A Study On The Penetration Resistance Of Targets Made Of Various Materials

A combined numerical and theoretical study is performed in this thesis on the penetration and perforation of targets struck normally by rigid projectiles. The target materials examined contain Fibre-reinforced plastic laminates (FRP laminates), metal and concrete. Failure modes of targets under normal impact by projectiles are discussed, and corresponding theoretical models for different failure modes are established to predict penetration depths, residual velocities and ballistic limits. Meanwhile, the critical condictions for the transition of different failure modes are proposed. Numerical Simulations using ABAQUS/VUMAT into which a modified Johnson-Cook constitutive relation is incorporated are performed to study the perforation of metal plates struck normally by rigid projectiles. The results obtained in the present investigation are useful for the optimization of projectile nose shapes, safety calculation and safety assessment. This thesis mainly consists of the following parts:A theoretical study is conducted on the reponse and perforation of FRP laminates by flat-ended projectiles. Ballistic impact on FRP laminates is a very complex problem and it can be generally classified into two categories, i.e. global deformation with local rupture and wave-dominated local failure. For the perforation of thin FRP laminates, the global deformation failure modes are considered, and a quasi-static approach was used to predict the energy absorption, which includes global deformation energy, local fracture energy due to shear and tensile tearing, and delamination energy for flat-ended projectiles. A shear failure criterion for flat-ended projectiles are employed to predict the the critical transverse deflection at which plate failure occurs. For the perforation of thick FRP laminates, the wave-dominated local failure modes are considered, the ballistic limits of the laminates can be solved by Wen’s semi-empirical equation. By combining the wave-dominated local failure model and the concept of Von Karman’s critical impact velocity, a condition for the transition of the above mentioned two failure modes is obtained. It is shown that the model predictions are in good agreement with available experimental observations in terms of ballistic limits and critical conditions for the transition of failure modes.An analytical investigation is conducted into the the penetration and perforation of thick metal and concrete targets struck normally by rigid ogival-nosed projectiles over a wide range of velocities. Based on the assumption that the deformation is localized and that the mean pressure offered by the target materials to resist the projectiles can be decomposed into two parts:a quasi-static part due to the elastic-plastic deformation of the target materials and a dynamic resistive pressure arising from velocity effects, a new formulation which represents an extension of Wen’s semi-empirical model is developed, by assuming that the target resistance is no longer a constant, but a function of penetration velocity, and by adding the free surface effect of target to the new formulation. Equations are derived for predicting the depth of penetration in the targets and the residual velocity in the case of perforation. Furthermore, the range of applicability of the perforation model for fully-clamped thick metal targets under impact by ogival-nosed projectiles is discussed. It transpires that the present model predictions are in good agreement with the test data for thick metal and concrete targets in terms of penetration depth and residual velocity.Numerical simulations with ABAQUS/VUMAT into which a modified Johnson-Cook constitutive relation is adopted are performed to study the perforation of Weldox460E steel plates struck normally by rigid conical-nosed and flat-ended projectiles. Comparisons of the numerical results and the experimental data show that the finite element model developed here are reliable. Whereafter, numerical simulations are conducted on the perforation of Weldox460E steel plates with various thickness struck normally by rigid conical-nosed projectiles and6mm thick Weldox460E steel plates struck normally by rigid conical-nosed projectiles with various cone angles. It is found that different failure modes, i.e. ductile hole enlargement, petalling, discing and plugging are observed. It is also shown that projectile cone angle has significant effect on the perforation modes of6mm thick Weldox460E steel plates and that for smaller cone angles plates fail by ductile hole enlargement, for medium cone angles plates fail by petalling and for larger cone angles plates fail by discing or plugging. The energy dissipated by discing is maximum, and one by plugging is minimum. Finally, the critical projectile cone angles with which the plates fail by plugging are obtained by the numerical simulations on the perforation of Weldox460E steel plates under impact by conical-nosed projectiles.A theoretical study is carried out on the transition of the failure modes of metal plates and the energy absorption of thin metal plates perforated by conical-nosed projectiles. Analytical models for petalling and ductile hole enlargement with global deformations are derived by an approximate quasi-static theoretical analysis method. The quasi-static energies dissipated by local perforation hole formation and global deformations are solved firstly, and then by using the well-known Cowper-Symonds empirical formula, equations for the perforation energies and the ballistic limits of plates are obtained. The critical condictions for the transition of petalling and ductile hole enlargement are discussed. By combining the transition of petalling and ductile hole enlargement and the transition of ductile hole enlargement with and without global deformations, the range of applicability of models for petalling and ductile hole enlargement is determined. Equations are obtained for the critical projectile cone angles with which the plates fail by plugging, and the failure map is constructed for Weldox460E steel plates under impact by conical-nosed projectiles. The present model predictions are found to be in good agreement with numerical results and available test data in terms of critical conditions for the transition of failure modes and ballistic limits.