The Competing Effects of Pre‐Load and Charge Diameter on Crack Initiation and Flame Propagation in Central‐Ignition Confined Explosives

ABSTRACT

Understanding the mechanisms of crack initiation and flame propagation in confined explosives under nonshock initiation accidents remains challenging due to the strong coupling between fracture and combustion. To address this, this work established a central‐ignition crack propagation experimental technique with adjustable axial pre‐load on the charge surface. In this setup, cracks are driven by high‐pressure gases from burning black powder, decoupling the crack propagation from the bulk explosive reaction. High‐speed photography was employed to capture crack evolution and flame propagation dynamics under different pre‐loads and charge diameters. The results indicate the consistent formation of 3 to 4 radially distributed initial cracks. It is proposed to be determined by the effects of axisymmetric stress fields, system energy optimization, and crack‐to‐crack interaction. The number of these initial cracks is competitively regulated by the charge diameter and the pre‐load. Furthermore, the propagation speed of the flame front within the cracks is quantified, revealing a distinct velocity jump (e.g., from 200 to 1000 m/s). This jump is attributed to a sharp decrease in flow resistance after the cracks fully penetrate the charge. This study provides novel experimental insights and data for understanding crack initiation and flame propagation behavior in nonshock initiation events.