Key Engineering Materials Vols. 345-346

Abstract: The cathode protection method is a very useful corrosion protection technology for the underground pipelines. However, it has some problems that hydrogen generated by electrochemical reaction on the wet surface of the pipelines is attacked into the pipe weld, and make degradation of their mechanical properties. Therefore, in this study, welding residual stresses around of the X65 pipe weld, which is generally used as a material of the gas pipelines, were previously calculated. And next, by using the cathode protection method, artificially degraded the X65 pipe weld including base metal, assessed its influence on the mechanical properties of the X65 pipe weld.

Abstract: In order to investigate the effect of hydrogen environment on fatigue crack growth characteristics of a low carbon steel JIS S10C, fatigue crack growth tests were conducted in a low pressure hydrogen gas environment. Fatigue crack growth rate in hygrogen gas is higher than that in nitrogen gas. It seems that a crack in the range of low growth rate prefers to propagate along the grain boundaries under hydrogen environment while in the range of high growth across the grains accompanied by brittle striation patterns or river patterns. It is important to clarify how hydrogen affects the crack growth behavior of different stages of crack growth.

Abstract: Quasi-nano filamentary copper-silver composites were irradiated and annealed to study irradiation degradation behavior. The specimen was irradiated in CT hole of HANARO of KAERI for 36 days at 320°C with the maximum neutron flux of 4.8x1020 n/cm2 (E>1.0 MeV). The gamma heating rate was in the range of 2.0-6.45 W/gm. Irradiation embrittlement was observed. Hardness determined by nano-indentation technique were 32.3 GPA for as-received condition, however, it decreased 24.6 GPa due to gamma heating, which was above the value of the specimen with same annealing effect without irradiation. Weight change of specimen with oxidation increased with annealing time, temperature and amount of dose 0.21-0.27 mR/h. Hardness change of the irradiated specimen followed by annealing was significantly dependent upon amount of dose of the specimen.

Abstract: In order to protect the global environment, especially on the point of the greenhouse effect, carbon dioxide should be used as a natural refrigerant. Because new compressors with CO2 are going to be operated under the high pressure, the interaction between sliding surfaces in the compressor becomes very important. To develop new compressor, especially rotary type, the friction and wear characteristics of sliding surfaces were very important. In this paper, the surface interactions between a shaft and a flange, which were one of the contacting parts in compressor, were evaluated. The frictional forces and wear amounts in boundary lubricated sliding condition were measured using the pin-on-disk tester. Two types of refrigerants were used, namely R410A and CO2 to compare the tribological characteristics of conventionally used one with new natural refrigerant. It was found that CO2 lead to a bad lubricity as compared with R410A or pure oil due to the formation of relatively thin protective layer on the sliding surface. Smooth surface of shaft produced lower values of friction and wear than rough surfaces. The smooth surfaces represented much more spheroidal graphite, which had very favorable tribological characteristics, on the sliding surfaces.

Abstract: In this study, an experiment program is presented to study the bonding mechanism between corroded bolts and grout and in particular the influence on bonding behavior in terms of different corrosion sections along anchor. With respect to four groups of manufactured bolt specimens, the noncorroded and the corroded, respectively, on the front, middle and rear section along anchor, a pullout test is conducted to reveal the relationship between load and loading-end slip and to investigate the bond-stress distribution characterization along full anchor. Experimental results show that corrosion product, acting as lubricating effect at the interface between bolts and grout, can result in the degradation of bonding mechanical behavior. Meanwhile, corrosion on different sections along anchor has a different effect on the anchorage capacity of bolts. Especially, corrosion on the front section induces the greatest decrease of anchorage capacity of bolts. Thus, it is concluded that the front section along anchor is the key region affecting the bonding mechanical behavior between bolts and grout.

Abstract: Microstructure, hardness and mechanical properties of the 1Cr5Mo steel tubes for the coking furnace at super temperature were investigated in this paper. It revealed that under super-temperature, oxidation corrosion for the furnace tubes was strengthened, wall thickness was evident thinner, pearlite in microstructure was spheroidised mostly, strength would be decreased and marked degradation in material occurred.

Abstract: Nanoimprint process is a simple and a low cost micro/nano fabrication method based on mold replication principle. Various kinds of applications such as optical devices for flat panel displays or electronic papers, patterned medias, bio-medical devices and electronics devices using nanoimprint process are expected. In the past a decade, many researches and developments on the process, the tool, the application relating to nanoimprint were carried out and partly commercialized. In this paper, overview on nanoimprint technology including recent progress is described. And important issues to be solved and solution idea for industrialization of nanoimprint process are pointed out. Also, our recent R&D activities on nanoimprint tool and process, which are UV/thermal nanoimorint tool and process, roll to roll type imprint system are introduced.

Abstract: The high specific strength of the magnesium alloy makes it a valuable choice for automotive, aerospace and sporting industries, where the weight reduction is a critical consideration in design. However, wrought magnesium alloys offer a poor formability at room temperature and a hot working condition is required for the forming process. This paper studies the application of finite element methods for the simulation of the forging of magnesium alloys. Numerical analysis of the forging process of an automotive magnesium wheel is conducted based on the tested flow curve of AZ80. The effect of friction on the final deformation of the upsetting of magnesium billets is also discussed.

Abstract: Stretch flange forming experiments of AA5182 and AA5754 sheet alloys were performed to characterize the forming properties. Identical blanks with the same cutout radius were deformed to 25, 50, 75, and 90% of the measured minimum punch depth to fracture. Strain development during stretch flange forming was tracked through strain measurement of the recovered deformation-interrupted samples. Finite element modeling of stretch flange forming was performed, and the resulted strain distribution along the stretch flange profile was compared to the experimental results. Good agreement was observed between the numerical and experimental results. Two failure modes observed in the stretch flange experiments, inner edge necking and circumferential cracking in sidewall, were related to the measured strain locus and sheet thickness.

Abstract: We have studied the fracture behavior of coating layer when low and high alloying galvannealed (GA) steels are subject to forming process. To understand better powdering features in the coating layer of the steel sheets, we carried out V-bending test and a series of finite element analysis which simulates damage characteristics in the coating layer. Results showed that the powdering behavior in the coating is significantly affected by the soundness and volume fraction of phases in the coating layer. The hardness variation of coating layers attributed to different phases leads to different deformation behavior of the coating layer itself.