reducing the overly conservative designs obtained by using conventional standard CT specimens [22].…”

Section: Validation Of Fracture Toughness Characteristics Using Esg S...mentioning

confidence: 83%

“…Figure 1 shows the schematic design of the ESG specimen, which replicates the crackopening stress gradient at the crack tip of the real piping with circumferential crack. Tao Shen et al evaluated the crack-opening stress gradients of real piping, a standard compact tension (CT) specimen, and a curved ESG specimen for SA312 TP304 stainless steel material through finite element (FE) analysis [22]. The results, as shown in Figure 2a, indicate that the crack-opening stress gradients of the CT specimen and the real piping were significantly different, whereas the curved ESG specimen and the real piping had similar crack-opening stress gradients.…”

Section: Validation Of Fracture Toughness Characteristics Using Esg S...mentioning

confidence: 99%

Leak-before-Break (LBB)-Based Safety Verification of Reverse Cyclic Loading for 316L Stainless Steel: A Study Using Flat ESG Specimens

Choi,

Lee,

Park

et al. 2023

Metals

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The leak-before-break design concept is based on J-R curves, which are obtained by J-R tests on various types of specimens and are known to be dependent on the cyclic load history. The J-R curves of standard specimens suggested by the American Society for Testing Materials are determined based on quasi-static tensile loading. However, seismic loading induces a reverse cyclic loading that alternately applies a tensile and a compressive load to nuclear plant piping. Therefore, it is very important to obtain the fracture toughness characteristics under reverse cyclic loading for the integrity estimation of nuclear plant piping. The objective of this paper is to study the effects of reverse cyclic loading on the fracture toughness characteristics of SA312 TP316L stainless steel, which is a nuclear plant piping material. J-R tests on a flat, equivalent stress gradient specimen with varying incremental displacement were carried out. The test results were reviewed by comparing the J-R test results under quasi-static loading. In addition, the safety margin of the nuclear plant piping was evaluated using a crack driving force diagram method. For the SA312 TP316L stainless steel, the results showed that the J-R curves were decreased with a decrease in the incremental displacement. When the incremental displacement was set to 0.25 mm, the unstable crack growth point value was about 73.0% of those for the quasi-static loading conditions.

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