The effect of filler particle size and orientation on the impact fracture toughness of a highly filled plasticized polymeric material

The effect of particle size and orientation on the inherent fracture toughness of a filled plasticized polymeric material has been determined by application of linear elastic fracture mechanics. Testing was caried out in a three-point bend mode under impact conditions. The material was a triple base gun propellant consisting of a matrix of nitrocellulose plasticized with nitroglycerine and filled with particles of nitroguanidine (NQ). The crystalline NQ was used in the “as-received” form of needles and in a “ground” state. The material containing as-received NQ consistently had a higher fracture toughness than the material with ground NQ, and the toughness was a maximum when the fillers were aligned perpendicularly to the fracture surface. The impact fracture toughness was found to be virtually independent of strain rate over the range from 3 to 90 sec⁻¹. Seven-perforated cylindrical grains of the material containing as-received and ground NQ crystals, and the grains were tested in a pneumatic gas gun and a Hopkinson bar apparatus. The grains containing the ground NQ have been shown to be generally less resistant to fracture than the grains containing as-received NQ.