• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.935-946
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• 2000

Elastic-plastic stress analysis has been performed to evaluate the fatigue life of an autofrettaged pressure vessel containing cross-bores subjected to pulsating internal pressure of 200 MPa. Finite element analyses were used to calculate the residual and operating stress distributions of the pressure vessel due to the autofrettage process and pulsating internal pressure, respectively. Theoretical stress concentration factors of 3.06, 2.58, and 2.64 were obtained at the cross-bore of the pressure vessel due to internal pressure, 50%, and 100% autofrettage loadings, respectively. Local stresses and local strains determined from the elastic-plastic finite element analysis were employed to calculate the failure location and fatigue life of the pressure vessel with radial cross-bores, incorporating the low-cycle fatigue properties of the pressure vessel steel and fatigue damage parameters. Increase in the amount of overstrain by autofrettage process moved the crack initiation location from the inner radius toward a mid-wall, and extended the crack initiation life. Predicted fatigue life of the fully autofrettaged pressure vessel with cross-bores increased about 50%, compared to the unautofrettaged pressure vessel. At the autofrettage level higher than 50%, the failure location and fatigue life of the pressure vessel were not significantly influenced by the autofrettage level.

• Nuclear Engineering and Technology
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• v.51 no.7
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• pp.1805-1815
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• 2019

While nickel-based alloys have been widely used for power plants due to corrosion resistance and good mechanical properties, during the last couple of decades, failures of nuclear components increased gradually. One of main degradation mechanisms was primary water stress corrosion cracking at dissimilar metal welds of piping and reactor head penetrations. In this context, precise estimation of welding effects became an important issue for ensuring reliability of them. The present study deals with a series of finite element analyses and crack growth rate evaluation of Alloys 690/152. Firstly, variation of residual stresses and equivalent plastic strains was simulated taking into account welding of a cylindrical block. Subsequently, extraction and pre-cracking of compact tension (CT) specimens were considered from different locations of the block. Finally, crack growth curves of the alloys and heat affected zone were developed based on analyses results combined with experimental data in references. Characteristics of crack growth behaviors were also discussed in relation to mechanical and fracture parameters.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.68-76
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• 1997

The welding-induced initial imperfections such as residual stresses and initial strains in plated structures of ships and offshore structures can be effectively evaluated by the thermal elasto-plastic analysis method proposed in this paper. In the analysis of heat conduction of plate structures, both the analytical method and the numerical method are used. For the thermal elasto-plastic analysis of plates, the finite element analysis is performed, based on the initial strain method. In the plastic domain during incremental process, the 2nd order terms of stress increments and yield stress increments were considered, so that time increment could be controlled for more stable solution. To measure temperature distribution and angular distortion of plates during welding, bead-on-plate experiment are perform with various heat input and plate thickness. Measured data show good agreement with the calculated results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.1-13
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• 1982

Transition process of plastic region. displacements, stresses and strains ahead the flaw tips were analysed by the finite element method on the steel plate with the circular hole and the one with the elliptical hole under completely alternating load (repetition of tensile loading, unloading and compressive loading). As the results, the followings were obtained. Transition process of elastic failure (yielding) region was estimated. From this the tendency was confirmed that the fracture would be initiated from ahead the flaw tip, and propagated along the $45^{\circ}$ direction. The fundamental data available in estimating the stress intensity factor that was considered as the core in analysing the fracture mechanism of steel plates were obtained. It was indicated that when unloading after tension the effect of compressive loading, and even the compressive reyield, was occured ahead the flaw tip. Similarly it was indicated that when unloading after compression the effect of tensile loading, and even the tensile reyield, was occured ahead the flaw tip. It was considered that these phenomena were occured because the unloading effect was constrained by the residual strains when unloading. It was considered that the fatigue phenomenon was occured ahead, the flaw tip by repetition of tensile yield, the above compressive reyield, compressive yeild and the above tensile reyield. In addition, the tendency was confirmed that the fracture ahead the flaw tip was occured as the flaw was changed from the circular hole to the elliptical hole and became to be the crack lastly.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.5-16
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• 2002

The pullout behavior of large-diameter steel pipe piles(diameter = 2,500mm, length = 38~40m), which were designed as compression piles but used as reaction piles during a static compression load test on a pile(diameter = 1,000m, length = 40m), was investigated. The steel pipe piles were driven by 20m into a marine deposit and weathered soil layer and then socketed by 10m into underlying weathered and soft rock layers. The sockets and pipe were filled with reinforced concrete. The steel pipe and concrete in the steel pipe zone and concrete and rebars in the socketed zone were fully instrumented to measure strains in each zone. The pullout deformations of the reaction pile heads were measured by LVDTs. Over the course of the study, a maximum uplift deformation of 7mm was measured in the heads of reaction piles when loaded to 10MN, and 1mm of residual uplift deflection was measured. In the reaction piles, about 83% and about 12% of the applied pullout loads were transferred in the weathered rock layer and in the soft rock layer, respectively. Also, at an uplift force of 10MN, shear stresses due to the uplift in the weathered rock layer md soft rock layer were developed as much as 125.3kPa and 61.8kPa, respectively. Thus, the weathered rock layer should be utilized as resisting layer in which frictional farce could be mobilized greatly.