Effect of Continuous Damage Accumulation on Ignition of HMX‐Based Polymer Bonded Explosives under Low‐Velocity Impact

Abstract

The ignition phenomena of polymer-bonded explosives (PBXs) due to hotspot formation from grit/friction, shear band formation, and friction between microcrack surfaces have not yet been clarified. Microcracks are known to play a critical role in PBX ignition under low-velocity impacts. Further, microcrack evolution determines whether or not a specimen ignites because of complex mechanicalthermal-chemical coupled processes. Although many studies have investigated the multiphysics processes of ignition under single impacts, few have investigated multiple-impact scenarios that are more likely in reality. The present study focuses on the influence of continuous damage accumulation during multiple impacts on the safety assessment of octahydro-1,3,5,7-Tetranitro-Tetrazocine (HMX)-based PBXs. The Visco-SCRAM model combined with restart technology is applied to conduct simulations with the standard confined Steven test. By controlling the first impact velocity, the damage accumulation could be designed. When the first impact velocity increases from 5 to 20 m/s, the second impact velocity threshold decreases from 34 to 22 m/s and specific mechanical energy decreases from 600 to 240 m 2 /s 2. Multiple impacts change the temperature distribution and ignition position. Further, different projectile shapes influence multiple impacts differently. Owing to continuous damage accumulation, the second impact velocity threshold decreases for flat and pin projectiles. Dimensionless analysis reveals that the trends of critical dimensionless parameters for flat and pin projectiles are similar, whereas oval projectiles show a different response.

A Combustion Model for Explosive Charge Affected by a Bottom Gap in the Launch Environment

“…where τ (n) is the relaxation time and G (n) is the shear modulus. The number of Maxwell bodies in the generalized viscoelastic body is five in this study [59].…”

“…The viscoelastic statistical crack mechanics (Visco-SCRAM) model successfully combines the macroscale behavior of materials and the micro-crack behavior to simulate complex mechanicalthermal-chemical processes [56]. The model describes the mechanism of microcrack extension, coupling the microcrack body with the viscoelastic body [55,57,58], and reflects the viscoelastic mechanical properties and damage process of explosives, thus providing a realistic reflection of the mechanical properties of explosives [59,60]. Therefore, the Visco-SCRAM model is applied to describe the mechanical properties of explosive charge in this study.…”

Analysis of thermomechanical coupled accelerated aging of HTPB propellants

“…In comparison to traditional engines, the alterations in the mesoscopic structure of propellants in these advanced engines, notably the increase in microcracks and micropores, exert a more profound impact on their macroscopic mechanical properties. This can potentially cause reliability issues, such as combustion instability [19][20][21]. Consequently, evaluating the safety and stability of highperformance solid rocket engines, particularly after prolonged storage and transportation in complex environments, becomes critically important.…”