Strength of water under pulsed loading

Abstract

EzTeT~ments we~ perfo~ncd to study the strength of water under conditions of pulsed extension. which is typical of the interaction between a triangular compression pulse and a free surface.The tests were perfo~ned in a wide (40-1000 MPa) range of 'variation According to theoretical concepts, liquids can sustain considerable tensile stresses reaching 1()0-1000 MPa [1][2][3]. At the same time, much smaller values were obtained in static tests (see [4]) and in cavitation studies in an intense acoustic field [5--7]. This discrepancy is due to the fact that in real liquids, the presence of heterogeneous sites (interfaces, solid inclusions, g~/.s bubbles, etc.) gives rise to pore growth, which leads to fracture of the liquids. Ill water, for example, the total amount of heterogeneities with characteristic dimeiL~ions of 0.0(}1-10 #m is 10 ' -10 ~i cm -3 [8,9]. Of all the impurities in the liquid, only bubbles in the bulk and in small cracks of undiluted particles can have a considerable effect on its strength [7].The strength of tt'm liquid under (lynamic loading is closer to the theoretical value. Ill the present study. for dymunic extension of the li(luid, we use sI)alling phenomena that occur in tile reflection of compression pulses fronl the free. surface of the substance to be examined [10]. The advantage of this approach is that tlm fracture caused by 1-#see pulses is volume (the effect of tim boundaries is negligible) and occurs ill a thin layer of the substance. This leads to a decre~sed nunlber of heterogeneous sites that can influence the fracture of the liquid. Moreover, the precompression in the shock wave is likely to result ill the collapse of the pores, which also intensifies homogeneous nucleation.The pulsed extension of liquids under shock-wave loading was used to study the cavitation of glycerin [11][12][13], water [14][15][16], ethyl(me glycol [15], ethanol [16], and mercury [17]. Glycerin is most extensively studied, for which a relation between the spall strength and the temperature was (tetermined [13] and it was shown that at 20~ its strength is equal to 60 MPa for any (tefbrmation rate [12]. The vahms of the spall fracture of water obtained by different authors differ by several orders (from 3.9 MPa [15] to 400 MPa [18]). There are no reliable experimental data on how tile deformation conditions influence the character of fracture. At tile same time, the phenonmnon of cavit[ttion is of considerable practical interest, which stinmlates the study of tile behavior of water upon I)ulsed extension. In this paper, the results of experimental deterinimttion of ttm spall strength of water are given fi)r wide ranges of compression-pulse amplitudes and durations and tile question as to whether tile honlogeneous-nucleation model can be used to interpret tlle results obt~dned is considered.

Dynamic tensile strength of silicone oils

“…Glycerol data has been included for comparison because it has a viscosity of 1.4 Pa s at room temperature and is therefore the closest widely studied analog to the viscous silicone oils used in this work. The spall strength measured for water in shot 0 compares relatively well to the values published by Bogach and Utkin for similar experimental parameters [21], which offers confidence in the experimental method used in this work. By contrast, there is significant variability between the measured spall strengths in the work of Erlich and Utkin et al in glycerol.…”

“…Also shown in Figure 2b are previously published data sets for spall experiments performed on water [21] and glycerol [22,10,8]. Glycerol data has been included for comparison because it has a viscosity of 1.4 Pa s at room temperature and is therefore the closest widely studied analog to the viscous silicone oils used in this work.…”

Formation mechanism of cavitating spalls

“…We note that, in [4], the occurrence of spalling in a metal sample under shock-wave loading is explained by features of the free-surface dynamics recorded experimentally. The same approach was used in [4,5] to describe the behavior of liquids under similar loading conditions. As noted above, there is no direct analogy between the fracture processes of liquids and solids does not exist, and this refers, first of all, to the concept of critical tensile stresses.…”

“…This is due primarily to the fact that real liquids, even in the unperturbed state, contain cavitation nuclei in the form of microheterogeneities of the type of free gas microbubbles, solid microparticles and their combinations [1][2][3]. The development of cavitation on these nuclei leads to significant changes in the parameters and structure of the external wave field, because of which the notion of critical tensile stresses for liquids is not defined.Nevertheless, in some experimental studies (see, for example, [4,5]), the occurrence of a mass-velocity jump on a free liquid surface upon reflection of the shock pulse from it is treated as a manifestation of spall type fracture. In this case, according to the data of [4], the value of the spall strength is determined from the formula p s = 0.5ρ 0 c 0 (W 0 − W min ) and depends on the velocity jump W 0 − W min (W 0 is the maximum velocity of the free surface at the moment of reflection and W min is its minimum value which is recorded before the spall pulse).…”

Measurements of the viscosity of water under shock compression

“…Here, a 0 is the initial amplitude of perturbations, λ is the perturbation wavelength, P is the shock wave pressure, and σ p is the dynamic ultimate strength [58,59]. The constancy of flow behind the shock front for different wavelengths, which is necessary for agreement between the theory and experiment, was provided by the use of fairly large-size explosive charges and assemblies with cuvettes.…”