The Influence of Initial Defects on Impact Ignition of Aluminum/Polytetrafluoroethylene Reactive Material

Abstract

Aluminum/polytetrafluoroethylene (Al/PTFE) reactive material is a typical multifunctional energetic material, which can release enormous energy under impact loading. To clarify its ignition mechanism, a Split Hopkinson pressure bar (SHPB) is used to conduct the impact ignition experiment on reactive materials with different initial defects. The experimental results show that the measured minimum specific incident energy that can cause the ignition for the specimen without pre‐impact (MSed specimen) increases slowly from 97.5 to 101 Jcm−2 with the molding pressure first, but drops substantially to 83.3 Jcm−2 as the molding pressure increases to 100 MPa. In addition, only the MSed specimens with the molding pressure above 100 MPa are ignited at the third stress pulse. Combined with the results of scanning electron microscopy, it is found that the existence of local larger pores inside the MSed specimens with high molding pressures (100, 120, and 150 MPa) contributes to the increase in damage level under impact and thus reduces the ignition threshold. The impact ignition experiment on the pre‐impacted specimens (MSed + PIed specimens) indicates that a phenomenon of damage sensitization exists in Al/PTFE reactive materials, confirming that the initial defects and damage evolution have significant effects on the impact ignition of the material.

Effect of Confining Pressure on Impact Reaction Threshold of Aluminum/Polytetrafluoroethylene Reactive Material

“…Under uniaxial impact loading, microcracks are generated and expand due to the deformation of the holes, resulting in the reduction of compressive strength. [ 17,26 ] The confining pressure exposes the specimen to triaxial compressive stress loading, preventing microporosity deformation and increasing the specimen's compressive strength.…”

“…The decomposition products come into contact with the metal particles and undergo a chemical reaction. For the studied Al/PTFE reactive material, the research [ 17 ] has indicated that the reaction threshold has a damage sensitization phenomenon. Specimens containing initial damage were obtained using preimpact experiments, and their reactive thresholds were compared with those of normal specimens.…”

“…The results have shown that the specimen fracture prior to the reaction, and the damage caused by internal cracks significantly affect the reaction. Furthermore, Ren [ 17 ] investigated the influence of initial damage on the reaction behavior of Al/PTFE through the impact reaction experiment with preimpact specimens and proved that the reaction threshold of Al/PTFE has damage sensitization characteristics.…”