Fatigue damage criteria classification, modelling developments and trends for welded joints in marine structures

Abstract

Fatigue is typically a governing limit state for marine structures. Welded joints are the weakest links in that respect. Physics involve several resistance dimensions, a range of scales and distinct contributions in different stages of the accumulative damage process. Fatigue damage criteria developed over time have been classified with respect to type of information, geometry, parameter and process zone including plane and life region annotations. The criteria are evaluated regarding model (in)capabilities, showing up to what extent (governing) physics are taken into account. Modelling developments and trends towards complete strength, multi-scale and total life criteria have been identified. Incorporating all four (interacting) fatigue resistance dimensions: material, geometry, loading & response and environment translates into a complete strength fatigue damage criterion. Considering macro-, meso-and micro-scale information provides a multi-scale fatigue damage criterion. Correlation of crack initiation and growth requires matching intact and cracked geometry parameters, revealing a total life fatigue damage criterion. HIGHLIGHTS• Classification of fatigue damage criteria with respect to type of information, geometry, parameter and process zone including plane and life region annotations.• Identification of modelling developments and trends towards complete strength, multi-scale and total life fatigue damage criteria for welded joints in marine structures. NomenclatureA notch strain energy density process zone area C crack growth or fatigue resistance curve intercept (endurance coefficient) D fatigue damage E normal strain at macro-scale E Young's modulus J crack tip energy density J 1 hydrostatic stress or strain component J 2 deviatoric stress or strain component K σ crack tip stress intensity factor K ɛ crack tip strain intensity factor K' work hardening coefficient K N notch stress intensity factor K N I mode-I notch stress intensity factor K N III mode-III notch stress intensity factor K I mode-I stress intensity factor K I T total mode-I stress intensity factor K I r residual mode-I stress intensity factor K III mode-III stress intensity factor K * FE dimensionless FE based notch stress intensity factor N (total) number of cycles until failure N i number of cycles corresponding to initiation N g number of cycles corresponding to growth R notch strain energy density process zone radius S stress based fatigue damage criterion S B Battelle structural normal stress range S e effective notch stress range S eq (equivalent) Von Mises stress range S n nominal stress range S s hot spot structural stress range S T total stress range T temperature T B Battelle structural shear stress range T σS strength scatter band index W energy based fatigue damage criterion W N notch strain energy W N A notch strain energy density Y n notch factor Y f far field factor a crack size (i.e. length) a 0 critical defect size a d long-term corrosion pit size (i.e. depth) a i (real) defect or initial crack size a n (root) not...

Fatigue design of welded double‐sided T‐joints and double‐sided cruciform joints in steel marine structures: A total stress concept

“…Since fatigue scaling requires both the peak value and gradient to be incorporated, the total weld notch stress distribution has been used to obtain the total weld notch stress intensity distribution. Turning an intact geometry parameter into a cracked geometry equivalent, the acquired damage criterion takes the complete distribution into account …”

“…For MCF and HCF, the far‐field structural response is predominantly elastic, explaining why typical fatigue strength criteria S are of the stress type. Involving the stress range S = Δ σ reflects the cyclic loading and response requirement to develop fatigue damage …”

“…range and ratio r lr = F min / F max = σ min / σ max , the ratio is not explicitly considered since the stress level in the notch affected region is assumed to be at yield magnitude because of the welding induced residual stress. Any small‐ and large‐scale specimen fatigue test result obtained at relatively low ratio has been translated to r lr ∼ 0.5 using a nominal mean stress correction . Exponential mean stress models have been developed in order to improve the life time estimates in case of relatively low stress range and high mean stress, e.g.…”

“…Generally speaking, a decreased life time estimate uncertainty is obtained because of reduced (strength) scatter. The structural response modelling time and local geometry and loading and response information increases on the other hand, increasing criterion complexity and effort …”

“…DNV‐GL) are available . Recently, the total stress concept has been developed, aiming to improve fatigue strength similarity with respect to weld notch stress distribution, weld notch stress intensity, weld notch affected micro‐crack and far field dominated macro‐crack growth as well as welded joint fatigue resistance. Complete and censored data have been used to establish one (family of damage tolerant engineering) joint fatigue resistance curve(s) for arc‐welded joints in aluminium marine structures.…”