• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4504-4517
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• 2023

After a loss of coolant accident (LOCA) in the prestressed concrete containment vessels (PCCVs) of nuclear power plants, the coupling of temperature and pressure can significantly affect the mechanical properties of the PCCVs. However, there is no consensus on how this coupling affects the failure mechanism of PCCVs. In this paper, a simplified finite element modeling method is proposed to study the effect of temperature and pressure coupling on PCCVs. The experiment results of a 1:4 scale PCCV model tested at Sandia National Laboratory (SNL) are compared with the results obtained from the proposed modeling approach. Seven working conditions are set up by varying the internal and external temperatures to investigate the failure mechanism of the PCCV model under the coupling effect of temperature and pressure. The results of this paper demonstrate that the finite element model established by the simplified finite element method proposed in this paper is highly consistent with the experimental results. Furthermore, the stress-displacement curve of the PCCV during loading can be divided into four stages, each of which corresponds to the damage to the concrete, steel liner, steel rebar, and prestressing tendon. Finally, the failure mechanism of the PCCV is significantly affected by temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.10
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• pp.5980-5987
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• 2014

As a response to exhaust gas regulations, the electronic control system was applied to the diesel engine. The injected fuel mass and injection timing are accurately controlled using it, and the fuel efficiency and the engine output are significantly increased. In addition, the noise and the vibration of vehicles are decreased. To maintain the optimal performance of an electronic control diesel engine, it is important to control the fuel injection pressure accurately using the fuel pressure regulator. When the fuel pressure regulator is not worked normally, the failure phenomena (starting failure, staring delay, accelerated failure, engine mismatch et al.) occurred because the fuel pressure is not stabilized and controlled accurately. In this study, the effects on a fuel pressure, return fuel mass flow, and engine rotating speed according to the control rate of fuel pressure regulator were investigated to analyze the performance variation under the failure conditions of a fuel pressure regulator. As a result, when the control rate of a fuel pressure regulator decreased by 4%~6% compared to that of the standard condition, the variation of engine rotating speed and return fuel flow were increased greatly, and the abnormal condition occurred. In addition, it is possible to diagnose the failure of a fuel pressure regulator by monitoring these conditions.

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.545-553
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• 2016

The failure probabilities of the reactor pressure vessel (RPV) for low temperature over-pressurization (LTOP) and cool-down transients are calculated in this study. For the cool-down transient, a pressure-temperature limit curve is generated in accordance with Section XI, Appendix G of the American Society of Mechanical Engineers (ASME) code, from which safety margin factors are deliberately removed for the probabilistic fracture mechanics analysis. Then, sensitivity analyses are conducted to understand the effects of some input parameters. For the LTOP transient, the failure of the RPV mostly occurs during the period of the abrupt pressure rise. For the cool-down transient, the decrease of the fracture toughness with temperature and time plays a main role in RPV failure at the end of the cool-down process. As expected, the failure probability increases with increasing fluence, Cu and Ni contents, and initial reference temperature-nil ductility transition ($RT_{NDT}$). The effect of warm prestressing on the vessel failure probability for LTOP is not significant because most of the failures happen before the stress intensity factor reaches the peak value while its effect reduces the failure probability by more than one order of magnitude for the cool-down transient.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.3
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• pp.47-62
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• 1993

The laboratorv model test was carried out to investigate the behavior of pore water pressure, the critical amount of rainfall for slope failure, the pattern of failure, and the variation of seepage line at the slope with the uniform material of embankment by changing the slope angles and rainfall intensities. The results were was summarised as follows : 1.At the beginning stage of rainfall, the negative pore pressure appeared at the surface of slope and the positive pore pressure at the deep parts. But, the negative one turned into the positive one as the rainfall continued and this rapidly increased about 50 to 100 minutes before the slope failure. 2.The heavier the rainfall intensity, the shorter the time, and the milder the slope, the longer the time took to reach the failure of slope. 3.As the angle of the slope became milder, the critical amount of rainfall for slope failure became greater. 4.Maximum pore water pressure was 10 to 40g/cm$^2$ at the toe of slope and 50 to 90g/cm$^2$at the deep parts. 5.In the respect of the pattern of slope failure, surface failure of slope occurred locally at the toe of slope at the A-soil and failure of slope by surface flow occurred gradually at the top part of slope at the B-soil. 6.As the rainfall continued and the saturation zone in the embankment was formed, the seepage line went rapidly up and also the time to reach the total collapse of slope took longer at the B-soil. 7.As the position of the seepage line went up and the strength parameter accordingly down, the safety factor was 2.108 at the A-soil and 2.150 at the B-soil when the slope occured toe failure. Minimum safety factor was rapidly down to 0.831 at the A-soil and to 0.936 at the B-soil when the slope collapsed totally at the top part of slope.

• Journal of Power System Engineering
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• v.18 no.1
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• pp.76-83
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• 2014

This study was carried out an experimental and finite element analysis on the fracture behavior of straight pipes with local wall thinning under internal pressure. Local wall thinning was machined on the pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area has an eroded ratio of d/t=0.80~0.92 and an eroded length of l=25, 50 and 102 mm. Three-dimensional elastic-plastic analyses were also carried out using the finite element method, which is able to accurately simulate failure behaviors. In regards to the relation ship between pressure and eroded ratio, the criterion that can be used safely under operating pressure and design pressure were obtained from this calculation. The results of this calculation were in relatively good agreement with that of the experiment.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.97-107
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• 2019

Based on the results of Han et al. (2016), in the failure zone ahead of the tunnel face it can be obviously identified that a shear failure band occurs in the lower part and a pressure arch happens at the upper part, which was often neglected in analyzing the face stability of shield tunnel. In order to better describe the collapse failure feature of the tunnel face, a new improved failure mechanism is proposed to evaluate the face stability of shield tunnel excavated in layered soils in the framework of limit analysis by using spatial discretization technique and linear interpolation method in this study. The developed failure mechanism is composed of two parts: i) the rotational failure mechanism denoting the shear failure band and ii) a uniformly distributed force denoting the pressure arch effect. Followed by the comparison between the results of critical face pressures provided by the developed model and those by the existing works, which indicates that the new developed failure mechanism provides comparatively reasonable results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.210-213
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined internal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity fur anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy parameter, strain hardening exponent on bursting pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• Transactions of Materials Processing
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• v.13 no.7
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• pp.629-634
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• 2004

Based on plastic instability, analytical prediction of bursting failure on tube hydroforming processes under combined infernal pressure and independent axial feeding is carried out. Bursting is irrecoverable phenomenon due to local instability under excessive tensile stresses. In order to predict the bursting failure, three different classical necking criteria such as diffuse necking criterion for sheet and tube, local necking criterion for sheet are introduced. The incremental theory of plasticity for anisotropic material is adopted and then the hydroforming limit and bursting failure diagram with respect to axial feeding and hydraulic pressure are presented. In addition, the influences of the material properties such as anisotropy Parameter, strain hardening exponent and strength coefficient on bursting Pressure are investigated. As results of the above approach, the hydroforming limit in view of bursting failure is verified with experimental results.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.230-232
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• 2006

Failure behaviors of thin cylinder with corrosion are very important for the integrity of boiler and pressure vessel system. In this study, FEM with internal pressure are conducted on 1000 mm diameter (length 3000 mm and thickness, 5.9 mm) SS400 carbon steel. Failure behaviors of locally wall thinned cylinders were calculated by elasto-plastic analysis using finite element method. The elasto-plastic analysis was performed by FE code ANSYS. We simulated various types of local wall thinning that can be occurred at cylinder surface due to corrosion. Locally wall thinned shapes were machined to be different in size along the circumferential or axial direction of straight cylinder. In case of local wall thinned length 30 mm, internal pressure, when the crack initiation and the plastic collapse occur, didn't decrease dramatically even though local wall thinned depth was deep. In 400 mm, the more local wall thinned depth is deep, the more internal pressure decreased dramatically. In degraded materials, crack is easily initiation but plastic collapse was difficult.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.6
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• pp.711-729
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• 2018

This paper reports on the experimental investigations on the failure modes of ring-stiffened cylinder models subjected to external hydrostatic pressure. Nine models were welded from general structural steel. The shells were initially formed by cold-rolling, and flat-bar ring frames were welded to the shell. The hydrostatic pressure tests were conducted by using water as the medium in pressure chambers. The details of the preparation and main test were briefly explained. The investigation identified the consequence of the structural failure modes, including: shell yielding, local shell buckling between ring stiffeners, overall buckling of the shell together with the stiffeners, and interactive buckling mode combining local and overall buckling. In addition, the ultimate strengths were predicted by using existing design codes. Non-linear numerical computations were also conducted by employing the actual imperfection coordinates. Finally, accuracy and reliability of the predictions of design formulae and numerical were substantiated with the test results.