Crack propagation velocity and fracture toughness of hydroxyl-terminated polybutadiene propellants: Experiments and simulations

Abstract A critical part of failure analysis in solid rocket motors is understanding the fracture behavior of solid propellants. For single-edge notched tension (SENT) specimens of hydroxyl-terminated polybutadiene (HTPB) propellant, self-developed in-situ video imaging was employed to characterize the crack propagation and the crack-path morphology. Combining this in-situ video recording system with image digitization, then the crack propagation velocity can be obtained. Due to the viscoelastic properties of the propellant, the fracture properties were studied under different tensile rates (5-500 mm/min). A fracture mechanics method based on the J-integral was used to evaluate the fracture behavior of propellants, and a fracture criterion considering the burning rate of the propellant was proposed. Experimental research revealed that the HTPB propellant had a pronounced blunt crack tip during the fracture process. The plastic region in front of the crack tip where voids form and coalesce could cause crack propagation. The distribution of voids in front of the crack tip mainly determined the direction of crack propagation. The fracture characteristics of the HTPB propellant had evident rate dependence, and the J-integral changed significantly under different tensile rates. A simulation study was carried out in this paper. The 1 / r singular elements were used to predict the J-integral of the SENT specimen during the tensile process. Two numerical simulation methods (XFEM: extended finite element method and CZM: cohesive zone model) were used to obtain crack propagation velocity and load–displacement curve. Furthermore, the simulation results were compared with experimental data.