• Journal of Welding and Joining
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• v.27 no.5
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• pp.81-87
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• 2009

Recently, extruded aluminium-alloy panels have been used in the car bodies for the purpose of the light-weight of railway vehicles and FSW(Friction Stir Welding), which is superior to the arc weldings, has been applied in the railway vehicles. This paper presents the optimum design of the FSW process on A6005 extruded alloy for railway vehicles to improve its mechanical properties. Rotational speed, welding speed and tilting angle of the tool tip were chosen as design parameters. Three objective functions were determined; maximizing the tensile strength, minimizing the hardness and maximizing the difference between the normalized tensile strength and hardness. The tensile tests and the hardness tests for fifteen FSW experiments were carried out according to the central composite design table. Recursive model functions on three characteristic values, such as the tensile strength, the hardness difference(${\Delta}Hv$) and the difference of normalized tensile strength and ${\Delta}Hv$, were estimated according to the classical response surface analysis methodology. The reliability of each recursive function was verified by F-test using the analysis of variance table. Sensitivity analysis on each characteristic value was done. Finally, the optimum values of three design parameters were found using Sequential Quadratic Programming algorithm.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.

• Journal of Korea Foundry Society
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• v.39 no.6
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• pp.103-109
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• 2019

Cu-added SKD11 was manufactured through the casting process and the effects of Cu addition with different contents (0, 1, 2 and 3 wt%) and aging treatment on microstructure, mechanical characteristics such as tensile strength and hardness, and thermal conductivity were investigated. The microstructure was analyzed by FE-SEM and XRD, the mechanical characteristics by Rockwell hardness tester and Tensile tester, and the thermal conductivity by Laser flash. As a result, SKD11 containing Cu had higher hardness than as-received SKD11. The hardness of as-cast SKD11 containing 1 wt% Cu was 42.4 HRC, whereas the hardness of asreceived SKD11 cast alloy was 19.5 HRC, indicating that the hardness was greatly improved when Cu was added. In the case of tensile strength, Cu-added SKD11 cast alloy had lower tensile strength than as-received SKD11, and the tensile strength tended to increase as Cu content increased. After heat treatment, however, tensile strength of as-received SKD11 was significantly increased, whereas in the case of Cu-added SKD11, as the Cu contents increased, the tensile strength increased less and even reduced at 3 wt% Cu. The thermal conductivity of Cu-added SKD11 cast alloy was about 13 W m^-1 K^-1, which was lower than that of the asreceived SKD11 cast alloy (28 W m^-1 K^-1). After the heat treatment, however, the thermal conductivity of as-received SKD11 was reduced, while the thermal conductivity of the SKD11 added with Cu was increased. Thermal conductivity was generally larger with less Cu content, and this tendency became more pronounced after heat treatment.

• Journal of Power System Engineering
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• v.18 no.5
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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.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.108-116
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• 1999

Gray cast iron with a high damping capacity has been used for controlling the vibration and noise in various mechanical structures. Nevertheless, its usage has been often restricted due to its poor tensile strength. Therefore, it is necessary to improve tensile strength at the expense of a loss in damping capacity. This study is aimed at finding the best combination of tensile strength and damping capacity by varying austempering time and temperature range from $320^{\circ}C$ to $380^{\circ}C$ after austenization at $900^{\circ}C$ for 1hr. The effect of austempering condition on hardness and the volume fraction of retained austenite is investigated as well. The results obtained are summarized as follows : (1) With an increase in austempering temperature, both tensile strength and hardness decrease while damping capacity improves. (2) Austempering at $350^{\circ}C$, resulting in a mixture of upper and lower bainite with partially retained austenite, exhibits the optimum combination of tensile strength and damping capacity.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.125-133
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• 1995

Rene80 superalloy was liquid phase diffusion bonded by using pure boron (B) as an insert material. As a basic study for the possibility of practical application of this bonding method, hardness and high temperature tensile strength of the bonded joint and metallurgical analysis were investigated. As experimental results, hardness of the bonded joint was homogenized after bonding and the tensile strength at 1144K was obtained to 90% of that of base metal. But there were some problems to be improved also, that means the joint was hardened after bonding due to increase of B content and elongation was much lower than that of base metal. Flat area and (Mo, Cr, W) boride, which should be harmful for bonding strength, were observed on the fractured surface of the tensile tested specimen.

• Design & Manufacturing
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• v.8 no.2
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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.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.3
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• pp.109-116
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• 2007

The present study examined mechanical properties according to the change of outer circumference in the friction welding of A2024-T4 stock, which is used much as aircraft structure, truck wheel, stainless materials and A2024-T4 stock with 10 hollow at the center. Welding conditions were fixed at RPM 2,000rpm, friction pressure of 50MPa, friction time of 1.5sec, upset pressure of 120MPa and upset time of 2.0 seconds. From the result of this study were drawn conclusions as follows : According to the result of a tensile strength test, the solid shaft showed linear increase of tensile strength with the change of outer circumference, the hollow shaft showed maximum tensile stength when the length (L) was 2mm and decrease of tensile strength with the change of outer circumference, hardness appeared to increase and then decrease for welding interface, and it showed maximum hardness 155Hv at L=5mm of the solid shaft. Bending strength increased linearly far change of the distance (L) of outer circumference in the solid shaft and then decreased linearly in the hollow shaft. the result of examining tissue, the tissue grew finer around the welding interface and divided the basic material and the welding surface.

• Corrosion Science and Technology
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• v.5 no.4
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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.

• Korean Journal of Materials Research
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• v.18 no.11
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• pp.604-609
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• 2008

The sintering behavior of zircon with silica was investigated. Zircon with 5 vol% of sedimentation $SiO_2$ resulted in the apparent density of $4.45\;g/cm^3$, the diametral tensile strength of $12.125\;kgf/cm^2$, and the micro Vickers hardness of 1283 HV. The dissociation temperature and mechanical characteristics of the $ZrSiO_4$ were changed with different kinds of $SiO_2$. $SiO_2$ addition prevented dissociation of $ZrSiO_4$. Zircon with 5 vol% of sedimentation $SiO_2$ and with 5 vol% of fused $SiO_2$ resulted in increased diametral tensile strength and increased micro Vickers hardness by suppression of $ZrSiO_4$ dissociation and low temperature liquid $SiO_2$ formation. Zircon with fumed $SiO_2$ and quartz $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of cristobalite and quartz phase formation and high temperature liquid $SiO_2$ formation. Zircon with 10 vol% of $SiO_2$ resulted in decreased diametral tensile strength and decreased micro Vickers hardness because of weak particle coupling due to excess formation of liquid $SiO_2$.