Abstract
A de ciency in current failure initiation criteria used in the structural design and service-life prediction of solid-rocket motors, where the critical failure mode is structural failure, is the uncertainties associated with the criteria used in predicting crack initiation and propagation. Also, the constitutive models that describe the propellants’ nonlinear behavior require an extensive experimental testing program to characterize the softening functions. A modi ed fracture mechanics method that accounts for bulk inelastic behavior in the calculation of a critical strain energy release rate and a relatively simple method for nonlinear viscoelastic analysis, where a three-dimensional interpolation scheme is used to solve the Prony series equations that represent Young’s and shear relaxation moduli as functions of time, temperature, and strain level, have been developed and implemented into a nite element code. Predictions for a thermal shock loading on an end-burning research and development motor were made using the fracture mechanics and nonlinear viscoelastic analysis capabilities developed in this study. Reasonable agreement between the measured stresses from instrumented rocket motors and the predicted von Mises stresses was obtained. The regions of high propensity for crack propagation corresponded to the critical regions of maximum tensile principal stress in the motor.
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