Stress singularity in a rectangular bond specimen of a solid rocket motor: Effects and elimination

The propellant/liner interface is the weakest and most concerning part of the grain structure in a solid rocket motor. Rectangular bond specimen tests have gradually become one of the standard methods to measure the bonding abilities of propellant/liner/insulation joints. We performed a three-dimensional numerical study to give full knowledge of this new test, paying close attention to the stress singularity at the crack tip. The asymptotic stress field was presented to show the singularity at the crack tip on the steel/insulation interface. Subsequently the stress singularity was investigated numerically. Numerical results show that the stress singularity has a considerable effect on the stress distribution of the nearby propellant. Also we proposed some methods to eliminate these effects, such as inserting a cohesive zone model into the steel/insulation interface or increasing the thickness of insulation layer. Moreover, Mises stress and maximum principle stress have completely opposite distributions on the propellant/liner interface; thus the accurate failure criterion can be confirmed by the damage initialization observed in experiments.