Develop Mechanical Aging Criterion for Energetic Materials

The standard failure criterion for solid rocket propellant requires the evaluation of current loads (stress or strain) and a comparison of those loads to the material capability for the given loading conditions (time and temperature). However, propellantoften fails at lower load levels than predicted using this method. This is a consequence of the failure to consider cumulative damage effects resulting from sometimes-extreme loading histories.A comprehensive method of evaluating cumulative damage for propellant needs to be developed. This is especially true for tactical motors that undergo extreme loading histories through their lifetime.In this proposal we approach cumulative damage model development in three stages: First, a review of existing cumulative damage models paying particular attention to the TTCP KTA 4-29 findings; Second the evaluation of existing cumulative damage models fortheir strengths, weaknesses and predictive capabilities; Third, the extension of existing model capability to include temperature effects, biaxial and triaxial effects, and high-strain modulus/Poisson's Ratio effects as is reasonable within the Phase 1SBIR scope. Consideration will also be given to other model needs identified via the TTCP KTA 4-29 work.The Phase I research will include a literature review of existing theories of propellant aging and cumulative damage in conjunction with the TTCP KTA 4-29 project. Using the vast history of propellant failure testing available at Thiokol, the differentavailable theories will be evaluated. Where shortcomings exist with the theories, a new theory (or modifications to exiting theories) will be proposed which better matches test results.At the end of this study, a theory for failure of aging solid propellant will be formulated, derived from the best available published work, extensions to that work, and backed by existing test data.