On the Controlled Restraint Fillet Weld Cracking Test

Various types of cold cracks, such as a toe, an underbead, a heel, and a root crack, are found in the fillet welds of 50 kg/mm2 grade high tensile strength steel.Many studies have been performed on each particular type of crack, giving useful information on the nature and mechanism of the cracking.This investigation was planned, firstly, to analyze the stress distribution by simple linear model, secondly, to develop a new cracking test which could produce each type of crack under the restraint quantitatively evaluated and finally, to use the test to obtain basic information on each crack, especially the correlation between the crack type and intensity, of restraint.Main results obtained are as follows.(1) The linear model used in this analysis provides a good approximation for the relative steress distributions in the fillet weldment.(2) In the small intensity of restraint, stress in HAZ of flange and its toe is larger than other parts of welds, and in large intensity of restraint, large stress concentrates at the root of the weld metal and the toe of web.(3) In the one pass fillet welding, toe crack in HAZ of web occurs not by angular displacement but by restraining vertical displacement of the plates.(4) The CRP (Controlled Restraint Fillet) test developed in this investigation can readily produce all types of the cold cracks in fillet welds.(5) The surface cracks appear at the web toe in the large intensity of restraint, and at the flange toe in the small intensity of restraint.(6) As regards the sectional cracks, the toe crack at the web occurs under the largest intensity of restraint and the heel crack under the smallest one. The root or underbead crack occurs the intermediate wide region between the above-mentioned two extremeities.(7) With the increase in the intensity of restraint, the cracking ratio of weld metal root cracks increases and that of the heel cracks decreases.(8) The cracking strongly depends on the intensity of restraint and also on the dimensions of the test piece even under the same intensity of restraint.(9) The toe and the underbead cracks are both the hydrogen induced cracks, but differ in the macroscopic appearance due to the different stress field induced by the condition of restraint.(10) Results of the analysis by the linear model are in good accordance with those of the CRF cracking test.