It is well known on Pb-Sn solders that the maximum spreading on a copper plate is obtained at near eutectic composition of the solder, and the maximum equilibrium rising height in vertical capillary copper joints or the maximum penetration coefficient in horizontal capillary copper joints are obtained respectively at pure tin component of the solder. But, the adequate cause of difference in these phenomena is not known at presentn. This investigation was made to clear the cause. The results obtained are as follows; 1) The maximum wetting between the solder and copper is obtained at the intermediate (near eutectic) composition of solder, and the shape of wetting curve is mountainous in each case described above. The solder of eutectic composition, accordingly, gave both properties of a good wetting and spreading. 2) The discrepancy in both spreading and penetration can be attributed to the tact that the surface (or interfacial) tension of pure tin is larger than that of the solder of the intermediate composition. 3) The flow of solder in contact with copper solid surface is controlled by factors such as the wetting between solder and copper, the density and viscosity of solder and flux used. A good flowing, therefore, is not always a good wetting and the converse holds good. 4) In the calculation of immersional wetting, it is a mistake to taking the "ideal" wetting condition into account.
Generally, it is suggested for the prevention of lamellar tearing that steel plate is selected and weldfabrication method is modified. In this paper, the selection of plate is dealt with. To obtain a criterion of selection of plate, RRC (Rigid Restraint Cracking) test method with multirun fillet weld is applied for 50 kg/mm2 class high tensile steel plates, and susceptibility of lamellar tearing is given by critical reaction stress or critical restraint intensity for crack intiation. From this result, in order to select the plate for . prevention of lamellar tearing, it became clear that plate would be selected in proportion to the actul restraint intensity of joints. Modified Cranfield test, that is, simple crack susceptibility test for lamellar tearing, is experimented and its susceptibility is given by critical volume of angular distortion for crack initiation or critical preheat and interpass temperature for crack arrest, and the result of Modified Cranfield test is compared with that of prior RRC test. Further, investigated is the effect of some properties of steel plate, that is, inclusions and tensile properties of through thickness direction, on the susceptibility of lamellar tearing. Conclusions obtained are as follows. (1) Sulphur content in steel plate is closely related to the susceptibility of lamellar tearing and it may be regarded as appropriate that sulphur content is substituted for selection-criterion of steel plate. Cleanliness and average length and volume fraction of inclusions, which are related to sulphur content, have good correlation with the susceptibility of lamellar tearing. However, classification of sulphur print has no correlation. (2) From the result of through thickness tensile test experimented by square-type, roundtype and Brodeau-type specimen, it has been clear that the value of reduction of area has good correlation with susceptibility of lamellar tearing. Therefore, round-type and Brodeau-type specimen, which is able to estimate by the value of reduction of area, may be adapted for through thickness specimen. (3) Decrease of plate thickness increases susceptibility of lamellar tearing in order that inclusions may be elongated by hot rolling. Generally, however, it would be considered that thicker plate increases susceptibility of lamellar tearing, because of a lot of deposition volume which causes local strain at the weld. (4) Result of Modified Cranfield test has good correlation with that of RRC test, and Modified Cranfield test method is proper method for the estimation of susceptibility of lamellar tearing.
Recently, welded joints subjected to restraining stresses in the thickness direction have often been adopted with an increase in the use of large welded structures and complicated weld designs. In these types of joints, weld cracking called lamellar tearing in various forms often occurs. This has been of great concern to fabricators as well as steel makers. In order to prevent the lamellar tearing in welded joints, it is necessary to investigate the causes for the lamellar tearing and to establish the lamellar tearing assessment method. In a present study, the causes for lamellar tearing under various conditions have been investigated. The results are as follows: 1) The causes for lamellar tearing differ depending upon the types of joints, the degree of restraints and the distribution and shape of inclusions in steels. When steel plates with great number of inclusions are welded under the high degree of restraint lamellar tearing occurs within a few minutes after the completion of welding. As the amount of inclusions and restraint decrease the influence of hydrogen embrittlement becomes dominant. 2) In some case, weld cracks such as root and toe cracks lead the occurrence of lamellar tearing. The gouging is a possible cause of lamellar tearing.
Many informations on the effect of the constant mean stress have been reported by Munse and other investigators. But in the case that the mean stress is fluctuating in a long period, it is considered that we can not estimate simply from the result of fatigue test with constant mean stress. In this report, the relation between the crack propagation rate and the mean stress was studied using the single notched specimens and that result was examined using the concept of effective stress in the vicinity of crack apex due to Erdogan and et. al.. After those studies, the effect of programmed mean stress on the fatigue strength and the relation between the crack propagation rate and the fatigue life about the both of the welded joint and the base metal were investigated by the analysis of fracture mechanics. The material used in this study was 14 mm thick plates of a steel for welded structure SM58. Fatigue tests were carried out from the high cycle region to the low cycle region in the axial loading condition with constant R-value or programmed R-value. Firstly in the fatigue test with constant R-value, it was found that in the high cycle region, the fatigue test result of base metal was well agreed with the equation of aeff⋅Nαf=C used the effective stress, but that of the welded joint was not because of the scatter of the welded reinforcement. In the low cycle region, though the elasto-plastic DM model could not be adopted and so the effective stress was not used, formally we could seem to use the assumption with m=0 in the high mean stress condition. The fatigue test with programmed R-value were carried out in the very small cycle ratio and it was found that the modified Miner's rule was coincided with the test result of the base metal, and we could estimate the fatigue life with programmed R-value from the result of that with R=0 using the effective stress. But in the case of the welded joint, the observed values had larger fatigue life than the estimated values from the modified Miner's rule. According to the crack propagation rule, the estimations of fatigue life were carried out on the fatigue test with programmed R-value, and it was found that considering the invalid cyclic portion in the vicinity of the threshold of crack propagation, we could have the more exact estimation of fatigue life with programmed R-value.
In conventional processes such as overlay and horizontal fillet welding, an important problem to be solved is associated with the bead shape. As easily seen at the hunging bead in horizontal fillet welding, the most dominant factor to be considered is the influence of gravity on the molten pool. Therefore, the purpose of this investigation is to make clear the effect of gravity on bead shapes. In the previous paper, we discussed surface profiles of bead on plate on the basis of surface tensional analysis of two dimensional molten pool and obtained satisfactory results. As for the bead surface profile, a more important problem is associated with the horizontal fillet welding process. Hence in this paper, surface profiles of horizontal fillet welds are discussed as follows; Firstly, the theoretical surface profile of two dimensional molten pool is treated when the non-dimensional leglengths and the cross sectional area of deposit are given. Secondly, such a calculated surface profile of the two dimensional molten pool is compared with the bead shape in a non shielded arc welding and, consequently, we have obtained good correspondence between the model analysis and the experiment. In conclusion, the two dimensional analysis used in this work is quite available to predict the bead shape in an arc welding where the digging action by arc force is relatively small.
It is well known that residual stresses due to welding influence the initiation of weld cracks and the strength of welded structures. In the present report, attention is forcussed to the effect of welding conditions on residual stress distributions in single-Vee-groove weld. Analysis and experiments described below are conducted: (1) Analysis of weld thermal stresses is carried out based on the thermo-elasto-plastic analysis by the finite element method. The residual stress distributions are obtained under the various conditions, such as weld heat input, plate width and thickness. (2) Experiments on residual stress distributions are carried out. Experiments are obtained under various materials and the various conditions such as welding current, welding speed, plate width plate thickness and length. The results obtained in this report are summarized as follows: (1) Residual stress distributions are determined by parameters: (a) Average temperature T*av=α0Q/2cρεY0hW (b) Initial temperature θi*=α0αi/εY0 (c) Temperature above which yield strength becomes zero θ*M=α0θM/εY0 Comparing of the experimental results with calculated results give evidence that parameters T*av, θ*M determines residual stress distributions. (2) Residual stress distributions are classified two patterns according to average temperature. Residual stress distributions are mainly determined by average temperature in the same material. (3) Conventional formulae are presented for the calculation of residual stress distributions produced in single-Vee-groove weld.
As described in previous papers, a different anode mode, i.e., the glow mode, was observed in a low pressure and small current arc. Mechanism of the glow anode mode and its transition process from the normal mode in case of a hydrogen arc with a water cooled copper anode was discussed from the view points of ionization process in the anode fall region. In an arc with consumable anode such as graphite electrode, however, the above anode mechanism must be modified, since the anode temperature is extremely elevated and considerable heat losses by radiation, evaporation, etc. should be taken into account. In low pressure helium atmospheres, where no chemical reactions between the electrodes and ambient gas take place, the anode mode of graphite electrode is basically classified into two types as it was in a water cooled copper anode. The glow anode mode, however, is further devided into two stages. The one (G1 mode) is characterized by zero consumption of graphite anode, while the another (G2 mode) is featured by eminent evaporation of carbon from the anode. In G1 glow mode, the current density at the anode is small and then the anode temperature is low. In G2 stage, on the other hand, the anode current density becomes high and eminent evaporation takes place from the anode spot area due to high temperature, hence the anode heat losses due to radiation and evaporation in this mode is higher than that of G1.