Experimental Evaluation of Fracture Models Parameters and its Validation for Naturally Aged Composite Solid Propellant

Parameters for the Fracture models namely the Inherent Flaw Model (IFM), Point Stress Criterion (PSC) and Average Stress Criterion (ASC) were experimentally determined for HTPB-Al-based composite Solid Propellant of three different compositions. A Compact Tension specimen with geometry, as suggested in ASTM-E399, was adopted to generate fracture data. Parameters were estimated from a zero-aged propellant and also from a propellant that was naturally aged up to 4 years. Failure Assessment Diagrams for composite propellants have been formulated based on Two Parameter Fracture Criterion (TPFC) for these three fracture models. The notched strengths estimated from the models agree with the experiment results. Measured fracture toughness values for aged propellant are less than un aged propellant. The estimated decrease in notch strength for three years naturally aged propellant (with an increase in crack size from 27 mm to 31 mm) for type-1, type-2 and type-3 propellant are 36.82 %, 39.90 % and 35.47 % respectively estimated from CT specimens. The study shows that the generated model can be utilized to predict the notched strength of cracked configuration in un-aged and aged HTPB-Al-based composite Solid Propellant.