- Compressive failure strength of brittle solids increases rapidly with the confining pressure whereas the yield stress of ductile materials is much less sensitive to the confinement. The presented experimental technique utilizes this difference in the effect of the confinement in order to reveal the mode of ceramics behavior under shockwave compression. A controlled confining pressure on the lateral surface of the disk-like ceramic specimen was produced by fixing the specimen into a shrink-fit metal sleeve. The effect of such confinement on the Hugoniot Elastic Limit should differ by a factor of about 2.5 for the materials whose ductile yielding is governed by Von Mises criterion and those obeyed the Griffith's criterion of brittle failure. Results of the tests performed exhibit unambiguously the ductile response of the alumina ceramics whereas the response of the boron carbide ceramics is certainly brittle.