According to the Zeldovich - Von Neumann - Doring (ZND) model, the detonation wave consists of a shock jump and a chemical reaction zone where the pressure decreases and the matter expands, i.e. the Von Neumann spike is formed. Numerous experimental data confirm the validity of this model for most high explosives. However, in recent years a number of detonation effects that don't correspond to classical ZND model have been found in several heterogeneous explosive materials (EM). One of the effects is the unusual reaction zone structure and detonation velocity dependence on initial porosity of samples in pressed TNETB high explosive. With the use of the VISAR laser interferometric system, it was found that in the range of initial porosity of 3.3 to 15.2% propagation of a steady-state detonation wave without the Von Neumann spike predicted by the classical detonation theory was possible in "coarse" (mean particle size of initial powder r_(av) ～ 120 μm) TNETB. In samples of "fine" (r_(av) ～ 5 μm) TNETB, the upper limit of porosity range increased to 29%. The discontinuities of the dependence of detonation velocity on initial density near the lower and upper limits of the specified range of porosity were also found. This observation can be the witness that the detonation regime without the Von Neumann spike is the steady-state underdriven detonation, which is fundamentally impossible according to the ZND detonation model.
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