Composite specimens with 3- and 5-layers composed of a mild steel and spheroidal graphite cast irons (steel/cast iron/steel, steel/cast iron/steel/cast iron/steel) were fabricated using diffusion bonding. The composite specimens were hot rolled and the final reduction was 88% and 92%. The main results obtained are as follows; (1) When the hot rollings of 92%-reduction were carried out for the composite specimens, cracks were not observed in the cast iron and on the bond interface between the mild steel and the cast iron. By the hot rolling, spheroidal graphites in the cast iron became the form of sheet. (2) The tensile strength of the rolled composite sheets with pearlitic structure was higher than that of the mild steel. In case of ferritic structure the strength of the sheet with 3-layers was a little lower than that of the mild steel, however, the strength of the sheet with 5-layers was higher than that of the mild steel. (3) The specific damping capacity of the rolled composite sheets was higher than that of the mild steel and increased with increasing the reduction and the number of the layer. (4) The damping effect of the sound pressure of the gear made of the rolled composite sheet with 9-layers was very high in comparison with that of the gear made of the mild steel.
This research was carried out to develop a new type of testing method on the solidification cracking of welded joints and to clarify effects of experimental parameters and glass fiber tape backing on cracking. Results obtained in this study are summarized as follows; the experimental result revealed that the local tensile force method was quite effective to reproduce solidification cracking in narrow gap welded joints in a laboratory. The crack length considerably depended on the strain rates. The effect of boron contents in glass fiber tape backing was not so significant to the solidification cracking tendency under normal welding procedures.
Effects of a neutron irradiation on mechanical properties of aluminum alloys have been studied using a miniature tensile testing method. In a present study, the aluminum alloys (A7N01, A5083 and A6061) for cryogenic structural materials were selected as the testing materials, and their base metals and electron beam welded joints were tested at cryogenic temperatures. Results obtained are as follows: (1) Tensile strength of base metals and welded joints became higher in the order of A7N01, A5083, and A6061, and their elongations became larger in the order of A5083, A6061 and A7N01 after neutron-irradiated up to 1.7×1023n/m2. (2) All the materials exhibited large serrations in the nominal stress-nominal strain curves at 4.2 K. Little effect of neutron irradiation on the serration was observed. (3) The base metal and the welded joint of A7N01 exhibited high strength at cryogenic temperature. Increase of strength by the irradiation was larger for the welded joint than the base metal. Decrease of ductility at cryogenic temperature by the irradiation was larger for the base metal than the welded joint. Both the base metal and welded joint became sensitive to the existence of a notch with the increase of a neutron fluence. (4) The neutron irradiation up to 1.7×1023n/m2 exhibited little effect on the strength of the base metal and the welded joint of A5083. Ductilities of the base metal and welded joint decreased slightly with the neutron irradiation. (5) Strength of the base metal of A6061 was little affected by the neturon irradiation, but the welded joint showed the increase of strength which was considered to be due to the effect of aging during the neutron irradiation. Sensitivity to the notch of the base metal and the welded joint increased, and notch toughness of the base metal and welded joint decreased with increase of the neutron fluence.
Hot isostatic pressing (HIP) of powders is the manufacturing process which forms high quality and fully dense components from such materials as superalloys, tool steels and a wide range of ceramics. It is well known that the powder compacts reduce their volume due to density change, and the products usually differ in size from the final desired shapes. With the increasing demand for "near net shape" forming, simple and systematic way is greatly required to select the optimum process variables without trial and error procedures. In this paper, analytical method is presented to predict the sintering deformation behavior during HIP process. Three parts of governing equations are made up: heat conduction equation including matter flow, densification rate equation which describes density change, and shape change equation based on the conservation of mass. Effects of particle radius, HIP temperature, pressure and HIP cycle are discussed on the results of computer simulation of alumina powders.
Steel structures in service condition, such as bridges, offshore-structures and steel towers, are subject to pulsating loads caused by vehicles, waves, current, wind, etc. "Welding under pulsating loads" cannot be avoided in the cases of repair, reinforcement and reconstruction works. In this study, weld cracking test under pulsating loads was carried out and solidification crack was considered from mechanical standpoint. The main results are as follows; (1) In weld cracking test under pulsating loads, solidification cracks occured in no solidification crack zone evaluated by Trans-Varestraint cracking test. (2) The accumulation of total strain, εt, at weld metal in solidification crack temperature zone was proposed as a mechanical measure for solidification crack. Solidification cracks under pulsating loads occur when εt exceeds the critical strain, εcr, for crack initiation dependent on material characteristics. (3) As an engineering and mechanical measure, the relative root gap opening displacement. Δδ, which is easily measured before welding was adopted. The relation between εt and Δδ was considered. Moreover, the practical evaluating method for prevention of solidification crack under pulsating loads using Δδ was proposed. (4) The practical use and useful evaluating equation for prevention of solidification crack under pulsating loads of constant value was derived. Moreover, validity of the equation was concretly shown.
An algorithm for optimal heat input control in arc welding has been discussed in this paper. An optimization problem of the temperature field during welding has been proposed and tackled in order to estimate an optimal sequence of heat inputs. In the expression of the problem, the analytical solution of heat flow equation is used for the estimation of temperature field, and the objective function is defined as the difference between calculated and required temperatures. The following two typical optimization problems have been investigated. The objective in the first problem is to make the temperatures at some given times and points coincide with the required temperatures, and the objective in the second problem is to make the maximum temperatures at given points coincide with the required ones. As the result of this work, it is made clear that the convex programming is a powerful means of solving the first problem and the steepest descent method is useful for the second problem.
The penetration in GTA welding is affected by the convective fluid flow in molten pool and the fluid flow is strongly influenced by the minor elements such as sulfur, oxygen and chlorine in base metal. The purpose of this work is to make clear the mechanism of the minor element effect on the fluid flow in GTA welding. In the first, the influence of the element on anode configuration on molten pool surface has been discussed experimentally under the condition of He-shielding, where the anode mode can be observed clearly. As the result of the experiment, it is made clear that the anode size is very sensitive to the elements and these elements such as sulfur, oxygen and chlorine depress the evaporation of metal vapor from the molten pool surface and make the anode zone constricted. In the second part of this paper, a defocused electron beam has been used as a heat source to discuss the influence of the minor element on the surface tensional convection, i.e. the influence of sulfur content in base metal on the penetration by the defocused electron beam has been discussed. It is clarified that the penetration shape by defocused electron beam is insensitive to the sulfur content in base metal. This result of electron beam melting, where the electromagnetic force is negligible as the driving force of covection, suggests that the minor element effect is peculiar to arc weld pool. From these experimental results, the minor element effect may be explained as follows, the element influences the anode size on molten pool surface and it causes the change of fluid flow mode in molten pool, because the convective flow by electro-magnetic force is directly dependent on the anode size.
The purpose of this investigation is to make clear the fundamental phenomena in cooling and solidification process and to establish the methods of estimating hot crack sensitivity and preventing hot crack on welds of Al alloy. In this experiment, temperature measurement was perforemed with CA thermocouple in cooline and solidification process on TIG arc spot welds of commercial Al alloy 2024 and 5083. Maximum temperature in molten pool (Tmax) and several cooling rates at some positions of molten pool (Cmax, Cfp, Cm) were analyzed. Distribution of Tmax in molten pool was helmet-shaped distribution, and the Tmax had a maximum value at the center of molten pool and it was in the range of 980°C-1050°C. And the difference of Tmax at any position of molten pool amonge three materials was under 100°C. It is not thought to be so large. In any cooling rate, the difference fo cooling rate in Al alloys was smale but there was some difference between Al alloy and pure Al apparently, and the coiling rate Al was larger than one of Al alloy. It is thought to be due to the difference of heat conductivity. Cooling rate in the case of small heat input was larger than in the case of large heat input, in any materials.
The effect of ambient pressure on the occurrence of porosity in weld metal of mild steel by gravity welding process was investigated. Welding was executed under the pressure range from 0.1 to 5.1 MPa (abs.). Ilmenite type (D4301), high titanium oxide type (D4313) and low hydrogen type (D4316) electrodes of 4 mm in diameter and SM41A steel base plates of 6 and 9 mm in thickness were used. Main results obtained are summarized as follows: 1) Pores occur over the pressure of 0.15 MPa by D4301 and D4313 electrodes. Pores tend to increase with an increasing pressure up to about 0.3 MPa and to decrease over 0.4 MPa. Pores are not observed over 0.7 MPa. 2) The contour of pore is relatively short and cylindrical under 0.15 MPa, long, thick and cylindrical under 0.2 to 0.3 MPa, horn type under 0.4 to 0.5 MPa and thin and cylindrical under 0.6 MPa. 3) The solidification distance from weld bond line to pore, Xp, tends to decrease with an increasing pressure up to 0.3 MPa and to increase over 0.3 MPa. 4) Diffusible hydrogen content in weld metal by D4316 electrode increases with an increasing pressure up to 1 MPa, then it has a tendency to decrease a little over 1 MPa. 5) Content of hydrogen in molten metal by D4313 electrode, C0, is seemed to increase with pressure up to 0.3 MPa and then it tends to decrease. The value of C0* is thought to be larger than the critical concentration of hydrogen Ccr* under the pressure range from 0.13 MPa to 0.65 MPa, therefore pores occur in weld metal in this pressure range.
This study intends to make clear experimentally physical reasons why in the case of the steel pipe with thicker wall thickness the arc rotates at low speed in the initial stage of heating and does at high speed in the final stage, why the arc rotates on the inner side of the pipe edge surface in the initial stage, and why the rotating position of the arc moves from the inner side to the outer side of the pipe edge surface as heating time passes. The results obtained were as follows: 1) The low speed rotation of the arc in the initial stage of heating is due to the lower driving force resulted from the lower flux density at the inner side of the pipe edge surface, and the high speed rotation of the arc in the final stage is due to the higher driving force resulted from the higher flux density at outer side. 2) The rotation of the arc on the inner side of the pipe edge surface in the initial stage is caused by the distribution of the magnetic field due to the heating current, according to the geometrical shape, the arrangement and the magnetic property of the pipe and other components for welding. 3) The reason for the moving of the rotating position of the arc from the inner side of the pipe edge surface to its outer side with the increase of heating time is the variation of the magnetic field due to the heating current, which is caused by the magnetic transformation due to temperature rising near the pipe edge.
It has been reported that the weldability of the spot weld joint with initial gap is strongly influenced by the contact between electrode and plate. The state of contact during the welding largely depends on the deformation in the squeezing process. On the other hand, the characteristics of the deformation change with the geometry of the joint and the material property. Thus, the authors analyzed the deformation under squeezing process by the Finite Element Method to clarify the effects of geometry and material properties. Based on the numerical analyses, the squeezing process is shown to be divided into three stages with respect to plastic deformation and large deformation. Further, to predict the electrode force required to close the initial gap, two methods, using parametric curves and approximatin curves respectively, are proposed.
A method is shown of knowledge acquisition of arc-welding by the use of fuzzy expression of experimental data, and its application is discussed to a decision support system of tuning of weld conditions (i.e. welding speed and arc-voltage) for gas metal arc-welding. Although an experimental data itself is quantitative and non-fuzzy information, it is very common and useful for man to extend the applicability of the data by qualitative inference. In such a process, knoweldge is often explained as fuzzy information. From the point of view of knowledge engineering, it is important to accomplish such a process on computer level. Fuzzy rules are constructed of the form of "if...then..." for tuning weld conditions from an experimental data which explains relationships between bead shape and weld conditions of CO2 arc-welding as a map. The map of the experimental data is divided into a few rectangular fuzzy regions where the information of the data is represented as a set of fuzzy rules to adjust weld conditions. The rules consist of a few input parameters in "if" part and an output one in "then" part. The input parameters of the rule are some of welding current, welding speed, arc voltage, bead shape, bead width, etc. The output parameters of the rule is adjustment value of arc voltage or weld speed. Fuzzy labels of the rule parameters are defined by simple triangular or trapezoidal membership functions. The fuzzy reasoning system is implemented on a personal computer and simulation results are shown.
Pure iron plates were welded using Fe-Ti alloy electrode wires in a controlled arc atmosphere. The effects of titanium on the oxygen contents and non-metallic inclusions in the weld metals were investigated under various welding conditions in Ar-O2 and Ar-CO2 welding atmospheres. The oxygen contents of the Fe-Ti weld metals increase with an increasing the partial pressure of oxidizing gases and decrease with an increasing titaninum contents in the weld metals. The oxygen contents of the weld metals welded in Ar-CO2 are lower than those in Ar-O2. The non-metallic inclusions are mainly titanium-oxide. The compositions of the non-metallic inclusion in the Fe-Ti weld metals take various form of Ti2O3, TiO2, FeO-TiO2, 2FeO-TiO2 and FeO depending to the increasing oxygen content and decreasing titanium content of the weld metals. Behavior of the oxygen absorption by the steel weld metal is discussed using thermodynamic data.
Impact characteristics of diffusion bonded joints of ferritic shperoidal graphite cast iron and the cast iron to mild steel have been investigated using an instrumented Charpy impact test machine. The tests were performed at 0°C after ferritizing the joints. Main results obtained are as follows; (1) Absorbed energy of the cast iron joints bonded without an insert metal had about 5 J, which was much lower than that of the base metal. (2) Absorbed energy of the cast iron joints bonded with Ni foil as an insert metal became higher than that of the joint without Ni foil. The absorbed energy increased with the increas of the thickness of Ni feil and the absorbed energy was reached the base metal level when 50-μm thick Ni foil was used an insert metal. (3) Bond toughness of the cast iron to the mild steel joint bonded without the insert metal increased with the increase of the bonding temperature. When the bonding temperature was upper than 900°C, the absorbed energy was higher than that specified by Japanese Industrial Standard, which is 12.7 J. (4) Bond toughness of the cast iron to the mild steel joints bonded with Ni foil of 10 or 20μm in thickness at 820°C was almost the same as that of the cast iron base metal.
Relationship between the microstructure and the fracture behavior of welds which were tested by Charpy impact on SUS329J1 (Fe-25Cr-5Ni-0.1N) stainless steel has been studied. Volume fraction of γ phase decreases at HAZ which has been heated over 1400K. At the region over 1600K, the morphology of γ also change to Widmanstatten and the Kurdjumov-Sachs relation exists between γ and α phase, so the phase boundary has good coherency. There is certain relationship between crack propagation and microstructure. When the Charpy test performed at room temperature, tearing or voids occur in α region, because the ductility and strength of γ phase are higher than ones of α. γ phase is deformed at the circumference of dimple and γ maintains the ductility of duplex steel. Consequently, the fracture toughness increases with increasing the γ volume fraction. At low temperature, cleavage fracture occurs in a phase, same time γ phase plays the part of a little obstacles to crack propagation. In Widmanstätten like γ, Charpy impact value slightly increases with increasing the volume fraction of γ phase. In band like γ, a separation of α-γ phase boundary occurs and the crack propagates zigzag manner, so the impact value increases more substantially than widmanstätten like γ in the case of crack propagation normal to the γ phase.
Deformability of welded frame-structures in buildings is greatly affected by mechanical properties, especially work-hardening behaviors of steels on deformability of welded frame-structures, bending tests of specimens having a column-beam connection (H-shape beam) were carried out. For these experiments SM41B steel, SM50B steel and two kinds of HT60 steels with the different yield to tensile ratio were used. Main results obtained are summerized as follows. (1) Local buckling occurs and develops first in flange and then in web of the H-shape beams under the bending load. The maximum plateau of load-deflection curve on the H-shape beam is attained after the local buckling in web. The maximum load depends on the geometry of the H-shape beam, and decreases as the width to thickness ratio increases. (2) The maximum load value in H-shape beam is greatly affected by the tensile strength of steels used. Deflection at the load point and the absorbed energy of beam up to the maximum load, which are typical measures of the deformability of frame structures, depend on the yild to tensile ratio and uniform elongation (εT) of steels. Beams made of steels with lower yield to tensile ratio have larger deformability. (3) In order to improve the deformability of beam using steels with small εT, it is effective to enlarge their εT. (4) H-shape beam with scallop has a possibility of fracturing from the corner of the scallop.
A procedure to investigate the effect of work-hardening properties of steel on the deformability of welded frame-structures having the H-shape section is described. The procedure consists of the elasticplastic deformation analysis and the local buckling analysis. The analytical results have proved to agree with the experimental results. The deformation analyses of the H-shape beam were carried out for the various combinations of the yield to tensile ratio and the uniform elongation of steel. It has been shown from the analytical results that it improves the deformability of H-shape beams, such as the amount of deformation or the absorbed energy up to the maximum load, to lower the yield to tensile ratio or to enlarge the uniform elongation of steel. In case of steels having larger uniform elongation (εT>10%), it is more effective to lower the yield to tensile ratio than to enlarge the εT. Whereas in case of steels having smaller uniform elongation (εT<10%), increasing the εT is more beneficial.
Thermal cycling tests of ceramic-coated structural steel specimens with various thicknesses of bond coating and adhesive strength tests of thermal-cycled ones were carried out to investigate the effect of bond-coating thickness on thermal cycling life. Effects of thickness of ceramic coating and stablizing additives for zirconia ceramic coating were also investigated. The increase in thickness of bond coating prevented oxidation of substrate near the interface and improved failuer lives in thermal cycling tests. The residual adhesive strength of thermal cycled specimen had a good correlation with the oxidation of substrate: The residual adhesive strength was reduced with increasing in width of the oxidized region. No significant effects of stablizing additive and ceramic-coating thickness on failure characteristics was observed the range of the present study.
Methods to measure the surface temperature and the velocity of thermally sprayed particles were developed and applied to plasma-sprayed Mo, Ni-Cr alloy, and alumina particles in the air. In the temperature measurement, radiation from particles within a cylindrical measurement volume is measured and its spectrum is analyzed by a monochromator. Then the spectrum is compared with the spectra of blackbody radiation to determine the surface temperature of the particles through the least squares method. Spatial filtering technique using a mask with four thin parallel slits was adopted in the velocity measurement. When a single particle travels in front of the plates, radiation passing through the spacings between the plates is detected by a photo-multiplier, which gives a signal with four peaks. Then the velocity v of the particle is given by υ=d/t, where d is the distance between the neighboring slits and t the period between the peaks. It was also found that the mean velocity of a high-density particle stream can be determined by analyzing the power spectrum of the signal by a method such as FFT. As the results of those measurements, the change in the temperature and the velocity of sprayed particles with the distance from the exit of a plasma-torch was obtained. Where as the metal powders exhibited similar history of cooling and deceleration with the distance, alumina particles were found to be accelerated to a much higher velocity close to 300 m/s but decelerated at a much faster rate. The temperature of alumina particles could be measured for only a limited region due to the weak radiation. Also the effects of particle size on the distribution of both the temperature and the velocity of sprayed Mo particles were examined.