Papers by Author: Weon Keun Song

Abstract: It is known that fracture characteristics are changed due to the geometric configuration. Also, it is known that toughness data obtained from the standard specimen test are conservative to predict fracture behavior of the real piping. Thus fracture behavior by tests of pipes would to be applied to the integrity evaluation for the piping system. However, fracture test with real pipe is not only difficult to perform but also very expensive, and requires lots of experience. So an estimation method of pipe’s fracture behavior is necessary to solve this problem. The objective of this thesis is to propose a method to estimate the fracture behavior of a pipe from the result of the standard specimen fracture test. For this, fracture tests for standard specimens and pipes are conducted. The resultant load - load-line displacement record of the standard specimen was transformed to that of a pipe by load separation method. To begin with, the load versus load-line displacement curve of a standard specimen extracted from a pipe is normalized by a geometry function of the CT specimen. Then this normalized curve was converted to pipe’s load versus displacement curve by a geometry function of pipe. To verify the constraint factor and the geometric function of pipe, finite element analyses were performed. To demonstrate the proposed method, experimental results of pipes are compared with predicted results. Calculated results from CT specimens are similar to experimental results of pipes. Therefore the transformability from a CT specimen to a pipe by load separation method is proved. Consequently the applicability of the proposed method was proved.

Abstract: The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many researches have reported that test results of standard specimens are very different from those of real structures or components. One reason for this difference is the constraint effects according to the geometrical difference. Therefore, to calculate more accurate fatigue life, the constraint effect must be considered by comparing test results of standard specimens with those of real structures or components. Another reason for this difference is the surface condition. All surfaces of a standard specimen are polished to obtain similar conditions in a fatigue test. However, in a piping system, surface conditions of components are different from each other and very different from that of a standard specimen. Because fatigue life is effected by a surface condition, to evaluate the fatigue life of a piping system, fatigue tests must be conducted with a specimen extracted from a pipe with the same surface condition. The objective of this paper is to evaluate the fatigue characteristic of a real waterworks pipe by conducting fatigue tests with standard specimens and non-standard specimens of base metal and weld metal. Standard fatigue specimens and non-standard specimens were extracted from a steel pipe used in waterworks. Also, fatigue tests of pipes used in water service were carried out and then compared with those of standard specimens and non-standard specimens. From these results the relation between the S-N diagram of a specimen and that of a pipe specimen was evaluated.

Abstract: This paper examined the fundamental problem of an interaction between a soil medium that experiences frost heave in a closed system and an underground pipeline. The coupled thermal transfer and structural analysis, considering the material nonlinearity of freezing soil, for an underground pipeline subjected to the low cyclic load was focused on the development of computational scheme by introducing the effective heat capacity concept and the effective thermal expansion coefficient into the study. The effective heat capacity model in the thermal transfer analysis took into consideration the phase-change effect in the frozen fringe of a soil medium. The comparative analyses between the theory and the actual performances were valuable in establishing a level of confidence in the application of introduced theory to the field. The numerical results in the paper illustrated the influence for the frost heave of a soil medium on the temperature-dependent development of stress fields on metallic underground pipe walls in South Korea.

Abstract: This study performs dynamic analysis of underground structures on multi-layered half planes in frequency domain by using the coupled finite and boundary element method. The near field including underground structures is modeled with onventional finite elements, while the far field is modeled with boundary elements which satisfies radiation conditions. In evaluating the dynamic fundamental solutions, semi-analytical solutions due to line loads are employed. Therefore, the range of wavenumber integration can be reduced significantly. These solutions satisfy the reflection and transmission conditions of waves at each layer interface, so that the multi-region problem can be analyzed. Numerical examples are given to demonstrate the accuracy and efficiency of the proposed method.