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

INDICE DE RÉFRACTION SOUS CHOC DE LA SILICE FONDUE ET DU SAPHIR

La validité du calcul de la vitesse matérielle à partir de la vitesse de surface libre mesurée par l'interféromètre de vitesse VTSAR, est examinée pour différents comportements habituellement rencontrés dans l'étude des matériaux en régime de déformation uniaxiale hautement dynamique. Dans le cas où ce calcul est entaché d'une erreur trop importante, il est préférable de mesurer une vitesse d'interface entre le matériau cible et un matériau fenêtre. Le passage de la vitesse d'interface à la vitesse matérielle s'effectue alors en corrigeant la désadaptation d'impédance d'une part, et en tenant compte de la variation d'indice de réfraction du matériau fenêtre d'autre part.The comparison between free surface velocities and particle velocities were examined for different constitutive laws in shock wave studies. Thus, the advantage of the windows were shown when the material behaviour was found to be not elastic

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