The electron-beam diameter and intensity distribution of the NRIM 1.5 kW electron-beam welder, home-made, were measured by interrupting the beam with a water-cooled copper plate. The effects of filament current, anode voltage, welding beam current and focusing voltage on beam focusing were studied experimentally. The following conclusions were obtained: 1) The intensity distribution of electron-beam current on the specimen surface showed approximately a normal distribution. 2) The electron-beam was of a cone shape with a vertex angle of 7 degrees. 3) The minimum diameter of electron-beam on the specimen is affected severely by filament current, anode voltage, welding current and focusing voltage. Greater values of filament current and anode voltage and smaller welding current contributed to making the diameter of electron-beam smaller. 4) In electron-beam welding, the beam diameter on the specimen should always be noted besides welding current, anode voltage and welding speed.
The new experimental "restraint joint" method has been proposed by the authors in order to obtain a welding joint with both ends of base plate fixed rigid. In this experimental method, the distance between the two fixed ends, which may be called " restrained distance " must always be maintained constant. For this purpose the joint test plates bound by Mohr's tension tester are set up as illustrated in Figs. 1 and 2. And the external load by the testing machine must be regulated through quick action so that the restraint distance may be kept constant. During the experiment carried not by the authors the welding reaction stress in weld metal under restraint varied with welding progress as shown in Fig. 5. In the figure, the final stress at each pass may be regarded. as a kind of yield stress or plastic flow stress in weld and it is considered that each final stress should be a maximnm stress at each pass. Extending this principle to many kinds of restraint joint in practice, the interesting results on actual welded construction have been obtained. The authors have examined and measured the reaction stress caused by erection butt weld on the seqeral ships which were built at Yokoyama Shipyard in recent years. Comparing thus obtained results with the above experimental results In " restraint joint ", it is clarified that the degree of restraint in such a heavy welded construction is very small, or such a joint should rather be regarded as so-called free shrinkake joint. Because mosl welded constructions are movable with welding shrinkage force, the reaction stress existing in a construction should be equivalent to the stress which would be obtained from the static friction force to the construction.
In the previous paper, experiments and considerations were carried out to determine the stress criterion for fatigue fracture of general welded beams having a extremely sharp incomplete penetration (notch). As the result, some stress criterion might be suggested. In this paper, the stress criterion for fatigue fracture of welded beams having dull notch made artificially and then effect of dull notch is comparatively smaller than that of sharp notch were investigated experimentally. The experiment has revealed the following ; namely, it was found that the fracture due to combined effect of flexural shear and normal stresses could be obtained in a beam having a dull notch as in the case of beam having a sharp notch, and moreover other stress criterion, though it was different from that of sharp notch, might be certified for dull one.
In the methods for estimation of the Charpy impact values, proposed up to now, the average value of a few specimens and the deviations from it (σ2), etc. are mainly considered. The authors have made a large number of impact tests with steel plates to clarify the physical meaning of the distribution of testing values. As the result of these experiments it has been found that the distri-bution of the Charpy-impact values seems to be not a normal, but a skewed one. The theory for such a skewed distribution was established. Proposal was made of a standard for the estimation of the notch-toughness of weld-metals ba-sed on the theory. According to this proposal the average value, the theoretical lowest value and σ2, etc. cand be obtained comparatively exactly by using a definite number of specimens, and the method of estimation seems to be reasonable.