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Experimental study of the disintegration of an instantaneously heated medium and the resulting impulse at energy concentrations less than the heat of evaporation

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Abstract

An experiment using the radiation from a Q-switched laser was carried out to confirm the phenomenon of detachment of the surface layer of a material when it is rapidly heated at energy concentrations less than the heat of evaporation Q [1]. The disintegration of the material was recorded by high-speed photography. Measurements were made of the impulse I for different energy concentrations, and it was shown that the dependence of I on the supplied energy E was in good agreement with the theoretical calculations reported in [1].

It is shown that by determining the pressure impulse produced during the disintegration of the rapidly heated material it is possible to investigate its thermodynamic properties at densities approaching the normal value.

The detachment of the surface layer of the material under instantaneous heating at energy densities less than the heat of evaporation was described in [1], where an estimate was made of the resulting pressure impulse. The results described in [1] show that when an energy Er is liberated in the surface layer of thickness xr or mass mr in a time τ < tg, where tg=xr/ c is the characteristic time for gas-dynamic processes and c is the velocity of sound in the medium, the pressure produced in the layer is p°=(γ - l)Er/xr. Interaction between rarefaction waves propagating from the boundaries of the heated layer results in the appearance of negative stresses. When these stresses exceed the dynamic strength of the material, detachment of the surface layer may take place. The pressure impulse produced during the surface-layer detachment in the case of a uniformly heated layer is given by

$$I = \frac{{(\gamma - 1)E_r }}{{2\sqrt {c_0 ^2 + \gamma (\gamma - 1)E_r /m_r } }}, (0.1)$$

where γ is the adiabatic exponent and Er/mr is the amount of energy per unit mass. It is clear from the dependence of I on Er that the values of I can be used to determine the adiabatic exponent y or the Grüneisen coefficient Γ=γ - 1 at normal density ρ0, i.e., it is possible to obtain data on the thermodynamic state of the instantaneously heated material. In this paper we report an experimental study of this detachment effect. We have investigated the general features of the formation of the pressure impulse predicted by I. V. Nemchinov, verified Eq. (0.1) and, finally, showed that the equation of state for the instantaneously heated medium can be determined by the method put forward in [1].

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References

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Additional information

The authors wish to thank Ya. T. Gnoev, B. M. Zubenko, and MFTI student V. S. Savinich for considerable help in this work.

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Kalmykov, A.A., Nemchinov, I.V. & Petrukhin, A.I. Experimental study of the disintegration of an instantaneously heated medium and the resulting impulse at energy concentrations less than the heat of evaporation. J Appl Mech Tech Phys 7, 1–8 (1966). https://doi.org/10.1007/BF00914324

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Keywords

  • Surface Layer
  • Energy Density
  • Thermodynamic Property
  • Energy Concentration
  • Photography