• Journal of the Korea Institute of Building Construction
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• v.6 no.4 s.22
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• pp.85-92
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• 2006

Urethane, epoxy, acrylic have common property to adhere on the concrete dried surface in the waterproofing materials at present. In the wet condition, however, the materials such as urethane, epoxy, acrylic need a long hardening time and it become a reason of water leakage as the materials breaking down. it is one of the problem to adhere to the substrate. Therefore, in this thesis, I focused to assure the structural safety and durability and quality for waterproofing and safe of construction cost by cut down the cost of labor and reduce the term of works as searching the application of field condition for high adhesive spray type of degenerated and rubberized asphalt membrane material.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.295-296
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• 2006

High hardness of P/M parts can be obtained in the cooling section of the sintering furnace by using sinter hardenable materials, thus the post-sintering heat treatment can be eliminated. However, the sinter hardened materials would have difficulties in secondary machining if it is required, which will limit the applications of sinter hardenable materials in the machined parts. Recent development in warm compaction technology can enable us not only to achieve the high green density up to $7.4\;g/cm^3$, but also the high green strength which is needed for green machining. Therefore by using warm compaction technology, the green machining can be applied to sinter hardenable materials for the high density, strength and hardness P/M parts. In the present study, a pre-alloyed steel powder, ATOMET4601, was used by mixing with 2.0% copper, 1.0% nickel, 0.9% graphite and a proprietary lubricant using a binder treatment process - FLOMET. The specimens were compacted and green machined with different machining parameters. The machined surface finish and part integrity were evaluated in selecting the optimal conditions for green machining. The possibility of applying the green machining to the high-density structural parts was explored.

• Journal of the Korea Furniture Society
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• v.17 no.1
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• pp.33-46
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• 2006

This study was carried out to investigate a radio-frequency/vacuum (RF/V) drying ability and physical properties of the green boards and the pre-kiln dried boards with 40 mm thickness, and the 70 mm-thick green board of Iroko (Milicia excelsa). The major results were summarized as follows; The drying time from initial moisture content (MC) of 110% to approximate 6% MC for a 40mm-thick green board was 192 hours, and about 200 hours for the 70 mm-thick green board, respectively and so the RF/V drying times were dramatically shortened compared to conventional kiln drying time. The case hardenings at the RF/V drying completion stage test were very negligible, thus represented almost no existence of the residual stress. The checks were very slightly formed on all of the boards during the RF/V drying test, but crook appeared quite severely. During the accelerating test, the water-resistant treated specimens had not experienced any signs of checking occurred, whereas the control boards had encountered very frequent occurrences of end checking and slight surface checking. There were no observations of warping and discoloring regardless of the treatment.

• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.3
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• pp.81-90
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• 1999

The purpose of this study is to examine the uses of fly ash asa type of construction material. This paper presents the results of research performed to identify optimum mix proportions for production of lowable fill with high volume fly ash content . The fly ash used in this study met the requirements of KS L 5405 and ASTM C 618 for Class F material. The flowable fill with high volume fly ash content was investigated for strength and flowability characteristics. Tests were carried out on flowable fill designed to have 10 ~15kgf/$\textrm{cm}^2$ compressive strength at 28 days with fly ash contents of approximately 260kgf/㎥. Slump was held at 25$\pm$1cm for all mixtures produced to range from 5kgf/$\textrm{cm}^2$ to 14kgf/$\textrm{cm}^2$ compressive strengths at 28 days. To produce flowable fill with high volume fly ash , first the influential variables were identified in an experimental study based on factorial design. Among the proportioning variables investigated, cement ,fly ash, and sand contents were found to have statistically significant effect on strength and slump of flowable fill . Subsequently, response surface analysis techniques were used to devise an experimental program that helped determine the optimum combinations of the selected influential variables based on material properties and cost. The optimized flowable fill were then technically evaluated. It is shown that flowable fill has acceptable compressive strength , slump flow, hardening time, and permeability.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.40 no.1
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• pp.55-61
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• 2008

The annals of Joseon Dynasty is the most valuable resource containing the record of Korean history and has been known as one of the UNESCO's Memory of the World Register. In some period, wax-treated paper was used in the annals of Joseon Dynasty to prevent the damage from pests. But, wax-treated volumes were discolored to brown, white or black, and partially cracked by the stiffened wax. It means that wax-treated volumes were damaged by the hardening and oxidizing of wax. The wax is considered as the first reason in damages on the wax-treated volume. Therefore, in this study we analysed the oxidation index of Korea traditional paper(Hanji) which is used as the restoration paper of the waxed volume in the annals of Joseon Dynasty by using FT-IR. As the analysis of FT-IR, the traditional two-layed stamping paper (Hanji sample F), which was treated by starch in its surface, was shown the most stable state after the accelerated ageing test.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.697-704
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• 2005

The deformation behavior of a bulk amorphous and crystallized amorphous $Zr_{22.5}Ti_{14}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy extracted from a commercial golf club head was characterized at room temperature ana $300^{\circ}C$. At room temperature, amorphous specimens revealed higher yield stress and ductility than partially crystallized alloy specimens. Amorphous alloy displayed some plasticity before fracture, which resulted from strain hardening and repeated crack initiation and propagation. The fracture is mainly localized on one major shear band, and the compressive fracture angle of the amorphous specimen between the stress axis and the fracture plane was about $40^{\circ}$ Scanning electron microscope observations revealed mainly a vein-like structure in the amorphous alloy But the fracture surface of partially crystallized amorphous alloy consisted of vein-like and featureless fracture structure. The partially crystallized alloy extracted from the thick part of the club fractured in the elastic region, at a much lower stress level than the amorphous, suggesting that relatively coarse crystal particles formed during cooling cause the brittle fracture.

• Korean Journal of Materials Research
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• v.15 no.1
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• pp.61-65
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• 2005

The titanium $diboride(TiB_2)$ has high strength(750MPa), high melting point $(3225^{\circ}C)\;and\;10\%$ IACS electrical conductivity. On this account, the dispersion hardening $Cu-TiB_2$ composites(MMCs) are a promising candidate for applications as electrical contact materials. MMCs for electrical contact materials can reduce material cost and resource consumption caused by wear, due to its good mechanical and electrical property. In this study, we attempt to prepare MMCs with various volume fraction and particle size of $TiB_2$ by means of hot extruded and cold drawn process. Dry sliding wear tests were performed on a pin-on-disk type wear tester, sliding against SM45C under the different applied loads. After wear testing, the microstructures of the worn surfaces were observed by SEM and the microhardnesses of the subsurface zone were measured.

• Geomechanics and Engineering
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• v.7 no.2
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• pp.213-231
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• 2014

An elastoplastic model for structured clays, which is formulated based on the fact that the difference in mechanical behavior of structured and reconstituted clays is caused by the change of fabric in the post-yield deformation range, is present in this paper. This model is developed from an elastoplastic model for overconsolidated reconstituted clays, by considering that the variation in the yield surface of structured clays is similar to that of overconsolidated reconstituted clays. However, in order to describe the mechanical behavior of structured clays with precision, the model takes the bonding and parabolic strength envelope into consideration. Compared with the Cam-clay model, only two new parameters are required in the model for structured clays, which can be determined from isotropic compression and triaxial shear tests at different confining pressures. The comparison of model predictions and results of drained and undrained triaxial shear tests on four different marine clays shows that the model can capture reasonable well the strength and deformation characteristics of structured clays, including negative and positive dilatancy, strain-hardening and softening during shearing.

• Structural Engineering and Mechanics
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• v.72 no.3
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• pp.313-327
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• 2019

Damage evolution in the form of void nucleation, propagation and coalescence is the primary cause that is responsible for the ductile failure of microalloyed steels. The Gurson-Tvergaard-Needleman (GTN) damage model has proven to be extremely robust for characterizing the microscopic damage behavior of ductile metals. Nonetheless, successful applications of the model on a given metal type are limited by the correct identification of damage parameters as well as the validation of the calculated void growth rate. The purpose of this study is two-fold. First, we aim to identify the damage parameters of the GTN model for Q345 steel (Chinese code), due to its extensive application in mechanical and civil industries in China. The identification of damage parameters is facilitated by the well-suited response surface methodology, followed by a complete analysis of variance for evaluating the statistical significance of the identified model. Second, taking notched Q345 cylinders as an example, finite element simulations implemented with the identified GTN model are performed in order to analyze their microscopic damage behavior. In particular, the void growth rate predicted from the simulations is successfully correlated with experimentally measured acoustic emissions. The quantitative correlation suggests that during the yielding stage the void growth rate increases linearly with the acoustic emissions, while in the strain-hardening and softening period the dependence becomes an exponential function. The combined experimental and finite element approach provides a means for validating simulated void growth rate against experimental measurements of acoustic emissions in microalloyed steels.

• Geomechanics and Engineering
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• v.17 no.3
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• pp.307-316
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• 2019

Dam deformation should be strictly controlled for the construction of 300 m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.