HOT SPOT STRESS APPROACH TO FATIGUE STRENGTH ANALYSIS OF WELDED COMPONENTS: FATIGUE TEST DATA FOR STEEL PLATE THICKNESSES UP TO 10 MM

Fatigue is a phenomenon, which needs to be considered in the present day’s vessel design. The welded joints are particularly affected by the fatigue damage due to high stress concentrations caused by the metallurgical discontinuities present in the weld. For oil tankers and bulk carriers adequate guidelines for the fatigue strength assessment have been established by the classification societies. But for navy vessel, like offshore patrol vessel, the design guidelines for the fatigue strength analysis are not widely available. In the present paper, an attempt has been made to calculate the fatigue life of offshore patrol vessel (OPV). In general five stages of work is involved in calculating fatigue life of any ship structure. These are, load calculation, nominal and hot spot stress computation, long-term stress distribution, selection of S-N curve and the fatigue damage calculation. In the present study, the wave loads are obtained by the rule based estimation. The finite element analysis with the submodeling approach has been used to get the hot spot stress at critical locations. The two-parameter Weibull curve has been used to get the long-term distribution of stress. And at the end, the fatigue damage and the fatigue life have been computed using the Palmgren-Miner linear cumulative damage theory at the critical locations of the vessel.

Download Full-text

An Empirical Approach to the Fatigue-Strength Analysis of Structures

Journal of Applied Mechanics ◽

10.1115/1.4009562 ◽

1946 ◽

Vol 13 (3) ◽

pp. A201-A206

Author(s):

Henry W. Foster ◽

Victor Seliger

Keyword(s):

Experimental Data ◽

Aluminum Alloy ◽

Fatigue Strength ◽

Fatigue Test ◽

Test Data ◽

Empirical Approach ◽

Strength Analysis ◽

Test Results ◽

Structural Fatigue ◽

Actual Test

Abstract A method of fatigue-strength analysis for fabricated structures, based on laboratory fatigue-test data, is proposed in this paper. To this end the nature of structural fatigue strength is discussed with the view of defining the necessary correlating assumptions and the type of experimental data needed. An example of this method is presented for structures fabricated from Alclad 24S-T aluminum alloy and analysis results are compared with actual test results.

Download Full-text

Hot Spot Stress Fatigue Evaluation to Duplex Stainless Steel Welded Joints

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.324-325.779 ◽

2006 ◽

Vol 324-325 ◽

pp. 779-782

Author(s):

Fa Yong Jia ◽

Li Xing Huo ◽

Gang Chen ◽

Qun Peng Zhong

Keyword(s):

Stainless Steel ◽

Fatigue Strength ◽

Duplex Stainless Steel ◽

Test Data ◽

Welded Joints ◽

Hot Spot ◽

Engineering Application ◽

Hot Spot Stress ◽

Flat Side ◽

Stress Fatigue

Fatigue strength of duplex stainless steel welded joints with longitudinal fillet welded guess and with longitudinal flat side guess welded on plate was evaluated by hot spot stress, hot spot stress S-N curves were produced and compared with normal stress S-N curves. The results show that the hot spot stress fatigue strength of the two kinds welded joints should be expressed by only single S-N curve while nominal stress S-N curves can only be regressed respectively. The test data are greatly above the S-N curves with slope m=3, recommended by IIW, which indicates that the slope m=3(IIW) has great safety factor in practical engineering application. But there is no appreciable difference in fatigue strength between duplex stainless steel and common structural steel with similar welded joints when fixed the test data to slope m=3.

Download Full-text

Analysis of Recent Fatigue Data Using the Structural Stress Procedure in ASME Div. 2 Rewrite

Volume 1: Codes and Standards ◽

10.1115/pvp2005-71511 ◽

2005 ◽

Cited By ~ 3

Author(s):

P. Dong ◽

J. K. Hong ◽

A. M. P. De Jesus

Keyword(s):

Fatigue Test ◽

Test Data ◽

Hot Spot ◽

Comparative Assessment ◽

Structural Stress ◽

Hot Spot Stress ◽

Classification Approach ◽

Fatigue Data ◽

Fatigue Evaluation ◽

Assessment Procedures

In support of the ASME Div 2 Rewrite, a master S-N curve approach has been developed using a mesh-insensitive structural stress procedure for fatigue evaluation of welded components. The effectiveness of the master S-N curve approach has been demonstrated in a number of earlier publications for many joint types and loading conditions for pipe and vessel components as well as plate joints. To further validate the structural stress method, a series of recent test data (small weld details and a full scale vessel) published by De Jesus et al (2004) were analyzed in this paper. A comparative assessment of various existing procedures and their effectiveness in correlating the fatigue test data by De Jesus et al (2004) is also presented. These assessment procedures include current ASME Sec. VIII Div 2, weld classification approach in PD 5500, and the surface extrapolation-based hot spot stress approach in recently approved European EN 13445 Standards.

Download Full-text

Improvement of trawler hull structure under condition of ensuring fatigue strength

Eastern-European Journal of Enterprise Technologies ◽

10.15587/1729-4061.2021.239159 ◽

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.

Download Full-text

Fatigue Strength Reduction Factors for Welded Joints: Another View

Volume 1: Codes and Standards ◽

10.1115/pvp2007-26691 ◽

2007 ◽

Author(s):

Arturs Kalnins

Keyword(s):

Standard Deviation ◽

Fatigue Strength ◽

Fatigue Test ◽

Test Data ◽

Welded Joints ◽

Welded Joint ◽

Fatigue Curve ◽

Strength Reduction ◽

Initial Estimate ◽

Curve Fit

The paper distinguishes between FSRFs that are used for two different purposes. One is to serve as a guideline for an initial estimate of the fatigue strength of a welded joint. That is the purpose of the FSRFs that are given in the ASME B&PV Code and various accompanying documents. If that estimate renders the fatigue strength inadequate, an FSRF can be sought that is limited to the joint under consideration. The paper shows how such FSRFs can be determined from fatigue test data. In order to make it possible to read the allowable cycles from the same design fatigue curve as that used for the FSRFs of the guidelines, a Langer curve [defined by equation (2) in the paper] is used to curve fit the data. The appropriate FSRF is obtained by minimizing the standard deviation between this curve and the data. The procedure is illustrated for girth butt-welded pipes. The illustration shows that for the data used in the analysis, a constant FSRF is applicable to less than one million cycles but not to the high-cycle regime.

Download Full-text

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

International Journal of Structural Integrity ◽

10.1108/ijsi-04-2014-0017 ◽

2016 ◽

Vol 7 (2) ◽

Cited By ~ 5

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.

Download Full-text

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

Dynamics ◽

10.3390/dynamics1010007 ◽

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.

Download Full-text