Testing and analysis of fatigue behaviour in edge details: A comparative study using hot spot and structural stresses

2008 ◽  
Vol 222 (12) ◽  
pp. 2351-2363 ◽  
Author(s):  
M-H Kim ◽  
S-W Kang
Keyword(s):  
Fatigue Strength ◽  
Stress State ◽  
Hot Spot ◽  
Mesh Size ◽  
Offshore Structures ◽  
Nominal Stress ◽  
Medium Size ◽  
Effective Measure ◽  
Fatigue Design ◽  
Weld Toe

At present, the fatigue design of welded structures is primarily based on a nominal stress or hot spot stress (HSS) approach with a series of classified weld S-N curves. Although well accepted by major industries, the nominal stress-based fatigue design approach is relatively cumbersome in terms of securing a series of S-N curves corresponding to each class of joint types and loading modes. Moreover, it is very difficult, if not impossible, to determine the nominal stress at each structural component, particularly in complex ship structures. The HSS-based fatigue design is based on the stress at the weld toes obtained by linear or quadratic extrapolation of stresses over two or three points in front of the weld toe. Finite-element analysis is mostly applied. However, this method has a difficulty of finding a proper stress through the global model, the medium size model and the detail model of ship structure. Besides, the calculated HSS values may vary depending on the extrapolation technique used. Recently, a mesh-size insensitive structural stress (SS) definition that gives a stress state at the weld toe with a relatively large mesh size has been proposed. The SS definition is based on the elementary structural mechanics theory and provides an effective measure of a stress state in front of the weld toe. As an experimental validation of the Battelle SS method in obtaining the fatigue strength of weldments, a series of experiments are carried out for various sizes of weldments. Based on the results from this study, it is expected to achieve the development of a more precise fatigue strength evaluation technique and saving on the time required in the fatigue design of ship and offshore structures.

Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress

2010 ◽  
Author(s):  
Nur Syahroni ◽  
Stig Berge
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Testing ◽  
International Association ◽  
Hot Spot ◽  
Mean Stress ◽  
Element Analysis ◽  
Structural Rules ◽  
Fatigue Design

Residual stress may have a significant effect on the fatigue strength of welded joints. As a non-fluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers (IACS 2006a) and bulk carriers (IACS 2006b). The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gages. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shake-down effect of residual stress, testing was performed for several pre-load conditions which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

Fatigue Design Criteria as Function of the Principal Stress Direction Relative to the Weld Toe

2008 ◽  
Author(s):  
Inge Lotsberg
Keyword(s):  
Principal Stress ◽  
Hot Spot ◽  
Stress Conditions ◽  
Design Criteria ◽  
International Institute ◽  
Proportional Loading ◽  
Principal Stress Direction ◽  
Fatigue Design ◽  
Stress Direction ◽  
Weld Toe

For fatigue design it is necessary to provide guidelines on how to calculate fatigue damage at weld toes based on S-N data when the principal stress direction is different from that of the normal direction to the weld toe. Such stress conditions are found at details in different types of plated structures. Some different fatigue criteria for these stress conditions are presented in design standards on fatigue design. Criteria used by the International Institute of Welding (IIW), Eurocode, British Standard and in the DNV standards have been assessed against some relevant fatigue test data presented in the literature. Only proportional loading conditions have been considered here. (By proportional loading is understood that the principal stress direction is kept constant during a load cycle). An alternative equation for calculation of an equivalent or effective stress range based on stress normal to the weld toe and shear stress at the weld toe has been proposed. The proposed methodology can be used for nominal S-N curves and it can be used together with a hot spot stress S-N curve with stresses read out from finite element analysis. The different design criteria are presented in this paper together with recommendations on analysis procedure.

scholarly journals Fatigue Strength Curve for Tubular Joints of Offshore Structures under Dynamic Loading

Dynamics ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 125-133
Author(s):  
Sudath C. Siriwardane ◽  
Nirosha D. Adasooriya ◽  
Dimitrios Pavlou
Keyword(s):  
Fatigue Strength ◽  
Hot Spot ◽  
Offshore Structures ◽  
Hot Spot Stress ◽  
Tubular Joints ◽  
Jacket Structures ◽  
Strength Curve ◽  
Tubular Joint ◽  
Stress Concentration Factors

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.

A Comparative Study on the Fatigue Evaluation for Weldments under Out-of Plane Bending Load Using Structural Stress and Hot Spot Stress

2006 ◽  
Vol 326-328 ◽  
pp. 995-998
Author(s):  
Myung Hyun Kim ◽  
Chung In Ha ◽  
Sung Won Kang ◽  
Jeong Hwan Kim ◽  
Jae Myung Lee
Keyword(s):  
Fatigue Strength ◽  
Hot Spot ◽  
Mesh Size ◽  
Structural Stress ◽  
Hot Spot Stress ◽  
Strength Assessment ◽  
Bending Load ◽  
Load Carrying ◽  
Out Of Plane ◽  
Plane Bending

Fatigue strength assessments with two types of load carrying fillet weldment under out-of-plane bending load have been carried out by using both hot spot stress and structural stress methods. Basis for the derivation of structural stress method is discussed in detail. Finite element analyses using shell elements models have been performed for the fatigue strength assessment of weldments. As a result of the fatigue strength evaluation for load carrying transverse fillet weldment, hot spot stress method is found to be consistent with structural stress method as well as measurement. Hot spot stress, however, estimated for the load carrying longitudinal fillet weldment exhibit large variation with respect to mesh size and element type while the calculated structural stress for the longitudinal fillet weldment is relatively independent of mesh size. The fatigue life estimation according to structural stress has been introduced with the master S-N curve.

Local strain for fatigue strength of welded structures

2001 ◽  
Vol 36 (6) ◽  
pp. 605-610 ◽  
Author(s):  
V Dattoma ◽  
C Pappalettere
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Structural Integrity ◽  
Strain Curve ◽  
Local Strain ◽  
Fatigue Design ◽  
Curve Versus ◽  
Weld Toe ◽  
Stress Ratios ◽  
Tip Radius

Field criteria, which are usually applied in fracture mechanics to ensure the structural integrity of cracked components, are extended to the fatigue design of welded joints, whose weld toe can be assimilated to a notch with a small tip radius. In particular, fatigue strength in terms of strain rather than of stress has been determined by applying stress cycles with different stress ratios R = σmin/σmax. Finally, for the evaluation of the fatigue strength of welded joints in structural steel, a strain curve versus different R ratios is given to be compared with the service measured local strain at the weld toe.

Geometrical Parametric Study and Development of Design Formulae for the SCF Distribution Along the Weld Toe in Multi-Planar CHS DKT-Connections of Offshore Structures

2011 ◽  
Author(s):  
Mohammad Ali Lotfollahi-Yaghin ◽  
Hamid Ahmadi ◽  
Sajad Shahverdi
Keyword(s):  
Offshore Structures ◽  
Geometrical Parameters ◽  
Axial Loads ◽  
Geometrical Properties ◽  
Fatigue Design ◽  
Assessment Study ◽  
Wide Range ◽  
Weld Toe ◽  
Complete Set ◽  
The Uk

In the present paper, effects of geometrical parameters on the SCF distribution along the weld toe of multi-planar tubular DKT-joints under the axial loads are investigated. In order to study the multi-planar effect, SCF distribution in multi-planar joints is compared with the distribution in a uni-planar joint having the same geometrical properties. Based on the multi-planar DKT-joint FE models which are verified against experimental results and the predictions of Lloyd’s Register (LR) equations, a complete set of SCF database is constructed. The FE models cover a wide range of geometrical parameters. Through nonlinear regression analysis, a new set of SCF parametric equations is established for the accurate and reliable fatigue design of multi-planar DKT-joints under axial loads. An assessment study of these equations is conducted against the experimental data and the acceptance criteria recommended by the UK DoE.

Uncertainty Modeling for Fatigue Strength Assessment of Welded Structures

1998 ◽  
Vol 120 (2) ◽  
pp. 97-102 ◽  
Author(s):  
W. Fricke ◽  
A. Mu¨ller-Schmerl
Keyword(s):  
Fatigue Strength ◽  
Hot Spot ◽  
Offshore Structures ◽  
Fatigue Tests ◽  
Published Data ◽  
Hot Spot Stress ◽  
Total Uncertainty ◽  
Strength Assessment ◽  
Characteristic Values ◽  
Fatigue Strength Assessment

The results of fatigue tests are characterized by much scatter. Such scatter is further increased if data from different test series are combined to derive, for instance, characteristic values for individual types of welded joints used in codes. Characteristic values are normally applied to the design of fatigue-resistant ship and offshore structures in connection with the nominal stress approach using S-N curves. More advanced approaches such as the hot-spot stress approach and the notch stress approach are applied to an increasing extent. Such approaches explicitly consider certain influence factors and allow the scatter of these factors to be treated individually. This way, probably even the total uncertainty can be reduced. After reviewing the different approaches used for fatigue strength assessment, the sources of scatter are addressed and assigned to factors considered in the different approaches. Based on published data of fatigue tests and imperfections observed in real structures, an attempt is made to quantify the uncertainties of the different factors and to draw conclusions for their individual consideration in the approaches mentioned.

Research on the Stress Fatigue Assessment about the Hot Spot Stress on the Bogie Frame

2011 ◽  
Vol 328-330 ◽  
pp. 1281-1286
Author(s):  
Bin Jie Wang ◽  
Qiang Li ◽  
Zhi Ming Liu
Keyword(s):  
Fatigue Strength ◽  
High Speed ◽  
Hot Spot ◽  
Nominal Stress ◽  
Bottom Flange ◽  
Bogie Frame ◽  
Hot Spot Stress ◽  
Shell Elements ◽  
Joint Section ◽  
Fatigue Evaluation

As the loading conditions for the railway vehicles are becoming more and more complex, nominal stress has been unable to fully satisfy the requirements for assessing fatigue strength for weld structures. Hot spots stress is much more closer to the actual stress of a weld structure, it can suit the demand of high speed trains’ fatigue evaluation better. In this paper, on the basis of UIC615-4 standard, the nominal stress of the welded bogie frame was calculated and its fatigue strength was assessed using FEA method. Also, set the joint section between drawbar seat and the transom bottom flange as the object of the study, succeeded in evaluating the hot spot stress of the welded bogie frame. Compared the hot spot stress calculation result with the nominal stress from shell elements, the result shows that hot spot stress is higher than the nominal stress. Using the hot spot stress to assess fatigue has the higher reliability

Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Nur Syahroni ◽  
Stig Berge
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Testing ◽  
International Association ◽  
Hot Spot ◽  
Strain Gauges ◽  
Mean Stress ◽  
Element Analysis ◽  
Fatigue Design

Residual stress may have a significant effect on the fatigue strength of welded joints. As a nonfluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers and bulk carriers. The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gauges. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shakedown effect of residual stress, testing was performed for several preload conditions, which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards a better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.

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