• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.1-7
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• 2008

When historical or cultural buildings need to be repaired or reinforced, the changes of original features should be minimized, and the strengths of structures should be improved. Among the existing methods to reinforce historical wood structures, the carbon fiber reinforcement polymer (CFRP) installation method is one of the best ones to achieve the afore-mentioned requirements. Therefore, this study aims at investigating the reinforcing effects and failure modes of timber beams reinforced with the inserted CFRP, a part of roof trusses in modern wood structures, and at providing the fundamental test data to estimate the CFRP rein-forced timber beam in the application of this reinforcing method. The primary parameters in this study were the layout and amount of CFRP. It was observed that, when $0.3{\sim}0.7%$ of CFRP were installed, the strengths of reinforced timber beams increased up to 173% compared to its original strength, but their strengthening effects were heavily influenced by the characteristics of timber such as burls. In order to improve the applicability of this strengthening method, fundamental understandings on the characteristics of wood would be necessary, and there would be in need of researches on the non-destructive test for wood structures as well.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1106-1114
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• 1993

A composite material is composed of a reinforcement and a matrix, which determine mechanical characteristics of the molded part. There is no doubt that the properties of a composite material depend not only on the characteristics of the matrix but also on the structure of glass fiber mat and a fiber type of reinforcement. Therefore it is very important to study the composites of reinforcement and the matrix, and to control the fiber type in the process of molding of composite materials. In this study, the specimen was made of a glass fiber mat of 6-7mm thickness by scattering it in the air after cutting the glass fiber mat with needle punching makes change according to the type of needle and the number of times of stretching. First the sheet was made by means of a hot-press after accumulating a matrix and a glass fiber according to each mat structure of glass fiber. It was heated the manufactured sheet with the dry oven and molded it a secondary high temperature compression by a 30 ton oilhydraulic press. A definition of a correlation coefficient is showed up during this period and find it out with the relation of the fiber-matrix separation and the fiber orientation. We studied effects of the glass fiber mat structures on the correlation coefficient.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.2
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• pp.19-26
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• 1991

This study has been constructed to establish the formation of the VC layer on various steels by immersion in fused borax bath containing Fe-V powder. The result obtained from the experiment are as follows. (1) The carbide is supposed to grow on the front surface of the carbide layers by the reaction between carbide-forming elements dissolved in the fused borax and carbon atoms successively supplied through the layer from the matrix. (2) The growth rate of the carbide layers was controlled by the diffusion rate of C in the carbide layer and C content in the matrix. (3) Carbide layer formed on the surface of the specimen is VC layer and the hardness of this layer is above $H_v$ 3000.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.668-677
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• 1993

The microstructural and shear tests of STS304/, STS430/ and low-C steel/Cu joints brazed using Cu-P, Cu-P-Sn(four type) and Cu-P-Sn-Ag(three type) filler metals at 1003 and 1033K for 1.2ks in Ar atomsphere were performed. Interfacial microstructures were divided into three type ; first, reaction layer contained cracks second, dispersed layer without cracks third, dispersed layer and reaction layer contained cracks. The joints composed only of dispersed layer without cracks have the high shear strength of above 40-60 MPa and result in failure in copper base metal. Low shear strength and joint failure result from the formation of reaction layer which induced cracks. The reaction layer is a Fe-P compound. This tendency of microstructure and shear strength depends on the existence and/or nonexistence of Sn in filler metals as well as Ni (and Cr) in base metals.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.35 no.4
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• pp.157-165
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• 2019

Recently, lean duplex stainless steel, STS329FLD with less nickel (reduced to 0.5~1.5%) has been developed as a substitute of austenitic stainless steel (8%~10.5% nickel in STS304) and included in Korean standards (KS). This paper investigates the block shear behavior of cold-formed duplex stainless steel (STS329FLD, nominal plate thickness of 1.5mm) fillet-welded connection with base metal fracture. Main variables are weld lengths in the longitudinal and the transverse directions of applied force ranged from 20mm to 50mm. As a result, specimens failed by typical block shear facture (the combination of gross section tensile fracture and shear fracture or shear yielding) and ultimate strength of the specimens got higher with the increase of weld length. Block shear fracture strengths predicted by current design specifications (KBC2016/AISC2016 and EC3) and existing proposed equations for welded connections by Topkaya, Oosterhof & Driver and Lee et al. were compared with test strengths. KBC2016/AISC2016 and EC3 design specifications underestimated block shear strength of STS329FLD welded connections by on average 24%, 29%, respectively and Oosterhof & Driver, Topkaya and Lee et al's equations overestimated the ultimate strength of the welded connection by the range of 3% to 44%.

• Composites Research
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• v.12 no.1
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• pp.68-75
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• 1999

This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.5
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• pp.415-421
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• 2013

CGI is gaining popularity in applications that require either greater strength, or lower weight than cast iron. Recently, compacted graphite iron has been used for diesel engine blocks, turbo housings and exhaust manifolds. This paper were assessed acoustic emission characteristics according to the mechanical properties change of degraded CGI340 during 1-24 hours at 873~1173 K. In results of pencil lead fracture test, the dominant frequency and the velocity of base metal were 97 kHz and 5490 m/sec, respectively. The base metal in a tensile test was obtained relatively high dominant frequency. However, the heat treated materials, the longer the heat treatment time, the higher the heat treatment temperature, were obtained in the area of lower frequencies. This phenomenon appears by long-term use.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.1
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• pp.57-65
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• 2019

In this study, the quality characteristics of the mother material of panel were evaluated for the production of moss panel using alumina cement and biological characteristics and environmental impact characteristics of moss panel were evaluated. The ratio of W/B 10%, Vs/Vm 20% and foaming agent 0.5% were selected as the basic mixing ratio for the mother panel of moss panel through pretest and SAP was added to improve the moisture content of panel. The optimal mixing ratio of SAP was considered to be less than 0.5% considering the quality characteristics. Also, through the use of alumina cement, the pH of the panel could be lowered to 10~11. The panel was able to improve the surface roughness through the foaming agent, and it was confirmed that the SAP had an effect of improving the moisture content of the panel. For the environmental impact characteristics of the moss panel, the moss panel evaluated the carbon dioxide reduction performance and the fine dust cleaning performance.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.298-303
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• 2001

The critical thickness of an epitaxial film on a substrate in electronic or optoelectronic devices is studied on the basis of equilibrium dislocation analysis. Two geometric models, a single dislocation and an array of dislocations in heteroepitaxial system, are considered respectively to calculate the misfit dislocation formation energy. The isotropic linearly elastic stress fields for the models are obtained by means of complex potential method combined with alternating technique, and are used for calculating the formation energies. As a result, the effect of elastic mismatch between film and substrate on critical thickness is presented and $Si_xGe_{1-x}/Si$ epitaxial structure is analyzed to predict the critical thickness with varying germanium concentration.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.33-42
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• 2004

Making use of SN steel in the building structure should be a prerequisite to adopt the design strength of said steel. As a preceding study, the material properties of STKN400B/490B tubes and SPAP235/325 and SPAR295 square pipes manufactured using SN400B/490B plates were evaluated. Compared with the yield and ultimate strengths of SN400B/490B plates, those of STKN400B/490B tubes increase. Nonetheless, the yield and ultimate strengths of STKN400B/490B tubes satisfied the design codes of STKN400B/490B tubes even though the tubes were fabricated via roll bending or press forming. On the other hand, the yield and ultimate strengths at the edges of SPAP235/325 square pipes did not satisfy the design codes based on the values at the sides. The maximum tensile and compressive residual stresses at the SN490B tube were equal to and 40% of the yield strength of the SN490B plate, respectively, In the case of the SPAP325 square pipe, both the maximum tensile and compressive residual stresses were 80% of the yield strength of the SN490B plate. The axial compressive loaded column test results snowed that the buckling strengths were not very different regardless of the mode of fabrication of STKN490B tunes. i.e., through roll bending or press forming. On the other hand, the buckling strength of the SPAP325 square pipe was higher than that of the built-up square pipe.