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

Fatigue Crack Initiation and Propagation in High Yeild-Strength Steel Weld Metal

Full penetration, double-vee butt welds with reinforcement removed have been fabricated using a high-yield-strength steel, HY-130. Various filler metals and welding techniques were used. Most welds contained intentionally incorporated weld discontinuities such as slag, lack of fusion and /or porosity. Fatigue specimens were cut from these welds and tested in zero-to-tension, axial fatigue. The point at which a fatigue crack began to propagate within the specimen was determined by radiographic measurements. The fatigue life of a specimen could therefore be separated into two parts-that portion spent in initiating a fatigue crack and that spent in fatigue crack propagation. The influence of flaw size and geometry upon the crack propagation portions of the fatigue life was found to be large and to depend upon the thickness of the member. The results of these studies were found to be in good agreement with the fatigue lives predicted on the basis of a fracture mechanics analysis.ASM

Fatigue Data Bank and Data Analysis Investigation

A library system has been developed for the acquisition, compilation and storage of information relating to the fatigue behavior of metal members and structures. Test data obtained from the various information sources are stored on both data sheets (for individual examination), and on standard computer punch cards. A computer program has been developed to sort the data into sets satisfying certain stipulated specimen types and loading conditions. A "best-fit" S-N curve for each specified data set is then established using a least squares error of estimate and correlation coefficient of the regression line, and the lower tolerance limits for 99 percent survival at 50 percent and 95 percent confidence levels. The data and S-N curve are visually displayed using a CALCOMP plotter printout. Information obtained from an analysis of the data in the Fatigue Data Bank for several selected details indicates that the current AASHO bridge design specification provisions, for these details, do not provide consistent correlations nor properly model the fatigue behavior of the details as established by laboratory tests.The State of Illinois. Department of Transportation, Division of Highway.The U.S. Department of Transportation. Federal Works Administration.Project IHR-6

Fatigue Behavior of Mechanically Peened HY-80 Weldments Subjected to Axial Loading

An evaluation of the axial fatigue behavior of mechanically peened transverse tee-weldments and transverse butt-welded joints in HY-80 steel is presented. The data show that mechanical peening along the toe of the weld results in an improvement In the fatigue resistance of both types of weldment relative to the behavior of similar joints tested in the as-welded condition. The process of fatigue crack initiation and propagation was examined for several of the mechanically peened weldments. In the majority of members cracks nucleated at the toe of the weld in the trough formed by the peening operation. Nucleation normally occurred within the first 20 percent of the cyclic lifetime of a specimen, and was followed by a long period of slow, erratic crack propagation, eventually culminating in a short final stage of rapid extension to failure.Bureau of Ships, U.S. Navy.Contract NObs 92240Project Serial No. SR-007-01-01, Task 85

Fatigue of Plates and Weldments in HY-100 and HY-130/150 Steels

An evaluation of the axial fatigue behavior of plain plates and full penetration weldments in HY-lOO steel is presented. Transverse butt-welded specimens welded with the MIL-11018 electrodes were found to contain minute internal weld flaws which often serve as critical locations for fatigue crack initiation. The weld flaws, although not detected by usual radiographic inspection, were successfully located with the use of ul trasonic detection equipment. The ultrasonic equipment was used also to study the initiation and propagation of fatigue cracks in several test weldments, A preliminary investigation of the axial fatigue behavior of HY-l30/l50 steel plain plates is reported.Bureau of Ships, U.S. Navy.Contract NObs 92226Project Series No. SR-007-01-01, Task 88

Fatigue of Plates And Weldments In High Strength Steels

An evaluation of the axial fatigue behavior of transverse buttwelded joints in HY-100 steel is presented. Welding procedures, using MIL-12018 and MIL-11018 electrodes, have been developed in which the defect density is held to a minimum. Specimens welded in accordance with these procedures initiated fatigue failures on the surface at the stress raiser created by the geometry at toe of the weld. Fore these members, the S-N curve for the life range from 10⁴ to 10⁶ cycles is presented for a stress cycle of zero-to-tension. Radiographic and ultrasonic inspections were used to study fatigue crack initiation and propagation originating at an internal weld flaw. A preliminary investigation of the axial fatigue behavior of MIG weldments in HY-130/150 steel is reported. The majority of the transverse butt-welded specimens prepared at each of three laboratories initiated fatigue failures at a variety of internal defects when subjected to a cyclic maximum stress of approximately half the ultimate strength of the base metal. Several alterations in the standard MIG welding procedures were studied in an effort to improve the weld quality; however no modification has been entirely successful in eliminating all the defects which have proven to be critical points for fatigue crack nucleation.The Naval Ship Systems Command, U.S. Navy, under Contract N0bs 94232, Project Serial No. SF-020-01-05, Task 729-

Final Report Low Cycle Fatigue of HY-130 (T) Butt Welds

A preliminary evaluation of the axial fatigue behavior of plates and transverse butt-welded joints in HY-130(T) steel is presented. The weldments were prepared using each of two experimental "second-generation" GMA welding wires and a coated electrode. Fatigue tests were conducted using both sound weldments and weldments containing various internal defects, including porosity, slag, lack of fusion, and lack of penetration. Radiographic and ultrasonic testing techniques were used to study the initiation and propagation of fatigue cracks originating at internal weld flaws. The fatigue studies have indicated that although the highest standards of quality may be used in the fabrication of HY-130(T) welded joints, it has not been possible to guarantee the elimination of all defects which have proven to be critical sites for internal fatigue crack nucleation under axial loading. Internal failures were as likely to occur in specimens rated as sound weldments under radiographic inspection as in weldments having regions containing readily detected flaws. Fatigue cracks originating at internal defects were found to initiate at approximately twenty to eighty percent of the total cyclic life-time of butt-welded joint, for tests conducted at a stress cycle of zero-to-tension. Within the normal limits of scatter for fatigue data, however, the number of cycles of crack propagation to failure beyond the point of internal initiation was found to be reasonably consistent at a specific test stress level, for weldments containing various types and percentages of weld defect area.Contract N00024-68-C-5125; Project Serial No. SF020-01-01, Task 72

Studies of the Fatigue Behavior of Butt-Welded Joints in HY-80 and HY-100 Steels

Bureau of Ships, U.S. Navy.Contract N0bs 88085Project Serial No. SR-007-01-01, Task 85