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 2010, Barack Obama, the former president of the United States, announced sending humans to the Red Planet in the 2030s. Outposts and habitats will be set up in the future by welding technique. In this study, effectiveness of previous AC-GTA welding was investigated in a like Mars atmosphere consisting only CO2 gas with pressure range from 600 to 1000Pa. In order to observe the AC-GTA phenomena, the arc appearances were filmed by a high-speed video camera. Furthermore, the arc voltage and the welding current waveforms were recorded to evaluate the AC-GTA stability. It was found that the cathode spots distribution area spreads and the AC-GTA stability decreases in the less pressure. In conclusion, the AC-GTA welding in the Mars atmosphere can be applicable by considering the ambient pressure and the EP time ratio.