• Magazine of the Korean Society of Agricultural Engineers
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• v.26 no.1
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• pp.52-72
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• 1984

This study was performed to obtain the basic data which can be applied to the use of epoxy resin mortars. The data was based on the properties of epoxy resin mortars depending upon various mixing ratios to compare those of cement mortar. The resin which was used at this experiment was Epi-Bis type epoxy resin which is extensively being used as concrete structures. In the case of epoxy resin mortar, mixing ratios of resin to fine aggregate were 1: 2, 1: 4, 1: 6, 1: 8, 1:10, 1 :12 and 1:14, but the ratio of cement to fine aggregate in cement mortar was 1 : 2.5. The results obtained are summarized as follows; 1.When the mixing ratio was 1: 6, the highest density was 2.01 g/cm$^3$, being lower than 2.13 g/cm$^3$ of that of cement mortar. 2.According to the water absorption and water permeability test, the watertightness was shown very high at the mixing ratios of 1: 2, 1: 4 and 1: 6. But then the mixing ratio was less than 1 : 6, the watertightness considerably decreased. By this result, it was regarded that optimum mixing ratio of epoxy resin mortar for watertight structures should be richer mixing ratio than 1: 6. 3.The hardening shrinkage was large as the mixing ratio became leaner, but the values were remarkably small as compared with cement mortar. And the influence of dryness and moisture was exerted little at richer mixing ratio than 1: 6, but its effect was obvious at the lean mixing ratio, 1: 8, 1:10,1:12 and 1:14. It was confirmed that the optimum mixing ratio for concrete structures which would be influenced by the repeated dryness and moisture should be rich mixing ratio higher than 1: 6. 4.The compressive, bending and splitting tensile strenghs were observed very high, even the value at the mixing ratio of 1:14 was higher than that of cement mortar. It showed that epoxy resin mortar especially was to have high strength in bending and splitting tensile strength. Also, the initial strength within 24 hours gave rise to high value. Thus it was clear that epoxy resin was rapid hardening material. The multiple regression equations of strength were computed depending on a function of mixing ratios and curing times. 5.The elastic moduli derived from the compressive stress-strain curve were slightly smaller than the value of cement mortar, and the toughness of epoxy resin mortar was larger than that of cement mortar. 6.The impact resistance was strong compared with cement mortar at all mixing ratios. Especially, bending impact strength by the square pillar specimens was higher than the impact resistance of flat specimens or cylinderic specimens. 7.The Brinell hardness was relatively larger than that of cement mortar, but it gradually decreased with the decline of mixing ratio, and Brinell hardness at mixing ratio of 1 :14 was much the same as cement mortar. 8.The abrasion rate of epoxy resin mortar at all mixing ratio, when Losangeles abation testing machine revolved 500 times, was very low. Even mixing ratio of 1 :14 was no more than 31.41%, which was less than critical abrasion rate 40% of coarse aggregate for cement concrete. Consequently, the abrasion rate of epoxy resin mortar was superior to cement mortar, and the relation between abrasion rate and Brinell hardness was highly significant as exponential curve. 9.The highest bond strength of epoxy resin mortar was 12.9 kg/cm$^2$ at the mixing ratio of 1:2. The failure of bonded flat steel specimens occurred on the part of epoxy resin mortar at the mixing ratio of 1: 2 and 1: 4, and that of bonded cement concrete specimens was fond on the part of combained concrete at the mixing ratio of 1 : 2 ,1: 4 and 1: 6. It was confirmed that the optimum mixing ratio for bonding of steel plate, and of cement concrete should be rich mixing ratio above 1 : 4 and 1 : 6 respectively. 10.The variations of color tone by heating began to take place at about 60˚C, and the ultimate change occurred at 120˚C. The compressive, bending and splitting tensile strengths increased with rising temperature up to 80˚ C, but these rapidly decreased when temperature was above 800 C. Accordingly, it was evident that the resistance temperature of epoxy resin mortar was about 80˚C which was generally considered lower than that of the other concrete materials. But it is likely that there is no problem in epoxy resin mortar when used for unnecessary materials of high temperature resistance. The multiple regression equations of strength were computed depending on a function of mixing ratios and heating temperatures. 11.The susceptibility to chemical attack of cement mortar was easily affected by inorganic and organic acid. and that of epoxy resin mortar with mixing ratio of 1: 4 was of great resistance. On the other hand, when mixing ratio was lower than 1 : 8 epoxy resin mortar had very poor resistance, especially being poor resistant to organicacid. Therefore, for the structures requiring chemical resistance optimum mixing of epoxy resin mortar should be rich mixing ratio higher than 1: 4.

• 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.

• Applied Microscopy
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• v.25 no.3
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• pp.99-107
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• 1995

The morphological changes of primary solid particles as a function of process time on hypereutectic Al-15.5wt%Si alloy during semi-solid state processing with a shear rate of $200s^{-1}$ are studied. In this alloy, it was observed that primary Si crystals are fragmented at the early stage of stirring and morphologies of primary Si crystals change from faceted to spherical during isothermal shearing for 60 minutes. To understand the role of Al dissolved in the primary Si crystal by shear stress at high temperature, lattice parameters of the primary Si crystals are determined as a variation of high order Laue zone(HOLZ) line positions measured from convergent beam electron diffraction(CBED) pattern. The lattice parameter of the primary Si crystal in the rheocast Al-15.5wt%Si alloy shows tensile strain of about 5 times greater than that of the gravity casting. Increase of the lattice parameter by rheocasting is due to the increased amount of Al dissolved in the primary Si crystal accelerated by shear stress at high temperature. The amounts of solute Al in the primary Si crystal are measured quantitatively by EPMA method to confirm the CBED analysis.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.2
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• pp.67-84
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• 1991

This study was carried out to investiagate the residual stress caused by the mismatch of thermal expansion and the bond failure resistance of alloy-porcelain specimens. The thermal expansions of alloys and porcelains were measured by using a straight push-rod dilatometer. Porcelain glass transition temperatures, thermal expansion coefficients, and thermal compatibility indices were derived from length-versus-temperature curves. Strain gauges were used to experimentally determine the Young's moduli of porcelains, the residual stresses of porcelain surface, and tensile bond strengths of the specimens of simulated porcelain metal crown. The obtained results were as follows: 1. The coefficients of thermal expansion for alloys were the minimum of $13.53\mu/^{\circ}C$ and the maximum of $20.11\mu/^{\circ}C$ in the range of $100\sim600^{\circ}C$ and those for porcelains were the minimum of $7.72\mu/^{\circ}C$ and the maximum of $31.24\mu/^{\circ}C$ in the range of $100\sim500^{\circ}C$. 2. The glass transition temperature of porcelains exhibited the same value without my relation to the healing rate, and the thermal disharmony of porcelain and alloy was more affected by porcelains than by the alloys. 3. The Young's moduli of body porcelains were larger than those of opaque porcelains(P<0.01) 4. It seemed that the residual stresses of porcelain surfaces in the porcelainalloy systems were more affected by porcelains than by alleys. 5. The bond strengths of the procelain-base metal alloy systems were larger than those of the porcelain-precious metal alloy systems. The fracture strengths of porcelain surfaces showed significant difference between porcelains (P<0.05).

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.145-156
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• 1999

The distribution of the second phase, the change of transformation temperature and mechanical properties with thermomechanical treatment conditions were investigated by metallography, calorimetry, EDS, tensile test and fractography in a Cu-Al-Ni-Ti-Mn alloy. The cast structure revealed Ti-rich precipitates($X_L$ phase) between dendrite arms, which have been identified as $(Cu,Ni)_2TiAl$ intermetallic compounds. By homogenizing above $900^{\circ}C$, the $X_L$ phase was melted in the matrix, while the Xs phase was precipitated in matrix and the volume fraction of it was increased. When hot-rolled specimen was betatized below $750^{\circ}C$, recrystallization could not be observed. However, the specimen betatized above $800^{\circ}C$ was recrystallized and the grain size was about $50{\mu}m$, while Xs phase was precipitated in matrix. With raising betatizing temperature, $M_s$ and $A_s$ temperatures were fallen and transformation hysteresis became larger. The strain of the specimen betatized at $800^{\circ}C$ was 8.2% as maximum value. The maximum shape recovery rate could be obtained in the specimen betatized at $800^{\circ}C$ but it was decreased due to the presence of Xs phase with increasing betatizing temperature.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.1
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• pp.11-21
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• 2006

The adjustable dental impression trays were made for being adjusted their width automatically along the width of patient's dental arch. The purpose of this study was to investigate the retentive force of adjustable dental impression trays made of different synthetic resin materials. Three pairs of adjustable trays were made of ABS(acrylonitrile butadiene styrene) synthetic resin, polyurethane synthetic resin and polycarbonate synthetic resin with a hole and without a rim on the border area of them. The experiment was done with the horse-shoe shaped metal plate to pull out the set impression body from the tray jig which was made for holding the tray on the lower part of Universal Testing Machine(UTM, Zwick Z020, Zwick Co., Germany). After the alginate impression in the tray was allowed to set four minutes, a tensile force was applied at right angles to the tray which had been previously seated on the jig. The force was applied to measure a maximum force by use of UTM at a constant strain rate 100mm per minute. The results obtained in this study were as follows : 1. The upper trays were showed higher retentive force than lower trays in three tray materials. 2. There was no significant difference in the retentive force of the tray materials(p>0.05).

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.182-190
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• 2020

This study reports a series of drop impact tests performed to generate denting damages on stiffened plates and their residual ultimate strength tests under axial compression. The models were fabricated of general structural steel, and each model has six longitudinal stiffeners and two transverse frames. Among six fabricated models, four were damaged, and two were left intact for reference. To investigate the effects of collision velocity and impact location on the extent of damage, the drop height and the impact location were changed in each impact test. After performing the collision tests, the ultimate axial compression tests were conducted to investigate the residual strengths of the damaged stiffened plates. Finite element analyses were also carried out using a commercial package Abaqus/Explicit. The material properties obtained from a quasi-static tensile tests were used, and the strain-rate sensitivity was considered. After importing the collision simulation results, the ultimate strength calculations were carried out and their results were compared with the test data for the validation of the finite element analysis method.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.11a
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• pp.71-74
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• 2007

With the changes of times the building materials tend to extend the demand for application under the special environment. Since high-ductile mortar is developed, the building materials show excellent performance like toughness, compression, tensile, and bending, etc. in the general concrete from the existing brittle point. And, recently they are widely used as repairing and reinforcing materials both at home and abroad because they are recognized as excellence like durability and fire-resistance. However, it is in a situation of creating problems in durability because it frequently happened deterioration of buildings that have already repaired and reinforced at a time when it requires reconstruction of recently deteriorated construction structure recently. Therefore, in this study improved with a more repair Material development and reinforcement of the second high-ductile mortar products for a variety of basic materials were presented want, research plans used include traditional repair materials and the newly developed PCM (polymer cement mortar) structural reinforcement type indicated that comparison. PCM analysis in order to present a rate depending on the types fiber 0, 1.2 and 2.0(%) at three levels and mixture water according to ratios of weight to Plain in the 2.0 and 1.85(kg) at two levels is set, the results were as follows. 1) This study has shown that PCM had excellent strain hardening behavior at the same time that the bending stress increased according to the fiber contents. 2) This study has shown that it had the durability performance due to the high substance transmission according to the fiber contents.

• Proceedings of KOSOMES biannual meeting
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• 2005.05a
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• pp.161-165
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• 2005

Recently, it is on the increase interest for Al alloy with new material for ship application to substitute for FRP ship. The reason is thatAl alloy ship has beneficial characteristics such as high sea speed, increase of loadage and easy to recycle compared with FRP ship. In this paper, mechanical and electrochemical properties are investigated by slow strain rate test experiment in various applied potential condition. These results will provide as reference data to design ship by deciding optimum protection potential regard to hydrogen embrittlement and stress corrosion cracking. In general, Al and Al alloys are not corroded with forming film which has the corrosion resistance property in neutral solution. However, it was observed that formation and destruction of passive film by $Cl^-$ ion in sea water environment. At comparison of current density after 1200 sec in potentiostatic experiment, the current density in the potential range of -0.68 $\~$-1.5 V is shown low value. The low current density means protection potential range. Elongation in applied potential of 0 V was high. However, the corrosion protection application in this condition is impossible potential because the toughness is low value by decreasing strength by active dissolution reaction at parallel part of specimen. The film composed with $CaCO_3$ and $Mg(OH)_2$ has a corrosion resistance property. However, the uniform electrodeposition coating at below -1.6 V potential is not formed since the time to form the uniform electrodeposition coating is short. Therefore, it is concluded that mechanical property is poor because effect by hydrogen gas generation is larger than that of electrodeposition coating. It is concluded that the optimum protection potential range from comparison of_maxim urn tensile strength, elongation and time to fracture is -1.3$\~$0.7 V (SSCE).

• Transactions on Electrical and Electronic Materials
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• v.12 no.1
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• pp.24-27
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• 2011

Effect of substitution of Mn for Ni on transformation behavior, shape memory characteristics and superelasticity of Ti45Ni-5Cu alloy has been investigated by means of electrical resistivity measurements, X-ray diffraction, thermal cycling tests under constant load and tensile tests. The one-stage B2-B19' transformation occurred when Mn content was 0.5 at%, above which the two-stage B2-B19-B19' transformation occurred. A temperature range where the B19 martensite exists was expanded with increasing Mn content because decreasing rate of Ms (60 K / % Mn) was larger than that of Ms' (40 K / % Mn). Ti-(45-x)Ni-5Cu-xMn alloys were deformed in plastic manner with a fracture strain of 60 % ~ 32 % depending on Mn content. Clear superelasticity was found in fully annealed Ti-(45-x)Ni-5Cu-xMn alloys with Mn content more than 1.0 at%, which was ascribe to a solid solution hardening by substitution of Mn for Ni.