Evaluation of a Multi-Axial, Temperature- and Time- Dependent Failure Mode

Abstract

To obtain a better understanding of the response of the structural adhesives used in the space shuttle's reusable solid rocket motor (RSRM) nozzle, an extensive effort has been conducted to characterize in detail the failure properties of these adhesives. This effort involved the development of a failure model that includes the effects of multi-axial loading, temperature, and time. An understanding of the effects of these parameters on adhesive failure is crucial to the prediction of safety of the RSRM nozzle. The use of this newly developed multi-axial, temperature, and time-dependent failure model for modeling failure for the adhesives TIGA 321, EA913NA, and EA946 is documented. The development of the mathematical failure model using constant load rate data for both normal and shear loading is presented. Verification of the accuracy of the failure model is shown through comparisons between predictions and measured creep and multi-axial failure data. The verification indicates that the failure model performs well for a wide range of conditions (loading, temperature, and time) for the three adhesives. The failure criterion is shown to be accurate through the glass transition for the EA946 adhesive. Though this failure model has been developed and evaluated with adhesives, the concepts should be applicable for other isotropic materials.