This chapter describes miniature stress sensor technology for monitoring the thermal stresses and
ignition pressurization loads in solid rocket motors. The study was part of a larger international (TTCP)
collaborative effort carried out from 1988 to 2002 to validate the instrumentation and analytical stress analysis
and service life prediction methodologies for solid composite rocket motors, and thus establish improved, more
reliable, cheaper and non-destructive capabilities for service life prediction and extension. Different motor
configurations were used by the different countries in this collaborative program. The Australian effort, described
in this chapter, used an end burning generic research motor (Pictor). The embedded transducers, in this end
burning motor and in the different motor designs used by the other TTCP countries, were found to be stable in the
temperature range used in the environmental testing program and gave consistent data during propellant cure,
environmental testing and static firing of the motors. The rocket motor instrumentation and data reduction
techniques were described. The data from the instrumented motors under various thermal storage loading
conditions (multiple thermal cycling, shocking, accelerated ageing at elevated temperature) were used to validate
the stresses and critical failure modes predicted by structural finite element modelling and a modified fracture
mechanics approach for nonlinear viscoelastic materials. These studies verified the ability of the miniature bond
stress sensors to detect cracking / damage in the propellant charge. The advancement in bond stress sensor
technology was further used to investigate failure analysis of rocket motors under ignition pressurization
conditions. Results from these studies demonstrated that the sensors are safe for static firing and could accurately
measure pressure in different regions of the burning motor. The stress sensor data from this international
collaborative program showed that the stress sensor technology could be used for real-time structural health
monitoring of solid rocket motors to detect cracks and debonds in the propellant and to continuously monitor the
extent of damage. The results from the instrumented Pictor motor verified and validated the thermal distributions,
stress / strain states and regions of high propensity for crack propagation predicted by finite element modelling
and fracture mechanics. The use of the instrumented motor data in probabilistic service life prediction
methodologies and other NDE methods are also discussed.
