Fatigue Assessment of Welded Joints by Local Approaches
Contents
Introduction
- Fatigue strength assessment of welded joints: Present state of the art; Demands from industrial product development - Basic aspects of assessment procedures: Multitude of parameters governing fatigue failure; Global and local approaches of fatigue strength assessment; Complications of local approaches for welded joints; Survey of subject arrangement
Nominal stress approach for welded joints - Basic procedures: Principles of the nominal stress approach; Procedures for welded joints - Analysis tools: Books, compendia, guidelines and design codes; Basic formulae; Permissible stresses and design S-N curves; Influence of mean and residual stresses; Influence of stress multiaxiality; Influence of plate thickness, weld dressing and environment; Normalised S-N curves; Fatigue strength reduction factors
Structural stress or strain approach for seam-welded joints - Basic procedures: Principles of the structural stress or strain approach; Structural strain approach as proposed by Haibach; Hot spot structural stress approach for tubular joints; Hot spot structural stress approach for non-tubular joints; Alternative definitions of hot spot structural stress; Structural stress approach as proposed by Dong; Structural stress approach as proposed by Xiao-Yamada; Structural stress approach to weld root fatigue - Analysis tools – structural stress or strain evaluation: General survey and relevant guidelines; Evaluation of hot spot stresses in tubular joints; Evaluation of hot spot stresses in non-tubular joints; Specific rules for finite element modelling; Further variants of structural stress evaluation; Definition of structural stress concentration factors; Hot spot stress concentration factors for tubular joints; Hot spot stress concentration factors for non-tubular joints - Analysis tools – endurable structural stresses or strains: Endurable structural strains in Haibach's approach; Endurable hot spot stresses in tubular joints; Endurable hot spot stresses in non-tubular joints; Endurable structural stresses in Dong's and Xiao-Yamada's approach; Endurable multiaxial stresses or strains; Structural stress based assessment of weld root fatigue; Demonstration examples: Welded tubular and butt joints – structural strain approach; Welded tubular joints – various design guidelines; Welded bridge girder with cope holes; Welded joints in ship structures – weld toe fatigue; Welded joints in ship structures – weld root fatigue
Notch stress approach for seam-welded joints - Basic procedures: Principles and variants of the notch stress approach; Critical distance approach; Fictitious notch rounding approach; Modified notch rounding approach; Highly stressed volume approach - Analysis tools: General survey and assessment procedures; Notch stress analysis for welded joints; Notch stress concentration factors of welded joints; Fatigue notch factors of welded joints; Critical distance approach; Fictitious notch rounding approach – basic procedures; Fictitious notch rounding approach – refined procedures; Fictitious notch rounding approach – links to structural stresses; Modified notch rounding approach; Highly stressed volume approach - Demonstration examples: Welded vehicle frame corner joint; Web stiffener of welded I section girder; Stress relief groove in welded pressure vessel; End-to-shell joint of boiler; Stiffener-to-flange joint at ship frame corner; Girth butt welds of unusual manufacture; Tensile specimen with longitudinal attachment; Gusseted shell structure; Laser beam welded butt and cruciform joints - Design-related notch stress evaluations: Comparison of basic welded joint types; Comparison of basic weld loading modes; Effect of geometrical weld parameters; Typical application in design
Notch strain approach for seam-welded joints - Basic procedures: Principles of the notch strain approach; Early application of the approach; Comprehensive exposition of the approach; Further refinements of the approach - Analysis tools: Basic formulae in early applications; Basic formulae for wider application; Special formulae for multiaxial fatigue; Assessment procedure - Demonstration examples: Fatigue life of stress-relieved butt-welded joints; Fatigue life of butt-welded joints with residual stresses; Fatigue life of fillet-welded cruciform joints; Fatigue life of welded containment detail; Fatigue strength of welded tubular joint
***** propagation approach for seam-welded joints - Basic procedures: Principles of the ***** propagation approach; Application to seam-welded joints; Short ***** behaviour; Applications of the ***** propagation approach - Analysis tools: General survey and relevant references; Methods of stress intensity factor determination; ***** propagation equations; ***** propagation life; Stress intensity factors for welded joints; ***** shape and ***** path; Material parameters of ***** propagation; Initial and final ***** size; Residual stress effects on ***** propagation; Particular ***** propagation approach; Refined ***** propagation approach - Demonstration examples: Longitudinal and transverse attachment joints; Cruciform and T joints; Lap joints and cover plate joints; Butt-welded joints; Refined analysis of longitudinal attachment joint
Notch stress intensity approach for seam-welded joints - General considerations: Formal aspects of presentation; Principles and variants of the approach - Basic procedures and results: Notch stress intensity of sharp corner notches; Notch stress intensity of blunt corner notches; Plastic notch stress intensity at corner notches; J-integral at corner notches; Strain energy density at corner notches; Fatigue limit expressed by notch stress intensity factors - Procedures and results for fillet-welded joints: Notch stress intensity factors for fillet-welded joints; Stress rise in front of fillet welds; Endurable notch stress intenstiy factors of fillet-welded joints; Endurable corner notch J-integral of fillet-welded joints; Endurable corner notch strain energy density of fillet-welded joints; Link to ***** propagation approach; Link to hot spot structural stress approach - Weak points and potential of the approach
Local approaches applied to a seam-welded tubular joint - Subject matter of investigation - Application of the structural stress or strain approach: Structural stress analysis and strain measurement; Comparison of structural stress concentration factors; Fatigue test results in terms of hot spot stress - Application of the elastic notch stress approach - Application of the elastic-plastic notch strain approach: Notch stress and strain concentration at weld toe; Fatigue strength assessment based on notch strains - Application of the ***** propagation approach: Basic ***** propagation models; ***** propagation life according to EU Report; ***** propagation life according to British Standard - Method-related conclusions
Structural stress or strain approach for spot-welded and similar lap joints - Basic procedures: Significance of fatigue assessment of spot-welded and similar lap joints; Principles of the structural stress approach; Weak points of the structural stress approach; Applications of the structural stress approach - Analysis tools – structural stress or strain evaluation: General survey; Modelling of weld spot resultant forces; Computation and decomposition of weld spot resultant forces; General theory of forces and stresses at weld spots; Structural stress analysis at weld spots; Nominal structural stress at nugget edge in plate; Nominal structural stress at nugget edge in nugget; Structural strain measurement at weld spots; Weld spot forces by correlation of strain patterns - Analysis tools – nonlinear structural behaviour: Elastic-plastic deformation at weld spots; Large deflections at weld spots in tensile-shear loading; Large deflections at weld spots in cross-tension loading; Buckling fatigue at spot welds - Analysis tools – endurable structural stresses or strains: Endurable structural stresses or strains at weld spots compiled by Radaj; Endurable structural stresses at weld spots compiled by Rupp; Endurable structural stresses at weld spots compiled by Maddox; Endurable structural stresses at weld spots and laser beam welds in comparison; Endurable structural stresses at GMA welds; Software for fatigue assessment at weld spots; Fatigue life assessment supporting car body design - Demonstration examples: Spot-welded axle suspension arm; Spot-welded engine support member; Laser beam welded pillar-to-rocker connection
Stress intensity approach for spot-welded and similar lap joints - Basic procedures: Principles of the stress intensity approach; Weak points of the stress intensity approach; Links to other approaches and application relevance - Analysis tools – evaluation of stress intensity factors: General survey and basic definitions; Stress intensity factors of lap joints based on structural stresses; Stress intensity factors of lap joints with unequal plate thickness; Stress intensity factors of lap joints in dissimilar materials; Stress intensity factors of lap joints under large deflections; Stress intensity factor early solutions for lap joints; Stress intensity factor formulae based on nominal structural stresses; Links to notch stress approach - Analysis tools – fatigue assessment based on stress intensity factors: Endurable stress intensity factors; Equivalent stress intensity factors under mixed mode loading; J-integral and nugget rotation variants - Comparative evaluation of spot-welded and similar specimens: General survey; Spot-welded tensile-shear specimens; Spot-welded cross-tension and peel-tension specimens; Spot-welded hat-profile specimens; Spot-welded H-shaped specimens; Spot-welded double-cup specimens; Seam-welded tensile-shear and peel-tension specimens
Notch stress, notch strain and ***** propagation approach for spot-welded and similar lap joints. - Basic procedures: Principles of the notch stress, notch strain and ***** propagation approach; Weak points and potential of the notch stress approach; Weak points and potential of the notch strain approach; Weak points and potential of the ***** propagation approach - Analysis tools: Fatigue assessment through conventional notch stress approach; Fatigue assessment through improved notch stress approach; Fatigue assessment through notch strain approach; Fatigue assessment through simplified small-size notch approach; Fatigue assessment through ***** propagation approach; Residual stress distribution in spot-welded joints; Hardness distribution in spot-welded joints - Comprehensive modelling examples: General survey; Modelling examples presented by Lawrence; Modelling examples presented by Sheppard; Modelling examples presented by Henrysson; Modelling example presented by Nyk
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