• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.981-988
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• 2023

A seismic event caused an accident at the Fukushima Nuclear Power Plant, which further resulted in simultaneous accidents at several units. Consequently, this incident has aroused great interest in the safety of nuclear power plants worldwide. A reasonable safety evaluation of such an external event should appropriately consider the correlation between SSCs (structures, systems, and components) and the probability of failure. However, a probabilistic safety assessment in current nuclear industries is performed conservatively, assuming that the failure correlation between SSCs is independent or completely dependent. This is an extreme assumption; a reasonable risk can be calculated, or risk-based decision-making can be conducted only when the appropriate failure correlation between SSCs is considered. Thus, this study analyzed the effect of the failure correlation of SSCs on the safety of the system to realize rational safety assessment and decision-making. Consequently, the impact on the system differs according to the size of the failure probability of the SSCs and the AND and OR conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.585-592
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• 2017

Most sewer lines buried in the city are likely to be collapsed due to serious aging. Also, due to the high concentration of development and high population density and traffic, the collapse of the sewer will cause enormous social and economic damage. Therefore, proactive maintenance is required to prevent accidents caused by deteriorated sewer pipe. In order to utilize limited budget effectively, risk-based prioritization methods should be proposed that simultaneously consider the consequence of failure and the probability of failure. In this study, the method of risk-based prioritization of sewer was examined by reviewing various cases of overseas studies and applied to the urban sub-catchment. First, the impact factors that can be secured through the sewer GIS DB in Seoul were derived, and the weight, sub-criteria, and impact score of each impact factor were determined and the consequence of failure was calculated by weight sum method. In addition, the probability of failure was calculated by dividing the service life by the estimated useful life, and the consequence of failure and the probability of failure were classified into five grades by the Jenks natural breaks classification method. The prioritization method was applied to sub-catchment in the Seoul to derive a risk matrix and a risk grade. As a result, 26% of all subjects were selected as the inspection priority subjects with 4-5 risk grade. Therefore, using the risk-based CCTV prioritization methodology, it will be possible to systematically determine the objects that need investigation first.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.4
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• pp.281-286
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• 2012

Single frame structures with notches were fractured by applying drop impact loadings at room temperature and low temperature. Johnson-Cook shear failure model has been employed to simulate the fractured single frame structures. Through several numerical analyses, material constants for Johnson-Cook shear failure model have been found producing the cracks resulted from experiments. Fracture strain-stress triaxiality curves at both room temperature and low temperature are presented based on the extracted material constants. It is expected that the fracture strain-stress triaxiality curves can offer objective fracture criteria for the assessment of structural fractures of polar class vessel structures fabricated from DH36 steels. The fracture experiments of single frame structures revealed that the structure on low temperature condition fractures at much lower strain than that on room temperature condition despite the same stress states at both temperatures. In conclusion, the material properties on low temperature condition are essential to estimate the fracture characteristics of steel structures operated in the Northern Sea Route.

• Computers and Concrete
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• v.14 no.6
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• pp.675-694
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• 2014

Annular and solid concrete specimens with different aspect ratios and static unconfined compressive strengths were studied for impact loading using SHPB test setup. Numerical simulations in LSDYNA were also carried out and results were validated. The stress-strain curves obtained under dynamic loading were also compared with static compressive tests. The mode of failure of concrete specimen was a typical ductile failure at high strain rates. In general, the dynamic increase factor (DIF) of thin solid specimens was higher than thick samples. In the numerical study, the variation of axial, hydrostatic and radial stresses for solid and annular samples was studied. The core phenomenon due to confinement was observed for solid samples wherein the applied loads were primarily borne by the innermost concrete zone rather than the outer peripheral zone. In the annular samples, especially with large diameter inside hole, the distribution of stresses was relatively uniform along the radial distance. Qualitatively, only a small change in the distribution of stresses for annular samples with different internal diameters studied was observed.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.3
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• pp.221-226
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• 2010

The failure of a Kevlar29/Phenolic composite plate under high-velocity impact from an fragment simulation projectile was investigated using the nonlinear explicit finite element code, LS-DYNA. The composite laminate and the impactor were idealized by solid elements, and the interface between the laminas was modeled as a tiebreak type in LS-DYNA. The interaction between the impactor and laminate was simulated using a surface-to-surface eroding contact algorithm. When the stress level meets the given failure criteria, the layer in the element is eroded. Numerical results were verified through existing test results and showed good agreement.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.1-8
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• 2014

In this study, the numerical simulation using AUTODYN-3D program was investigated angle trajectory prediction for inclined impacts of projectiles. The penetration and perforation of polycarbonate plate by 7.62 mm projectile was investigated numerically. The characteristic structure of the projectile's trajectory in the polycabonate plates was studied. Two combined failure criteria were used in the target plate, and the target plate was modeled with the properties of polycarbonate for simulating the ricochet phenomenon. The effect of the angle of inclination on the trajectory and kinetic energy of the projectile were studied. The dynamic deformation behaviors tests of polycabonate were compared with numerical simulation results which can be used as predictive purpose. From the simulation, the ricochet phenomenon was occurred for angles of inclination of $0^{\circ}{\leq}{\theta}{\leq}20^{\circ}$. The projectile perforated the plate for ${\theta}{\leq}30^{\circ}$, thus defining a failure envelope for numerical configuration. The numerical analyses are used to study the effect of the projectile impact velocity on the depth of penetration (DOP). It can be observed that the residual velocities were almost linear relative to penetration velocities. It means that polycarbonate has high resistance at higher velocities.

• Structural Monitoring and Maintenance
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• v.6 no.1
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• pp.19-32
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• 2019

One way to provide safe buildings and to protect tenants from the terrorist attacks that have been increasing in the world is to study the behavior of buildings members after being exposed to dynamic loads. Buildings behaviour after being exposed to attacks inspired researchers all around the world to investigate the effect of impact loads on buildings members like slabs and to deeply study the properties of High Performance Concrete. HPC is well-known in its high performance and resistance to dynamic loads when it is compared with normal weight concrete. Therefore, the aim of this paper is finding out the impact of dynamic loads on RPC slabs' flexural capacity, serviceability loads, and failure type. For that purpose and to get answers for these questions, three concrete slabs with 0.5, 1, and 2% steel fiber contents were experimentally tested. The tests results showed that the content of steel fiber plays the key role in specifying the static capacity of concrete slabs after being dynamically loaded, and increasing the content of steel fiber led to improving the static loading capacity, decreased the cracks numbers and widths at the same time, and provided a safer environment for the buildings residents.

• Composites Research
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• v.22 no.2
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• pp.18-23
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• 2009

Failure of Kevlar29/Phenolic composite plate under high velocity impact of FSP(Fragment Simulation Projectile) is investigated using a non-linear explicit finite element code, LS-DYNA. Composite laminate and impactor are idealized by solid element and interface between laminas are modeled by tied-break element in LS-DYNA. Interaction between impactor and laminate is simulated face-to-face eroding contact algorithm. When the stress level meets a failure criteria, the layer in the element is eroded. Numerical results are verified by existing test results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.506-516
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• 2007

In this paper, a study on low-velocity impact response of four different sandwich panels for the hybrid bodyshell and floor structure application of the Korean low floor bus vehicle was done. Square samples of 100mm sides were subjected low-velocity impact loading using an instrumented testing machine at six energy levels. Impact parameters like maximum force, time to maximum force, deflection at maximum force and absorbed energy were evaluated and compared for four different types of sandwich panels. The impact damage size and depth of the permanent indentation were measured by 3-Dimensional Scanner. Failure modes were studied by sectioning the specimens and observed under optical microscope. The impact test results show that sandwich panel with composite laminate facesheet could not observe damage mode of a permanent visible indentation after impact and has a good impact damage resistance in comparison with sandwich panel with metal aluminum facesheet.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.16-22
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• 2012

We performed impact test to estimate necessary explosive charge weight for cutting the cable whose diameter is 22 mm. The impact test results were analyzed by Probit method. The cutting energy was calculated 37.7 J with 99.99% probability at 99% reliability compared to the average energy of 24.9 J. The cable was cut 3 times without failure with 150 mg of Zirconium Potassium Perchlorate (ZPP), which was considered to generate 24.5 J of mechanical energy with assumption that only 10% of explosive energy converts to mechanical energy. The calculated energy from measured pressure with 150 mg ZPP was 26.1 J, which is almost same with both impact test result and expected mechanical energy. We can argue that the cable can be cut with 99.99% probability at 99% reliability by 230 mg of ZPP.