• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.69-73
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• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact force is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. The distribution of delamination along the thickness direction of curved laminates are also different from that of flat plates. Delamination was distributed rather even]y at each interface along the thickness direction of curved laminates. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.207-212
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• 2020

To decide a separation distance of the redundant vital equipment in a naval ship, the damage radius due to an aerial explosion should be estimated. In this research, a simplified formula for the damage radius has been developed by using existing empirical formulae for reflected shock pressure and shock lethality value of equipment. As a numerical example, the damage radius for a typical pump aboard a naval ship has been calculated by the developed formula and compared with the results calculated by Measure of Total Integrated Ship Survivability (MOTISS) which is one of survivability analysis codes verified, validated and accredited by the US Navy. Also, comparison with the results calculated by existing other simplified formulae has been made.

• Geomechanics and Engineering
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• v.21 no.3
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• pp.289-300
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• 2020

Estimating the damage induced by an explosion around a blast hole has always been a challenging issue in geotechnical engineering. It is difficult to determine an exact dimension for damage zone since many parameters are involved in the formation of failures, and there are some uncertainties lying in these parameters. Thus, the present study adopted a probabilistic approach towards this problem. First, a reliability model of the problem was established and the failure probability of induced damage was calculated. Then, the corresponding exceedance risk curve was developed indicating the relation between the failure probability and the cracked zone radius. The obtained risk curve indicated that the failure probability drops dramatically by increasing the cracked zone radius so that the probability of exceedance for any crack length greater than 4.5 m is less than 5%. Moreover, the effect of each parameter involved in the probability of failure, including blast hole radius, explosive density, detonation velocity, and tensile strength of the rock, was evaluated by using a sensitivity analysis. Finally, the impact of the decoupling ratio on the reduction of failures was investigated and the location of its maximum influence was demonstrated around the blast point.

• Composites Research
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• v.14 no.2
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• pp.22-32
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• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates and with the results by nonlinear finite-element analysis. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact farce is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. Delamination was distributed rather evenly at each interface along the thickness direction of curved laminates on the contrary to the case of flat laminates, where delamination is typically concentrated at the interfaces away from the impact point. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.92-97
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• 2000

Low-velocity impact damage of a thick pressure vessel by composite materials was studied using the modified Herzian contact radius theory. Impactors of various masses and various tup shapes were dropped freely in the range of 20m to 200mm height. With acceleration gage and strain gage installed on the impactor, impact force and acceleration and Contact radius were measured. After a test, the samples were radiographed to scan the state of damage. Compared with hemispherical tup of 12.7mm diameter, the contact radius of hemispherical tup of 25.4mm diameter was bigger. And the experimental data and the theoretical data was different due to the mechanical properties difference. The acceleration value was changed linearly according to the height.

• Journal of Korean Association for Spatial Structures
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• v.16 no.3
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• pp.67-78
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• 2016

Determining of the shape in the process of design for natural draught cooling tower is very important, because the shape of hyperbolic shell is respond sensitively to dynamic behavior of the whole cooling tower against wind load. In engineering practice, the geometric parameters have been determining based on the natural frequency. This study analyses influence of the tower shell geometric parameters on the structural behavior. For three representative models were selected, they were analyzed based on evaluation of damage by means of nonlinear FE-method. As a result, a hyperbolic rotational shell with the small radius overall was the lowest damage index induced by sufficient capacity of the stress redistribution and thus a wind-insensitive structure.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2008.04a
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• pp.154-156
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• 2008

• Structural Monitoring and Maintenance
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• v.7 no.4
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• pp.367-392
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• 2020

The specific characteristics of near-field earthquake records can lead to different dynamic responses of bridges compared to far-field records. However, the effect of near-field strong ground motion has often been neglected in the seismic performance assessment of the bridges. Furthermore, damage to horizontally curved multi-frame RC box-girder bridges in the past earthquakes has intensified the potential of seismic vulnerability of these structures due to their distinctive dynamic behavior. Based on the nonlinear time history analyses in OpenSEES, this article, assesses the effects of near-field versus far-field earthquakes on the seismic performance of horizontally curved multi-frame RC box-girder bridges by accounting the vertical component of the earthquake records. Analytical seismic fragility curves have been derived thru considering uncertainties in the earthquake records, material and geometric properties of bridges. The findings indicate that near-field effects reasonably increase the seismic vulnerability in this bridge sub-class. The results pave the way for future regional risk assessments regarding the importance of either including or excluding near-field effects on the seismic performance of horizontally curved bridges.

• Structural Engineering and Mechanics
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• v.68 no.6
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• pp.735-745
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• 2018

The Big Bang-Big Crunch (BB-BC) algorithm is an effective global optimization technique of swarm intelligence with drawbacks of being easily trapped in local optimal results and of converging slowly. To overcome these shortages, an improved BB-BC algorithm (IBB-BC) is proposed in this paper with taking some measures, such as altering the reduced form of exploding radius and generating multiple mass centers. The accuracy and efficiency of IBB-BC is examined by different types of benchmark test functions. The IBB-BC is utilized for damage detection of a simply supported beam and the European Space Agency structure with an objective function established by structural frequency and modal data. Two damage scenarios are considered: damage only existed in stiffness and damage existed in both stiffness and mass. IBB-BC is also validated by an existing experimental study. Results demonstrated that IBB-BC is not trapped into local optimal results and is able to detect structural damages precisely even under measurement noise.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.426-431
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• 2007

Hydroformability and fracture criteria of FE analysis based on ductile fracture were investigated in warm hydroforming of A16061 tube. To evaluate the hydroformability, uni-axial tensile test and bulge test were performed at room temperature and $200^{\circ}C$. The measured flow stresses were used as input parameters for FE analysis. The damage values were calculated by FE analysis based on ductile fracture criteria at maximum radius of free bulged tubes. Damage values were compared of hexagonal shaped hydroformed parts. As a result, the formability by critical damage value for extruded tube is lower than that of full annealed tube up to 0.5.