• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.5
• /
• pp.160-167
• /
• 2000

In this research, the fatigue behaviors of carbonitrided Cr-Mo(SCM415) steel are examined. From fatigue test results, we propose a modified fatigue strength evaluation model and modified formulae. That is, we develop improved models fur evaluating and predicting the fatigue strength of carbonitrided SCM415 by modifying specific terms in the Murakami and Endo's model which is the representative fatigue strength evaluation formulae fur high strength steel.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.8
• /
• pp.135-144
• /
• 1998

In this research, the fatigue behaviors of Cr-Mo(SCM415) steel and carbonitrided CrMo(SCM415) steel are examined. The description of experiments in detail as follows. For SCM415 and carbonitried Cr-Mo(SCM415) steel, smooth specimens and hole defected specimens are fabricated and tested under a rotary bending tester, respectively. By performing the rotary bending fatigue test for smooth and hole defected specimens, the characteristics of the fatigue strength are examined for parameters such as tensile strength, hardness at surface, and residual stresses.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.10
• /
• pp.1315-1321
• /
• 2011

Prior to the experimental and production stages of goods, the strengths should be evaluated in the design stage. The introduction of commercial codes at the design stage gives benefits such as cost and time economies in the production and strength evaluation. In this study, structural analysis and fatigue analysis are carried out using ANSYS modeling of the 3D geometry of the wheel. In a comparison of dish-type and spoke-type wheels, it is shown that the deformation and maximum equivalent stress for the dish-type wheels are lower than those for spoke-type wheels. Nevertheless, spoke-type wheels are often used because they are light and have exhibit excellent cooling performance. Furthermore, according to the results of life analysis, aluminum wheels show improved resistance to fatigue compared to steel wheels.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.9
• /
• pp.1137-1143
• /
• 2010

This paper presents a fatigue design method for plug- and ring-type gas-welded joints, which takes into account the effects of welding residual stress. To develop this method, we simulated the gas-welding process by performing nonlinear finite element analysis (FEA) To validate the FEA results, numerically calculated residual stresses in the gas welds were then compared with experimental results obtained by the hole-drilling method. To evaluate the fatigue strength of plug- and ring-type gas-welded joints influenced by welding residual stresses, the use of stress amplitude $(\sigma_a)_R$, which includes the welding residual stress in gas welds, is proposed $(\sigma_a)_R$ on the basis of a modified Goodman equation that includes the residual stress effects. Using the stress amplitude $(\sigma_a)_R$ at the hot spot point of gas weld, the relations obtained as the fatigue test results for plug and ring type gas welded joints having various dimensions and shapes were systematically rearranged to obtain the $(\sigma_a)_R-N_f$ relationship. It was found that more systematic and accurate evaluation of the fatigue strength of plug- and ring-type gas-welded joints can be achieved by using $(\sigma_a)_R$.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.3
• /
• pp.339-344
• /
• 2013

Hot forming using boron steel is currently used for manufacturing low-weight automobile body parts, and a high tensile strength of about 1,500 MPa is obtained after hot forming. However, a high fatigue life is a more important factor than high strength when it is used for automobile suspension parts. A tubular torsion beam axle (TTBA) is one of these suspension parts, and this research deals with the fatigue characteristic of TTBA using hot forming. The low cyclic fatigue life of boron steel is investigated according to the cooling method. In addition, a structural and fatigue analysis of TTBA is performed to predict the fatigue life. The stress concentration that occurs in the tubular torsion beam is found, and the longest fatigue life occurs when rapid cooling is utilized in the TTBA fabrication.

• Journal of Welding and Joining
• /
• v.10 no.4
• /
• pp.259-267
• /
• 1992

In this report, a method to predict the fatigue strength in welded structure member of ship construction is studied considering the effects of statistical characteristics of mild steels and weld toe shapes on the fatigue crack initiation life. The fatigue test under pulsating bending load is carried out with the model specimens of the web frame in double bottom of ship hull. The propriety of the fatigue life curve with probability of failure in the transverse strength members of ship hull construction is confirmed by the comparison with the results of fatigue test on the model of the various transverse strength members.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.5
• /
• pp.651-657
• /
• 2010

A composite piston with a crown made of steel and a skirt made of NCI is used in a marine diesel engine, which has a maximum firing pressure of over 180 bar and a high thermal load. In the fatigue design of the composite piston, the fatigue is influenced by factors such as the load type, surface roughness, and temperature; further, the distribution ratio of the firing force from the crown to the skirt is important for optimizing the design of the crown and skirt. In this study, the stress gradient method was used to consider the effect of the load type. The temperature field on the piston was predicted by cocktail-shaking cooling analysis, and influence of high temperature on fatigue strength was investigated. The load transfer ratio and contact pressure were optimized by design of the surface shape and accurate tolerance analysis. Finally, the cooling performance and durability design of the composite piston were verified by performing a long-term prototype test.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.7 no.3
• /
• pp.241-249
• /
• 2003

The service life of steel bridges can be assured only when their strength, serviceability and fatigue safety are fulfilled. However, at the present time, the continuous research for fatigue of steel bridges is desperately required since not much research work has been done so far. In this study, a guideline on the fatigue design is suggested for the practical purpose in order to establish the long-term safety of steel bridges against fatigue. The continuous steel truss bridge was analyzed for the cumulative reversals of the actual traffic, stress ranges and fatigue strength. From the results, the domestic fatigue design procedure was found to be fairly overestimated in comparison to the design code of other foreign countries. Therefore, it is necessary to review the current fatigue design specifications and have the new and rationalized design criteria in the future domestic fatigue design guidance.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.4
• /
• pp.667-674
• /
• 1992

Recently advantages in composite and light weight material technique have led to the increased use of structural adhesives in various industries. In spite of such wide application of the adhesive joints, the evaluation method of fracture strength and design methodology of them, have not been established. In this study finite element method, theoretical and experimental analyses were investigated according to changes of lap length and adhesive for adhesive single-lap joint. As the results, the strength evaluation of adhesive joint by conventional nominal stress, was pointed out inadequate strength evaluation and design method regardless stress singularity, stress distribution and crack propagation in its adhesive layer. Also, it was examined the problems to apply fracture mechanics by means of static and fatigue test.

• International Journal of Highway Engineering
• /
• v.6 no.3 s.21
• /
• pp.27-35
• /
• 2004

There are two methods in estimating the remaining life of in-service airfield concrete pavement. They are a method simply using the past accumulated traffic and a method using the theoretical mechanistic analysis. Since the former method is somewhat far from the actual condition, the latter method is widely used by most engineers and researchers. The most essential component of the latter method is the fatigue model of the concrete slab. A fatigue model for airfield concrete pavement is developed in this study by a series of fatigue tests using 30 concrete cylinder specimens obtained from a 10 year old in-service airfield concrete slab. Strengths for the stress ratio calculation were obtained from the split tensile test of the cores sliced. Fatigue test mode was repeated split tensile test. The R2 of developed fatigue model was 0.5. Specimens taken from another airport had been tested for validation of the model. The results showed a good fit to the model. It was also found that the fatigue life predicted from the model was a tittle greater when the stress ratio is greater than 80 percent than other fatigue models developed earlier in America.