The compression depth of explosives is obtained on the basis of Lee penetration equation and the upper bound method to analyze the critical initiation threshold of finite thickness explosives. According to the pop curve, a theoretical model that reflects the relationship between critical initiation threshold and explosive thickness is established. Numerical simulation was carried out to simulate the initiation process and initiation threshold of explosives with different cover plate thicknesses. At the same time, we combine with the experimental data, to compare with the theoretical results. The calculations are in good agreement with data. Results show that the height of the bulge on the back of the cover plate and the compression depth of the explosive gradually increase with the thickness of the cover plate. When the cover plate reaches a certain thickness, there is no significant change on the final height of the bulge and the compression depth of the explosive. The decrease in explosive thickness increases the critical initiation threshold value, and the logarithm of the critical initiation threshold of the finite thickness explosive is approximately linearly related to the logarithm of the explosive thickness minus the compression depth. Therefore, this study can provide a reference for the initiation and simple calculation of the critical threshold of finite thickness explosives.

This work aims to study the critical initiation conditions of a confined finite‐thickness explosive under jet impact and the influence of shell constraints on the explosive initiation threshold. A theoretical calculation model for jet impact initiation of a confined explosive is established based on the Pop plot of the explosive. A jet impact test is conducted on a confined TNT explosive covered by a 50SiMnVB cover plate by using Φ40 mm shaped charge. A high‐speed camera is utilized to record the reaction process of shelled explosives. Numerical simulation software is adopted to calculate the reaction process of the confined explosive under the jet impact, and the critical initiation threshold of the confined explosive is obtained. Experimental results are verified, and the propagation and development of bow shock in the confined explosives under different cover thicknesses are analyzed. Then, the calculation results of the theoretical model are compared with the experimental simulation results. The findings show that the critical cover thickness of the confined TNT with a thickness of 43 mm is 20 mm, and the critical initiation threshold is 31 mm3 μs−2. The theoretical model can accurately calculate the critical initiation threshold and change the law of explosives under unconfined and confined conditions. When the thickness of the explosive and the acoustic impedance of the shell material increase, the critical initiation threshold of the explosive decreases. The shell reduces the critical jet velocity for explosive initiation, and the influence of the shell on the critical jet velocity gradually decreases as the thickness of the explosive increases.