Effect of Fillet Geometry to Joint Strength of Four-Pipe-Brazed Specimen for Rocket Nozzle Skirt

The strength of the brazed joint of the four-pipe-brazed specimen (4PB), which imitates the rocket nozzle skirt’s wall, is analyzed numerically. The 4PB specimen comprises four pipes brazed side by side with JIS BPd-6 palladium brazing filler metal. The effect of the fillet geometry to the joint strength of the 4PB specimen is investigated. The numerical analysis is conducted for the 4PB of 10mm diameter with various root gaps from 0.05 to 3.0mm and various apparent fillet widths from 1.0 to 4.0mm. The nominal rupture strain is obtained by the comparison of von Mises’ equivalent stress of the fillet and the pipes with their maximum tensile stress. The results show that the fracture of the 4PD specimens always occurs at the fillet. The nominal rupture strain tends to have weak correlation with the root gap, but in positive proportion to the apparent fillet width.