Numerical Simulation of Failure Modes of Solid Propellants with Internal Cavities Under Various Loading Conditions

Area of Science:

• Materials Science
• Mechanical Engineering
• Aerospace Engineering

Background:

• Solid rocket motor reliability hinges on propellant structural integrity.
• Internal cavities in hydroxyl-terminated polybutadiene (HTPB) propellants degrade mechanical properties and pose safety risks.
• Understanding cavity effects is crucial for propellant design and motor safety.

Purpose of the Study:

• To develop and validate a constitutive model for HTPB propellant incorporating damage.
• To numerically investigate the influence of initial modulus, impact rate, and confining pressure on propellant failure modes with internal cavities.
• To establish a basis for optimizing propellant structural safety concerning cavity size and engineering parameters.

Main Methods:

• Developed a constitutive model for HTPB propellant using the generalized incremental stress-strain damage model (GISSMO).
• Validated the model through uniaxial tensile tests at various strain rates.
• Performed numerical simulations to analyze failure mechanisms of propellants with cavities (40-100 mm radii) under varying conditions.

Main Results:

• The validated model accurately predicted force-displacement curves and captured rate-dependent material behavior (elastic-plastic to elastic).
• Large cavities (80-100 mm) led to stress concentration, inner wall damage, extrusion, collapse, and potential fracture.
• Smaller cavities (40-60 mm) exhibited greater stability, with damage primarily limited to volume compression.

Conclusions:

• Initial modulus significantly affects damage propagation; higher modulus (>24 MPa) suppresses damage in large cavities.
• Cavity behavior under impact varies with velocity and confining pressure, influencing structural stability and damage localization.
• Optimizing engineering parameters in relation to cavity size is key to enhancing propellant structural safety.