Fracture behaviour of mullite fibre reinforced-mullite matrix composites under quasi-static and ballistic impact loading

The fracture behaviour and damage development in mullite fibre reinforced-mullite matrix composites have been investigated using chevron notch technique and ballistic impact tests. Fracture toughness (KIc) values in the range of 1.8-3.3 MPa m1/2 were determined using the chevron notched specimen technique. A large variability of KIc data due to the complex (heterogeneous) composite microstructure was found. Extensive fibre pull-out occurred during failure, which was due to a favourable matrix/fibre interfacial bond given by NdPO4 coating of the fibres. The materials response under ballistic impact loads was studied using a gas gun. The projectiles were glass balls of 10.15 mm in diameter and weighing 1.4 g. The projectile velocity was in the range 77.6-207.5 m/s. The remanent load carrying capability of composite samples after ballistic tests was measured to quantify ballistic impact induced microstructural damage. The composites retained some of their load bearing capacity even after penetration of the projectile, since structural damage caused by projectiles remained localised, preventing catastrophic failure. Penetration by the projectile occurred at impact energy of about 4 J for the conditions investigated. Understanding crack propagation and damage development under ballistic impact loads may open new opportunities for the use of these composites in lightweight armour applications.