Double ceramic sphere's sympathetic implosions triggered by local impacts

Due to sophistications in experimental studies, the implosions in chain reaction, also named as sympathetic implosions, demand numerical models to understand the phenomena caused by various impacts to the primary sphere. We developed a 3D air-solid-water model considering the influence of brittle sphere failures of two alumina spheres to simulate the outbreak of the sympathetic implosion in the seawater of 114 MPa. According to the triggering mode, two cases of simultaneous implosions and five cases of sympathetic implosions of a double-sphere were numerically studied. We found that the induced fracture of the secondary sphere happened before the outbreak of the positive pressure wave, i.e., the induced fracture is caused by the uneven pressure around the sphere lower than the hydrostatic pressure. To our knowledge, the present paper is the first report on the early fracture of the secondary solid sphere in sympathetic implosions. With various triggering modes of the primary sphere, the secondary fractures are all induced at the proximal side and extend to the other side. The formed ring-shaped implosion cores are caused by individual fracture mode. The shifting of the two implosion cores eventually affects the pressure pulses at a position. A higher or similar values of the secondary pulse are found closely related to the double sphere's fracture modes, i.e., related to the triggering modes of the local impacts. This work help to estimate the damage of the sympathetic implosion to the surroundings, and prevent further implosions by understanding spatial superposition of a series of pulses.