• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.6
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• pp.1015-1022
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• 2001

The objective of this paper is to develop an expert system called NPIES for nuclear piping integrity. This paper describes the structure and the development strategy of the NPIES system. The NPIES system consists of 3 part; the data input part, the analysis part and the output part. The data input part consists of the material properties database module and the suer interface module. The analysis part consists of the LEFM, CDFD, J/T, limit load modules and the 12 analysis routines for different cracks and loading conditions are provided respectively. Analysis results are presented to screen, printer and text file in the output part. Several case studies on circumferentially cracked piping were performed to evaluate the accuracy and the usefulness of the code. Maximum piping loads predicted by the NPIES system agreed well with those by the 3-dimensional finite element analysis. In addition, even if the material properties were not fully given, the NPIES system provided reasonable evaluation results with the predicted material properties inferred from the material properties database module.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.1-6
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• 2013

Three Surface cracks are among the more common flaws in aircraft and pressure vessel components. Accurate stress intensity analyses and crack growth rate data of surface-cracked components are needed for reliable prediction of their fatigue life and fracture strengths. Three Dimensional finite element method (FEM) was used to obtain the stress intensity factor for surface cracks existing in structures. A geometry model, i.e. a solid containing one or several 3D cracks is defined. Nodes are generated by bucket method, and quadratic tetrahedral solid elements are generated by the Delaunay triangulation techniques. To examine accuracy and efficiency of the present system, the stress intensity factor for a semi-elliptical surface crack in cylindrical structures subjected to pressure is calculated. Analysis results by present system showed good agreement with those by ASME equation and Raju-Newman's equation.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.3
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• pp.96-102
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• 2005

Acoustic Emission(AE) technique has been applied to not only material characterization evaluation but also on-line monitoring of the structural integrity. The AE source location technique is very important to identify the source, such as crack, leak detection. Since the AE waveforms obtained from sensors are very difficult to distinguish the defect signals, therefore, it is necessary to consider the signal analysis of the transient wave-form. In this study, we have divided the region of interest into a set finite elements, and calculated the arrival time differences between sensors by using the velocities at every degree from 0 to 90. A new technique for the source location of acoustic emission in fiberboard plates has been studied by introducing Wavelet Transform(WT) do-noising technique. WT is a powerful tool for processing transient signals with temporally varying spectra. If the WT de-noising was employed, we could successfully filter out the errors of source location in fiberboard plates by arrival time difference method. The accuracy of source location appeared to be significantly improved.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1187-1194
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• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.4
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• pp.98-104
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• 2006

In this paper, for the purpose of investigation the acoustic emission(AE) behaviors during resistance spot welding process and tension test of spec steels. As the results present the resistance spot welding method that can get suitable welding qualities or structural integrity estimating method. The resistance spot welding process consists of several stages: set-down of the electrodes; squeeze; current flow; forging; hold time; and lift-off. Various types of AE signals are produced during each of these stages. For tensile-shear test and cross tensile test in resistance spot welded specimens, fracture pa 야 ems are produced: tear fracture; shear fracture; and plug fracture. Tensile-shear specimens strength appeared higher than cross tensile specimens one. In case of tensile-shear specimen happened tear fracture that crack happens in most lower plate. Also, in case of cross tensile specimens, upper plate and lower plate are detached perfect fracture was exposed increases a little as acting force is lower than ordinary welding condition. Therefore, the structure which is combined by resistance spot welding confirmed that welding design must attain so that shear stress may can interact mainly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.1 s.256
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• pp.70-76
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• 2007

Elastic-plastic fracture mechanics is popularly used for integrity evaluation of major components, however, it is not easy to extract standard specimens from operating facility. This paper examines how ductile fracture toughness is characterized by a small punch testing technique in conjunction with finite element analyses incorporating a damage model. At first, micro-mechanical parameters constituting Rousselier model are calibrated for typical nuclear materials using both estimated and experimental load-displacement (P-$\delta$) curves of miniaturized specimens. Then, fracture resistance (J-R) curves of relatively larger standard CT specimens are predicted by finite element analyses employing the calibrated parameters and compared with corresponding experimental ones. It was proven that estimated results by the proposed method using small punch specimen is promising and might be used as a useful tool for ductile crack growth evaluation.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.5
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• pp.233-241
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• 2020

This paper is to investigate the retrofitting effect for a non-seismic reinforced concrete frame strengthened by perimeter steel moment frames with indirect integrity, which ameliorates the problems of the direct integrity method. To achieve this, first, full-scale tests were conducted to address the structural behavior of a two-story non-seismic reinforced concrete frame and a strengthened frame. The non-seismic frame showed a maximum strength of 185 kN because the flexural-shear failure at the bottom end of columns on the first floor was governed, and shear cracks were concentrated at the beam-column joints on the second floor. The strengthened frame possessed a maximum strength of 338 kN, which is more than 1.8 times that of the non-seismic specimen. A considerable decrease in the quantity of cracks for the strengthened frame was observed compared with the non-seismic frame, while there was the obvious appearance of the failure pattern due to the shear crack. The lateral-resisting capacity for the non-seismic bare frame and the strengthened frame may be determined per the specified shear strength of the reinforced columns in accordance with the distance to a critical section. The effective depth of the column may be referred to as the longitudinal length from the border between the column and the foundation. The lateral-resisting capacity for the non-seismic bare frame and the strengthened frame may be reasonably determined per the specified shear strength of the reinforced columns in accordance with the distance to a critical section. The effective depth of the column may be referred to as the longitudinal length from the border between the column and the foundation. The proposed method had an error of about 2.2% for the non-seismic details and about 4.4% for the strengthened frame based on the closed results versus the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.5
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• pp.453-460
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• 2015

Since the Fukushima nuclear accident, several researchers are extensively studying the effect of torsion on the piping systems In nuclear power plants. Piping installations in power plants with a circumferential crack can be operated under combined loading conditions such as bending and torsion. ASME Code provides flaw evaluations for fully plastic fractures using limit load criteria for the structural integrity of the cracked pipes. According to the recent version of Code, combined loadings are provided only for the membrane and bending. Even though actual operating conditions have torsion loading, the methodology for evaluating torsion load is not established. This paper provides the results of limit load analyses by using finite element models for circumferentially cracked pipes under pure bending, pure torsion, and combined bending and torsion with tension. Theoretical limit load solutions based on net-section fully plastic criteria are suggested and verified with the results of finite element analyses.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.75-82
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• 2019

Slab panels are very important to develop asphalt concrete (AC) track for minimizing the roadbed stress due to the train load and reducing the plastic deformation of infrared-sensitive AC. In this study, the slab panel for AC track was developed through the shape design and the indoor performance test and its structural integrity has been investigated through the finite element analysis under the flexural tensile stress and the design moment according to various static load combination by KRL-2012 standard train load model and KR-C code. In order to verify the suitability of the slab panel for AC track, static bending strength test and dynamic bending strength test were performed according to EN 13230-2. Results show that the slab panel for AC track satisfies all the performance standards required by European standards such as crack loads and crack extension.

• Structural Engineering and Mechanics
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• v.87 no.1
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• pp.47-56
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• 2023

Any pre-existed delamination defect present during manufacturing or induce during service loading conditions in the wingskin adherend invariably shows a greater loss of structural integrity of the spar wingskin joint (SWJ). In the present study, inter-laminar delamination propagation at the critical location of the SWJ has been carried out using contact and multi-point constraint finite elements available with commercial FE software (ANSYS APDL). Strain energy release rates (SERR) based on virtual crack closure technique have been computed for evaluation of the opening (Mode-I), sliding (Mode-II) and cross sliding (Mode-III) modes of delamination by sequential release of multi point constraint elements. The variations of different modes of SERR are observed to be significant by considering varied delamination lengths, material properties of adherends and radius of curvature of the SWJ panel. The SERR rates are seen to be much different at the two pre-embedded delamination ends. This shows dissimilar delamination propagation rates. The maximum is seen to occur in the delamination front in the unstiffened region of the wingskin. The curvature geometry and material anisotropy of SWJ adherends significantly influences the SERR values. Increase in the SERR values are observed with decrease in the radius of curvature of wingskin panel, keeping its width unchanged. SWJs made with flat FRP composite adherends have superior resistance to delamination damage propagation than curved composite laminated SWJ panels. SWJ made with Boron/Epoxy (B/E) material shows greater resistance to the delamination propagation.