Crack tip stress and formation of Plastic/influence zone for composite solid rocket propellant

Crack tip stress and formation of Plastic/influence zone for composite solid rocket propellants

The necessity to understand the crack behaviour of composite solid rocket propellants as it helps in analysis of service life of rocket motors. Experimental data reveals that a material’s microstructure at the crack tip can have a significant effect on the local damage near the crack tip and crack growth behaviour in particulate composites. 

For two-dimensional finite element simulations, a centrally cracked specimen is used to study local damage near the crack tip and crack growth behaviour in a particulate composite solid rocket propellant under constant displacement rate at room temperature.> For finite element simulation in ANSYS perfect bond is created at particle/matrix interface using Glue function and corresponding material properties are assigned to particles and matrix. For simulations results elemental solution von-Misses stress is selected as it considers stresses in all almost directions to find the maximum stress value at crack tip. For this simulation plane stress condition without any thickness is considered.

A Plastic zone also known as influence zone is the region where high stresses are induced and it’s generally ‘cusp’ in shape. Below the crack tip higher stresses are induced in this plastic zone. This region generally lies in between the crack tip and particle in the crack propagation path. The shape of plastic zone is comparable to average particle size and changes dramatically as the crack approaches towards the particle. As crack tip propagating towards the particle along crack propagation path, the maximum stress induced at crack tip is first increases and then decreases as crack tip reaches close to particle.

In contrast to this the maximum von-Mises stress at a particle, especially the part facing crack tip, increases correspondingly for every increment in crack tip position propagating towards the particle. In addition to this as crack propagates closer to particle the shape of the plastic zone increases as the stress at the crack tip decreases. A particle traps a short crack with a plastic zone which is larger than the particle size results in reduction of stress at crack tip. A particle's constraint on the plastic zone arises from the mechanical incompatibility at the interface between the particle and matrix.