Weld Toe Crack Propagation Predication

Fatigue fracture at the weld toe is the main failure mode of thewelded joint. Welded joints strength played an important role on theoverall strength and fatigue life of entire engineering structures. Therefore,it is necessary for us to do the Fatigue Crack Propagation prediction forwelded joints. This has a great significance on the structure design andengineering safety. Currently, there exist several methods for the Fatiguelife prediction of weld joints, the nominal stress method; local stress-strainmethod; Fatigue Crack Propagation (FCP) method based on fracturemechanics and fatigue life prediction based on damage mechanics. TheFCP method based on fracture mechanics can better explain varieties ofphysical phenomena in fatigue experiment, and it also can effectivelyconsider the initial imperfection, stress ratio, residual stress, random loadfrequency and loading sequence. What’s more, FCP method caneffectively simulate the initial state and the final state of fatigue crackpropagation. So the FCP method based on the fracture mechanics has ahigh practical significance in engineering use.One of the important works while using FCP method is to accuratelycalculate the stress intensity factor (SIF) under residual stress distribution.Existing SIF manuals only give simple empirical formula for simple geometry structures under basic load type such as tension, compressionand bending, the calculating of SIFs for surface cracks at weld toe inresidual stress field is still a difficult problem. Based on this, this paperwill propose a new weight function to evaluate the SIFs for surface cracksat weld toe under residual stress field and predict fatigue strength ofwelded joints under random load based on FCP method, the main structureof paper is as follows:(1) Reviewed the research on the welded joints fatigue strength,illustrate the research trends and shortcomings of fatigue life prediction forwelded joint.(2) Summarized the weight function method and its applicationprocess to calculate the stress intensity factor (SIF).(3) Numerically conducted flat plate welding, T-butt welding andspherical shell welding process. Obtained the typical welding residualstress distribution and compared it with typical empirical residualdistribution. Pave the way for calculating residual SIFs.(4) Proposed a new Weight Function for both deepest and surface pointto calculate stress intensity factor under high-order stress distribution. Basedon the new weight function, calculated the residual stress intensity factorKresfor semi-elliptical surface cracks at T-butt weld toe.(5) Using two different fatigue crack growth models——Paris modeland Huang model to study fatigue crack growth at the weld toe. Specially investigate the effect of the initial crack size, residual stress on fatiguecrack propagation.