Nicolò Grilli

Dynamic fracture and hot-spot modeling in energetic composites

Defects such as cracks, pores, and particle-matrix interface debonding affect the sensitivity of energetic materials by reducing the time-to-ignition and the threshold pressure to initiate an explosion. Frictional sliding of preexisting cracks is considered to be one of the most important causes of localized heating. Therefore, understanding the dynamic fracture of crystalline energetic materials is of extreme importance to assess the reliability and safety of polymer-bonded explosives. Phase field damage model simulations, based on the regularization of the crack surface as a diffuse delta function, are used to describe crack propagation in cyclotetramethylene-tetranitramine crystals embedded in a Sylgard matrix. A thermal transport model that includes heat generation by friction at crack interfaces is coupled to the solution of crack propagation. 2D and 3D dynamic compression simulations are performed with different boundary velocities and initial distributions of cracks and interface defects to underst...

Effect of initial damage variability on hot-spot nucleation in energetic materials

Mechanical insult may be able to produce chemical transformations in solids when the energy is released in highly localized regions. This phenomenon is responsible for the nucleation of hot-spots that are responsible for ignition of energetic materials. The concentration of energy at microstructural defects leads to the probabilistic nature of ignition. The effect of the microstructure of the energetic particles, specifically the influence of the initial crack distribution on the sensitivity to ignition, is studied for a particle embedded in a polymeric matrix at impact velocities 100 m/s and 400 m/s with finite element simulations that couple fracture dynamics and heat transport. A phase field damage model that includes heat sources due to frictional heating at the crack surfaces and heat dissipation during crack propagation is developed and verified. These heat sources are compared and, in the range of impact velocities studied, heat generation due to friction is more important than dissipation due to c...