Identification of Johnson-Cook Model Parameters of an AP Projectile Core Based on Two Shear-Compression Specimen Geometries and One Dog-Bone Sample
Identification des Paramètres du Modèle de Johnson-Cook d'un Noyau de Projectile AB (Anti-Blindage) Basée sur Deux Échantillons Compression-Cisaillement et une Géométrie en Os de Chien
Résumé
Armour-Piercing (AP) projectiles constitute a major issue when designing military armours for personal and vehicle protection. Bi-layer shieldings are made of a ceramic front plate and a ductile composite/metal backplate to stop, erode and fragment the projectile. The bullet’s core, made of tungsten or strong steel alloy, defines the penetration capability of the projectile so its characterisation is crucial for both understanding failure modes occurring in the core and performing a numerical simulation of impact. Nevertheless, such simulations require constitutive models for which the identification of parameters is often sensitive and even dependent on the specimen itself. In this work, a high-strength steel core extracted from a 7.62 x 39 mm API-BZ projectile is tested in quasi-static loading conditions at room and high temperatures and at dynamic loading rates in order to determine parameters used in the Johnson-Cook plasticity and failure models. Three geometries are investigated: a dog-bone specimen, a Shear-Compression Specimen (SCS) and a modified SCS. The equivalent von Mises stress and the equivalent plastic strain in the sample are deduced so the Johnson-Cook model parameters can be obtained. Results show that, while flow stress resistance is similar for the three specimens, the ductility and failure strains vary to some extent, thus changing some of the parameters used in the Johnson-Cook model. This question raises the concern of the appropriate choice of sample geometry to identify the model parameters.