- The present paper is concerned with the static and the dynamic mechanical properties at strain-rates up to 10 3 s −1 , of ceramic composites based on porous B4C infiltrated with molten Si. The static mechanical properties of the infiltrated composites depend on the amount of the residual silicon. The Young’s modulus and the hardness increase, while the flexural strength and K1C decrease with decreasing fraction of residual silicon. The dynamic strength and the initiation fracture toughness K1D have significantly higher values than the corresponding static properties, and are insensitive to both the residual silicon fraction and the strain-rate up to u = 10 3 s −1 . © 2007 Elsevier B.V. All rights reserved.