• Journal of Welding and Joining
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• 제30권1호
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• pp.72-77
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• 2012

Recently, according to the increase of income and development of quality of life, the leisure industry has been developed. In particular, the interest of design and manufacture technology of leisure yacht has significantly increased. However, domestic market of leisure ships is currently in its initiating stage. So research and development for structural strength of leisure yacht need to be investigated. In this study, lug of yacht's mast which is known for a critical damage region is explicitly considered. This paper deals with the estimation of stress concentration factors (SCFs) for lug of yacht's mast depending on dimensions of lug using hot spot stress. Also, SCF formulae is suggested using parametric study.

• Ocean Systems Engineering
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• 제14권3호
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• pp.237-259
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• 2024

Although the investigation on the effect of loaded out-of-plane braces on the values of the stress concentration factor (SCF) in offshore tubular joints has been the objective of numerous research works, a number of quite important cases still exist that have not been studied thoroughly due to the diversity of joint types and loading conditions. One of these cases is the multi-planar tubular KK-joint subjected to axial loading. Tubular KK-joints are among the most common joint types in jacket substructure of offshore wind turbines (OWTs). In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified against available experimental data, was used to study the effects of geometrical parameters on the chord-side SCFs in multi-planar tubular KK-joints subjected to axial loading. Parametric FE study was followed by a set of nonlinear regression analyses to develop three new SCF parametric equations for the fatigue analysis and design of axially loaded multi-planar KK-joints.

• Ocean Systems Engineering
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• 제12권1호
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• pp.1-22
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• 2022

The majority of tubular joints commonly found in offshore jacket structures are multi-planar. Investigating the effect of loaded out-of-plane braces on the values of the stress concentration factor (SCF) in offshore tubular joints has been the objective of numerous research works. However, due to the diversity of joint types and loading conditions, a number of quite important cases still exist that have not been studied thoroughly. Among them are internally ring-stiffened two-planar TT-joints subjected to axial loading. In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified against available numerical and experimental data, was used to study the effects of geometrical parameters on the chord-side SCFs in two-planar tubular TT-joints reinforced with internal ring stiffeners subjected to two types of axial loading. Parametric FE study was followed by a set of nonlinear regression analyses to develop six new SCF parametric equations for the fatigue analysis and design of axially-loaded two-planar TT-joints reinforced with internal ring stiffeners.

• 풍력에너지저널
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• 제13권4호
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• pp.42-49
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• 2022

Today, the power capacity of a wind turbine and the size of a blade is increasing to capture more wind resources, reduce the number of wind turbines on a wind farm, and reduce the cost of energy. As the blade size becomes larger, attention is being paid to the structural integrity of the blade root connection due to the heavy gravitational load effect and increased aerodynamic loads on the large blade, which could cause catastrophic failure of the blade. Therefore, the secure bolted joint connection of the blade to the hub is very important. In this paper, attention was given to the stress concentration factor (SCF) at the first thread between the M42 bolt and nut. The effect of various design parameters on the stress concentration factor was investigated, which included nut type, nut height, and reduced shank bolt. From a close design investigation of the numerical results, it turned out that the use of a reduced shank bolt resulted in the largest reduction of the stress concentration factor by 40 %, and the round nut type also reduced the SCF by 10 %, which will be beneficial to large wind turbine blades over 100 meters.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.73-78
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• 2004

The conventional SLT(Shear Lag Theory) which has been proven that it can not provide sufficiently accurate strengthening predictions in elastic regime when the fiber aspect ratio is small. This paper is an extented work to improve it by modifying the load transfer mechanism called NSLT(New Shear Lag Theory), which takes into account the stress transfer across the fiber ends and the SCF(Stress Concentration Factor) that exists in the matrix regions near the fiber ends. The key point of the model development is to determine the major controlling factor among the material and geometrical coefficients. It is found that the most affecting factor is the fiber/matrix elastic modulus ratio. It is also found that the proposed model gives a good result that has the capability to correctly predict the elastic properties such as interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• Journal of Mechanical Science and Technology
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• 제18권5호
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• pp.808-813
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• 2004

The stress analysis on orthotropic composite cylindrical shells with one circular or one elliptical cutout subjected to an axial force is carried out by using an analytical and experimental method. The composite cylindrical shell governing equation of the Donnell's type is applied to this study and all results are presented by the stress concentration factor. The stress concentration factor is defined as the ratio of the stress on the region around a cutout to the nominal stress of the shell. The stress concentration factor is classified into the circumferential stress concentration factors and the radial stress concentration factors due to the cylindrical coordinate of which the origin is the center of a cutout. The considered loading condition is only axial tension loading condition. In this study, thus, the maximum stress is induced on perpendicular region against axial direction, on the coordinate. Various cutout sizes are expressed using the radius ratio, (equation omitted), which is the radius of a cutout over one of the cylindrical shell. Experimental results are obtained using strain gages, which are attached around a cutout of the cylindrical shell. As the result from this study, the stress concentration around a cutout can be predicted by using the analytical method for an orthotropic composite cylindrical shell having a circular or an elliptical cutout.

• Steel and Composite Structures
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• 제49권2호
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• pp.181-196
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• 2023

Marine structures including offshore wind turbines (OWTs) always work under cyclic loads, which arouses much attention on the fatigue design. The tripod substructure is one of the typical foundation forms for fixed OWTs. The three-planar tubular Y-joint (3Y joint) is one of the important components in fatigue design as it is most likely to have cracks. With the existence of the multiplanar interaction effect, calculating the hot spot stress (HSS) of 3Y joints is complicated. To assist with fatigue design, the distributions of stress concentration factor (SCF) and multiplanar interaction factor (MIF) along weld toe curves induced by the out-of-plane bending moment are explored in this study. An FE analysis method was first developed and verified against experimental results. This method was applied to build a numerical database including 1920 FE models covering common ranges of geometric parameters. A parametric study has been carried out to reveal the distribution patterns of SCF and MIF. After multidimensional nonlinear fittings, SCF and MIF distribution formulas have been proposed. Accuracy and reliability checking prove that the proposed formulas are suitable for calculating the HSS of 3Y joints.

• Steel and Composite Structures
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• 제22권1호
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• pp.203-216
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• 2016

To study the stress concentration factors (SCFs) of concrete-filled tubular Y-joints subject to in-plane bending, experiments were used to investigate the hot spot stress distribution along the intersection between chord and brace. Three concrete-filled tubular chords forming Y-joints were tested with different reinforcing components, including doubler-plate, sleeve, and haunch-plate reinforcement. In addition, an unreinforced joint was also tested for comparison. Test results indicate that the three different forms of reinforcement effectively reduce the peak SCFs compared with the unreinforced joint. The current research suggests that the linear extrapolation method can be used for chords, whereas the quadratic extrapolation method must be used for braces. The SCF is effectively reduced and more evenly distributed when the value of the axial compression ratio in the chord is increased. Furthermore, the SCFs obtained from the test results were compared to predictions from some well-established SCF equations. Generally, the predictions from those equations are very consistent for braces, but very conservative for concrete-filled chords.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.148-153
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• 2004

This paper represents that parts of a large generator operating in 1000 MW are affected by centrifugal forces due to high-speed rotation in 3600 rpm and 3D FEM Analyses are required to obtained the structural reliability of the generator. From these results, one would know the weakest locations and the stress distributions. The fatigue life is calculated in order to grasp the remaining life of generator. 2D and 3D analyses are performed to calculate stresses of the generator rotor and the retaining ring. From 2D results, we find the SCF at the slot and sub-slot of the rotor. 3D analysis is applied at the end part of generator rotor, which represents complex geometry, and rotor and retaining ring shrink thermally. With these results, designers of rotor and retaining ring can compare with the results of design code and verify the stress distributions of generator rotor and retaining ring, and then calculate the remaining life from the low-cycle fatigue data.

• 한국해양공학회지
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• 제8권2호
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• pp.141-150
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• 1994

In designing, the strength of tubular joint has been an important problem for integrity of steel structures in which many tubular members are used. This paper presents the results of FEM analysis on stress concentration and fatigue crack initiation life for two types of tubular joints. One is circular and rectangular T type joints which consist of circular brace and rectangular chord. Another is circular and circular T type joints which consist of circular brace and circular chord. FEM analyses were performed under the axial load and in-plane bending moment. The fatigue crack initiation life can be estimated by using $\varepsilon$-N curve and by applying the Palmgren-Miner linear damage rule. According to the results, the stress concentration factor(SCF) of circular and rectangular joints is higher than that of circular and circular joints. The fatigue crack initiation lives of circular-circular joints and circular-rectangular joints were calculated.