Masahiro Kusaka

To reduce weigh of the transportation machines, joining of the FRP and the light metal is considered as important technique. In this study, the punching rivet method was applied to make joints between a GFRP sheet and an aluminum alloy A6061 sheet and joint strength was examined. The punching rivet method is possible to join the sheets without drilling by using a rivet and a rivet holder. The punching-out process of the sheets using a rivet shank as a punch and the joining process of the sheets using the rivet and the rivet holder are continuously performed. From the experimental results of joining of the GFRP sheet and the A6061 sheet, the joints made by the punching rivet method had no large crack and out-of-plane deformation of the joints was suppressed. From the results of the joint strength tests, the joints made by the punching rivet method had almost the same joint strength as the bolted joints which were tightened by regulated torque. In addition, the fatigue life of the joints made by the punching rivet method was longer than that of bolted joints. It could be confirmed that the punching rivet method was effective to join the GFRP sheet and the A6061 sheet.

This paper describes the stud shape and joint strength of low carbon steel joints fabricated by friction stud welding with low load force requirement. To reduce the load force during the welding process, the stud side with the circular hole at the weld faying surface part was used. The outer diameter of a cylindrically shaped stud side had 12.0mm and that was welded to the circular solid bar with a diameter of 24.0mm as the work side. The joint was made with a friction speed of 27.5s-1, a friction pressure of 60MPa, and a forge pressure of 60MPa, which was determined as the low force condition for obtaining good joint in the previous study. When joints were made by a cylindrically shaped stud with a hole diameter of 6.0mm and its depth of 0.5mm, all joints at a friction time of 0.6s, i.e. the friction torque reached to the initial peak, had the same tensile strength as that of the base metal with the base metal fracture. All joints with flash from the initial weld interface had the fracture on the base metal, the bend ductility of over 15 degrees with no cracking at the initial weld interface through an impact shock bending test, and a high fatigue strength of the base metal. That is, the sound joint could be successfully achieved, and that could be obtained with the same friction stud welding condition of the circularly shaped solid stud. As a conclusion, the joining technique for the friction stud welding method with low load force requirement was proposed in accordance with using a cylindrically shaped stud that has the circular hole with the shallow depth at the weld faying surface part.

In this study, the condition for applying the fracture splitting method to the aluminum alloy die casting connecting rod was investigated. The inside diameter changes in the big end hole after the fracture splitting and the bolt tightening were clarified by FEM analytical results. Then, the effects of the notch shape and the splitting speed on the roundness of the big end hole were examined by the fracture splitting test. As a result, it was found that high roundness was obtained on the conditions of a deep notch length, a small notch radius, and a fast splitting speed for the connecting rod made from ADC12-T5. On the other hand, it became clear that high roundness was obtained on the conditions of a short notch length, a large notch radius, and a slow splitting speed for the connecting rod made from ADC14-T5.

The effect of the direction and the size of aluminum circular pipes filled with an aluminum square pipe on energy absorption characteristics by the finite element method and the impact crushing test was investigated. The model which perpendicularly arranged circular pipes had higher load than the model that horizontally arranged circular pipes, and the energy absorption amount increased. In adition, the aluminum square pipe was filled with the circular pipes that the outer diameter was increased. From numerical results, the energy absorption characteristics per unit mass of the model which perpendicularly arranged circular pipes with the large outer diameter was able to be improved. Circular pipes were able to suppress the drop amount of the load by generating wrinkles.

A punching rivet method can fasten sheets without pre-drilled hole, and out-of-plane deformation of joints is also small. This method is carried out by using a rivet and a rivet holder. The punching rivet method has been applied to fastening of an acrylic sheet and A5052 sheet. In this study, the rivet and the rivet holder were improved to enhance the joint strength. Tensile test was carried out for the improved joints. From experimental results, the joint strength was higher than the strength of the acrylic base material because of the seating pressure on seat surface between the rivet head and the rivet holder. Furthermore, when the joint was made under the condition that the upper sheet is acrylic and the under sheet is A5052, the joint strength of joints with improved rivet was higher than the joint strength of previous one.

In this study, the method of estimating low cycle fatigue life of solders from the prompt fatigue test using a step-up method was investigated. Two kinds of solders of Sn-3Ag-0.5Cu (SAC) and Sn-58Bi (SB) were used. The fatigue testing using the step-up method was carried out with test temperature of 25°C, 60°C, and 125°C. The fatigue life equation of Manson-Coffin law was estimated from the reduction of area obtained from tensile test and the cyclic strain hardening coefficient obtained from fatigue test. The low cycle fatigue life obtained from a traditional fatigue testing was compared with the estimating fatigue life. As a result, this estimating result was corresponding to the low cycle fatigue life at each test temperature by the SAC solder. On the other hand, the low cycle fatigue life was estimated long with the SB solder at 25°C.

This paper described the results of the impact energy absorption characteristics of the Al cellular structure using finite element analysis (FEA) and an experiment. Cellular structure has various features such as low density and low thermal conductivity, and it can be changed from low rigidity to high rigidity. We focused on the energy absorption characteristics of woods and proposed the Al cellular structure that was composed of cells with a hole in one direction. We investigated the effect of cell arrangement on impact energy absorption. The cellular structure with a hole arranged in vertical direction enhances the load in the initial stage of collision, and when it was arranged near both side surfaces of the structure, the strength and energy absorption were improved. The model in which the hole size in the cell gradually decreased lowered the initial load and increased the amount of energy absorption per unit mass.

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.