Applicability of empirical formula for flexible joint structural stress

An 8cm pivot radius flexible joint with reinforcement hoop stress measuring system was designed, and the reinforcement hoop stress due to different vessel pressures and vector angles was tested. The results were compared with the empirical formula and finite element analysis. Moreover, the effect of pivot radius on the reinforcement hoop compressive stress was investigated by finite element analysis. New formulas to compute the reinforcement hoop compressive stress for the pivot radius within the 6-10cm were proposed. The effect of throat diameter on the reinforcement hoop compressive stresses of flexible joint was also studied, and the applicability of conversion empirical formula between cold-flow vessel pressure and hot fire motor pressure was discussed. Results showed that a good agreement for the reinforcement hoop compressive stress between test and finite element analysis was obtained. Empirical formulas for reinforcement hoop compressive stresses were not applicable. The flexible joint structural stresses in vessel and the fire test of soild motor rocket were different. The reinforcement hoop compressive stresses for the hot fire test of flexible nozzle can be converted by the joint test in vessel through empirical formula. The elastomer shear stresses were more serious for the joint test in vessel than the fire test of solid motor rocket with flexible nozzle.