Formulas proposed for predicting fatigue crack intitation and propagation agree well. The methodology estimates the fatigue crack propagation rate as. Effect of welding residual stress on alongwind fatigue. Nominal stress approaches are based on extensive tests of welded joints and connections. Assuming the existence of cracklike flaws after the welding process, the stage of a fatigue crack initiation becomes insignificant and the threshold for the initial. Weld joints are classified by type, loading and shape. The welding process will very often produce defects which can act as crack initiation sites slag inclusions, incomplete fusion, porosity etc. Estimation of longcycle fatigue strength of girth welds. An empirical method which is based principally on estimates of the fatigue crack initiation life n i has been developed which predicts the fatigue resistance of tensileshear spot welds in the long life regime. The effect of four offshore welding procedures on the fatigue crack initiation and propagation from the weld toe region of fillet welded joints was. The results of these comparisons indicate that a very good estimate of the fatigue crack initiation life can be obtained if the material properties at the critical location are well known. It is important to note that estimation of this period is highly. To begin the process cracks must nucleate within a material. The following conditions and parameters are important on the quantification of the fatigue life.
Strainlife for welds this method is used for finite fatigue lives where plasticity around the weld toe is important. Estimation of fatigue propagation life in resistance spot. Estimating the fatigue crack initiation life of welds astm. The method uses basquins law and petersons equation to estimate n i and thus is founded on the fatigue behavior of smooth specimens and modelling of the. Fracture mechanics based estimation of fatigue life of welds a. Fatiguestrengthreduction factors for welds in pressure. Fatigue fahure fatigue failure is the formation and growth of. The approach suggested here, in order to estimate the fatigue crack initiation life, can be split into two stages. Highresolution 3d weld toe stress analysis and acpd.
Hoeppner dw, editor, fatigue testing of weldments, astm stp 648, american society for testing and materials. The fatigue life of a welded joint is calculated on basis of initiation of a crack followed by crack propagation. Hot spot stress approach to keep pace with the increasing use of fea is discussed. The effect of the welding process on the fatigue crack growth i welds produced by the sa w process displayed favorable fatigue life and low initial discontinuities by t. Estimating the fatigue behaviour of welded joints core. Fatigue crack initiation life estimation in a steel welded. Estimation of the fatigue crack initiation life in welds using low. Total fatigue life prediction for welded joints based on. The nonlinear through thickness stress distribution and the weight function method can be used for the determination of stress intensity factors and for the analysis of subsequent fatigue crack growth. The localstrain or strainlife en method, commonly referred to as the crack initiation method, was more recently developed and is intended to describe only the initiation of a crack. Lowcycle fatiguewhere significant plastic straining occurs.
The fatigue crack initiation life cycles to obtain a 0. Lawrence f v, mattos r j, higashida y and burk j d, 1978. Fillet welds cause more fatigue problems than groove welds for two reasons. Local stress fatigue strength estimates in girth weld. An empirical method for estimating the fatigue resistance of tensileshear spot welds. In previous work 1, it was found that structural stress could be successfully used to estimate life for crack initiation and growth to a length of 0. Pdf estimating the fatigue behaviour of welded joints. This study examines the lowcycle fatigue of circular hollow section chs xjoints made of s355 steels, through a combined experimental and numerical. Probabilistic crack growth for welds this is a probabilistic version of the crack growth for. In those cases where a crack is present, the fatigue life. The local approach method is used to calculate the fatigue crack initiation early crack growth lives ni in high strength structural steel weldments. Fatigue tests and estimation of crack initiation and propagation lives in aisi 304l buttwelds with reinforcement intact article in engineering failure analysis 104.
Weld toe fatigue crack initiation is highly dependent on the local weld toe stressconcentrating geometry including any inherent flaws. In this paper a method involving a notch strain and fracture mechanical approach, which considers the. The nonlinear throughthickness stress distribution and the weight function method can be used for the determination of stress intensity factors and for the analysis of subsequent fatigue crack growth. Fatigue crack initiation and propagation life of welded joints. A method of fatigue life estimation for the spotwelds of vehicle body structures by means of finite element analysis fea was studied. Weld toe geometries, welding residual stresses and haz heat affected zone cyclic mechanical properties are taken into account in the ni estimation procedure. An empirical method which is based principally on estimates of the fatigue crack initiation life ni has been developed which predicts the fatigue resistance of tensileshear spot welds in the long life regime. The fatigue life of welded joints is associated with crack initiation and propagation life. Fatigue design rules for welded structures january 2000.
This work deals with the fatigue behaviour of s355nl steel welded joints classically used in naval structures. Assuming the existence of cracklike flaws after the welding process, the stage of a fatigue crack initiation becomes insignificant and the threshold for the initial crack propagation can be taken as a criterion for very. The analytical procedure used to address straincontrolled fatigue is commonly referred to as the strainlife, crackinitiation, or critical location approach. The fatigue life of structures can be considered in two stages. Thus the fatigue life of a connection containing welds is entirely due to crack growth. The crack process in a fatigue failure initiating at the toe of a butt weld with reinforcement intact normally comprises two major stages. Fatigue crack initiation lives are calculated from either a basquin type or a. Fatigue tests and estimation of crack initiation and. Around the fusion zone, there is a heat affected zone haz where the parent material has.
Their inherentshape produces more severe stress conamtrations. The crack initiation phase normally takes many more cycles than the propagation phase. A stress analysis method for fatigue life prediction of. In this work, a datarich methodology has been developed to capture the true weld toe. Further refinement of a methodology for fatigue life. Estimating the fatigue crack initiation life of welds, in proc. Read fatigue tests and estimation of crack initiation and propagation lives in aisi 304l buttwelds with reinforcement intact, engineering failure analysis on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at. Fatigue analysis of seam welded structures using ncode. Lowcycle fatigue involves large cycles with significant amounts of plastic deformation and relatively short life.
The initiation period was found to occupy approximately twothirds of the total fatigue life and consists of the cycles necessary to shake down the residual stresses in. The effect of the welding process on the fatigue crack growth. Covers how they are applied in different specifications, including consideration of residual stresses, size effect, material, welding process and environment. These flaws are responsible for premature fatigue crack initiation fci and must be minimised to maximise the fatigue life of a welded joint. An analytical model for calculating the fatigue crack initiation life of welds has been developed. Estimation of the fatigue crack initiation life in welds using low cycle fatigue concepts. A fracture mechanics approach for estimating fatigue crack. Fatigue crack initiation life prediction in high strength. Estimation of the fatigue crack initiation life in welds using low cycle fatigue concepts welcome to the ideals repository javascript is disabled for your browser. The proposed method expresses the stress intensity factor, and the boundary between crack initiation and propagation period is taken into consideration. The wholelife fatigue method in ncode designlife addresses this analysis gap, bringing powerful new analysis capabilities for a more accurate prediction of weld fatigue life that results in improved product durability, reduced overdesign, and lower weight and cost. In order to verify the ability of the methodology to estimate the fatigue behaviour of welded joints, a dedicated experimental. Fracture mechanics based estimation of fatigue life of welds. Final failure usually occurs in a tension region when the reduced section is no more sufficient to carry the peak load.
The peak stress at the weld toe can be subsequently used for estimating the fatigue crack initiation life. In order to use the model, the stresses and strains at the critical location toe of the weld and a mechanics analysis to relate these local stresses and strains to the remotely applied stresses and strains are needed. Wholelife uses an integrated approach to model fatigue over the entire lifetime of the component from very. This paper outlines the basis of current fatigue design rules for welded structures. The fatigue life of welded joints is associated with crack initiation and. Lawrence et al, astm symposium on fatigue testing of weldnents, may 23, 1977. The approach suggested here, in order to estimate the fatigue crack initiation life. Fatigue crack initiation and propagation analysis by flarp. The local approach method is used to calculate the fatigue crack initiationearly crack growth lives n i in high strength structural steel weldments. These stress categories are then used by designers to estimate the fatigue life of welded components.
Fatigue crack initiation and propagation in butt joint. Development and application of fatigue data for structural steel b. The estimated total fatigue life as a sum of crack initiation and propagation life was found. The local approach method is used to calculate the fatigue crack initiationearly crack growth lives ni in high strength structural steel weldments. Fatigue crack initiation lives are calculated from either a basquin. As far as the examples in this paper are concerned, the fatigue crack initiation life of the dangerous point is increased by about 76% after considering the welding residual stress. This was the first fatigue analysis method to be developed over 100 years ago. Fatigue crack initiation and propagation in butt joint welds of an. Fatiguestrengthreduction factors for welds in pressure vessels and piping. General formulas for the fci life and the fcp rate of the welds are examined, and an approach to predicting the fci life is offered. Menzemer a number of localized failures have developed in welded steel bridge components because of fatigue crack propagation, which in some instances has led to brittle fracture. In the case of ultrasonic impact treatment both stages must be taken account into fatigue life estimations.
An empirical method for estimating the fatigue resistance. Estimating the fatigue crack initiation life of welds. Estimating longendurance fatigue strength of girthwelded pipes using local stress approach. Fatigue failures, both for high and low cycle, all follow the same basic steps process of crack initiation, stage i crack growth, stage ii crack growth, and finally ultimate failure.
Key developments which facilitated these estimates were the assumption of kfmax conditions the largest value of kf possible for a given weld shape, the use of computer simulation methods. Crack growth for welds use this method to determine how long it will take a crack in a weld to grow to a critical size. Enhanced crack sizing and life estimation for welded. Data from mattos and lawrence estimation of the fatigue crack initiation life in welds using low cycle fatigue concepts fracture control program report 19, 1975 was curve fit to obrtain this expression for k f.
Fatigue crack initiation and propagation life of welded. Fatigue life studies of various metals have shown that there are two distinct phases in the history of a fatigue failure. Pdf crack initiation and propagation fatigue life of ultra high. First, stabilized stressstrain cycles are obtained in all points of the welded joint by a finite element analysis, taking constant or variable amplitude loadings into account. Estimating the fatigue life of steel welded structures and. Based on the analytical model developed, an analysis of the factors influencing the fatigue crack initiation life of welds was made. Estimation of the fatigue crack initiation life in welds. The initiation period was found to occupy approximately twothirds of the total fatigue life and consists of the cycles necessary to shake down the residual stresses in the weld. In some situations, the initiation may be the most significant part of fatigue life. New analysis capabilities for fatigue life of welded. Estimation of the fatigue crack initiation life in welds using low cycle fatigue concepts r j mattos. Fatigue life prediction for toe ground welded joints.