• 한국생산제조학회지
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• 제7권2호
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• pp.15-22
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• 1998

The effects of shot peening an the fatigue strength are studied in this paper. Applying the multistage shot peening on the material. the relation between the residual stress and fatigue strength compressive is investigated. Observing tensile strength elongation. reduction of area. hardness. and roughness. the results can be summarized as follows ; 1.The change of mechanical properties is small before and after the shot peening is carried out. The change of hardness is also small in high hardness material. 2.The surface roughness does not affect the fatigue strength. but the surface roughness is improved by multi-stage shot peening. 3.The fatigue strength of multi-stage shot peening material is 756MPa and is 1.78 times higher than that of un-peened material. 4.The maximum compressive residual strength of multi-stage shot peening material is -792MPa the fatigue strength seems to be improved by residual stress.

• Corrosion Science and Technology
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• 제5권4호
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• pp.123-128
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• 2006

It was analyzed the causes of boiler tube rupture due to a degradation and corrosion on the boiler tubes in fossil power plant. The experiments were carried out among samples taken from the operating facilities. The result were analyzed based on experimental results from mechanical strength, microstructure observation, and hardness measurement in order to determine the cause of local rupture on boiler tubes. In general, 2.25Cr-1Mo steel generates carbides, it is coarsened, its ductility and strength abruptly decreased as degradation is in progress, In order to confirm this phenomenon, we observed changes of the mount of Cr and Mo of carbide by carrying out EDX chemical composition analysis. The amount of Cr and Mo in the degraded material or service exposed material gradually increased the amount of Mo but initially they were almost maintained at the same amount. Furthermore, we observed that the carbide become coarsened both in the grain and at the grain boundary. Tensile test was carried out to measure a material hardness and to recognize a drop-off of hardness. Overall result for tensile strength and hardness turned out to be lower than new material and mechanical strength and hardness was degraded as the material degradation was in progress.

• 한국표면공학회지
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• 제16권1호
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• pp.3-9
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• 1983

The change of the hardness and yield strength depending upon the electrolysis conditions was investigated for Watts and bright nickel electrodeposits. The hardness of Watts nickel electrodeposits decreased with increasing current density in the range of 1-15A/Am2, while it increased with increasing bath temperature. The hardness of bright nickel deposits increased noticebly in comparison with that of Watts nickel electro-deposits. The hardness and the yield strength of the bright nickel electrodeposits increased considerably with decreasing current density and the highest value was obtained at the lowest current density (1A/dm2), while they decreased noticebly at the bath temperature of 80$^{\circ}C$ in comparison with that of 40-60$^{\circ}C$. The change of the hardness and the yield strength of bright nickel electrodeposits depending upon the electrolysis conditions could be mainly attributed to the variation of organic additives codeposited in the electrodeposits. The recrystallizatioin temperature(50% softening temperature) of the Wattss and the bright nickel electro-deposits was 520-280$^{\circ}C$ and 350-410$^{\circ}C$ respectively and then the recystallization temperature of bright nickel deposits was lower than that of the Watts nickel electrodeposits.

• 동력기계공학회지
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• 제18권5호
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• pp.106-114
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• 2014

For the purpose of development of polyurethane sealing material, polyurethane resins reinforced with CuO were prepared from polyol and MOAC(4,4'-Methylenebis(2-chlorobenzeneamine)). And the effects of compositions on the mechanical properties of the reinforced polyurethane resin were experimentally examined. The polyurethane resin got to be thermally decomposed at $260^{\circ}C$ and completely carbonized around $500^{\circ}C$. Tensile strength, elongation and hardness of the polyurethane resin increased with the content of MOCA. CuO was uniformly dispersed in the polyurethane resin by 1 minute's ultrasonic radiation. Tensile strength, elongation and hardness of the polyurethane resin reinforced with CuO increased with the content of CuO. Tensile strength and hardness of the reinforced polyurethane resin increased with particle size of the CuO, but elongation decreased. CuO showed higher tensile strength and hardness than any other additives, and lowest elongation.

• 한국기계가공학회지
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• 제10권1호
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• pp.67-72
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• 2011

The main objective of this paper is obtaining the optimal carburizing hours which impacts geometric tolerances, OPD(Over Pin Diameter), runout, hardness and fatigure strength of SCM415 spur gear. In order to observe the deformation of the gear, the circularity, squareness, OPD(Over Pin Diameter) and runout were measured at 3hour, 4hour and 5hour respectively. As the result, the 3hour situation is the best, which very similar with the 4hour one. Afterwards, with the purpose of getting the result of gear hardness, the surface hardness, maximum hardness and interior hardness were measured. The result is 5h situation is the best, and it's similar with 4hour one. At last, the fatigue tests have been done which receive the result that the 4h situation showed 9~12% fatigue strength improvement compared with the 3h and 5h ones. To sum up the results, the 4hour situation shows the best performance in accuracy, hardness and fatigue strength.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.637-642
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• 2003

The Modified 9Cr-1Mo steel identified as T91, P91 and F91 in the ASME specification has been widely used for the construction of modern power plants. The available data on the influence of process parameters during manufacturing and fabrication on its properties are not sufficient. In this study, the influence of various thermal cycles on the hardness and the creep rupture strength was analyzed in the base metal and the weldments made in tube and pipe of a Mod.9Cr-1Mo steel. The low hardness, 155Hv, showed low creep rupture strength below the allowable stresses of T91 base metal in the ASME specification. This low value was attributed to the fully recovered dislocation structure and the weakening of precipitation hardening associated with the abnormal thermal cycles.

• 한국해양공학회지
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• 제26권2호
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• pp.33-38
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• 2012

The effects of the diffusible hydrogen content and hardness on the cold cracking in high strength weld metal were investigated. The diffusible hydrogen contents were influenced by welding parameters such as the voltage and contact tip-to-work distance (CTWD). The diffusible hydrogen content increased with an increase in voltage. However, it was decreased with an increase in CTWD. CTWD also influenced the weld metal hardness,especially when the wire used had a higher strength than the base metal. This showed that weld metal hardness had a more powerful effect on weld metal cold cracking than the diffusible hydrogen content in this experiment.

• Design & Manufacturing
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• 제8권2호
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• pp.23-29
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• 2014

Salt bath heat treatment is usually used but recently vacuum heat treatment is increased for the heat treatment of hot work die steels. The differences in two heat treatment processes were compared by testing the mechanical properties of heat treated products. With two different features of processes, mechanical properties such as hardness, tensile strength and impact strength of products show very different results. In this study salt bath heat treated products showed higher tensile strength and impact strength than vacuum heat treated products but hardness was not much different. These lower mechanical properties of vacuum heat treated products are due to differences in heating and quenching process.

• 열처리공학회지
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• 제33권3호
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• pp.117-123
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• 2020

Due to high corrosion resistance, Zinc has been widely used in the automobile, shipping or construction industries as a galvanizing material. Zinc is popular as a coating element, but its low mechanical strength impede the expansion of applications as a load-bearing structure. The mechanical strength of Zinc can be increased through zinc based alloy process, but the ductility is significantly reduced. In this study, the mechanical strength and ductility of Zinc-Magnesium alloys with respect to heat treatment hold time was investigated. In order to enhance the mechanical strength of Zinc, a Zinc-Magnesium alloy was fabricated by a melting process. The heat treatment process was performed to improve the ductility of Zinc-Magnesium alloy. The microstructure of the heat-treated alloy specimen was analyzed using SEM. The hardness and compressive strength of the specimen were measured by a micro-hardness tester and a nano-indenter, respectively.

• The Journal of Advanced Prosthodontics
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• 제8권6호
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• pp.433-438
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• 2016

PURPOSE. The aim of this in vitro study was to evaluate the mechanical properties (bending strength and hardness) of seven different fiber reinforced composite posts, in relation to their microstructural characteristics. MATERIALS AND METHODS. Two hundred eighty posts were divided into seven groups of 40, one group for each type of post analyzed. Within each group, 15 posts were subjected to three-point bending strength test, 15 to a microhardess meter for the Knoop hardness, and 10 to Scanning Electron Microscope in order to determine the diameter of the fibers and the percentage of fibers embedded in the matrix. To compare the flexural strength in relation to the type of fiber, matrix, and the hardness of the posts, a Kruskal-Wallis H test was used. The Jonckheere-Terpstra test was used to determine if the volume percent of fibers in the post influenced the bending strength. RESULTS. The flexural strength and the hardness depended on the type of fibers that formed the post. The lower flexural strength of a post could be due to deficient bonding between the fiber and the resin matrix. CONCLUSION. According to the results, other factors, besides the microstructural characteristics, may also influence the mechanical properties of the post. The feature that has more influence on the mechanical properties of the posts is the type of fiber.