Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

Abstract

A submerged cavitation water jet (SCWJ) is an effective method to recycle solid propellant from obsolete solid engines by the breaking method. Solid propellant’s breaking modes and mechanical process under SCWJ impact are unclear. This study aims to understand those impact breaking mechanisms. The hydroxyl-terminated polybutadiene (HTPB) propellant was chosen as the research material, and a self-designed test system was used to conduct impact tests at four different working pressures. The high-speed camera characterized crack propagation, and the DIC method calculated strain change during the impact process. Besides, micro and macro fracture morphologies were characterized by scanning electron microscope (SEM) and computed tomography (CT) scanning. The results reveal that the compressive strain concentration region locates right below the nozzle, and the shear strain region distributes symmetrically with the jet axis, which increases to 4% at first 16th ms, the compressive strain rises to 2% and 6% in the axial and transverse direction, respectively. The two tensile cracks formed first at the compression strain concentrate region, and there generate many shear cracks around the tensile cracks, and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks, forming the tensile-shear cracks and the impact parts eventually fail. The HTPB propellant forms a breaking hole shaped conical after impact 10 s. The mass loss increases by 17 times at maximum, with the working pressure increasing by three times. Meanwhile, the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole. The breaking efficiency is closely affected by working pressures. The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.