• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.309-316
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• 2015

A state-based peridynamic model is able to describe a general constitutive model from the standard continuum theory. The response of a material at a point is dependent on the deformation of all bonds connected to the point within the nonlocal horizon region. Therefore, the state-based peridynamic model permits both the volume and shear changes of the material which is promising to reproduce the complicated dynamic brittle fracture phenomena, such as crack branching, secondary cracks, cascade cracks, crack coalescence, etc. In this paper, the two-dimensional state-based peridynamic model for a linear elastic plane stress solid is employed. The damage model incorporates the energy release rate and the peridynamic energy potential. For brittle glass materials, the impact of the crack-parallel compressive stress waves on the crack branching pattern is investigated. The peridynamic solution for this problem captures the main features, observed experimentally, of dynamic crack propagation and branching. Cascade cracks under strong tensile loading and secondary cracks are also well reproduced with the state-based peridynamic simulations.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.5
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• pp.510-519
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• 2009

Ship structure is composed of the welded mixture members which are plate and stiffeners. Ship structure is also influenced by variable loadings such as wave and inertia load. There have been several fatigue damage problems on the connection between longitudinal and transverse web due to wide usage of high tensile steel and adoption of wide web space to improve shipbuilding productivity. It is impossible to estimate the fatigue lives for all connection details through refined fatigue analysis. It is necessary to use the simplified approach for the fatigue life estimation of the connection details. PLUS analysis, which is suggested by the classification society, is one of the simplified approaches and is widely adopted to get fatigue lives for the connection details along whole cargo hold area. However, ship building yards still have difficulties to get fatigue lives due to large amount of calculation and time even if this approach reduce the time and amount of calculation. This paper treats the computing system developed to reduce efforts of estimating the fatigue lives. The influence factors of mean shear stress and local dynamic pressure are easily calculated and fatigue lives for all hot spots can be estimated automatically by the developed computing system. It is possible to reduce computing time and efforts to get the fatigue lives for the connection details between longitudinals and transverse webs along the ship. This system was applied to get fatigue lives on the connection details of a VLCC and verified the availability.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.111-120
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• 2009

This paper presents a fundamental findings of the functional and structural performance of the porous asphalt concrete coated with MMA resin. To evaluate the structural performance, cantabro, wheel tracking, moisture sensitivity and indirect tensile fatigue tests are performed. The tests results show that the cantabro loss is reduced three times and fatigue resistance is significantly increased after the specimens are coated with MMA resin. However there are little changes in the rutting and moisture damage resistances before and after the coating. Air voids, permeability and BPT(British Pendulum Test) tests are conducted to study the functional performance. It is observed form the tests that the air voids and permeability are slightly decreased after the coating. However, the changes in the air voids and permeability are negligible. The skid resistance of the coated specimens is lower than reference specimens. However, the skid resistance is maintained beyond the level of the reference specimens when silica sands are chipped on top of the coated surface.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.429-438
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• 2003

The effects of fiber orientation on acoustic emission(AE) characteristics have been studied for the unidirectional and satin-weave, continuous glass-fiber reinforced plastic(UD-GFRP and SW-GFRP) tensile specimens. Reflection and transmission optical microscopy was used for investigation of the damage zone of specimens. AE signals were classified as different types by using short time fourier transform(STFT) : AE signals with high intensity and high frequency band were due to fiber fracture, while weak AE signals with low frequency band were due to matrix and interfacial cracking. The feature in the rate of hit-events having high amplitudes showed a process of fiber breakages, which expressed the characteristic fracture processes of individual fiber-reinforced plastics with different fiber orientations and with different notching directions. As a consequence, the fracture behavior of the continuous GFRP could be monitored as nondestructive evaluation(NDE) through the AE technique.

• Composites Research
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• v.18 no.4
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• pp.21-26
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• 2005

Nondestructive damage sensing and load transfer mechanisms of carbon nanotube (CNT) and nanofiber (CNF)/epoxy composites have been investigated by using electro-micromechanical technique. The electrospun PVDF nanofibers were also prepared as a piezoelectric sensor. The electro-micromechanical techniques were applied to evaluate sensing response of carbon nanocomposites by measuring electrical resistance under an uniform cyclic loading. Composites with higher volume content of CNT showed significantly higher tensile properties than neat and low volume$\%$ CNT composites. CNT composites showed humidity sensing within limited temperature range. CNT composites with smaller aspect ratio showed higher apparent modulus due to high volume content in case of shorter aspect ratio. Thermal treated electrospun PVDF nanofiber showed higher mechanical properties than the untreated case due to crystallinity increase, whereas load sensing decreased in heat treated case. Electrospun PVDF nanofiber web also showed sensing effect on humidity and temperature as well as stress transferring. Nanocomposites and electrospun PVDF nanofiber web can be applicable for sensing application.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.149-154
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• 2012

The size and distribution of welding residual stress and welding deformation in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, non-destructive technique using laser electronic speckle pattern interferometry, plate of welding specimen according to the external load on the entire behavior of residual stress are presented measurement techniques. Once, welding specimen force tensile loading, using electronic speckle pattern interferometry is measured. welding specimen of base metal and weld zone measure strain from measured result, this using measure elastic modulus. In this study, electronic speckle pattern interferometry use weld zone and base metal parts of the strain differences using were presented in residual stress calculated value, This residual stress value were calculated by numerical calculation. Consequently, weld zone of modulus high approximately 3.7 fold beside base metal and this measured approximately 8.46 MPa.

• Tunnel and Underground Space
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• v.14 no.6 s.53
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• pp.411-422
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• 2004

Sinkhole subsidence occurs over abandoned mine workings and can be detrimental to human lives, damage to properties and other surface structures. In this study, simulation of sinkhole development process is performed using special finite element procedure. Especially, creation of mine voids due to roof falls and generation of goaf from broken rocks are simulated using active-passive-active finite elements. An active or solid element can be made passive or void once the tensile failure criterion is satisfied in the specified sinkhole formation zone. Upon completion of sinkhole development process, these passive elements in again be made active to simulate goal region. Several finite element models are analyzed to evaluate the relationships between sinkhole formation with width of gallery. depth of mine, roof condition and bulking factor of roof rocks. This study demonstrates that the concept of passive elements in numerical analysis can be used effectively for analyzing sinkhole formation or roof fall phenomenon in general.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.5
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• pp.417-425
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• 2007

The ferritic 9Cr-1Mo-V-Nb heat-resisting steel was experimentally studied in order to characterize its microstructural evolution during creep-fatigue by coercivity measurement. The creep-fatigue test was conducted at $550\;^{\circ}C$ with the tensile holding time of 60s and 600s, respectively. The coercivity decreased until the failure and the hardness monotonously decreased for the whole fatigue life. As the life fraction of creep-fatigue increased, the $M_{23}C_6$ carbide coarsened following the Ostwald ripening mechanism. However, the MX carbonitrides did not grow during creep-fatigue due to so stable at $550\;^{\circ}C$. The width of martensite lath increased because of the dislocation recovery at the lath boundaries. The magnetic coercivity has an influence on the microstructural properties such as dislocation, precipitates and martensite lath boundaries, which interpreted in relation to microstructural changes. Consequently, this study proposes a magnetic coercivity to quantify the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.33-42
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• 1999

In the present study, crack initiation criteria, static failure and tensile mode fatigue behavior for a rail steel are evaluated to assure the railway vehicle's safety. The transverse fissure, which is the most critical damage in the rail, is initiated by the maximum shear stress and its location is subsurface. In addition, the possibility of transition from the shear mode to the mixed mode increases with increasing the length of subsurface crack. Because of the brittleness by the welding, the fracture toughness of the welded part is lower than of the base metal. For low ${\Delta}K$, the stage II fatigue crack growth rates of the welded part is slower than of the base metal but, for high ${\Delta}K$, this different behavior for fatigue crack growth rate is nearly diminished. These trends are more remarkable for low stress ratio, R=0.1. It is believed that this behavior is caused by the change of the microstructure which that of the welded part is coarser than of base metal.

• Journal of Korean Society of Steel Construction
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• v.28 no.3
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• pp.139-149
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• 2016

Roof cladding of buildings are required for the measures about the 'screw pull-out' which causes the casualties and the property damage by typhoons. In this study, the pull-out resistance was increased by increasing the penetration depth of the screw installing a ironware called 'insert nut' on the roof cladding frame. Tensile tests were conducted to compare the pull-out strengths of a general screw-joint and a nut insert joint. Roof cladding that is actually being used in the field was produced using the 'solid work' and then the roof claddings using a general screw-joint and a nut insert joint were compared by a static test and dynamic test.