In Fatigue Branch of National Research Institute for Metals, the experimental program had been carried out from 1975 for standardizing the axial fatigue testing method in order to make the fatigue data sheets on weldments of the domestic metallic structural materials. In this program, the following basic factors were investigated; (1) the effect of the specimen size, (2) the effect of frequency, (3) the effect of testing machine. Materials used in this program were the rolled steel for welded structure, SM50B, SM58Q and HT80, and the type of joint were the butt welded joint with reinforcement and the non-load tarring fillet welded joint. Fatigue test was earring out under an axial loading condition with the stress ratio of zero using the strip-type specimens. In this report, the above factors were investigated about SM50B butt welded joint. And it was found that the difference of thickness (from 9 mm to 40 mm) has remarkable effect on the fatigue strength which is unexplainable only by the static strength and that this effect seems to be mainly caused by the difference of the stress concentration due to the shapes of reinforcement for each thickness. Also, it had been ob-, served that those factors of the specimen width (from 25 mm to 160 mm), frequency (from 1Hz to 100 Hz) and testing machine have no significant effect on the fatigue strength.
As the purpose that reheat cracking testing method of steel by the stress relaxation test is to be a much simpler and highly reproducible, the present study is check up on the testing condition for the reheat cracking test of steel by conducting an examination with the test specimen for the synthetic weld thermal cycle. Also, the evaluating method of the sensitivity of steel to reheat cracking with the test specimen for the synthetic weld thermal cycle was discussed. The results of the study obtained are summarized as followes: 1)The effects of the notches in steel and the heating rate on the sensitivity of steel to reheat cracking are remakable. The sharper notches or slower heating rate lead to the liability of cracking. Consequently, it is necessary to make these factors being constant in Evaluating the sensitivity to reheat cracking. 2) As compared the results of the reheat cracking test with the test specimens for the synthetic HAZ and the weld reinforced test specimens, there was a good consensus between cracking phenomenon and cracking sensitivity of both test specimens. 3) The reheat cracking test with the test specimen for synthetic HAZ is simple and highly reproducible. Moreover, by use of amount of the plastic deformation (Δlp') at the time of occurrence of the cracking, it is possible to evaluate the sensitivity of steel to its cracking.
Delayed crack initiation and propagation behavior from a notch of poor penetration in a weldment of HT80 steel of 31 mm thickness has been investigated, to apply a fracture mechanical technique to a evaluation of the susceptibility to delayed cracking. Three points bend specimen of 70 mm width with weld defect of poor penetration were welded, and the tip of the notch was located on a fusion line in modified-Vee joints. Crack opening displacement and Acoustic Emission signals given off have been recorded as a function of time. Results can be summarized as follows: (1) Fracture mode of the presure vessel at proof loading, that is the transition behavior from delayed cracking to unstable cleavage fracture, can be easily reappeared by the laboratory test proposed in this report. (2) The susceptibility to delayed cracking of the weldment of HT80 steel can be successfully evaluated as a function of stress intensity factor or COD. (3) Specimen actively emits Acoustic Emission accompanying delayed crack growth.
Indirect measurement of the crack propagation rate through thickness using the relationship with the crack opening displacement is performed and the fatigue crack initiation and propagation behavior are discussed experimentaly and analytically in connection with the cyclic plastic zone size at the apex of initial notch which is caused by early cyclic loading before crack initiation. A kind of master curve that shows the correlation between the crack initiation life and the cyclic plastic zone size caused by the initial notch is established.
Crack Opening Displacement (COD) tests were carried out in submerged arc weld metals. The fracture initiation properties of wled metals were related to the microstructures. The relationship, between them was investigated in the view point of unit crack path on the fracture surface of COD specimen. The results obtained are as follows: (1) The evaluation method of the fracture toughness of submerged arc weld metal was established by means of COD test. (2) The crack initiation properties were related to the microstructures of weld metal. (3) The growth of the uniform fine ferrite structure improves the low temperature toughness of weld metal. (4) The brittle fracture surfaces in COD specimens were closely related to the microstructure, and it was found that the crack initiation temperature at δc=0.2 mm has a good correlation with the unit crack path based on the direct observation of fracture surface.
A basic study of aluminum brazing has been made of the reaction between aluminum base metal and Al-Si-Mg brazing filler metals from the viewpoint of dissolution kinetics. The dissolution of solid aluminum in molten Al-Si-Mg alloys was studied under static and isothermal conditions. The solid aluminum cylinders were immersed in molten Al-12.6%Si-Mg alloys with magnesium increasing up to 5% under the argon atmosphere in the temperature range from 571 to 603°C. The rates of dissolution of solid aluminum in molten Al-Si-Mg alloys were dependent on the temperature and the magnesium concentration. The obtained values of dissolution rate constant increased with increasing magnesium concentration in solutions and temperature. The natural convections were produced by the large density defferences between the boundary layer adjacent to the solid aluminum and the molten alloy. Consequently, the natural convections exerted an influence on the dissolution phenomenon. It was concluded that the rates of dissolution were controlled by the diffusion process of dissolved atoms through the boundary layer adjacent to the dissolving surface of the solid aluminum. The dissolution of solid aluminum in molten Al-Si-Mg alloys was studied under static and isothermal conditions. The rates of dissolution of solid aluminum in molten Al-Si-Mg alloys were dependent on the temperature and the magnesium concentration. The obtained values of dissolution rate constant increased with increasing Mg concentration in solutions and temperature. It was concluded that the rates of dissolution were controlled by the diffusion process in the solutions.
The influence of absorbed water of coated electrodes on porosity of weld metals were experimentaly investigated by bead on plate and horizontal fillet welding, using various types of coated flux with various water contents. The experimental results were as follows: 1) Ilmenite, lime-titania, high cellulose, high titanium oxide and iron-powder iron oxide type electrodes were not influenced very much by absorbed water of coated electrodes on porosity of weld metals and sound weld metals were obtained in the all experimental range of absorbed water contents. 2) In the case of low-hydrogen type electrode the porosity of weld metal began to occur when absorbed water content of coated electrode was over about 1.3% and remarkably increased in proportion to the amount of absorbed water contents. 3) Diffusible hydrogen content of weld metal by low-hydrogen type electrode, in which porosity began to occur, was about 7 cc/100 g. This diffusible hydrogen content was smaller than that of sound weld metals by dried other coated electrodes, which was about 32.7-45.0 cc/100 g.
In this paper we describe an experimental study of the shielding gas flow state in a still atmosphere and windy conditions by visualization of the flow and analyzing the gas concentration around the nozzle. Then a simple method to obtain the suitable gas flow rate of CO2 arc welding in windy condition can be suggested. Results of the experiments are summarized as follows. 1) CO2 gas concentration in the wall jet in a still atmosphere is maximum on the plate surface. It decreases lineally parting from the plate surface and decreases exponentially by increasing of X/d. 2) CO2 gas concentration of the shielding gas jet in windy conditions is decided by Us, uj, H and d. Each curve showing the relation between qCO2/qCO2+AIR and U0/uj has the similarity throughout the experiment. 3) The suitable gas flow rate of the CO2 arc welding in windy conditions can be estimated by the qCO2/qCO2+AIR-U0/uj curve with some H/d used in welding. 4) Application of this oil smoke method to visualization of the shielding gas flow is usefull over the wide range of Reynolds number. And this method will be avialble to investigate the shielding gas effect of the narrow-gap welding.