• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.5
• /
• pp.724-733
• /
• 2003

Fatigue design rules for welds in the ASME Boiler and Pressure Vessels Code are based on the use of Fatigue Strength Reduction Factors(FSRF) against a code specified fatigue design curve generated from smooth base metal specimens without the presence of welds. Similarly, stress intensification factors that are used in the ASME B3l.1 Piping Code are based on component S-N curves with a reference fatigue strength based on straight pipe girth welds. But the determination of either the FSRF or stress intensification factor requires extensive fatigue testing to take into account the stress concentration effects associated with various types of component geometry, weld configuration and loading conditions. As the fatigue behavior of welded joints is being better understood, it has been generally accepted that the difference in fatigue lives from one type of weld to another is dominated by the difference in stress concentration. However, general finite element procedures are currently not available for effective determination of such stress concentration effects. In this paper, a mesh-insensitive structural stress method is used to re-evaluate the S-N test data, and then more effective method is proposed for pressure vessel and piping fatigue design.

• Wind and Structures
• /
• v.32 no.5
• /
• pp.501-508
• /
• 2021

The turbine industry demands a reliable design with affordable cost. As technological advances begin to support turbines of huge sizes, and the increasing importance of wind turbines from day to day make design safety conditions more important. Wind turbines are exposed to environmental conditions that can affect their installation, durability, and operation. International Electrotechnical Commission (IEC) 61400-1 design load cases consist of analyses involving wind turbine operating conditions. This design load cases (DLC) is important for determining fatigue loads (i.e., forces and moments) that occur as a result of expected conditions throughout the life of the machine. With the help of FAST (Fatigue, Aerodynamics, Structures, and Turbulence), an open source software, the NREL 5MW land base wind turbine model was used. IEC 61400-1 wind turbine design standard procedures assessed turbine behavior and fatigue damage to the tower base of dynamic loads in different design conditions. Real characteristic wind speed distribution and multi-directional effect specific to the site were taken into consideration. The effect of these conditions on the economic service life of the turbine has been studied.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.4 no.2
• /
• pp.43-49
• /
• 2005

The purpose of a fatigue crack arrest design is to prevent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flanges, crack arrest is possible; arrest occurring when the fatigue crack reaches the second element. In the present work, a numerical analysis was carried out to estimate the effect of shape parameters on fatigue crack growth and arrest behavior of integrally stiffened panels. Based on these results, a set of fatigue crack arrest design chart is presented as "non-dimensional arrest load - thickness ratio" relationship.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.241-246
• /
• 2003

In order to develop a method of corrosion fatigue design and estimate reliability of TMCP steel using as the material of heavy industries and plants, its corrosion susceptibilities, corrosion fatigue strength, and determination of fatigue design criterion considering corrosion degradation were investigated. From the results, the corrosion characteristic of TMCP steel is very susceptible in 3.5wt.% NaCl solution. Its susceptibility was linearly increased with the solution temperature increase. The corrosion fatigue strength in $25${\circ}$, 3.5wt.% NaCl solution is very lower than that of in air. And also, it was decreased with the frequency decrease in the same environment. It is expected that the developed corrosion fatigue design method for TMCP steel is useful. However, it is necessary to verify its reliability for actual application.

• Journal of Mechanical Science and Technology
• /
• v.18 no.1
• /
• pp.106-113
• /
• 2004

Recently, a new issue in designing spot welded structures such as automobile and train car bodies is to predict an economical fatigue design criterion. One of the most typical and traditional methods is to use a ΔP-N$\sub$f/ curve. However, since the fatigue data on the ΔP-N$\sub$f/ curve vary according to the welding conditions, materials, geometry of joint and fatigue loading conditions, it is necessary to perform the additional fatigue tests for determining a new fatigue design criterion of spot-welded lap joint having specific dimension and geometry. In this study, the stress distributions around spot welds of various spot welded lap joints such as in-plane bending type (IB type), tension shea. type (TS type) and cross tension type (CT type) were numerically analyzed. Using these results, the ΔP-N$\sub$f/ curves Previously obtained from the fatigue tests for each type were rearranged into the Δ$\sigma$-N$\sub$f/ relations with the maximum stresses at the nugget edge of the spot weld.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.2
• /
• pp.81-88
• /
• 2020

The damping hinge of a built-in refrigerator was examined in terms of its stress and fatigue life. Analysis of the initial design showed that stress concentration occurred at the concave surface of the hinge lever, which was broken during the door opening-and-closing endurance test of the prototype. The maximum von Mises stress at this location exceeded the yield strength. In addition, Goodman fatigue analysis of the initial design showed that the fatigue life at this location was consistent with the failure observed during the endurance test. Based on these results, an improved design for the damping hinge was derived. Analysis of this improved design showed that the stress concentration in the hinge lever of the initial design was eliminated. In this case, the maximum stress occurred at the position where the hinge lever was in contact with the door stopping pin, and the maximum von Mises stress was smaller than the yield strength. Goodman fatigue analysis of the improved design indicated that the fatigue life of the entire damping hinge was infinite. It was therefore concluded that the improved design does not suffer from fatigue damage during the endurance test.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.2
• /
• pp.290-296
• /
• 2012

Cold-rolled carbon steel sheets are commonly used in railroad car or commercial vehicles such as the automobile. These are mainly fabricated by spot welding which is a kind of electric resistance welding. But fatigue strength of spot welding joint is lower than that of base metal due to high stress concentration at nugget edge of the spot welded part. And fatigue strength of them is especially influenced by not only geometrical and mechanical factors but also welding conditions of the spot welded joint. So for fatigue design of gas welded joints such as TS-type joints, it is necessary to obtain design information on stress distribution at the weldment as well as fatigue strength of spot welded joints. And also, the influence of the geometrical parameters of spot welded joints on stress distribution and fatigue strength must be evaluated. And analysis approach for fatigue test using design of experiment are evaluated optimum factor in TS-type welded joint and geometrical parameters of materials. Using these results, that factors applied to fundamental information for automation of fatigue design.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.9
• /
• pp.1408-1414
• /
• 2004

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue lift of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear hi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2$^{nd}$ DOE was conducted to obtain RSM equation far the choose 3 design parameter. The coefficient of determination ($R^2$) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430$\mu$m, and 78$\mu$m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.

• Journal of the Korean Society of Safety
• /
• v.33 no.5
• /
• pp.164-169
• /
• 2018

A detailed fatigue evaluation procedure was developed to mitigate the excessive conservativeness of the conventional environmental fatigue evaluation method for the pressurizer spray line elbow of domestic new nuclear power plants. The pressurizer spray line is made of austenitic stainless steel, which is relatively sensitive to the environmentally assisted fatigue, and has a low degree of design margin in terms of environmentally assisted fatigue due to the thermal stratification phenomenon on the pipe cross section as a whole or locally. In this study, to meet the environmental fatigue design requirements of the pressurizer spray line elbow, the new environmental fatigue evaluation has been performed, which used the ASME Code NB-3200-based detailed fatigue analysis and the environmental fatigue correction factor instead of the existing NB-3600 evaluation method. As a result, the design requirements for environmentally assisted fatigue were met in all parts of the pressurizer spray line elbow including the fatigue weakened zones by thermal stratification.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.13 no.1
• /
• pp.147-152
• /
• 2005

The exhaust system of automobile is faced with random or spectrum types of fatigue loads during usage life and so needs to be closely estimated for quality and performance to have enough certainty on design endurance lift during preliminary design process. Structural operation conditions, operation load history, property of material and manufacturing process etc. should be considered by performing experiment approach. Using the software program for predicting fatigue life quickly and exactly in preliminary design stage saves plenty of time and cost generated by fatigue tests. In this paper, fatigue life prediction was performed on the basis of fatigue analysis using MSC/FATIGUE and load data from field test and the life of development items was estimated and compared through the results.