• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.173-181
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• 2006

Many isolated bridges are designed and constructed after the introduction of the seismic design. However those bridges designed in engineering fields have unnecessarily high serviceability limit and brittle failure mechanism, which do not satisfy the seismic design concept. Such design results are due to the excessive substructure stiffness of the conventional design method as well as the misunderstanding of the seismic design method. In this study an isolated bridge designed with the conventional design method is selected and the same bridge with steel bearings is modelled for the comparative seismic design. From the comparison, the seismic design procedures satisfying the required performance levels are provided for the two bridges. It is confirmed that the isolated bridge requires more complicated design procedure with trial and error methods and reanalyses but provides higher serviceability limit compared to the bridge with steel bearings. However, because the required serviceability limit can also be obtained by adjusting substructure stiffness, it is a resonable seismic design process that an isolated bridge is to be considered as an alternative design when the ductile failure mechanism is not obtained with a bridge with steel bearings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.529-536
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• 2008

The failure behavior of structures is changed under different loading rates, which might arise from the rate dependency of materials. This phenomenon has been focused in the engineering fields. However, the failure mechanism is not fully understood yet, so that it is hard to be implemented in numerical simulations. In this study, the numerical experiments to a brittle material are simulated by the Molecular Dynamics (MD) for understanding the rate dependent failure behavior. The material specimen with a notch is modeled for the compact tension test simulation. Lennard-Jones potential is used to describe the properties of a brittle material. Several dynamic failure features under 6 different loading rates are achieved from the numerical experiments, where remarkable characteristics such as crack roughness, crack recession/arrest, and crack branching are observed during the crack propagation. These observations are interpreted by the energy inflow-consumption rates. This study will provides insight about the dynamic failure mechanism under different loading rates. In addition, the applicability of the MD to the macroscopic mechanics is estimated by simulating the previous experimental research.

• Tunnel and Underground Space
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• v.18 no.6
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• pp.457-464
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• 2008

Dynamic fracture mechanism of rock is important to improve rapid excavation method and develop precise damage assesment of rock mass in the vicinity of an excavation. In order to investigate dynamic fracture characteristics and dynamic damage mechanism of brittle materials, this study employed pulse shape-controlled Split Hopkinson Pressure Bar (SHPB) system. The P- and S-wave velocities of the tested samples were measured before and after tests to examine damage of the samples. The decay ratios of the Ultrasonic wave velocities increased with impart velocities and the samples which have lower strength showed higher permanent strain significantly.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.4
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• pp.85-90
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• 2011

With regard to reliability of solder joint, the significant failures include open defects that occurs from alignment problem, Head in Pillow by PCB's warpage, the crack of solder by CTE mismatch, and the crack of IMC layer by mechanical impact. Especially as PCB down-sizing and surface finish is under progress, brittle failure of IMC layer between solder bump and PCB pad becomes a big issue. Therefore, it requires enhancing the level of difficulty in the existing assessment method and improving the measurement through the study on the mechanism of IMC formation, growth and brittle failure. Under this circumstance, this study is intended to suggest the direction of research for improving the reliability on the crack such as improvement of IMC brittle fracture.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.73-76
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• 2008

According to the survey of earthquake disaster, low-rise reinforced concrete building larger by the extent of damage and because of the underlying distribution of reinforced concrete structures more, it is very likely to be disasters. The purpose of this study is to discuss how strength and stiffness of each system in low-rise reinforced concrete buildings consisted of extremely brittle, shear and flexural failure lateral-load resisting systems have influence on seismic capacities of the overall system. Generally, if shear failure members including extremely brittle failure members are failed during an earthquake, the lateral-load resisting seismic capacities of RC buildings are lower rapidly, and if the seismic capacities of shear failure members were higher than that of flexural failure members, failures of shear failure members have influence on failures of the overall system. The result of this paper will provide pseudo-dynamic test of carried out to estimate the possibility of proposals.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.1013-1028
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• 2017

This paper presents key findings obtained from the numerical experiment investigating into the use of the cylindrical cavity for rock splitting operations. The stress and strain path analyses were carried out in order to provide a better insight into the crack formation. The principal stress analysis carried out along the crack line using the results obtained from these numerical analyses allowed the failure of the brittle material and the crack propagation to be investigated. This paper also suggested possible reasons for the change in crack direction observed during the rock splitting operations using the results obtained.

• Composites Research
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• v.16 no.2
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• pp.62-67
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• 2003

Interfacial properties and damage sensing for the carbon fiber/epoxy-amine terminated (AT)-polyetherimide (PEI) composite were performed using microdroplet test and electrical resistance measurements. As AT-PEI content increased, the fracture toughness of epoxy-AT-PEI matrix increased, and interfacial shear strength (IFSS) increased due to the improved fracture toughness by energy absorption mechanisms of AT-PEI phase. The microdroplet in the carbon fiber/neat epoxy composite showed brittle microfailure mode. At 15 phr AT-PEI content ductile microfailure mode appeared because of improved fracture toughness. After curing, the change in electrical resistance $\Delta\textrm{R}$) with increasing AT-PEI content increased gradually because of thermal shrinkage. Under cyclic stress, in the neat epoxy case the reaching time until same stress was faster and their slope was higher than those of 15 phr AT-PEI. The result obtained from electrical resistance measurements under curing process and reversible stress/strain was correspondence well with matrix toughness properties.

• Journal of the Korean Society for Railway
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• v.12 no.4
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• pp.590-596
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• 2009

In this study, the failure modes and energy absorption characteristics of four different kinds of circular tubes made of carbon, glass, Kevlar and carbon-Kevlar hybrid fibres composites with epoxy resin have been evaluated. To achieve these goals, compressive tests were conducted for the tubes under 10mm/min loading speed. Based on the test results, the carbon/epoxy tube showed the best energy absorption capability, while carbon-Kevlar/epoxy tubes were worst. In the failure mode during crushing, both of the carbon/epoxy tubes and the glass/epoxy tubes were crushed by brittle fracturing mode. The Kevlar/epoxy tubes were collapsed by local buckling mode like steel, while the carbon-Kevlar hybrid tubes were collapsed by mixed mode of local buckling and lamina bending.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.3-10
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• 2010

This study evaluates the seismic performance of reinforced concrete (RC) flat plate structures relation to the gravity shear ratio. For this purpose, 3 and 7 story framed buildings were designed for gravity loads only. Subsequently, a nonlinear static pushover analysis and a nonlinear time history analysis for the prototype buildings were carried out. In the nonlinear analysis, newly propose analytical slab-column joint model was utilized to capture punching shear failure and fracture mechanism in the analysis. The analytical results showed that seismic performance of RC flat plate frame is strongly influenced by the gravity shear ratio. In particularly, in the RC flat plate frame with a large gravity shear ratio the lateral strength and maximum drift capacity decreased significantly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.5 s.236
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• pp.689-697
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• 2005

This paper presents the reliability estimation of door hinge for home appliances, which consists of bushing and shaft. The predominant failure mechanism of bushing made of polyoxymethylene(POM) is brittle fracture due to decrease of strength caused by voids existing, and that of shaft made of acrylonitrile-butadiene-styrene(ABS) is creep due to plastic deformation caused by excessive temperature and lowering of glass transition temperature by absorbed moisture. Since the brittle fracture of bushing is overstress failure mechanism, the load-strength interference model is used to estimate the failure rate of it along with failure analysis. By the way, the creep of shaft is wearout failure mechanism, and an accelerated life test is then planned and implemented to estimate its lifetime. Through the technical review about failure mechanism, temperature and humidity are selected as accelerating variables. Assuming Weibull lifetime distribution and Eyring model, the life-stress relationship and acceleration factor, $B_{10}$ life and its lower bound with $90\%$ confidence at worst case use condition are estimated by analyzing the accelerated life test data.