Pyrometric Measurement of the Temperature of Shocked Molybdenum

Measurements of the temperature of Mo shocked to ~60 GPa and then released to ~28 GPa were previously attempted using high explosive driven flyer plates and pyrometry. Analysis of the radiance traces at different wavelengths indicates that the temporal evolution of the radiance can be explained by a contribution from the LiF window to the measured thermal radiation. Fitting the radiance traces with a simple model, supported by continuum dynamics studies which were able to relate structures in the radiance history to hydrodynamic events in the experiment, the contribution of the window was obtained and hence the temperature of the Mo sample. The shock-and release temperature obtained in the Mo was 762+/-40K which is consistent with calculations taking the contribution of plastic work to the heating into account. The radiance obtained for the LiF window shows a non thermal distribution which can be described by a bulk temperature of 624+/-112K and hot spots (less than 0.5% in total volume) within the window at a temperature of about 2000K

Using dense seismo-acoustic network to provide timely warning of the 2019 paroxysmal Stromboli eruptions

Stromboli Volcano is well known for its persistent explosive activity. On July 3rd and August 28th 2019, two paroxysmal explosions occurred, generating an eruptive column that quickly rose up to 5 km above sea level. Both events were detected by advanced local monitoring networks operated by Istituto Nazionale di Geofisica e Vulcanologia (INGV) and Laboratorio di Geofisica Sperimentale of the University of Firenze (LGS-UNIFI). Signals were also recorded by the Italian national seismic network at a range of hundreds of kilometres and by infrasonic arrays up to distances of 3700 km. Using state-of-the-art propagation modeling, we identify the various seismic and infrasound phases that are used for precise timing of the eruptions. We highlight the advantage of dense regional seismo-acoustic networks to enhance volcanic signal detection in poorly monitored regions, to provide timely warning of eruptions and reliable source amplitude estimate to Volcanic Ash Advisory Centres (VAAC)

An Equation of State of a Carbon-Fibre Epoxy Composite under Shock Loading

An anisotropic equation of state (EOS) is proposed for the accurate extrapolation of high-pressure shock Hugoniot (anisotropic and isotropic) states to other thermodynamic (anisotropic and isotropic) states for a shocked carbon-fibre epoxy composite (CFC) of any symmetry. The proposed EOS, using a generalised decomposition of a stress tensor [Int. J. Plasticity \textbf{24}, 140 (2008)], represents a mathematical and physical generalisation of the Mie-Gr\"{u}neisen EOS for isotropic material and reduces to this equation in the limit of isotropy. Although a linear relation between the generalised anisotropic bulk shock velocity $U^{A}_{s}$ and particle velocity $u_{p}$ was adequate in the through-thickness orientation, damage softening process produces discontinuities both in value and slope in the $U^{A}_{s}$-$u_{p}$ relation. Therefore, the two-wave structure (non-linear anisotropic and isotropic elastic waves) that accompanies damage softening process was proposed for describing CFC behaviour under shock loading. The linear relationship $U^{A}_{s}$-$u_{p}$ over the range of measurements corresponding to non-linear anisotropic elastic wave shows a value of $c^{A}_{0}$ (the intercept of the $U^{A}_{s}$-$u_{p}$ curve) that is in the range between first and second generalised anisotropic bulk speed of sound [Eur. Phys. J. B \textbf{64}, 159 (2008)]. An analytical calculation showed that Hugoniot Stress Levels (HELs) in different directions for a CFC composite subject to the two-wave structure (non-linear anisotropic elastic and isotropic elastic waves) agree with experimental measurements at low and at high shock intensities. The results are presented, discussed and future studies are outlined.Comment: 12 pages, 9 figure

An analysis of the propagation of front shock in concrete

The aim of the authors is to model the shock response of concrete structures submitted to the effects of projectile penetration or contact detonation, in a range of pressure levels from 0 to 20 GPa. The limitations of current computers imply the need to homogenize the response of the different constituents of concrete into a single macroscopic model. Though concrete is widely used as a construction material, the knowledge concerning its response under shock loading response remains rather modest. An exhaustive review of the research effort in this field shows that the limited available data is affected by an important dispersion. As a consequence, any general rule correlating the composition of concrete to its shock properties have not yet been evidenced. A simple method to predict the shock Hugoniot of concrete based on a mixture theory is developed considering concrete as a mix of cement hydrates, free water, rock and voids. Experimental results obtained on special concrete compositions are presented. They illustrate the relation between the wave structure and the size of the aggregates, and so, the level of heterogeneity of the composition. Numerical simulations demonstrate the ability of a mesoscopic model to describe this phenomenon, and the failure of the homogenized approach to do so

Temperature measurement of tin under shock compression

The results of pyrometric measurements performed at the interface of a tin target with a LiF window material are presented for stresses ranging from 38 to 55 GPa. The purpose of the study is to analyze the part of the interface in the temperature measurement by a multi-channel pyrometric device. The results show that the glue used at the tin/LiF interface remains transparent under shock. The values of temperature measured at the tin/LiF interface are consistent with the behavior of tin under shock

Influence of shock induced polymorphic transition on penetration in steel

The effects of polymorphic transition for the impact of a 27NCD10 steel projectile on a 27NCD10 steel target at 1280 m/s is presented. Comparisons between results of 2D numerical calculations performed with and without polymorphic transition show the influence of this phenomenon on stress distribution and tension zones in the target and in the projectile. Good agreement between experimental and calculated flee surface velocity profiles is obtained with polymorphic transition and damage models taken into account.Les effets de la transformation polymorphique dans le cas de l'impact d'un projectile en acier 27NCD10 contre une cible en acier 27NCD10 à une vitesse d'impact de 1280 m/s sont présentés. Les comparaisons entre les résultats des simulations numériques 2D réalisées avec et sans modèle de transformation polymorphique montrent l'influence de ce phénomène sur la distribution des contraintes et sur la localisation des zones de tension. Un bon accord entre les diagrammes de vitesse de surface libre expérimentaux et calculés a été obtenu en considérant un modèle de transformation polymorphique associé à un modèle d'endommagement

Shock induced polymorphic transition and melting of tin up to 53 GPa (experimental study and modelling)

To investigate shock behavior of tin, particularly β-bct polymorphic transition and melting, shock compression measurements have been carried out up to 53 GPa peak stress. Interface velocity measurements between tin target and LiF window have been recorded using VISAR measurement technique. Interface velocity profiles show not only direct and reverse polymorphic β-bct transition but also melüng of tin on release for shock pressure above 34 GPa. In order to determine phase diagram of tin an analytic method of the experimental results has been developped. The equation of state of tin developped as part of this study has been implemented in a 1D wave propagation lagrangian code. Experimental results and calculations obtained with this model of tin are in good agreement

Lagrangian analysis. Modern tool of the dynamics of solids

Explosive metal-working, material synthesis under shock loading, terminal ballistics, and explosive rock-blasting, are some of the civil and military fields of activity that call for a wider knowledge about the behavior of materials subjected to strong dynamic pressures. It is in these fields that Lagrangian analysis methods, the subject of this work, prove to be a useful investigative tool for the physicist. Lagrangian analysis was developed around 1970 by Fowles and Williams. The idea is based on the integration of the conservation equations of mechanics using stress or particle velocity records obtained by means of transducers placed in the path of a stress wave. In this way, all the kinematical and mechanical quantities contained in the conservation equations are obtained. In the first chapter the authors introduce the mathematical tools used to analyze plane and spherical one-dimensional motions. For plane motion, they describe the mathematical analysis methods pertinent to the three regimes of wave propagation encountered : the non-attenuating unsteady wave, the simple wave, and the attenuating unsteady wave. In each of these regimes, cases are treated for which either stress or particle velocity records are initially available. The authors insist that one or the other groups of data (stress and particle velocity) are sufficient to integrate the conservation equations in the case of the plane motion when both groups of data are necessary in the case of the spherical motion. However, in spite of this additional difficulty, Lagrangian analysis of the spherical motion remains particularly interesting for the physicist because it allows access to the behavior of the material under deformation processes other than that imposed by plane one-dimensional motion. The methods expounded in the first chapter are based on Lagrangian measurement of particle velocity and stress in relation to time in a material compressed by a plane or spherical dilatational wave. The Lagrangian specificity of the required measurements is assured by the fact that a transducer enclosed within a solid material is necessarily linked in motion to the particles of the material which surround it. This Lagrangian instrumentation is described in the second chapter. The authors are concerned with the techniques considered today to be the most effective. These are, for stress : piezoresistive gauges (50 Ω and low impedance) and piezoelectric techniques (PVF2 gauges, quartz transducers) ; and for particle velocity : electromagnetic gauges, VISAR and IDL Doppler laser interferometers. In each case both the physical principles as well as techniques of use are set out in detail. For the most part, the authors use their own experience to describe the calibration of these instrumentation systems and to compare their characteristics : measurement range, response time, accuracy, useful recording time, detection area... These characteristics should be taken into account by the physicist when he has to choose the instrumentation systems best adapted to the Lagrangian analysis he intends to apply to any given material. The discussion at the end of chapter 2 should guide his choice both for plane and spherical one-dimensional motions. The third chapter examines to what extent the accuracy of Lagrangian analysis is affected by the accuracies of the numerical analysis methods and experimental techniques. By means of a discussion of different cases of analysis, the authors want to make the reader aware of the different kinds of sources of errors that may be encountered. This work brings up to date the state of studies on Lagrangian analysis methods based on a wide review of bibliographical sources together with the contribution made to research in this field by the four authors themselves in the course of the last ten years

Comportement dynamique d’un composite 3D C/C : méso-modélisation et prévision de la rupture sous choc

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