Designing, Processing and Properties of Advanced Engineering Materials

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Authors: Young Seon Lee, J.H. Lee, Yong Nam Kwon, T. Ishikawa
Abstract: The dimension of cold forged part is larger than that of the die cavity. The difference could be originated from the various features, such as the elastic characteristics of die and workpiece, thermal influences, and machine-elasticity. Among these features, elastic behavior of die and workpiece has been considered as the most important element for the precision cold forging. In the present study, the effect of material properties of both workpiece and die on the dimensional precision of forged part was investigated using FE and experimental analyses. Three materials, such as SCM420H, Cu-OFHC and Al6061 alloy, were used to divide the effect of the elastic modulus and flow stress on the dimension specifically. From the results of FEA, the elastic deformation of die was found to be more dominant than that of workpiece. The die expansion depends on the flow stress of workpiece during a loading stage. On the other hand, the die contraction during unloading was affected by both the flow stress and elastic modulus of workpiece. The elastic modulus of workpiece affects the elastic recovery of forged part after ejecting stage.
Authors: Hiroyuki Muto, Mototsugu Sakai
Abstract: A novel indentation method is proposed to study the mechanical properties of porous and/or heterogeneous materials by the use of a cylindrical indenter with line loading on test specimens. The problems in line contact are examined. The indentation load P versus penetration depth h relation in line contact is expressed in terms of the radius R of cylindrical indenter and the contact length L. An application of a cylindrical indentation to a polycrystalline graphite leads to a successful determination of the Young's modulus and the yielding strength. It is concluded that the line contact rather than the conventional pyramidal point contact is more efficient for the experimental deternination of mechanical properties of porous and/or heterogeneous materials.
Authors: Shigeki Morita, Toshiro Kobayashi
Abstract: Instrumented Charpy impact test method is possible to obtain various dynamic fracture characteristics from the load-deflection or load-time curve. Recently, instrumented Charpy impact test method is widely used for the evaluation of toughness of various specimens of different materials with different sizes. It is important to record an accurate impact load in order to improve the reliability of this test method. In some standards of instrumented Charpy impact test method such as ISO and ASTM, they haven.t clearly standardized striker geometry which seem to directly influence the obtained impact load. There are some differences between standards, although standard procedures are well defined. Therefore, instrumented Charpy impact test method has a problem that measurement value is different depending on each standard. In the present study, the effect of striking edge geometries, which are difference between ISO and ASTM, on load-deflection curve and absorbed energy were investigated. According to ISO and ASTM, two types of striker having different radius were machined. There was no difference between the two different striking edge geometries for values of absorbed energy per unit ligament area less than 0.75J/mm2. However, striking edge geometry according to ASTM is not propriety for Charpy impact test method because of four, instead of three, point bending on process of fracture at high level of absorbed energy. The effect of brinelling deformation, which was considered as an advantage of striking edge geometry according to ASTM, is very small on instrumented Charpy impact test. Consequently, there seem to be not an advantage of striking edge geometry according to ASTM. Therefore, standards should be unified in the striking edge geometry according to ISO.
Authors: Hi Won Jeong, Y.S. Kim, Seung Eon Kim, Yong Taek Hyun, Yont Tai Lee, J.K. Park
Abstract: New titanium alloys with a low elastic modulus have been developed for biomedical applications to avoid the stress shielding effect of the artificial prosthesis. The newly developed alloys contained the transition elements like Nb, Ta, Zr which were non-cytotoxicity elements. These elements produced β, ω, and α'' phases with heat treatment conditions in titanium alloys and determined the elastic modulus of the alloys. However, the clear mechanism of the low elastic modulus alloys has not been known. In the present paper, the total energy and elastic modulus of β and α'' phases were calculated using a first principle calculation employing the generalized gradient approximation (GGA). The mechanism of the low elastic modulus was discussed with calculated values.
Authors: Young Mok Rhyim, Kuk Tae Youn, Wee Do Yoo, Young Sang Na, J.H. Lee
Abstract: The influence of thermal fatigue test temperature on crack propagation behavior of the surface treated tool steel for die-casting was investigated. For this purpose, thermal fatigue system consisted of induction heating and water spray quenching unit was constructed to simulate the service condition and Lm is proposed as the index representing the susceptibility to crack initiation and propagation. The thermal fatigue tests were conducted at the maximum temperature of 600°C, 700°C and 720°C using as-heat treated or nitrided specimens. The ion nitrided specimen showed lower Lm value than as-heat treated at all test temperature. But in the case of maximum and average crack length, the ion nitrided specimen exhibited higher value than those of as-heat treated specimen.
Authors: Moo Young Huh, J.P. Lee, Jae Chun Lee, Jong Woo Park, Young Hoon Chung
Abstract: The evolution of texture and microstructure during the equal channel angular rolling (ECAR) and subsequent annealing in aluminum alloy 3003 sheets was investigated. The tools of ECAR were designed to provide a constant shear deformation of the order of 0.5 per passage while preserving the original sheet shape. Samples of the aluminum alloy 3003 sheets were repeatedly deformed by ECAR up to twelve passages. Shear textures developed after the first passage of ECAR. However, the intensity of shear texture components decreased with increasing number of ECAR passages. After a large number of ECAR passages, a random texture developed at the expense of shear texture components. Observations by TEM and EBSD revealed that the degree of misorientations within the deformed grains increased with increasing number of ECAR passages. After recrystallization annealing, samples deformed by ECAR displayed pronounced {111}//ND fiber orientations. The annealed sheets comprising of ultra-fine grains were successfully produced in the samples deformed by a large number of ECAR passages.
Authors: Ji Hyun Yoon, Jun Park, Soon Dong Park, Bong Sang Lee, Eui Pak Yoon
Abstract: The influence of the microstructure on the J-R ductile crack growth resistance of austenitic stainless steel AISI Type 347 welds was examined. The optical and electron microscopy, and chemical examinations and XRD analysis were conducted on a series of J-R test specimens which were tested at 316oC. It was concluded that the J-R property of the Type 347 weld decreased with increasing the contents of the Nb(C, N) precipitates which were dependant on the carbon contents of the filler metals. The higher δ-ferrite content also deteriorated the J-R property of the Type 347 weld.
Authors: Do Won Seo, Ho Chel Yoon, Jin Yi Lee, Jae Kyoo Lim
Abstract: Ceramics are significantly used in many industrial applications due to their excellent mechanical and thermal properties such as high temperature strength, low density, high hardness, low thermal expansion and good corrosion properties. To combine the specific advantages of ceramics with that of metals, they are often used together within one composite component. In this study, the effect of temperature on fracture characteristics of silicon nitride joined to 304 stainless steel brazed with Ti active alloy are investigated in room and high temperature regions. And analytical studies on the residual stress of dissimilar brazed joint are performed by the finite element method. Four-point bending strength and deflection of interlayer increase with increasing strain rate in room temperature. As the test temperature increases, the bending strength decreases, but the deflection of interlayer is almost constant. The residual stresses redistribute after cutting of joint and the maximum tensile stress occurs on the new free surface at the ceramic near the interface. The singularity of residual stresses at the ceramic near the interface is characterized by elastic-plastic properties of ceramic and inserted materials.­
Authors: Chang Seog Kang, Sung Kil Hong
Abstract: A mechanical spectroscopy study has been made on fine-grained Ni-10vol%TZP(ZrO2-3mol.%Y2O3) composite in an attempt to assess the following micromechanical prediction. A dual-phase material with fine-grained constituents deforming by Coble-type boundary-diffusion creep exhibits viscoelastic behavior. Dynamic Young's modulus and internal friction are measured over a temperature range of 25 to 800oC at frequencies of 0.01, 0.05 and 0.1Hz using a specially designed tension-compression apparatus. Two relaxation peaks are observed in the composite. An exponential involved in the peak and background components are determined and, by making a further analysis based on the micromechanical formulation and also taking the well-known relaxation due to viscous grain-boundary sliding into account, the implications of these quantities are discussed in terms of constituent material parameters(boundary diffusivity, grain size, etc.).
Authors: H.K. Lee, Chung Yun Kang, C.S. Woo, S.H. Kim, Dae Up Kim
Abstract: Microstructures of 0.18wt% nitrogen-contained duplex stainless steel, SUS329J3L brazed in a vacuum furnace of 10-4 torr, have been investigated as a function of bonding temperatures (1453-1523K) and holding times (0-1.8ks). An amorphous alloy, MBF50 (Ni-19.5wt%Cr-7.3wt%Si -1.5wt%B), was used as an insert metal. At an early stage at 1453K and 1473k, a morphology change of the insert metal, BN and CrB phase appeared only at the joints. The BN and Cr-Si-N phase were observed at the interface of the joints brazed under other conditions. The volume fraction of BN increased rapidly at an early stage and decreased with increasing holding time. The phase seemed to have been formed by dissolution of the base metal and the diffusion process. BN was formed easily due to the lowest Gibbs free energy. Boron content in liquid insert metal becomes low due to the formation of a large number of BNs at the bonded interlayer by holding for a few minutes at brazing temperature. This caused the rapid isothermal solidification of the liquid insert metal. Thus, it is clear that the isothermal solidification process of this bonding is controlled by the formation of boron nitrides as opposed to the diffusion process of depressant elements(B and Si) in the base metal.

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