Kyung Dong Bae

Determination Method of Ramberg-Osgood Constants for Leak Before Break Evaluation

In this study, a method for determining Ramberg–Osgood constants for leak-before-break evaluation was investigated. The Ramberg–Osgood constants were calculated for SA312, TP316, and SA-508 Gr.1a in an operating temperature of 316 oC. Incremental plasticity, using stress–strain data obtained from experiment, and deformation plasticity, using the Ramberg-Osgood constants, were considered in a finite element analysis. Using incremental plasticity and deformation plasticity, J-integrals and crack opening displacement values were calculated and compared. By comparing the results of incremental plasticity and deformation plasticity, a suitable method for determining Ramberg–Osgood constants for leak-before-break evaluation was confirmed. † Corresponding Author, kimy0308@korea.ac.kr C 2015 The Korean Society of Mechanical Engineers 배경동 · 류호완 · 김윤재 · 김진원 · 김종성 · 오영진 646

Ductile fracture simulation for toughness specimens from low alloy and stainless steel pipes

This paper describes ductile fracture simulation for Battelle fracture toughness and full-scale pipe tests (1). Materials in this research are low carbon steel and TP304 stainless steel. Tensile and Compact tension (CT) specimens are simulated to determine the fracture criteria with finite element (FE) method. Then, pipes containing through wall crack and surface crack are predicted by proposed damage method. The results from simulations are compared with test data for verification of proposed method and to check the applicability on industrial field. It is shown that predicted simulation results are compared with experimentally measured values, showing overall good agreements.

Reference stress-based J Estimation of circumferential through-wall cracked elbow with unequal thickness under bending

In large plant facilities, elbow and straight pipe have large potion in whole piping system. When the cracks are initiated in pipe, the cracks have to be evaluated using fracture mechanics parameter such as J-integral. Unlike calculating J-integral of straight pipes, estimation J-integral of elbow using finite element analysis is not easy. Because the effect of geometries for crack behavior of elbow are more complex than straight pipes. Also, there is another difference between elbow and straight pipe. That is unequal thickness in intrados and extrados. Unequal thickness of elbow pipes generally occurs by the manufacturing process. Thickness in intrados is getting thicker than nominal thickness but thickness in extrados is getting thinner than nominal thickness. So first, this paper provides a reference stress-based J-integral estimation of circumferential through-wall cracked elbow with equal thickness. And this paper provides also a reference stress-based J-integral estimation of circumferential through-wall cracked elbow with unequal thickness. To find the reference stress-based approximate J-integral, various ratio of thickness (t), pipe radius (r), pipe bend radius (R) and crack length (θ) are considered. And three-dimensional finite element analyses using elastic property for elastic crack behavior and elastic–perfectly plastic property for limit load are performed. Finally Results in this research are presented in the failure assessment diagram (FAD) space.Copyright

Element and Crack Geometry Sensitivities of Finite Element Analysis Results of Linear Elastic Stress Intensity Factor for Surface Cracked Straight Pipes

This study provides the elastic stress intensity factors, K, for circumferential and longitudinal surface cracked straight pipes under single or combined loads of internal pressure, bending, and torsion based on three-dimensional (3D) finite element (FE) analyses. FE results are compared with two different types of defect assessment codes (API-579-1 and RCC-MR A16) to prove the accuracy of the FE results and the differences between the codes. Through the 3D FE analysis, it is found that the stress intensity factors are sensitive to the number of elements, which they were believed to not be sensitive to because of path independence. Differences were also found between the FE analysis results for crack defining methods and the results obtained by two different types of defect assessment codes.

Limit Loads for Circular Wall-Thinned Feeder Pipes Considering Bend Angle

In CANDU, feeder pipes supply heavy water to pressure tube and steam generator. Under service conditions, Flow-Accelerated Corrosion (FAC) produces local wall-thinning in the feeder pipes. The wall-thinning in these pipes affects the integrity of the piping system, as verified in previous research. This paper provides limit loads for wallthinned feeder pipes with and bend angles, and proposes an equation that predicts the limit loads for wallthinned feeder pipes with arbitrary bend angles. On the basis of finite element limit analyses, limit loads are obtained for wall-thinned feeder pipes under in-plane bending and internal pressure. There are two cases of in-plane bending: the in-plane closing direction and the in-plane opening direction. The material is considered the effect of the large deformation, so an elastic-perfectly-plastic material is assumed in the calculations.