• 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.

• International Journal of Highway Engineering
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• v.13 no.4
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• pp.41-50
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• 2011

It is well-known that pavement is easily damaged by several factors including permanent deformation and fatigue crack, causing service life of the pavement to be shorter than expected. It is very important to predict amount of permanent deformation for designing pavement and developing design method of pavement. A new model of permanent deformation of pavement materials based on concept of shear stress ratio has been proposed because the lower pavement materials are highly affected by shear strength of the material. In this study a large repetitive triaxial load test has been adapted for performing test of permanent deformation of crushed subbase materials. The test procedure which includes concept of shear stress ratio has been newly developed. Several important model parameters can be obtained from the test that can be used for making correct permanent deformation model of the material.

• Journal of Fisheries and Marine Sciences Education
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• v.9 no.2
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• pp.198-208
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• 1997

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environment and in the air. These experiments were carried out to investigate the surface crack propagation behavior, the value of experimental constant for Paris' rule(da/dN=$C(K)^m$), the crack depth propagation rate and the accelerative factor of the surface crack propagation rate. The main results obtained are as follows ; 1) As the specific resistances of marine environment decreases, the exponential value of slope m of Paris' rule(da/dN=$C(K)^m$) decreases and the value of intercept C increases. 2) The surface crack propagation rate and the crack depth propagation rate are delayed, as the specific resistances of marine environment is increased. 3) The accelerative factor of the surface crack propagation rate by corrosion fatigue is higher, according as the stress intensity factor range ${\Delta}K_A$ is small.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.4
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• pp.521-528
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• 2021

In this study, to repair damaged economizer fin tubes on ships, sealing treatment was performed after applying arc thermal spray coating technology using Inconel 625. A solid particle erosion (SPE) experiment was conducted according to ASTM G76-05 to evaluate the durability of the substrate, thermal spray coating (TSC), and thermal spray coating+sealing treatment (TSC+Sealing) specimens. The surface damage shape was observed using a scanning electron microscope and 3D laser microscope, and the durability was evaluated through the weight loss and surface roughness analysis. Consequently, the durability of the substrate was superior to that of TSC and TSC+Sealing, which was believed to be owing to numerous pore defects in the TSC layer. In addition, the mechanism of solid particle erosion damage was accompanied by plastic deformation and fatigue, which were the characteristics of ductile materials in the case of the substrate, and the tendency of brittle fracture in the case of TSC and TSC+Sealing was confirmed.

• Composites Research
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• v.30 no.2
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• pp.138-144
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• 2017

Damage sensing of polymer composite films consisting of poly(dicyclopentadiene) p-DCPD and carbon nanotube (CNT) was studied experimentally. Only up to 1st ring-opening polymerization occurred with the addition of CNT, which made the modified film electrically conductive, while interfering with polymerization. The interfacial adhesion of composite films with varying CNT concentration was evaluated by measuring the wettability using the static contact angle method. 0.5 wt% CNT/p-DCPD was determined to be the optimal condition via electrical dispersion method and tensile test. Dynamic fatigue test was conducted to evaluate the durability of the films by measuring the change in electrical resistance. For the initial three cycles, the change in electrical resistance pattern was similar to the tensile stress-strain curve. The CNT/p-DCPD film was attached to an epoxy matrix to demonstrate its utilization as a sensor for fracture behavior. At the onset of epoxy fracture, electrical resistance showed a drastic increase, which indicated adhesive fracture between sensor and matrix. It leads to prediction of crack and fracture of matrix.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.149-163
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• 2021

Damage characteristics of granite, marble and sandstone whose properties were different were investigated by uniaxial compression test and cyclic loading-unloading test. Strength, elastic constants and damage threshold stresses were measured by uniaxial compression test and were compared with those measured by cyclic loading-unloading test. Average rock strengths measured by cyclic loading-unloading test were either lower than or similar with those measured by uniaxial compression test. Rocks with high strength and low porosity were more sensitive to fatigue than that with low strength and high porosity. Although permanent strains caused by cyclic loading-unloading were different according to rock types, they could be good indicators representing damage characteristics of rock. Damage threshold stress of granite and marble might be measured from stress-permanent strain curves. Acoustic emissions were measured during both tests and felicity ratios which represented damage characteristics of rocks were calculated. Felicity ratio of sandstone which was weak in strength and highly porous could not be calculated because of very few measurements of acoustic emissions. On the other hand, damage threshold could be predicted from felicity ratios of granite and marble which were brittle and low in porosity. The deformation behaviors and damage characteristics of rock mass could be investigated if additional tests for various rock types were performed.

• International Journal of Highway Engineering
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• v.8 no.3 s.29
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• pp.49-61
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• 2006

This study suggests long-life asphalt pavement method which can save maintenance cost by increasing the design and performance period of pavements. The high modulus asphalt binder developed and then various physical tests are performed. Laboratory performance tests and accelerated pavement test are conducted for the high modulus and conventional mixtures. The test results show that dynamic modulus values of high modulus mixtures are higher than those of the conventional mixtures, The high modulus mixtures yield better fatigue, rutting and moisture damage performance than conventional mixtures. Structural analysis is performed and a database is built up for long life asphalt pavement design. Pavement response model is developed through a multiple regression analysis program, SPSS using the database. A design software for the long life pavements is developed based on the pavement response model and laboratory and field performance tests results. In addition, optimum pavement sections and materials are suggested. The suggested AC thickness of long life asphalt pavement is 29cm. A Life cycle cost analysis(LCCA) is conducted to check the economical efficiency of the long life pavement section. The LCCA result shows that initial construction costs of long life and conventional pavements are almost equal, but long life pavement is more profitable in terms of the LCCA.