In a recent study published in Engineering, researchers from Harbin Engineering University have conducted an in-depth experimental investigation into the complex coupling dynamics of metal jets, waves, and bubbles generated during the underwater explosion of shaped charges. This research provides valuable insights into the behavior of shaped charges in underwater environments, which is crucial for understanding their potential applications and impacts.

The study was designed to analyze the characteristics of metal jets, ballistic waves, shock waves, and bubbles produced during underwater explosions of shaped charges. Unlike conventional spherical charges, shaped charges generate a high-strain-rate metal jet and a ballistic wave in addition to the strong shock wave and pulsating bubble. The researchers explored how different parameters, such as liner angle and charge weight, influence these phenomena.

The experiments were conducted in a large water tank, with shaped charges detonated at a depth of 1.7 meters. High-speed cameras and pressure sensors were used to capture the dynamics of the metal jet penetration, wave propagation, and bubble pulsation. The researchers also employed the Eulerian finite element method (EFEM) to numerically simulate the formation and initial penetration of the metal jet in water, providing a detailed understanding of the processes involved.

Key findings of the study include the observation that the metal jet's maximum head velocity is related to the liner angle through the formula 1/(α/180°)^0.55, where α is the liner angle. The maximum head velocity of the metal jet was found to be 2.68 times the speed of sound in water, with a penetration length reaching up to 16.1 times the height of the shaped charge. The study also revealed that the shock wave from a shaped charge can superimpose with the ballistic wave, a phenomenon not observed in conventional spherical charges.

The researchers noted that the metal jet carries away some of the explosive products, hindering bubble development and causing an inward depression of the bubble wall near the metal jet. This results in a maximum bubble radius and pulsation period that are 5.2% and 3.9% smaller, respectively, than those of a conventional spherical charge of the same weight. Additionally, the uneven axial energy distribution in the shaped charge leads to the formation of an oblique bubble jet.

The study also examined the effects of varying liner angles and charge weights on the characteristics of metal jets, waves, and bubbles. It was found that different liner angles result in different deformation modes of the liner, leading to the formation of various types of metal jets, such as shaped charge jets (SCJ), jetting projectile charges (JPC), and explosively formed projectiles (EFP). The maximum head velocity of the metal jet decreases as the liner angle increases. Furthermore, increasing the weight of the shaped charge increases the total explosion energy and the metal jet's head velocity, but the proportion of the metal jet's kinetic energy to the total energy decreases.

This research provides a comprehensive understanding of the coupling dynamics between metal jets, ballistic waves, shock waves, and bubbles during underwater explosions of shaped charges. The findings have significant implications for the design and application of shaped charges in underwater environments, contributing to the broader field of underwater explosion dynamics.

The paper “Experimental Study on the Coupling Dynamics of Metal Jet, Waves, and Bubble During Underwater Explosion of a Shaped Charge,” is authored by Yu Tian, A-Man Zhang, Liu-Yi Xu, Fu-Ren Ming. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.04.001. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.