• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1726-1746
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• 2022

This paper presents fracture mechanics analysis results for various cracks located at pressurized water reactor pressure vessel nozzle crotch corners taking into consideration constraint effect. Technical documents such as the ASME B&PV Code, Sec.XI were reviewed and then a fracture mechanics analysis procedure was proposed for structural integrity assessment of various nozzle crotch corner cracks under normal operation conditions considering the constraint effect. Linear elastic fracture mechanics analysis was performed by conducting finite element analysis with the proposed analysis procedure. Based on the evaluation results, elastic-plastic fracture mechanics analysis taking into account the constraint effect was performed only for the axial surface crack of the reactor pressure vessel outlet nozzle with cladding. The fracture mechanics analysis result shows that only the axial surface crack in the reactor pressure vessel outlet nozzle has the stress intensity factor exceeding the low bound of upper-shelf fracture toughness irrespectively of considering the constraint effect. It is confirmed that the J-integral for the axial crack of the outlet nozzle does not exceed the ductile crack initiation toughness. Hence, it can be ensured that the structural integrity of all the cracks is maintained during the normal operation.

• Geomechanics and Engineering
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• v.37 no.4
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• pp.371-382
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• 2024

Measurement or prediction of compression index (C_c) of soils is essential for assessment of total and differential settlement of structures. It is a well-known fact that this parameter is controlled by several index identifiers of soil including initial void ratio, Atterberg limits, overconsolidation ratio, specific gravity, etc. Many studies in the past proposed relationships for prediction of C_c based on different index properties. Therefore, this study aims to present a comparison of previously proposed equations for estimation of C_c. Data from literature was compiled, and a total of 90 and 623 test results on remolded and undisturbed specimens were used to question the validity of previously proposed equations. Nevertheless, the modeling ability of 7 and 12 equations for estimation of C_c of remolded and undisturbed soils were questioned by use of compiled data. Moreover, new empirical relationships based on initial void ratio and toughness limit for prediction of C_c was proposed by use of nonlinear multivariable regression and evolutionary based regression analyses. The results are promising-the performances of models established are quite acceptable, which are verified by statistical analyses.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.5
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• pp.67-73
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• 2012

Failure mechanisms for a solid propellant were discussed, and the stip-yield and the inherent flaw models were applied to them. Then, failure assessment diagram methods were investigated by means of modified two models. Fracture toughness tests using CCT(center-cracked tension) specimens made of a solid propellant were conducted to generate the failure assessment diagrams. The failure assessment diagram of the inherent flaw model was normalized in order to compare with that of the modified strip-yield model. From the comparison of two failure assessment diagrams, it was found that the failure assessment diagram of the modified inherent flaw model more conservatively assesses the failure than that of the modified strip-yield model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.532-538
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• 2012

Failure mechanisms for a highly filled elastomer were discussed, and the stip-yield and the inherent flaw models were applied to them. Then, failure assessment diagram methods were investigated by means of modified two models. Fracture toughness tests using CCT(center-cracked tension) specimens made of a highly filled elastomer were conducted to generate the failure assessment diagrams. The failure assessment diagram of the inherent flaw model was normalized in order to compare with that of the modified strip-yield model. From the comparison of two failure assessment diagrams, it was found that the failure assessment diagram of the modified inherent flaw model more conservatively assesses the failure than that of the modified strip-yield model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.667-670
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• 2001

For major structural components periodic inspections and integrity assessments are needed for the safety. However, many flaws are undetectable because sampling inspection is carried out during in-service inspection. Probabilistic integrity assessment is applied to take into consideration of uncertainty and variance of input parameters arise due to material properties and undetectable cracks. This paper describes a Probabilistic Fracture Mechanics(PEM) analysis based on the Monte Carlo(MC) algorithms. Taking a number of sampling data of probabilistic variables such as fracture toughness value, crack depth and aspect ratio of an initial surface crack, a MC simulation of failure judgement of samples is performed. For the verification of this analysis, a comparison study of th PFM analysis using a commercial code, mathematical method is carried out and a good agreement was observed between those results.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.459-464
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• 2001

For major nuclear power plant components periodic inspections and integrity assessments are needed for the safety. But many flaws are undetectable due to sampling inspection. Probabilistic integrity assessment is applied to take into consideration of uncertainty and variance of input parameters arise due to material properties, applied load and undetectable flaws. This paper describes a Probabilistic Fracture Mechanics(PFM) analysis based on Monte Carlo(MC) algorithms. Taking important parameters as probabilistic variables such as fracture toughness, crack growth rate and flaw shape, failure probability of major nuclear power plant components is archived as a results of MC simulation. For the verification of these analysis, a comparison study of the PFM analysis using other commercial code, mathematical method is carried out and a good agreement was observed between those results.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.219-223
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• 2009

This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

• Transactions of Materials Processing
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• v.11 no.7
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• pp.575-580
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• 2002

To evaluate elastic and micro-failure properties of MEMS materials, the electro-statically operated test devices were designed and fabricated by micro machining technology. The test structures consist or comb drives for loading and suspending beams in testing. From the analysis of beam displacement based on elastic beam theory, elastic modulus and yield strength of Al film were measured. And, by introducing the micro notch and cyclic loading, the micro-failure was Induced and the micro-fracture toughness of Si film was evaluated. Moreover, the cycles to failure were estimated from the degradation of resonant frequency. Finally, the effects of notch on micro failure were discussed.

• Structural Engineering and Mechanics
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• v.8 no.1
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• pp.103-118
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• 1999

The structural integrity of the reactor pressure vessel under pressurized thermal shock (PTS) is evaluated in this study. For given material properties and transient histories such as temperature and pressure, the stress distribution is found and stress intensity factors are obtained for a wide range of crack sizes. The stress intensity factors are compared with the fracture toughness to check if cracking is expected to occur during the transient. A round robin problem of the PTS during a small break loss of coolant transient has been analyzed as a part of the international comparative assessment study, and the evaluation results are discussed. The maximum allowable nil-ductility transition temperatures are determined for various crack sizes.

• Steel and Composite Structures
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• v.17 no.5
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• pp.549-560
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• 2014

The paper provides the test results and analysis on the behavior of steel 1.7147 at different temperatures. Mechanical uniaxial tests were used to determine mechanical properties, resistance to creep and Charpy impact tests to determine impact energy. Test results are presented in the form of engineering stress-strain diagrams, creep curves as well as numerical data related to impact energy. The results show that the tensile strength has the highest value at room temperature, and the same goes for the yield strength as well as for modulus of elasticity. After room temperature both of mentioned properties decrease with temperature increasing. Some of creep curves were modeled using rheological models and analytical equation. Based on Charpy impact energy an assessment of fracture toughness was made.