Final Report : Low Cycle Fatigue of Butt Weldments of Hy-100 (T) and HY-130(T) Steel

An evaluation of the axial fatigue behavior of plain plates and full penetration butt-welded joints in HY-130(T) steel is presented. The weldments were fabricated using GMA and SMA welding processes. Fatigue tests were conducted with sound weldments and weldments containing internal defects including slag, porosity, and lack of fusion. Radiographic and ultrasonic inspection techniques were used to- study the initiation and propagation of fatigue cracks originating at internal weld flaws. Acoustic emission measurements were taken for smooth and notched HY-130(T) specimens tested in static tension and in fatigue. The results of preliminary tests of plain plates and butt weldments of HY-100(T) [HY-IIO] steel are presented. Comparison of the fatigue results for the HY-130(T) specimens with equivalent data for HY-80 and HY-IOO steel has indicated that, within the range of lives from approximately 104 to 106 cycles, the fatigue behavior of as-rolled (mill-scale intact) plain plates of the three materials may be described by a single S-N regression line. Surface treatments, including gritblasting and polishing, were found to significantly increase the fatigue lives of the HY-130(T) plate specimens. Wide variations in fatigue life were exhibited by the HY-130(T) and HY-100(T) butt-welded specimens in which cracking initiated at internal weld discontinuities. The scatter in lives could not be explained on the basis of the type of weld defect initiating failure, nor could it be attributed to differences in the weld metal composition or the welding process. However, through application of the concepts of fracture mechanics, it was found that the fraction of the total fatigue life spent in macroscopic crack propagation could be estimated with reasonable reliability if the through-thickness dimension of the crack-initiating defect, its position relative to the specimen surface, and the nominal cyclic stress are known. Results obtained from the monitoring of the acoustic emission from specimens subjected to both static and cyclic loading have indicated that this technique is potentially an effective tool for in-service nondestructive testing of structural components.The Naval Ship Systems Command, U.S. Navy ; Contract N00024-69-C-5297; Project Serial No. SF51-541-002; Task 72