The rate-dependent fracture toughness of silicon carbide- and boron carbide-based ceramics

Thirteen silicon carbide and boron carbide ceramics and ceramic composites manufactured through pressureless sintering and reaction bonding techniques have been tested in a four-point bend, chevron notch testing procedure to determine their static and dynamic fracture toughness values. Dynamic fracture toughness testing was performed in a modified Hopkinson pressure bar to investigate the effect of high-rate loading on fracture toughness values and fracture characteristics. Fracture surfaces were investigated through optical profilometry and scanning electron microscopy to examine the surface roughness and fracture morphology. Reaction-bonded ceramic composites were found to have elevated fracture toughness values compared to pressureless-sintered ceramics. This enhancement is attributed to a change in fracture mode of the reaction-bonded materials and processing-induced residual compressive stresses within the silicon phase.