Studies On The Dynamic Behaviour Of Ceramic/metal Armour Plates Under Deformable Projectile Impact

The main requirements of materials involved in armour design are: low density and high dynamic strength. Metals, in general, fulfil all the requirements except that of density. Ceramics satisfy the both demands but are brittle, which makes for extensive fragmentation due to the tensile waves generated by the compressive waves reflected from the free surfaces. Mixed armours, however, made of ceramic tiles and a metallic backup plate, form a very efficient shield against projectiles since they combine the lightweight and high resistance of ceramic with the ductility of metallic materials.This paper aims at the problem of ceramic/metal armours impacted by deformable projectile. The researches are outlined as following: 1. A new experimental method for brittle high-compressive-strength materialsAl2O3 ceramics is a brittle material with high compressive strength so that only small strain is produced when breaking. It is very difficult to study the dynamic behavior of ceramics by classical SHPB technology. Firstly, the stress-strain curves in the rigid of low strain rate of Al2O3 ceramics are measured adopting the classical SHPB apparatus. At the same time, we have a sight of several disadvantages of classical SHPB technology. In order to obtain more desirable results, several modifications on classical SHPB technology were implemented. A new experimental method is presented for brittle materials with high compressive strength. By the use of the improved SHPB apparatus, the uniaxial compression tests for Al2O3 ceramics in the strain-rate range of 560-750 s-1 were carried out and the stress-strain curves of Al2O3 ceramics were obtained. It is shown that ceramics is a nonlinear elastic-brittle material. It is sensitive to strain-rate at higher strain-rate. The modulus of elasticity and dynamic compressive strength of ceramics increases with increasing the strain rate. Based on the theory of damage mechanics, an elastic-brittle damage-modified constitutive model is given. The parameters are obtained by fitting the SHPB test data. A strain-rate dependent damage-modified constitutive equation of Al2O3 ceramics is obtained.2. A new simple model for the deformation of projectile impacting a deformable targetUp to now several analytical models aiming at the mushrooming deformation of projectile impacting a target have been developed, but in which the deformation of target was not been taken into consideration. Based on Taylor's model and Hawkyard's, A new simple model for the deformation of projectile impacting a deformable target is installed considering the penetration of the projectile to the deformable target. In the model, the following time-dependent variables are involved in: the extent and the particle velocity in the rigid zone; the extent, the cross-section area and the particle velocity in plastic zone; the velocity and depth of the penetrating of projectile to the target. Solving the set of equations, analytic solution is given. The profiles of projectile and shape parameters for different initial impact velocities are shown. The duration time of deformation increases with increasing the impact velocity. The analytical results by using this model are coincident with experimental result.3. A new analytical model of ceramic/metal armours impacted by deformable projectileA new analytical model is established to describe the complex behavior of ceramic/metal armours under impact of deformable projectile by assuming some hypotheses. Three aspects are taken into account: the mushrooming deformation of the projectile, the fragment of ceramic tile and the formation and changement of ceramic conoid and the deformation of the metal backup plate. Solving the set of equations, all the variables are obtained. For the different impact velocities, we get: the extent and the particle velocity in the rigid zone; the extent, the cross-section area and the particle velocity in plastic zone; the velocity and depth of the penetrating of projectile to the target; the reduction in volume and compressive strength of the f...