It is well known that the fatigue strength of reinforced butt welded joint has a always large scatter. It this case, the fatigue crack almost originates at the toe of a weld. Therefore it is considered that the fatigue strength of the welded joint is primarily related to the shape of reinforcement, and the scatter of the stress concentration due to that shape causes the scatter of the fatigue strength of welded joint. In this report, the above correlation was investigated and the result was examined by a statistical analysis. The material used in this study was 6mm thick plate of a steel for welded structure SM50A. V-groove was used for edge preparation and after arc welding with covered electrode, only the parts of sound weld were used as specimens from the result of X-ray examination. Specimens for welded joint and base .metal were machined to 25mm width. After measurement of the height of reinforcement h and the toe radius of weld r were chosen as the shape parameters. It was found that the statistical distribution of h was normal and that of r was log-normal. It was also shown that the effect of sampling the specimens from different welding lots could be neglected. Fatigue tests were carried out in axial loading with R=-1 using a Vibrophore type fatigue testing machine. After each tests, the point of crack initiation was confirmed and the two parameters h and r were measured at that point. The stress concentration factor Kt was obtained from h and r using a formula due to Heywood. From the experimental relation between Kt and Kf (the fatigue notch factor) for the base metal, Kf for the welded joint was obtained. Then the scatter of fatigue strengths of the welded joint revised by Kf was examined statistically. It was found that the scatter of fatigue strengths revised by Kf was of the same order of magnitude as that of the base metal, and was much smaller than that of non-revised fatigue strengths of the welded joint. Therefore, it was confirmed that the scatter of the stress concentration due to the shape of reinforcement caused the scatter of fatigue strengths of the weldment. Moreover, from an experimental relation between the height of reinfrocement h and the toe radius of weld r, the fatigue strength of the welded joint could be estimated using only h from that of the base metal. Also in this report, the fatigue strength at 2 × 108 cycles for the welded joint was investigated statistically using the staircase method. It turned out that the estimated mean value was 12.5 kgf/mm2 and the estimated standard deviation was 2.5 kgf/mm2.
The effect of heat input on mechanical properties of thick 5083-O welds were investigated using high current MIG process. The results obtained are as follows: 1. Mechanical properties of Al-Mg alloy 5083-O welds are.influenced markedly with the change of heat input. To be specific, tensile strength, yield strength, elongation and reduction in area tend to be lowered with increase in heat input. 2. Heat input'per unit plate thickness must be kept below 20kJ/cm/em to satisfy the required strength, 28 kg/mm2, for JIS specified value (base plate; 4.6% Mg, electrode wire; 4.9% Mg) 3. Permissible heat input can be increased by increasing Mg content of base, plate and electrode wire. 4. Deterior ation in mechanical properties due to the increase in heat input isinfluenced both by composition factor, i. e., variation in Mg content due to dilution or vaporing loss and by structural factor, i. e., solidification structure of-weld metal.
Square-butt welding was performed on 25mm thick plates of commercial high tension steels (HT50, 60 and 80) with electron-beam welding. Two electron-beam welders (conventional high voltage and low voltage types) were used for this investigation, and the weld heat input was respectively varied with and. without 100°C preheating. Some results of the mechanical properties of the welds of HT-50, 60 and 80 steels such as hardness. distribution, tensile and fatigue properties were investigated in this paper. Most of welds have had no-defects that were detectable by dye pencetrant and X-ray inspections. It seemed that only Mn in weld. metal was a little vaporized during electron-beam welding. The average hardness of weld metal was. decreased with an adoption of preheating, but even in weld metal without preheating it was not so high to originate some cold cracks. Most of tensile-tested specimen for the welded joint fractured in the base metal, and all of face-and. root-bended specimens showed a complete bend angle of 180 degree without any defects. In case of fatigue test, the fatigue limit of welded joint showed the adequate value which corresponded. to that of respective base metal of HT-50, 60 and 80 steels, and it seems that the fatigue limit was raised with an increase of the hardness of weld metal. From the results of these mechanical tests, it is anticipated that the electron beam welding process will be promising for the welding of these constructional high tension steels.
Surface treatment of the interface to be welded is very important factor affecting the weld characteristics of diffusion welds. The purpose of this study is to investigate the influence of the surface treatment by glow discharge in argon gas (0.01-0.6 Torr) as the surface cleaning technique on diffusion welds of copper and aluminum. The following results were obtained. 1. The surface treatment by glow discharge cleans the weld interface uniformly, and at the same time heats it. 2. The surface treatment by glow discharge gives higher weld strength than the wire-brushing surface treatment. 3. The surface of cathode is sputtered and cleaned by argon ion bombardment. 4. The cleaning action of glow discharge depends on discharge voltage and current. The increase of discharge voltage makes the weld interface cleaner than the increase of discharge current. 5. Cleanliness of the weld interface depends upon the correlation between the cleaning action by ion bombardment and the contamination due to residual, objectionable gas. The cleaner the weld interface is, the better the weld characteristcs is. 6. It is recommended for decision of discharge conditions that discharge voltage, discharge input and vacuum are as high as possible.
Surface profiles of beads on plate are theoretically discussed on the basis of surface tensional theory. In the first part of this paper, the theoretical surface profile of molten pool is made clear by using the two dimensional model of molten pool under the following assumptions. (1) The molten pool is long enough in the welding direction (two dimensional model), i. e. the curvature of pool surface along the welding direction is ignored. (2) The arc force, acting on the pool surface, is negligibly small. (3) The surface tension of molten metal is constant all over the pool surface. In the second, the calculated surface profile at the two dimensional molten pool is compared with the bead shape on plate in non shielded arc welding or submerged arc welding with strip electrode. At all over the practical welding conditions, it is consequently clarified that the experimental result is in good qualitative agreement with the calculated one for molten pool. Thus, it is concluded that the two dimensional analysis, based on the simple assumptions, is quite available to foreknow the bead surface shape when three boundary conditions, the bead width, the cross sectional area of deposit and the capillary constant of molten metal, are given. In other words, the two dimensional analysis, used in this work, may be valid for the other positional processes such as horizontal fillet welding and horizontal welding.