• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.10
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• pp.879-886
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• 2016

Tractrix dies, used in the deep drawing process, can be used to form CNG pressure vessels without a blank holder. Previous studies had only applied tractrix profiles to perform the first deep drawing process of DDI; but an optimal design of the tractrix die that focuses on improving die life and reducing production cost has not been performed yet. In this study, finite element analyses of deep drawing processes were conducted according to heights of the tractrix die by using translating asymptotes. In addition, researchers analyzed von-Mises stresses at the part of stress concentration of the die according to the forming punch loads in order to propose an optimal tractrix die design.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.57-62
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• 2013

Because there is no suspension and differential devices at cart body, the deformation of the frame happened during kart driving affects the driving performance caused by the elastic deformation and the fatigue life of kart frame resulted from the permanent deformation. The dynamic behavior of kart caused by the torsional deformation during circular driving is the important factor of these two kinds of deformations. In order to analyze the dynamic behavior of kart at this curved section, GPS is used to trace the track of kart and the torsional stress at kart-frame has been measured with real time. The mechanical properties of kart-frames for leisure and racing are investigated through material property analysis and tensile test. Torsional stress concentration and frame distortion are investigated through stress analysis on frame on the basis of study result. The real karts for leisure and racing kart are also tested in each driving condition by using the driving analysis equipment. The driving behavior of kart at the curved section are investigated through this test. As the phenomenon of load movement due to centrifugal force at car is happened during circular driving, the torsional stress occurs at cart steel frame.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.901-907
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• 2013

In this study, flexural strength properties of concrete under biaxial stress state were experimentally investigated. Tests for size effect and fatigue behaviour of concrete under biaxial stress were carried out by the ASTM C 1550 and the biaxial flexure test(BFT). The results given by the biaxial tests were compared to those by the third-point bending test. Test results showed that biaxial flexural strengths obtained from the ASTM C 1550 and the biaxial flexure test are greater than the strength by the third-point bending test. As the size increases, the uniaxial and biaxial flexural strength decreases. However, the slope of the size effect of the biaxial strength was greater than that of the uniaxial strength. Finally, the fatigue response of concrete under the biaxial stress state was similar with that for uniaxial stress state.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2475-2482
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• 1993

The effects of the hole size(2R) and the specimen width(W) on the fatigue strength and the fatigue life in plain woven glass/epoxy composite plates are experimentally investigated under constant amplitude tensile fatigue loading. It is shown in this study that the notch sensitivity under fatigue loading is lower than that under static loading. It can be explained by the fact that the stress concentration is relaxed by the damage developed at the boundary of circular hole. To predict the fatigue strength at a specific cycle, the modified point stress criterion represented as a function of the geometry of the specimen(2R and W) is applied. It is found that the model used in the prediction of the notched tensile strength predicts the fatigue strength with reasonable accuracy. A model for predicting the fatigue life in the notched specimen, based on the S-$N_f$, curve in the smooth specimen, is suggested.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1119-1124
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• 2017

The stabilizer bar mounted on the vehicle underbody makes for a more comfortable ride by holding the vehicle itself when the vehicle is cornering. Stabilizer bars are available in two types: solid and tube. To lighten the weight of the vehicle, and owing to weight reduction requirements, tubular stabilizer bars are increasingly being used. Tubular stabilizer bars can be fabricated to be over 34％ lighter than solid bars, but the lifetime of the product tends to decrease rapidly as the weight ratio increases. However, the durability can be improved by utilizing high-strength and high-hardness materials for the stabilizer bar or by improving the shot peening method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.10
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• pp.1158-1162
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• 2009

Fatigue limit of the copper film coated by Sn was estimated using Goodman diagram and Gerber diagram. To obtain the high cycle fatigue life curve, S-N curve, of the film, the high cycle fatigue test was carried out by applying the constant amplitude load to the film specimen with three different stress ratio of 0.05, 0.3 and 0.5 and the frequency of 40 Hz at room temperature in air. The free-standing film specimen 15.26${\mu}m$ thick was fabricated by etching process. The fatigue limits and S-N curves at the respective stress ratios were determined from the experimental works. It was shown that the S-N curves were dependent on the stress ratio and the fatigue limit was increased with decreasing the stress ratio. The dependency of the fatigue behavior was presented in empirical relationship. Using these relationships, the fatigue limit was predicted.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.134-140
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• 2014

The paper presents an overview of the present state of study on the fatigue behaviors at very high number of cycles ($N_f$ > $10^7$). A classification of materials with typical S-N curves and influencing factors such as notches, residual stresses, temperatures, corrosion environments and stress ratios are given. The microstructural inhomogeneities of materials and micro-cracks played an important roles in very high cycle fatigue behaviors. The failure mechanisms for the fatigue design of materials and components are mentioned.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.125-130
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• 2011

Technological mode progress demands the use of materials at high temperature and pressure. Constant load creep tests have been carried out over the range of stresses at high temperatures. One of the most critical factors in considering such applications as the most critical one is the creep behavior. In order to investigate the creep behavior in this study, the stress exponents during creep were determined over the temperature range of $275^{\circ}C$ to $325^{\circ}C$ and the stress range of 36MPa to 72MPa. The applicability of modified Monkman-Grant relationship was also discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.166-173
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• 2007

Fatigue fracture behavior of a hybrid bolted joint was evaluated in comparison to the case of static fracture. Two kinds of specimens were fabricated for the mechanical tests; a hybrid bolted joint specimen for the shear test and a hybrid joint part specimen applied in the real tilting car body for the bending test. Characteristic fracture behaviors of those specimens under cyclic toads were obviously different from the case under static loads. For the hybrid bolted joint specimen, static shear loading caused the fracture of the bolt body itself in a pure shear mode, whereas cyclic shear loading brought about the fracture at the site of local tensile stress concentration. For the hybrid joint part specimen, static bend loading caused the shear deformation and fracture in the honeycomb core region, while cyclic bend loading did the delamination along the interface between composite skin and honeycomb core layers as well as the fracture of welded joint part. Experimental results obtained by static and fatigue tests were reflected in modifications of design parameters of the hybrid joint structure in the real tilting car body.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.3
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• pp.429-436
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• 2013

This study considers how the fatigue behavior and probabilistic properties of SAE1055 steel are related to its hardness level. SAE1055 steel was heat-treated using induction hardening. Five types of specimens were prepared (A: base material, B: through hardened material with HV390, C: through hardened material with HV510, D: through hardened material with HV700, and E: surface hardened material with HV700). Fatigue tests were performed under a stress ratio of R = -1 using a 4-point rotary bending fatigue tester. The fatigue behaviors were greatly influenced by the hardness, but the fatigue limit did not increase over a hardness of HV510. In addition, the effect of the hardness level on the failure mechanism was evaluated using a scanning electron microscope. The probabilistic properties of the fatigue life were investigated using a probabilistic S-N approach, and the effect of the hardness level on these properties was evaluated using a residue analysis.