title: Hypervelocity impacts into porous graphite: experiments and simulations.
abstract: We present experiments and numerical simulations of hypervelocity impacts of 0.5 mm steel spheres into graphite, for velocities ranging between 1100 and 4500 m s-1Experiments have evidenced that, after a particular striking velocity, depth of penetration no longer increases but decreases. Moreover, the projectile is observed to be trapped below the crater surface. Using numerical simulations, we show how this experimental result can be related to both materials, yield strength. A Johnson-Cook model is developed for the steel projectile, based on the literature data. A simple model is proposed for the graphite yield strength, including a piecewise pressure dependence of the Drucker-Prager form, which coefficients have been chosen to reproduce the projectile penetration depth. Comparisons between experiments and simulations are presented and discussed. The damage properties of both materials are also considered, by using a threshold on the first principal stress as a tensile failure criterion. An additional compressive failure model is also used for graphite when the equivalent strain reaches a maximum value. We show that the experimental crater diameter is directly related to the graphite spall strength. Uncertainties on the target yield stress and failure strength are estimated.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France david.hebert@cea.fr.
authors.forename: D
authors.identifier: http://orcid.org/0000-0003-3926-5228
authors.initials: D
authors.lastname: Hébert
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France.
authors.forename: G
authors.initials: G
authors.lastname: Seisson
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France.
authors.forename: J-L
authors.initials: JL
authors.lastname: Rullier
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France.
authors.forename: I
authors.initials: I
authors.lastname: Bertron
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France.
authors.forename: L
authors.initials: L
authors.lastname: Hallo
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France.
authors.forename: J-M
authors.initials: JM
authors.lastname: Chevalier
authors.affiliation: CEA CESTA, 15 avenue des Sablières CS60001, 33116 Le Barp Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Thessieux
authors.affiliation: CEA LR, BP 16, 37260 Monts, France.
authors.forename: F
authors.initials: F
authors.lastname: Guillet
authors.affiliation: Insitut P' UPR3346 CNRS-ENSMA-Université de Poitiers, 1 avenue Clément Ader, 86961 Futuroscope Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Boustie
authors.affiliation: Laboratoire PIMM UPR8006 CNRS-Arts et Métiers ParisTech, 151 boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: L
authors.initials: L
authors.lastname: Berthe
keywords: cratering; fragmentation; graphite; impact; steel; yield strength