In the welded structures with thin wall, some initial distortions occur due to misalignment in assembling and thermal deformation during welding and so on. Considerably large amount of strain is induced at the distorted part by the additional bending stress to applies tensile stress. This large strain occasionally affects the fatigue strength, stress corrosion cracking and the others. Therefore, the rational determination of allowable amount of the initial distortion is considered very important. One of the authors has previously reported a theoretical analysis based on the large deformation theory of plates and shells. This analysis was, however, applicable only to a simple shape of initial distortion. In the present paper, the authors widely extended the theoretical analysis, and consequently obtained the new calculating formulae of strain which were applicable to the arbitrary shape of initial distortion, and showed by numerical calculation that the difference of initial distortion shape has apparently the important influence on the amount of strain.
Angular distortions and mis-fitted ones often occur in joints of a large pressure vessel by errors and deformations in assembling parts and welding those. When internal pressure is loaded to a vessel with distortions, a tensile strain is considerably concentrated at the distorted joints. Such a strain concentration usually affects the fatigue strength and the stress corrosion. cracking (SCC) of materials. It is therefore very important to be suitably determined for allowable amount of distortions in order to predict the remained life of the pressure vessel. The present paper shows the difference of the stress-strain behavior in the case of concave distortion and in that of convex one. Even if the relative amount of distortion is very small as compared with the radius of the pressure vessel, an expression for the distortion part based on initial spherical surface is indispensable for an accurate estimation of the strain concentration.
In this study, thermo-elasto-plastic analyses are carried out with the purpose of elucidating mechanical behavior of circular patch welding. The characteristics of restraint stress/strain produced in circular patch welding and their production mechanism are studied from results of analysis. Then, the analytical calculation method of restraint stress/strain produced by circular patch welding is developed based on the production mechanism of restraint stress/strain. The formula to get restraint stress/strain is proposed. Moreover, applicability of the restraint intensity in circular patch welding for the mechanical measure of cold cracks is investigated. Severity of mechanical restraint in the elastic range can be evaluated by using the restraint intensity in circular patch welding as a parameter. Meanwhile, severity of mechanical restraint in the plastic range can not directly evaluated by using it. However, relative severity of that may be evaluated by using it only in the limited range.
In recent years, bridge and highways have been, occasionally damaged because of increased in the volume of traffic and/or the gross weights of vehicles, and therefore it has been often become neccesary to perform welding for repair and reinforcement work, if possible in daytime without traffic control. In this study, the welding crack by the pulsating load in bridge under service condition was studied under the welding crack test by the pulsating load, the trans-varestraint test for weld metal and the high temperature tensile test for weld metal. The following main results were obtained; 1) The welding crack by pulsating load is hot crakcs in solidification-liquid mixed and solidification, and often occur due to external strain caused by pulsating load. 2) The welding crack in solidification occurs more than about 1100°C. 3) The critical loading strain of welding crack are follows; D4316, D5816 : About 1% in solidification-liquid mixed D4316:About 2% in solidification D5816:About 3% in solidification
Pure iron plates were welded using Fe-Al alloy electrode wires in a controlled arc atmosphere. The effects of aluminum on the oxygen contents and non-metallic inclusions were in the weld metals investigated under various welding conditions in Ar-O2 and Ar-CO2 welding atmospheres. The oxygen contents of the Fe-Al weld metals decrease with an decreasing traveling speed at low oxidizing gas partial pressure. The oxygen contents of the Fe-Al weld metals increase with an increasing the partial pressure of oxidizing gases and decrease with an increasing aluminum contents in the weld metals. The oxygen contents of the weld metals welded in Ar-CO2 are lower than those in Ar-O2. The nonmetallic inclusions in the Fe-Al weld metals increase with an increasing oxygen contents of the weld metals. The nonmetallic inclusions are aluminum-oxide accompanying with iron-oxide. Behavior of the oxygen absorption by the steel weld metal is discussed using thermodynamic data.
In this study, transient responses of thermal cycle and bead geometry to step change in welding conditions are investigated. The experiments are made on automatic TIG arc welding of mild steel and aluminum alloy plates, and the thermal cycles and bead size are examined. These experimental results are compared with theoretical values calculated by FEM of three-dimensional heat conduction, from which the transient behaviors and factors controlling them are discussed. The main results are summarized as follows. The transient response of maximum temperature is corresponding to that of penetration, and their transient behaviors from one quasi-state to another one depend upon the difference of heat input between two welding conditions and upon the thermal properties of materials. These results are confirmed by theoretical calculation by FEM. There are two fundamental phenomena referring to the transient response of bead geometry and maximum temperature. One is abrupt change in the molten pool due to the step change in welding condition, which results in the abrupt change of penetration and maximum temperature. Another is the delayed phenomenon due to the heat conduction which depends upon the thermal properties of material and the variation of heat input.
Compared to conventional MIG welding, the MIG welding with filler wire, where a filler wire is fed into MIG welding arc, improves efficiency by minimizing the heat input and increasing the deposition rate. However, discussion arises on controlling the convex bead which arises at increased deposition rate. In this study, it is attempted to control the uneven bead in the MIG welding with filler wire by applying magnetic control of the arc. Furthermore, possibility of controlling the weld metal content is investigated which is favourable for cladding by welding of dissimilar metal i.e. clad steel, corrosion and heat resistant alloys and so on. The diameter of the filler wire was 1.2 mm, the electric current for the welding was 180-350A, the magnetic field for oscillating the arc was 0.004-0.006T and 5Hz. Experimental results showed that the bead of excellent appearance was obtained and it could be flattened by applying magnetic field even at increased deposition rate of MIG welding with filler wire. The penetration was found to be approximately 50% of conventional MIG welding. It was also found possible to control the amount of Ni and Cr, which are important elements for corrosion and heat resistant alloys, and to deviate for them to the bead surface by varying composition and feed rate of the electrode wire and the filler wire. It is said from these findings that this welding method is suitable for cladding by welding to improve efficiency and quality.
Copper to copper lap joints were press-soldered using a resistance heating apparatus. In this process heating and pressure were applied simultaneously. The copper plate was pre-soldered using Pb-50Sn solder and the alloyed layer was formed. The tensile strengths increased at a pressing load above 45N and the fracture occurred in the copper base metal above a 75N pressing load. The joints fractured in the copper base metal in 150°C and 250°C tensile testing and showed excellent thermal resistance.
In our previous reports on underwater gas cutting in various cutting positions, it was suggested that the most important factor having influence on the maximum cut thickness of thick steel plate was the flow velocity of cutting oxygen jet in the kerf. In this report, the velocity of cutting oxygen jet was measured using pitot-tube method under water and in air, for making clear the difference of velocity of jet among those in various cutting positions. The results obtained are summarized as follows. (1) The velocity of oxygen jet (U m/s) decreased with the increase of the distance from the cutting tip (X mm), and the relation between U and X was shown as U=kXα (α: decrease coefficient of velocity of jet, k: constant). In case of the free jet, the value of α under water wsa -1.6 in flat position, and -1.3 in horizontal position respectively. The other side, that value in air was -1.0 in the both positions. (2) The velocity of oxygen jet in the kerf was simulatively measured in the kerf of the acrylic resin model. The value of a was -0.73 in air. And also, it was -0.78 in horizontal and in vertical up position, -0.91 in vertical down position and -0.95 in flat position respectively under water. (3) It was shown that decrease coefficient of velocity of jet was closely connected with the value of the maximum cut thickness in each cutting position.
Determination method on geomoetrical arrangement of optical equipments and selection of photographic parameters are shown for construction of Visual Sensing System. Incident angle of laser spot light from laser project to the surface of object-hot rolled steel sheet- is neccesarry to be selected as more different degree more than 15° from observatory angle, from the viewpoint of decreasing the intensity variation of laser scattered light by variation of angle. Laser scattered light with little variation in space and time and high intensity is required for improving the detection limit for root gap information, and so, both laser diameter and size of surface on the object equivalent to I pixel at picture in camera are very important parameters for it. Furthermore, optimum vale of F-number at lense in camera exists and depends on the surface properties of the object and the intensity of laser light.
Welding control system for Narrow gap GTAW was developed. It is capable of simultaneous control of both welding torch position and welding heat input by image processing the thermal pattern of melting zone. This system is characterized in that an isothermal pattern of weld zone is detected with infrared camera, and the thermal pattern of melting zone is selected by image processing. The position of welding torch is controlled according to the judgement of asymmetric extend of thermal pattern. Welding heat input control is conducted by comparing the area of thermal pattern with the area of standard pattern, too. According to this system, it is possible to maintain an optimum welding condition nn real time.
Metallurgical studies on the bonded interlayers of Ni-base superalloy MM 007 joints were carried out during transient liquid insert metal diffusion bonding (TLIM bonding). The formation and growth mechanism of solid during isothermal solidification process in TLIM bonding was also investigated. Based on these results, the mechanism of TLIM bonding was considered. Main experimental results obtained in this research are as follows. (1) Microstructures of the bonded interlayers of joints made at 1423K for 3.84ks were characterized by the insert metals. In the case of Ni-Si-B alloys, MBF-30 and MBF-35, coarse γ' phase were produced in the bonded interlayer. In the case of Ni-Cr-B alloy, MBF-80 and Ni-Co-Si-B alloy, MBF-90, coarse γ' phases were not produced, and fine γ' phases were produced in the bonded interlayer. (2) In the isothermal solidification process of TLIM bonding, solids grew epitaxially from mating base metal inward the liquid insert metal and grain boundaries were formed at the intersections of growing solids. (3) The growth mechanism of solid into transient liquid phase in TLIM bonding was equal to that in the fusion welding.
A microcracking in 35Ni-20Cr-2Mo-3Cu-lNb alloy multi-layer weld metal had been investigated by a hot cracking test applying enforced strain and metallurgical examination. The microcracking of this weld metal was a liquation cracking which occured above 1100°C on heating and above 1050°C during cooling. It is considered that this liquation cracking was induced by eutectic remelting between NbC and matrix on austenite grain boundary. In order to prevent the microcracking the degrease of the amount of NbC in a weld metal is necessary, and it is desirable to lower C content in a welding material less than 0.002%.
In order to investigate the harmful effect of phosphorus on quenching crack type cold cracking in weld HAZ of medium/high carbon low alloy steels, fracture behavior and grain boundary segregation have been studied by the simulated cold cracking test and Auger electron spectroscopic analysis with vacuum induction mélted JIS SNCM447 containing low (about 0.001wt.%) and high level (about 0.030wt.%) of phosphorus and sulphur. The effect of cerium on the harmful effect of phosphorus has been also studied by the same procedures. Phosphorus enhances the intergranular embrittlement and greatly reduces fracture stress. On the other hand, sulphur does not the detrimental effect. The AES results clearly indicate that phosphorus was segregated at grain boundaries. Carbon was also found to be segregated at the grain boundaries. The phosphorus segregation to grain boundary is fairly increased by grain boundary liquation and decreased with increasing in cooling time. These tendencies are closely correlated with the fracture stress and the fraction of intergranular fracture. The decrease of phosphorus segregation in relation to increasing cooling time occurred at the temeprature region below Ms during cooling, however, this is inconsistent with general tendency of equilibrium segregation described in Fe-P binary alloy. Therefore, it was thought that some complex mechanisms seem to play a role in the temperature region. Cerium has a beneficial effect to reduce the harmful effect of phosphorus due to reducing the degree of phosphorus segregation at grain boundaries.
The weld deposits of 17.5Cr-16.5Ni-6.5Mn-2.3Mo system was previously investigated using SMA welding process for the welding construction of superconducting coil container which was used at cryogenic temperature. The combination of yield strength and fracture toughness was not sufficiently attained by the SMA weld deposits. The fracture toughness was about 150MPa√m when the yield strength was controlled to be 1000 MPa for the weld deposits at 4.2K. It is very desirable to increase the fracture toughness of the weld deposits without decrease of the yield strength for the application to the container. The fracture surface of the JIC test specimen of the weld deposit entirely consisted of dimples. So, the crack extension of the weld deposits is thought to be dominated by the nucleation and growth of the void in the vicinity of'the crack tip. In order to increase the fracture toughness, it should be effective to decrease the distribution density of inclusions in the weld deposits. Then, TIG and MIG Welding processes were applied to vary the distribution of inclusions in the weld deposits which have the same chemical composition as above mensioned and have the yield strength of about 1000 MPa. The relationship between the fracture toughness and inclusion spacing in the weld deposits was investigated. The results of the investigations are summerised as follows: (1)Fracture toughness increases with the increase in the inclusion spacing in the weld deposits, (2)The inclusion spacing in the weld deposits was longest for the TIG process, medium for the MIG process and shortest for the SMA process.
Fatigue crack propagation properties of welded joints were investigated for five types of steels, SB42, SM50B, SPV50, HT80 and SUS304. Propagation data for all materials were found to be coinciding with each other. This was due to the presence of tensile residual stress around the crack tip which made the crack surfaces to open. A total of 3, 335 data plots were used to fit a regression curve. For design purpose, it is advisable to adopt the fatigue crack propagation curve at 99.5% confidence limit. It is also shown that the proposed curve is applicable to random loadings.
This study proposes a ultrasonic measurement of nugget geometry in resistance spot welding of twoplate lap joint of thin plate below 1 mm in thickness. This measurement is immersion method with point focussed probe and is based on the composite effects of convergence of ultrasonic beam and attenuation due to the multiple reflection. Under the condition which the focus of ultrasonic beam places beneath the backwall, there appears a echo from the backwall within the weld region or from the faying surface with an observable time delay behind the surface echo. Since the time delay of backwall echo is as same as that of interface echo but these two echoes provide different amplitude, the weld region is distinguished from unbonded zones. According to the line scanning, three distinct patterns appear; the flat pattern peculiar to the faying surface, decreasing pattern at the vicinity of nugget boundary and increasing or flat pattern at weld region. The nugget size is determined by the distance between two points changing from the decreasing pattern to increasing or flat one, from which the measurement of nugget size is performed with the accuracy of 0.3 mm. A series of parallel line scanning with aid of personal computer provide the configuration of nugget, which is displayed on the CRT with two methods, that is, colour mode and white-black mode evaluated by the amplitude and gradient of amplitude, respectively.
Effects of the insert metals on the crack initiation in Si3N4 to SCM435 joints were investigated by paying attention to the thickness of copper enriched layer and the diameter of specimen. The 10 mm diameter joints without crack using Cu-5%Cr, Cu-1%Nb, Cu-3%V, Cu-5%Ti and Cu-10%Zr insert metals were obtained in case that the thickness of copper enriched layers were more than about 0.2 mm, 0.2 mm, 0.3 mm, 0.5 mm and 0.8 mm, respectively. As for Cu-5%Cr insert metal, the 13 mm diameter joints without crack were obtained in case of the thickness of copper enriched layer being more than about 0.4 mm. On the basis of residual stress analysis in Si3N4 to SCM435 joint, the critical maximum principal stress in Si3N4 to prevent crack in the joint were almost the same level of 350-400MPa in any cases. It was concluded that copper enriched layer had the function of relieving the thermal stress occurred in the bonding process.
In order to study possibilities of application of rapid solidification ribbons to an insert metal for solid phase diffusion welding of Ni-base supearlloy, welding was carried out by changing the welding pressure, time, and temperature using Ni-base superalloy ribbons (IN738LC, TMP-3, René 80, and Ni-Al-X three compositional alloys) produced by twin-roll rapid solidification process. The ribbon has almost similar composition to the base metal (René 80) and superplastic potential, then it needs relatively small flow stress on deformation. In this report, the influence of ribbon usage as an insert metal and carbon content in the ribbon on the joint strength were studied. The results are as follows, (1) The joint strength increases by using the ribbon for an insert metal compared to that without ribbons. (2) Carbide and oxide are formed on the welded interface during welding, resulting in decrease in welding strength. (3) The joint strength is increased and fractured position changes from the welded interface to the base metal, as the carbon content in the ribbon is decreased.
In this study, a series of Fe-Cr-Ni ternary alloys were treated by CO2 laser surface melting and effects of rapid solidification on solidification modes and microstructures were investigated. It was found that two new type solidification modes; rod-like eutectic mode and massive solidification mode, occurred in laser surface melted alloys in addition to the four types observed in conventional welding metals. The rod-like eutectic solidification formed in the compositional range in which primary ferrite solidification occurs in TIG welding metals with iron content of less than 65%. The compositional range of rod-like eutectic first increased and then decreased a little with increasing cooling rate. It was also shown that massive solidification took place only at a small compositional range in which primary ferrite solidification occurs in TIG welding metals but iron content is larger than 65%, when a critical cooling rate was achieved. The solidification modes can be classified into six types in laser surface melted alloys. With increasing cooling rate it changed. largely depending onto compositions of alloys. For the experimental conditions of present study, six kinds of changes in solidification mode were seen as shown below: (1) full austenite to full austenite, (2) primary austenite to full austenite, (3) primary ferrite to primary austenite to full austenite, (4) primary ferrite to rod-like eutectic to full austenite or massive solidification mode, (5) primary ferrite (to full ferrite) to massive solidification mode, and (6) full ferrite to full ferrite.