SBIR-STTR Award

This proposal is in response to announcement DTRT57-13-R-SBIR2 in the area 13.2-FH1, Development of Innovative Welding for High Performance Bridge Steel. It is proposed to use Homopolar Generator (HPG) Welding to join the high performance bridge steel in the 3? by 30? cross sections mentioned in the announcement in under 1 second. All of the energy required to perform the weld is stored in the spinning rotor of the pulsed power supply. Through electromechanical conversion the rotational energy is converted to a high discharge current that passes directly through the weld interface. Electrodes are clamped to the workpiece either side of the weldment and high current is passed through the plates to bring them to forge temperature. At this time, an upset pressure is applied and the weld is created by resistance-forge welding process. This process has been used to weld High Performance Steel pipe, 12? in diameter, with a 9/16? wall thickness. The pipes show good strength and toughness in the in both the weld metal and the heat ?affected zone. These welds were accomplished with 3, 10 Megajoule, generators operating in parallel and the larger cross sections can be welded by adding generator units in parallel.

With this research, we would like to provide new materials joining methods to the DOT. This will be achieved with a pulse energy store that has already demonstrated game changing capability in welding a wide variety of metals and alloys. The process we are proposing is known as Homopolar Welding. The weld is created by a solid state fusion welding process whereby high current is passed through the weld interface until the metal reaches forging temperature and then an upset force is applied to the weld interface to complete the process. Some of the steels welded with this process are API 5L Grade X52, X60, and X65. Although they are pipeline steel, they meet the requirements of high performance steel and give confidence that bridge steel will also be welded with good results with this process. Typical test results analyzed from welds of the Nippon X65 series material include tensile yield strengths between 71 and 81 ksi with ductile fracture location predominantly in the parent material. Hardness test results in the heat affected zone demonstrate minimum values ranging from 163 to 175 HV10. In Charpy V notch testing, a mean value of 91 ft-lb was recorded.