Koichi Kaizu

This paper describes the joint strength of low carbon steel joints and the selection guide of friction welding conditions for low force requirements, which was made by friction stud welding. When joints were made at a friction pressure of 30MPa with a forge pressure of 30MPa, all joints did not have the fracture on the base metal. All joints, which were made with a friction time of 1.5s (just after the initial peak) and a forge pressure of 60MPa, had the fracture on the base metal. However, all joints with a long friction time such as 5.0s did not have the fracture on the base metal. Furthermore, when joints were made with a friction pressure of 10MPa, the joint efficiency of 100% was not successfully achieved regardless of increasing forge pressure. The cause of the joint with the fracture between the initial weld interface and the base metal was that the peripheral portion of that interface of the stud side (small diameter side) was not completely joined with low friction pressure such as 10 MPa. On the other hand, the fracture on the base metal and the joint efficiency of 100% were successfully achieved when joints were made at a friction pressure of 60MPa, a friction time of 0.6s (just after the initial peak), and a forge pressure of 60MPa. All those joints with flash at the initial weld interface had the fracture on the base metal, and it also had the bend ductility of over 15 degrees with no cracking at the initial weld interface by impact shock bending test. However, all joints with a long friction time such as 5.0s in this friction pressure did not also have the fracture on the base metal. Hence, to obtain the joint possessing the fracture on the base metal with no cracking at the initial weld interface, the joint should be made with a friction pressure of 60MPa and a friction time of 0.6s, i.e. an optimum friction pressure and friction time such as the friction torque reached to just after the initial peak. By setting to this condition, the forge pressure will be able to set up the identical friction pressure.

<p>Joining of plastics and light metals contributes to the reduction of a product weight. In this study, the punching rivet method was applied to joining of an acrylic resin sheet and an aluminum alloy sheet. The punching rivet method can join the sheets without drilling. The riveting process of this method is constituted of the punching process of the sheets using the rivet shank and the fastening process of the sheets using the rivet and the rivet holder. The sheets are fastened by using the plastic deformation of the rivet shank. From the observation of the joints made by the punching rivet method, it was found that the acrylic resin sheet of the joint had no crack and out-of-plane deformation of the joint was small. From the results of the joint strength tests, it was considered that the joint made by the punching rivet method had high strength due to the effect of the pressures on seating faces of the rivet and the rivet holder. As a result, the punching rivet method was effective to join the acrylic resin sheet and the aluminum alloy sheet.</p>

<p>In order to ensure the safety of passengers in the event of an accident, side member and crash box are mounted on automobiles. Cylindrical tubes, rectangular pipes and hat-shaped members have been examined as structural members that subjected to an axial compressive load. However, these structures have problems that the initial peak load is very high and the load rapidly decreases due to buckling during crushing. To solve the problems, we proposed a cellular solid with mimetic woody structure as a new structural member. Some woods have no initial sharp peak load and have a plateau region which the load is constant in the relationship between the load and the displacement, when the impulsive load are applied to them. We considered that those features were suitable for structural members like a side member or a crash box. The basic cell was a square block with a side length of 10 millimeters and it had a hole in the center. The cellular solid was constituted by combining some basic cells. Therefore, a homogeneous cellular solid was fabricated by making small holes in the aluminum cube. From results obtained from the impact crushing test and simulation by the FEM software LS-DYNA<sup>®</sup>, it was demonstrated that the proposed cellular solid had crushing characteristics similar to the wood, and the energy absorption characteristics were influenced by the shape and arrangement of the cells. As a result, it was shown that the results of experiment and analysis substantially corresponded. Since the load during crushing depended on the shape and arrangement of the cells, the possibility of controlling the energy absorption characteristics was shown.</p>

This paper describes the effect of friction welding condition on joint properties of austenitic stainless steel (SUS304) joints, which was made by friction stud welding. When the joint was made at a friction pressure of 30MPa with a forge pressure of 30MPa, the joint efficiency of 100% was not successfully achieved. The joint with a forge pressure of 270MPa was not obtained the fracture in the base metal, although the joint efficiency increased. The cause of the joint with the fracture between the weld interface and the base metal was that the peripheral portion of the weld interface of the stud side was not completely joined at this friction pressure. On the other hand, the fracture on the base metal and the joint efficiency of 100% were successfully achieved when the joint was made at a friction pressure of 90MPa and a friction time of 0.3s (just after the initial peak) with a forge pressure of 240MPa or higher. This joint had the bend ductility of over 90 degrees with no crack at the weld interface by three-point bending test, and it also had that of over 45 degrees with no crack at the weld interface by impact shock bending test. In conclusion, to obtain the joint efficiency of 100% and the fracture in the base metal with no cracking at the weld interface, the joint must be made with high friction pressure, opportune friction time such as the friction torque reached to just after the initial peak, and with adding high forge pressure.

In the punching rivet method, it is possible to fasten the sheets without drilling. The joint has high strength and out-of-plane deformation of the joint is also small because of the rivet and the rivet holder that are peculiar to this method, hi this study, the punching rivet method was applied to joining of an acrylic resin sheet and an aluminum alloy sheet. The fastening condition and the strength of the joints made by the method were examined. From obtained results, it was possible to fasten an acrylic resin sheet and an aluminum alloy sheet by an aluminum alloy rivet. The acrylic resin sheet of the joint after joining had no crack and joint strength was high. It was certified that the punching rivet method became new joining method for a resin sheet and a metal sheet.

Critical for the use of aluminum alloys for engine pistons are strength and durability behind customers demand high power and low fuel consumption to protect environment. In general, there are many case of generating cracks in a top part of the piston by thermal load of combustion during car driving. As a countermeasure, AC8A casting aluminum on a top part of the piston partially substitutes with A6061 wrought aluminum which is more strengthen than the ACS A. This paper deals with the joint characteristics of friction welded joint between the A6061 solid cylinder and the AC8A casting pipe. If the joint was made by a conventional friction welding machine, it was clarified that the friction welding of A6061 solid cylinder and ACS A casting pipe was difficult because the travelling phenomenon of the weld interface was cause by the combination of the shapes of the friction welding specimens. To prevent braking deformation until rotation stop, the joint was made by a continuous drive friction welding machine that has an electromagnetic clutch. In addition, the joining strength improved through the joining cross section of both specimens are the same shape of pipe by digging out the surface of the A6061 cylinder. As a result, the joining could be successfully achieved and that had the joint efficiency of 80 - 97% when the joint was made with a friction pressure of 25MPa, a friction time of 0.7s, and a forge pressure of 75MPa and post-weld heat treatment with the T6 of AC8A.

This paper described the joining phenomena and joint strength of friction welded joint between Ti-6Al-4V and low carbon steel (S15CK) . When the joint was made with a friction pressure of 30MPa, the adjacent region of the weld interface reached to about 1,075 ℃ at a friction time of 8.0s or longer. This joint had the intermetallic compound layer (IMC interlayer) at the weld interface, and the joint efficiency of 100% was not achieved. It was demonstrated that the joint inhibited the generating of the IMC interlayer on the weld interface by increasing friction pressure, because the temperature at the weld interface was able to estimate a propensity to decrease with increasing friction pressure. Then, the joint, which was made with a friction pressure of 120MPa, a friction time of 7.0s or longer, and a forge pressure of 330MPa, had the 100% joint efficiency and it fractured from the S 15CK base metal with no cracking at the weld interface. This joint did not have the IMC interlayer on the weld interface. In conclusion, the joint should be made with the opportune high friction pressure and opportune long friction time for it without IMC interlayer with the high forge pressure for completely joining of the weld interface.

This paper describes the effect of the inclination of the weld faying surface on joint strength of friction welded joint and its allowable limit for austenitic stainless steel (SUS304) solid bar similar diameter combination. In this case, the specimen was prepared with the inclination of the weld faying surface pursuant to the JIS Z 3607, and the joint was made with that diameter of 12mm, a friction speed of 27.5s-1, and a friction pressure of 30MPa. The initial peak torque decreased with increasing inclination of the weld faying surface, and then the elapsed time for the initial peak increased with increasing that inclination. However, the steady torque was kept constant in spite of the inclination of the weld faying surface increasing. The joints without the inclination of the weld faying surface, which were made with friction times of 1.5 and 2.0s with a forge pressure of 270MPa, had achieved 100% joint efficiency with the base metal fracture. Those joints had 90 degrees bend ductility with no crack at the weld interface. The joints with the inclination of the weld faying surface of 0.3mm (gap length of 0.6mm), which were allowable distance, was also obtained the same result with this condition. Furthermore, those joints with a friction time of 2.5s were obtained the same result. On the other hand, the joints with the inclination of the weld faying surface of 0.6mm (gap length of 1.2mm), which was twice inclination of the allowable distance, were also obtained the same result in a friction time of 2.5s. However, the joints without the inclination of the weld faying surface at this friction time were not obtained the base metal fracture, although those achieved 100% joint efficiency. In conclusion, to obtain 100% joint efficiency and the base metal fracture with no cracking at the weld interface, the joint must be made with the inclination of the weld faying surface, which was allowable distance pursuant to the JIS Z 3607.

Crash safety of a vehicle is based on impact energy absorbed by crashing the structure in a situation that a cabin is protected. Side impact is extremely dangerous for passengers of vehicles. Energy absorption capabilities of the vehicle in side impact are low because there is little room for large deformation of the safety element to absorb impact energy. On the other hand, weight reduction of the vehicle is also important for the fuel efficiency. The purpose of this study is to develop a light and effective energy absorbing member for side impact. In this paper, an energy absorbing tubular member made by a combination of a thin-walled circular tube and a thin-walled square tube was proposed. The effect of the cross-sectional shape of the tubular member on energy absorption capacities under bending impact was investigated by the experiment and the analysis of the finite element code LS-DYNA. From the obtained results, bending strength decreased significantly when the cross section of the member which was subjected to impact bending load was crushed in flat shape. Therefore, energy absorption capacities were able to be improved by preventing flattening deformation of the cross section. Energy absorption capacities of the tubular member were able to be improved by changing its cross-sectional shape without increasing of the weight.

Estimation method of fatigue life for textile composites was proposed. Because textile composites have a many design parameters such as fiber type, resin type, architecture of reinforced fibers, volume fraction of fiber and fiber orientation, etc., it is difficult to obtain enough fatigue test data for all combinations by experimental procedures. In the proposed method, textile composites were treated as heterogeneous bodies with anisotropy for fiber bundles and isotropy for matrix, respectively. The stress distribution under cyclic loading was evaluated by FEM. On the other hand, each element of FE model was considered as unidirectional materials and their properties under cyclic loading are estimated from fatigue test. The proposed method was applied to plain woven CFRP. It was confirmed that the proposed method is applicable to estimation of fatigue life of textile composites. © 2014 The Society of Materials Science, Japan.

This paper described the effect of friction welding condition on joining phenomena and tensile strength of ABS resin friction welded joint. When the joint was made with a friction speed of 4.2 s^-1 and a friction pressure of 0.3 MPa, the temperature at the weld interface at a friction time of about 45 s or longer exceeded 130 ℃. That is, the temperature at the weld interface of the ABS resin friction welding exceeded the glass transition temperature of its resin. When the joint was made with a friction time of 60.0 s, it obtained approximately 67% joint efficiency. However, the joint efficiency decreased with increasing friction speed, and it also decreased with decreasing friction speed. The joint efficiencies with other friction pressures showed a similar change although the friction speed differed. When the joint was made with a friction speed of 2.5 s^-1, a friction pressure of 0.3 MPa and a friction time of 180.0 s, it obtained over approximately 90% joint efficiency. However, the joint efficiency decreased with increasing friction time, and it also decreased with decreasing friction time. Furthermore, the joint efficiency increased with decreasing parallel part diameter of the joint tensile test specimen, and that achieved 95% joint efficiency. In conclusion, to obtain the higher joint efficiency, the joint should be made with opportune friction speed, friction pressure and friction time, and the friction welding should be completed when the whole weld interface became melting state.

The joining phenomena during the friction process and the joint tensile strength of ABS resin friction welded joint were investigated. When the joint was made with a friction pressure of 0.5MPa or lower, the temperatures at the weld interface during the friction process exceeded 130 ℃. This temperature was higher than that of the glass transition temperature of ABS resin. That is, the temperature at the weld interface of the ABS resin friction welding exceeded the glass transition temperature, of which was differed with the friction welding of various metals. When the joint was made with a friction speed of 4.2s^<-1> and a friction pressure of 0.3MPa or a friction speed of 3.3s^<-1> and a friction pressure of 0.5MPa, it was obtained about 67% joint efficiency. However, the joint efficiency decreased with increasing friction time, and that also decreased with decreasing friction time. The joint efficiencies with other friction pressures were showed with similar change although the friction speed differed. In conclusion, to obtain the higher joint efficiency, the joint should be made with opportune friction speed and friction pressure.