Shear creep and failure model of bonded interface in solid rocket motors

During vertical storage, the bonded interface of solid rocket motors (SRMs) is susceptible to gravity-induced shear creep, which can lead to debonding, cracking, and other damage that compromise the structural integrity and service life of SRMs. Focusing on the creep damage problem in vertically stored SRMs, this study utilizes simulation methods to analyze the stress-strain response of the bonded interface, and the results indicate that, under the combined effects of curing cooling and gravity loading, the interfacial shear stress in the head debonding area of vertical storage motors can be up to 0.3 MPa, and there is a risk of inducing creep damage. Based on this result, shear creep tests were conducted on the bonded interface under applied stresses ranging from 0.1 MPa to 0.85 MPa. The experimental results revealed interfacial shear failure occurs when the shear stress exceeds a critical threshold of 0.5 MPa. A shear creep model for the bonded interface was developed that can simultaneously characterize viscoelastic creep and progressive damage behavior by integrating a crack propagation element into the improved Burgers model. Model validation demonstrates that the fitting error is kept below 6.3 % during the non-destructive stage and does not exceed 11.9 % during the destructive stage, effectively achieving accurate characterization of the entire process from interfacial creep damage to failure.