Impulsive Tension of Ethanol under Shock Loading

Abstract

This paper reports results from experimental studies of the strength of ethanol under impulsive tension due to interaction of a triangular compression pulse with the free surface. The experiments were performed in the range of strain rates 4 · 10 4 -4 · 10 5 sec −1 . It is established that the failure of ethanol is a two-stage process. In the first stage at a negative pressure of about 14 MPa, pore formation begins, which proceeds at a rather low rate and is manifested as an inflection on the free-surface velocity profile. In the second stage, the porosity growth rate increases, resulting in formation of a spalling pulse. The possibility of using the model of homogeneous nucleation to interpret experimental data is discussed.According to theoretical concepts, liquids can endure high tensile stresses of up to 0.1-1 GPa [1][2][3]. It is assumed that discontinuity of the material results from pore formation by a homogeneous nucleation mechanism. At the same time, considerably smaller values are observed [4] in practice under static test conditions, which is explained by the presence of heterogeneous centers in real liquids, at which pore growth is initiated.Conditions of liquid fracture during homogeneous nucleation can be obtained using dynamic tension. In the present study, this is done by analyzing the spalling phenomena involved in the reflection of compression pulses from the free surface of the examined material [5]. An advantage of this method is that at a pulse duration of order of 1 µsec, the fracture is volume (with no effect of the boundaries) and occurs in a thin layer of the material, which considerably reduces the number of heterogeneous centers capable of influencing the fracture of the liquid. In addition, one might expect that precompression in a shock wave leads to partial pore collapse, which also enhances the role of homogeneous nucleation.Impulsive tension under shock-wave loading has been used previously to study the cavitation of liquids (glycerol [6-9], water [10-13], ethylene glycol [11], ethanol [12], hexane [9] and mercury [14]). It has been shown, in particular, that the kinetics of pore formation and, as a consequence, the nature of the dependence of strength on strain rate are largely determined by the physicochemical properties of the liquids. To elucidate the general features of cavitation, it is of interest to compare the fracture patterns of liquids of various structures. The present paper considers the results of experiments on determining the spall strength of ethanol, which has not been studied previously, and discusses the possibility of using the homogeneous nucleation model to interpret the results obtained. Dremin et al. [12] obtained an estimate P s ≈ 48 MPa for the spall strength of ethanol, but the employed method did not allow regularities of the fracture kinetics to be established. This is one of the objectives of the present study.Diagram and Results of Experiments. A diagram of the experiments on impulsive tension of liquids is presented in Fig. 1. Shock waves were pr...

Theory and molecular dynamics modeling of spall fracture in liquids

“…The strain rates in shockwave experiments reach 10 4 -10 6 s −1 . [11][12][13] The strength of liquid depends on heterogeneous processes and on homogeneous void nucleation and growth as well. The fracture rate is determined by the initial concentration of impurities due to heterogeneous processes.…”

“…14 In the case of dynamic stretching, the threshold value of nucleation rate may depend on the strain rate. [11][12][13] This approach can be referred to as the nucleational approach. It is assumed that strength of liquid is determined solely by void nucleation kinetics.…”

Solid–fluid phase transitions under extreme pressures including negative ones

“…This explosive fragmentation is very similar to the sudden, explosive boiling of liquids close to the mechanical spinodal (i.e. during homogeneous nucleation under very high metastability), also called sometimes spall [41,42]. The spallation strength for a solid is the strain needed to separate the material along a plane surface instantaneously.…”

“…Reaching these values, the solids must break, just like a liquid must cavitate upon reaching the homogeneous nucleation limit. Just for comparison, the spall strength of liquid ethanol [41] is around À30 MPa, i.e. two orders of magnitude smaller than for these solid metals.…”

Molecular dynamics study of nanobubbles in the equilibrium Lennard-Jones fluid

“…11 In the shockwave experiments, a liquid was first subject to compression and then to stretch in the rarefaction wave. [12][13][14] Observed spallation of a liquid can be accounted for by nucleation of bubbles of extremely small sizes. Similar phenomena were registered upon spallation in laser shock-loaded tin in solid and liquid states 15 and in material decomposition upon femtosecond laser ablation.…”