Simulation Study on the Structure of a Shaped Charge Liner for Metal Jet Impact Initiation and the Stable Initiation Distance

Gob-Side Entry Retaining by Roof Cutting and Pressure Relief is widely employed in coal mining. However, the multi-segment air-decked charge structure used in its pre-splitting blasting requires a separate detonator for each charge segment, leading to problems such as high detonator consumption per borehole, elevated costs, operational complexity, and significant safety risks.To address this engineering challenge, the application of shaped metal jet impact-induced initiation technology in composite roof pre-splitting blasting has been proposed. Using LS-DYNA numerical simulation, a systematic investigation was conducted on liner structure optimization, factors affecting metal jet impact initiation, and the stable initiation distance.The findings demonstrate that the aluminum liner exhibits the optimal overall performance. With a cone angle of 60° and a wall thickness of 1 mm, it generates a shaped jet with high velocity, considerable length, and good continuity. In contrast, the copper liner, due to its high strength and high collapse energy threshold, fails to form an effective jet under low-power explosive charge conditions. Although the lead liner is readily accelerated, it produces jets with poor stability that are susceptible to necking and fragmentation.When the charge length-to-diameter ratio exceeds 3, the effective charge mass reaches saturation. Additional explosive energy is primarily dissipated through radial expansion and heat loss, resulting in the stabilization of both the maximum jet velocity and stable jet velocity.In an unconfined air environment, the maximum reliable initiation distance for a shaped jet from an aluminum liner (1 mm wall thickness, 60° cone angle) is 90 cm. Beyond this distance, jet stretching and attenuation lead to insufficient pressure to initiate the emulsion explosive.Confinement provided by steel pipes can significantly suppress the radial expansion of detonation products, enhancing energy utilization efficiency and consequently extending the initiation distance of the metal jet./t/nKewordsmetal jet; impact initiation; liner structure; decked charge; stable initiation