• Journal of Welding and Joining
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• v.27 no.6
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• pp.74-79
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• 2009

Titanium and titanium alloy can be reproduced immediately even if oxide films($TiO_2$) break apart in sea water. Therefore, since titanium demonstrates large specific strength and outstanding resistance to stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion in sea water environment, it has been widely applied to heat exchanger for ships. In particular, with excellent elongation, pure titanium may be deemed as optimal material for production of heat exchanger plate which is used with wrinkles formed for efficient heat exchange. Conventional plate type heat exchanger prevented leakage of liquid through insertion of gasket between plates and mechanical tightening by bolts and nuts, but in high temperature and high pressure environment, gasket deterioration and leakage occur, so heat exchanger for LPG re-liquefaction device etc do not use gasket but weld heat exchanger plate for use. On the other hand, since welded plate cannot be separated, it is important to obtain high quality reliable welds. In addition, for better workability and production performance, lasers that can obtain weldment with large aspect ratio and demonstrate fast welding speed even in atmospheric condition not in vacuum condition are used in producing products. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through quantitative analysis of oxygen and nitrogen and measurement of hardness as fundamental experiment for the evaluation of titanium laser welding, and evaluated the welding performance and mechanical properties of butt welding. This study welded specimens in various conditions by using laser and GTA welding machine to apply edge welding to heat exchanger, and evaluated the mechanical strength through tensile stress test. As a result of tensile test, laser weldment demonstrated tensile strength 4 times higher than GTA welds, and porosity could be controlled by increasing and decreasing slope of laser power at overlap area.

• Journal of the Korean Geotechnical Society
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• v.23 no.8
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• pp.5-16
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• 2007

The stone column method is widely used in Europe as an alternative to conventional pile foundations. Several benefits of using the stone column method include sound performance, low cost, expediency of construction, and liquefaction resistance among others. Recently, geosynthetic-encased stone column approach has been developed to improve its load carrying capacity through increasing confinement effect. Although such a concept has been successfully applied in practice, fundamentals of the method have not been fully explored. This paper presents the results of an investigation on the load carrying capacity of geogrid-encased stone column using a series of 2D finite element analyses. A parametric study was then conducted for influencing factors such as effect of geogrid encasement, encasement length, geogrid strength, among others. The results of the analyses indicated improved short- and long-term load carrying capacity of the geogrid-encased stone column method has advantages over the conventional stone column method without encasing.

• Journal of the Korean Geotechnical Society
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• v.28 no.7
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• pp.31-40
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• 2012

In most design codes, soils are classified as either sandy or clayey soils, and appropriate design equations for each soil type are used to estimate their soil behaviour. However, sand-fine mixtures, which are typically referred to as intermediate soils, are somewhere at the middle of sandy or clayey soils, and therefore a unified interpretation of soil behaviour is necessary. In this paper, a series of cyclic shear tests were carried out for three different combinations of sand-fine mixtures with various fines content. Silica-sand mixture and fines (Iwakuni natural clay, Tottori silt, kaolinite) were mixed together with various mass ratios, while paying attention to the changes of void ratios expressed in terms of sand structure. The cyclic shear strengths of the mixtures below the threshold fines content were examined with the increasing fines contents. As a result, as the fines contents increased, their cyclic deviator stress ratios decreased for dense samples while it increased for loose samples. Additionally, cyclic deviator stress ratio of the mixtures was estimated using the concept of equivalent granular void ratio.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.71-83
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• 2007

Liquefaction resistance depends strongly upon the degree of saturation, which is expressed in terms of the pore pressure coefficient, B. The B-value has been widely used to quantify the state of saturation of laboratory samples. However, it is practically impossible to determine in situ state of saturation by using the B-value. So, P-wave velocity can be alternatively used as a convenient index for evaluating the in situ state of saturation. In this paper, the Stokoe type torsional shear (TS) testing system was modified to saturate the specimen, with which it is also possible to measure P ($V_p$), S-wave velocity ($V_s$) and the excess pore water pressure buildup In order to examine the effect of B-value for nearly saturated sands. A series of the tests were carried out at 3 relative densities (40%, 50% and 75%) and various B-values using Toyoura sand. Based on the test results, the variations of $V_p\;and\;V_s$ with B-value were analyzed and compared with a existing theoretically derived formula. The normalized pore water pressure, $du/{\sigma}{_0}'$ and cyclic threshold shear strain, ${\gamma}^c_{th}$ with B-value were also analyzed. Additionally the test results related to pore water pressure were analyzed by $V_p$ to apply to the field seismic analysis.