Fatigue Strength Characteristics of Cast Steel Weld Joints

2011 ◽  
Author(s):  
Ho Jung Kim ◽  
Seong Min Kim ◽  
Jae Myung Lee ◽  
Myung Hyun Kim
Keyword(s):  
Fatigue Strength ◽  
Hot Spot ◽  
Cast Steel ◽  
Geometrical Parameters ◽  
Steel Weld ◽  
Hot Spot Stress ◽  
Butt Weld ◽  
Weld Joints ◽  
Fatigue Design ◽  
Notch Stress

The aim of the present paper is to investigate and compare the fatigue characteristics of weld joints in terms of S-N curve between cast steel and conventional mild steel. Two different joints such as thick butt weld joints and fillet weld joints are considered in this study. Fatigue strength of cast steel weld joints with various geometric designs are tested and compared. The fatigue life and the fatigue crack propagation characteristics are investigated by experimental and numerical methods in a systematic manner. The conventional hot spot stress, structural stress and notch stress approaches are employed for the precise interpretation of the fatigue test result of cast steel weld joints. Finally, the estimation of the fatigue limit of cast steel weld joints are attempted based on material properties and geometrical parameters. The results can be used for the efficient fatigue design of various cast steel welded joints.

scholarly journals Notch Stress Intensity Factor (NSIF)-Based Fatigue Design to Assess Cast Steel Porosity and Related Artificially Generated Imperfections

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1097
Author(s):  
Manuel Schuscha ◽  
Michael Horvath ◽  
Martin Leitner ◽  
Michael Stoschka
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fatigue Strength ◽  
Intensity Factor ◽  
Cast Steel ◽  
Experimental Investigations ◽  
Fatigue Assessment ◽  
Notch Stress Intensity Factor ◽  
Fatigue Design ◽  
Notch Stress

Shrinkage porosities and non-metallic inclusions are common manufacturing process based defects that are present within cast materials. Conventional fatigue design recommendations, such as the FKM guideline (“Forschungskuratorium Maschinenbau”), therefore propose general safety factors for the fatigue assessment of cast structures. In fact, these factors mostly lead to oversized components and do not facilitate a lightweight design process. In this work, the effect of shrinkage porosities on the fatigue strength of defect-afflicted large-scale specimens manufactured from the cast steel G21Mn5 is studied by means of a notch stress intensity factor-based (NSIF-based) generalized Kitagawa diagram. Additionally, the mean stress sensitivity of the material is taken into account and establishes a load stress ratio enhanced diagram. Thereby, the fatigue assessment approach is performed by utilizing the defects sizes taken either from the fracture surface of the tested specimens or from non-destructive X-ray investigations. Additionally, a numerical algorithm invoking cellular automata, which enables the generation of artificial defects, is presented. Conclusively, a comparison to the results of the experimental investigations reveals a sound agreement to the generated spatial pore geometries. To sum up, the generalized Kitagawa diagram, as well as a concept utilizing artificially generated defects, is capable of assessing the local fatigue limit of cast steel G21Mn5 components and features the mapping of imperfection grades to their corresponding fatigue strength limit.

Fatigue strength assessment of ship structures accounting for a coating life and corrosion degradation

2016 ◽  
Vol 7 (2) ◽  
Author(s):  
Yordan Garbatov
Keyword(s):  
Finite Element ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Limit State ◽  
State Function ◽  
Fatigue Reliability ◽  
Hot Spot Stress ◽  
Notch Stress ◽  
Fatigue Limit State

Purpose Fatigue strength and reliability assessment of complex double hull oil tanker structures, based on different local structural finite element approaches, is performed accounting for the uncertainties originating from load, nominal stresses, hot spot stress calculations, weld quality estimations and misalignments and fatigue S-N parameters including the correlation between load cases and the coating life and corrosion degradation. Design/methodology/approach Ship hull wave-induced vertical and horizontal bending moments and pressure are considered in the analysis. Stress analyses are performed based on the nominal, local hot spot and notch stress approaches. A linear elastic finite element analysis is used to determine the stress distribution around the welded details and to estimate structural stresses of all critical locations. Fatigue damage is estimated by employing the Palmgren-Miner approach. The importance of the contribution of each random variable to the uncertainty of the fatigue limit state function is also estimated. The probability of fatigue damage of hot spots is evaluated taking into account random coating life and corrosion wastage. Fatigue reliability, during the service life, is modelled as a system of correlated events. Findings The fatigue analysis showed that the fatigue damage at the hotspot, located at the flange of the stiffener close to the cut-out, is always highest in the cases of the structural hot spot stress and effective notch stress approaches, except for the one of the nominal stress approach. The sensitivities of the fatigue limit state function with respect to changes in the random variables were demonstrated showing that the uncertainty in the fatigue stress estimation and fatigue damage are the most important. Fatigue reliability, modelled as a parallel system of structural hot spots and as a serial system of correlated events (load cases) was evaluated based on the Ditlevsen bounds. As a result of the performed analysis, reliability and Beta reliability indexes of lower and upper bounds were estimated, which are very similar to the ones adopted for ultimate strength collapse as reported in literature. Originality/value This paper develops a very complex fatigue strength and reliability assessment model for analysing a double hull oil tanker structure using different local structural finite element approaches accounting for the associated uncertainties and the correlation between load cases and the coating life and corrosion degradation. The developed model is flexible enough to be applied for analysing different structural failure modes.

Fatigue Strength Study on Different Structure Type of Hatch Corner

2011 ◽  
Vol 233-235 ◽  
pp. 2580-2583
Author(s):  
Yong He Xie ◽  
Wei Wang ◽  
Heng Zhang
Keyword(s):  
Fatigue Strength ◽  
Scale Effect ◽  
Hot Spot ◽  
Structure Type ◽  
Cumulative Damage ◽  
Hot Spot Stress ◽  
Fatigue Design ◽  
Miner’S Rule ◽  
Curve Method ◽  
Miner's Rule

The fatigue strength study of the hatch corner is carried out ,based on the S-N curve method and the assumption of the linear cumulative damage of Palmgren-Miner's rule, using the hot spot stress method. Study on the effect of the structure different type to the fatigue strength of the hatch corner is carried out through changing its construction details and thickness. By comparing, the reasonable structure is obtained, and the scale effect should be put into consideration in fatigue design.

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.

scholarly journals Improvement of trawler hull structure under condition of ensuring fatigue strength

2021 ◽  
Vol 4 (7(112)) ◽  
pp. 50-59
Author(s):  
Leontii Korostylov ◽  
Dmytro Lytvynenko ◽  
Hryhorii Sharun ◽  
Ihor Davydov
Keyword(s):  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Fatigue Cracks ◽  
Bending Moment ◽  
Theoretical Method ◽  
Corrosive Wear ◽  
Hot Spot Stress ◽  
Hull Structure ◽  
Internal Forces

The structure of the hull of the project 1288 trawler in a region of fore hold was improved to ensure fatigue strength of assemblies of the intersection of main frames with the second bottom. To this end, a study of the fatigue strength of these assemblies was carried out for the original side structure and two versions of its modernization. Values of internal forces at the points of appearance of fatigue cracks in the compartment have been determined for three design versions of the side. It was found that the greatest forces act in the middle of the fore half of the compartment. Calculations of parameters of the long-term distribution of magnitudes of ranges of total equivalent operating stresses according to the Weibull law in the points of occurrence of fatigue cracks for different design versions of the side grillage have been performed. These parameters were determined for the middle of the fore hold of the vessel and for the areas in which maximum values of bending moment ranges are in effect with and without corrosive wear. Values of total fatigue damage and durability of the studied assemblies were determined. Calculations were carried out by nominal stress method, hot spot stress method, and experimental and theoretical method. It was shown that in order to ensure fatigue strength of the assembly under consideration, it is necessary to extend the intermediate frames of the original version of the side structure to the level of the second bottom fixing them to the deck. It is also necessary to attach a cargo platform to the side thus reducing the frame span. As a result, the level of fatigue damage over 25 years of operation will decrease by about 3.5 times. As it was found, approximate consideration of the slamming effect does not significantly increase the amount of fatigue damage to the assembly. The results of the development of recommendations for modernization of the side structure can be implemented both on ships of the 1288 project and on other ships with a transverse side framing system.

Differences in Fatigue Strength Between Arc and Laser Hybrid Welded Joints

2008 ◽  
Vol 24 (03) ◽  
pp. 139-146
Author(s):  
H. Remes ◽  
P. Varsta
Keyword(s):  
Fatigue Strength ◽  
Welded Joints ◽  
Fatigue Tests ◽  
Notch Depth ◽  
Butt Joints ◽  
Fatigue Design ◽  
Notch Stress ◽  
Notch Geometry ◽  
Laser Hybrid ◽  
Fatigue Endurance

This paper presents the results of fatigue tests, including tests of laser hybrid and arc welded butt joints, for two plate thicknesses, 6 and 12 mm. Pure laser welded joints were also tested. The S-N curves based on nominal stresses for the different welded joints are presented. The results were further analyzed using the notch stress approach, where the fatigue notch factors were determined from the measured geometries of the welded joints. Unexpected differences in the S-N curves based on the notch stresses were found between the laser hybrid and arc welded joints and between the laser hybrid and pure laser welded joints. The reasons for this difference were studied with the help of extensive measurements of weld notch geometries. Significant differences in the geometries were observed. Taking into account the notch geometry and the notch depth, the notch stress approach partially explains the differences between the fatigue endurance limits of the laser hybrid and arc welded joints. The applicability of the notch stress approach to the fatigue design of laser hybrid welded joints is also discussed.

Fatigue Damage Estimation of Welded Joints Considering Mechanochemical Interaction

2017 ◽  
Author(s):  
Gang Liu ◽  
Yi Huang ◽  
Qi Zhang ◽  
Zhiyuan Li ◽  
Jingjie Chen ◽  
...  
Keyword(s):  
Corrosion Rate ◽  
Fatigue Damage ◽  
Coupling Effect ◽  
Hot Spot ◽  
Plate Thickness ◽  
High Stress ◽  
Uniform Corrosion ◽  
Hot Spot Stress ◽  
Butt Weld ◽  
Applied Loading

The high stress region around weld joints accelerates corrosion and may induce non-uniform corrosion. In this study, the effect of loading on corrosion behavior of the steel in NaCl solution was investigated. The relationship between the corrosion rate and applied loading was deduced based on the electrochemical theory. Electrochemical experiments were carried out to investigate the interaction between loading and corrosion rate on Q235 steel. A butt weld joint of ship deck structure was selected as a case study. Time-dependent stress concentration factor of welded joint as a function of the corrosion deterioration was analyzed, and the iterative process of stress and corrosion degeneration of plate thickness was used to simulate the coupling effect based on results of the experiment. The hot spot stress approach was adopted to calculate the fatigue damage.

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.

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