• Proceedings of the KSME Conference
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• 2001.11a
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• pp.258-265
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• 2001

Turbine blade is subject to force of three type ; torsional force by torsion-mount, centrifugal force by rotation of rotor and cyclic bending force by steam pressure. Cyclic bending force of them is main factor on fatigue fracture. In the X-ray diffraction method, the change in the values related to plastic deformation and residual stress near the fracture surface mat be determined, and information of internal structure of material can be obtained. Therefore, to find a fracture mechanism of torsion-mounted blade in nuclear plant, based on the information from the fracture surface obtained by fatigue test, the correlation of X-ray parameter and fracture mechanics parameter was determined, and then the load applied to actual broken turbine blade parts was predicted. Failure analysis is performed by finite element method and Goodman diagram on torsion-mounted blade.

• Transactions of Materials Processing
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• v.31 no.5
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• pp.296-301
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• 2022

In this study, influence of the process parameters of the roller leveling process on the straightness of the steel wire was analyzed using numerical analysis. To construct the numerical analysis model, cross-sectional and longitudinal element sizes, which affect the prediction accuracy of longitudinal stress caused by bending deformation of the steel wire, were optimized, and mass scaling that satisfies prediction accuracy while reducing computational time was confirmed. By using the constructed numerical analysis model, the influence of various process parameters such as input direction of the steel wire, initial diameter of the steel wire, back tension and intermesh on the straightness was confirmed. The simulation result shows that the 3^rd and 4^th roller of vertical straightener had a significant influence on vertical shape of the steel wire.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.6
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• pp.1209-1216
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• 2002

The requirements of coil spring fer higher fatigue strength have been increased to achieve the weight reduction of a vehicle. As the possible increase in fatigue strength by using the conventional shot peening treatment is found to be limited, it is necessary to modify the shot peening treatment. The warm shot peening is a shot peening treatment carried out within warm temperature range. The aim of this paper is to analyze some experimental results concerned with the effect of warm shot peening and to discuss the mechanism of warm shot peening in detail. By the results of rotating bending fatigue test, the fatigue strength of test specimen increases up to 23.8% in the production condition of warm shot peening at 200$\^{C}$ compared with conventional shot peening. The major reason why the warm shot peening is effective to the improvement of fatigue strength is the increase of a compressive residual stress distribution, which can be caused by more effective deformation under the condition of warm temperature.

• Journal of Ocean Engineering and Technology
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• v.25 no.6
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• pp.72-79
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• 2011

In this paper, the fatigue characteristics of shot peened A7075-T651 alloy were compared with those of the specimens without the shot peening. The multi-spindle and single-spindle rotating bending fatigue testing machines were employed for the evaluation. Shot peening (SP) with various pressure (5 psi, 10 psi, 15 psi, 25 psi and 35 psi) were used in this test. In order to investigate the effect of the applied pressure during the SP, we carried out the surface roughness test, compressive residual stress test, hardness test, tensile test, VHCF (Very high cycle fatigue) test and SEM observation. SP induced the formation of remarkable compressive residual stress from the surface to certain depth of sample by means of the plastic deformation. The surface hardness and the fatigue characteristics of the specimens were also modified by the SP. According to the S-N curves, fatigue lives of shot peended sample with 25 psi measures 50 times higher than that of the untreated sample. The fatigue lives of shot peened sample with 15 psi and 35 psi measure approximately 10 times higher than that of the untreated ones.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.56-56
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• 2018

Transparent conductive oxides (TCOs) have attracted attention due to their high electrical conductivity and optical transparency in the visible region. Consequently, TCOs have been widely used as electrode materials in various electronic devices such as flat panel displays and solar cells. Previous studies on TCOs focused on their electrical and optical performances; there have been numerous attempts to improve these properties, such as chemical doping and crystallinity enhancement. Recently, due to rapidly increasing demand for flexible electronics, the academic interest in the mechanical stability of materials has come to the fore as a major issue. In particular, long-term stability under bending is a crucial requirement for flexible electrodes; however, research on this feature is still in the nascent stage. Hydrogen-incorporated amorphous In-Sn-O (a-ITO) thin films were fabricated by introducing hydrogen gas during deposition. The hydrogen concentration in the film was determined by secondary ion mass spectrometry and was found to vary from $4.7{\times}10^{20}$ to $8.1{\times}10^{20}cm^{-3}$ with increasing $H_2$ flow rate. The mechanical stability of the a-ITO thin films dramatically improved because of hydrogen incorporation, without any observable degradation in their electrical or optical properties. With increasing hydrogen concentration, the compressive residual stress gradually decreased and the subgap absorption at around 3.1 eV was suppressed. Considering that the residual stress and subgap absorption mainly originated from defects, hydrogen may be a promising candidate for defect passivation in flexible electronics.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.347-356
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• 2006

In this paper, practical nonlinear inelastic analysis method of 3-dimensional steel structures accounting for gradual yielding with fibers on a section is developed. Geometric nonlinearities of member(p-$\delta$) and frame(p-$\Delta$) are accounted for by using stability functions. Residual stresses are considered by assigning initial stresses to the fiber on the section. The elastic core in a section is investigated at every loading step to determine the axial and bending stiffness reduction. The strain reversal effect is captured by investigating the stress change of each fiber. The proposed analysis proves to be useful in applying for practical analysis and design of three-dimensional steel frames.

• Journal of the Korean institute of surface engineering
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• v.34 no.5
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• pp.421-428
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• 2001

New WC-CrN superlattice film was deposited on Si substrate (500$\mu\textrm{m}$) using cathodic arc ion plating system. The microstructure and mechanical properties of the film depend on the superlattice period (λ). In the X-ray diffraction analysis (XRD), preferred orientation of microstructure was changed according to various superlattice periods(λ). During the Transmission Electron Microscope analysis (TEM), microstructure and superlattice period (λ) of the WC - CrN superlattice film was confirmed. Hardness and adhesion of the deposited film was evaluated by nanoindentation test and scratch test, respectively. As a result of nanoindentation test, the hardness of WC - CrN superlattice film was gained about 40GPa at superlattice period (λ) with 7nm. Also residual stress with various superlattice period (λ) was measured on Si wafer (100$\mu\textrm{m}$) by conventional beam-bending technique. The residual stress of the film was reduced to a value of 0.2 GPa by introducing Ti - WC buffer layers periodically with a thickness ratio ($t_{buffer}$/$t_{buffer+superlattice}$ ). To the end, for the evaluation of oxidation resistance at the elevated temperature, CrN single layer and WC - CrN superlattice films with various superlattice periods on SKD61 substrate was measured and compared with the oxidation resistance.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.211-218
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• 2000

It is desirable but difficult to predict springback quantitatively and accurately for successful tool and process design in sheet stamping operations. The result of springback analysis by the finite element method (FEM) is sensitively influenced by numerical factors such as blank element size, number of integration points, punch velocity, contact algorithm, etc. In the present work, a parametric study by Taguchi method is performed in order to evaluate the influence of numerical factors on the result of springback analysis quantitatively and to obtain the combination of numerical factors which gives the best approximation to experimental data. Since springback is determined by the residual stress after forming process, it is important to evaluate stress distribution accurately. The oscillation in the time history curve of stress obtained by the dynamic-explicit finite element method says that the stress solution at termination time is in very unstable state. Therefore, a variability study is also carried out in this study in order to assess the stability of implicit springback analysis starting from the stress solution by explicit forming simulation. The U-draw bending process, one of the NUMISHEET '93 benchmark problems, is adopted as an application model because it is most popular one for evaluating the springback characteristic.

• International journal of steel structures
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• v.18 no.4
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• pp.1440-1463
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• 2018

The Wagner coefficient is a key parameter used to describe the inelastic lateral-torsional buckling (LTB) behaviour of the I-beam, since even for a doubly-symmetric I-section with residual stress, it becomes a monosymmetric I-section due to the characteristics of the non-symmetrical distribution of plastic regions. However, so far no theoretical derivation on the energy equation and Wagner's coefficient have been presented due to the limitation of Vlasov's buckling theory. In order to simplify the nonlinear analysis and calculation, this paper presents a simplified mechanical model and an analytical solution for doubly-symmetric I-beams under pure bending, in which residual stresses and yielding are taken into account. According to the plate-beam theory proposed by the lead author, the energy equation for the inelastic LTB of an I-beam is derived in detail, using only the Euler-Bernoulli beam model and the Kirchhoff-plate model. In this derivation, the concept of the instantaneous shear centre is used and its position can be determined naturally by the condition that the coefficient of the cross-term in the strain energy should be zero; formulae for both the critical moment and the corresponding critical beam length are proposed based upon the analytical buckling equation. An analytical formula of the Wagner coefficient is obtained and the validity of Wagner hypothesis is reconfirmed. Finally, the accuracy of the analytical solution is verified by a FEM solution based upon a bi-modulus model of I-beams. It is found that the critical moments given by the analytical solution almost is identical to those given by Trahair's formulae, and hence the analytical solution can be used as a benchmark to verify the results obtained by other numerical algorithms for inelastic LTB behaviour.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.619-625
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• 2008

The effects of thermal cycling on residual stresses in both inorganic passivation/insulating layer that is deposited by plasma enhanced chemical vapor deposition (PECVD) and organic thin film that is used as a bonding adhesive are evaluated by 4 point bending method and wafer curvature method. $SiO_2/SiN_x$ and BCB (Benzocyclobutene) are used as inorganic and organic layers, respectively. A model about the effect of thermal cycling on residual stress and bond strength (Strain energy release rate), $G_c$, at the interface between inorganic thin film and organic adhesive is developed. In thermal cycling experiments conducted between $25^{\circ}C$ and either $350^{\circ}C$ or $400^{\circ}C$, $G_c$ at the interface between BCB and PECVD $ SiN_x $ decreases after the first cycle. This trend in $G_c$ agreed well with the prediction based on our model that the increase in residual tensile stress within the $SiN_x$ layer after thermal cycling leads to the decrease in $G_c$. This result is compared with that obtained for the interface between BCB and PECVD $SiO_2$, where the relaxation in residual compressive stress within the $SiO_2$ induces an increase in $G_c$. These opposite trends in $G_cs$ of the structures including either PECVD $ SiN_x $ or PECVD $SiO_2$ are caused by reactions in the hydrogen-bonded chemical structure of the PECVD layers, followed by desorption of water.