Time-dependent yield behavior and delayed failure characteristics of HTPB propellant under long-term loading

This work investigated yield and failure characteristics of HTPB propellant under long-term loading. Constant speed tensile test with four types of strain rates, 1000s short-term relaxation test and 30d long-term relaxation test were designed and carried out, and failure modes were discussed. Based on loading time-varying initial yield surface, the yield function and viscoelastic-viscoplastic constitutive model were developed, and model parameters were fitted and verified. The results show that the initial yield surface and failure criterion of propellant decrease with loading time. During long-term loading, it will show two special failure modes of wire drawing and delayed fracture. The yield function and constitutive model successfully captured the time-dependent yield behavior of propellant, which is in close agreement with test data, and realizes the criterion of wire drawing. The yield strength will decrease from 0.42 MPa to 0.09 MPa with increasing loading time, with a drop of 77.3 %. A new perspective is provided to discuss failure mechanism of particle reinforced polymer, which is of guiding significance for improving failure mode cognition of materials and predicting service life of structures.