Estimate The Fatigue Life Of Welded Hollow Spherical Joints In Grid Structure Based On Cumulative Damage Theory

With the rapid development of spatial structure in recent years, the welded hollow spherical joints grid structure with hanged crane has been widely used. The fatigue problem of grid structure caused extensive concerns from domestic and international academic and engineering area; study shows that grid structure's fatigue was mainly in the welded hollow spherical joints'fatigue, So the fatigue problem of welded hollow spherical joints in grid structure became the main contents, the fatigue life is the final determination of fatigue problem, the determination of fatigue life, there are two general approaches, one is determined through experiments,the other is to use the appropriate formula to determine the fatigue life. As long cycle fatigue test, costing large and many influencing factors, so find a reasonable estimation formula and estimation methods is very important.This paper summarized the existed cumulative damage formulas and research results, based on the experimental data, estimated the fatigue life of welded hollow spherical joints.1 Estimate the fatigue life with cumulative damage formulasBased on the constant amplitude data, estimated the amplitude fatigue life with cumulative damage formulas. Compared and analyzed the applicability of the cumulative damage formulas,obtained four kinds of practical cumulative damage theory: Miner theory, Amended miner theory, Manson bilinear theory and Corten-Dolan theory.calculated with amplitude test data.Comparison of 4 methods of calculation, excluding Manson bilinear theory, and gave the lmits and distribution range of the three remaining kinds of theory.2 Estimate the fatigue life with finite element method Estimate the fatigue life with the fatigue life estimation software Msc.fatigue fatigue.1) Using Msc.fatigue for constant amplitude fatigue life prediction, got life cloud formation which can directly show the fatigue life distribution; comparing the actual damage which was consisted with the actual destruction,and obtained regularity, quantitativly estimated the fatigue life.2) Using Msc.fatigue for amplitude fatigue life prediction, comparing the differences of results got from finite element methods and formulas; estimation the fatigue life with nominal stress method, got life cloud formation which can directly show the fatigue life distribution, comparing the actual damage which was consisted with the actual destruction,and obtained regularity, quantitativly estimated the fatigue life.3 Analysis of fatigue factorsAnalyzed the influnces on the fatigue life of stress concentration, mean stress, a small number of high stress, stress order, load, low fatigue stress, stress cycle of the intermittent time, processing defects and installation errors, repeat the cycle of the block size, internal defects, loading forms and materials.