Computational Inverse Identification And Effect Rule Of Key Parameters In Penetration

The study of penetration problems is important for the development and improvement of weapons, and is useful for some relevant civil industries. Penetration is a very complex mechanical process, where material responses and structure responses of the projectile and target complete in a very short time. Also, it involves many uncertain factors and complicated projectile-target meeting conditions. For the penetration study, conventional experimental method mainly focuses on the observation of damage effects, and analytical method requires a number of simplifications. Both two methods can’t give enough details of the penetration process, so they are limited in actual applications. With the development of computational technology, numerical simulation has become an alternative approach for penetration study, which is as important as the experimental and analytical methods. Numerical simulation can obtain many kinds of data, but it requires accurate material constitutive model and boundary conditions. Furthermore, numerical simulation of penetration, especially3D simulation, is still very computationally expensive. Using numerical simulation for penetration study has just begun. There are still many problems required to solve, such as the obtainment of parameters in material constitutive models and load boundary conditions, the effect rules of some key parameters in penetration and so on.In this paper, we systematically studied the key parameters in penetration problems and tried to develop some effective methods for obtaining key parameters and the effect rules of them in penetration process. In the aspect of obtaining key parameters, two kinds of inverse technology are constructed. In these two inverse technologies, material dynamic properties and penetration load parameters are inversely obtained based on dynamic responses and structure-selection technique, respectively. This part of work forms the basis of the whole paper. In the aspect of effect rules of key parameters, numerical models of high accuracy and efficiency are established by using some key parameters inversely obtained, and effect rules of material properties and uncertain projectile-target meeting conditions are analyzed. The main work of the paper is given as follows:(1) Inverse technologies based on dynamic responses are proposed to overcome the difficulties in obtaining parameters of dynamic material properties. Two inverse technologies using different loading conditions are presented for identifying parameters of ceramic material, which are difficult to get by traditional methods. The methods provide a new approach to determine material parameters which are difficult for conventional experiments. With the one-dimensional stress model of SHPB, an inverse technology using reflecting and transmission wave is presented to identify the parameters in constitutive model of ceramic. This technology eliminates stress concentration since dumbbell-shaped specimens are used. It also avoids the problem of the dissatisfaction of1D stress wave theory induced by the variational sections of dumbbell-shaped specimen and the problem of the coupling of stress wave effect and strain rate effect. The technology can determine the constitutive model parameters of brittle materials rapidly by using a few experimental data. With the one-dimensional strain model of plate impact, an inverse technology using velocity histories at the sample-window interface in plate impact experiments is presented to identify the damage parameters. In this technology, the mapping between the transient velocity profile at the sample-window interface and material parameters are firstly established based on the simulation of the stress propagation in flyer, sample and window materials, and the damage parameters are then identified by using the velocity profile responses. The technology provides an alternative approach to quickly determine parameters of constitutive model under high strain rate.(2) An inverse technology based on the structure-selection technique is proposed to identify penetration force. In this technology, numerical simulation model is firstly established and validated by experimental data of penetration depth. Pressure data on the projectile nose are then sampled from numerical simulation results of a high-velocity projectile penetrating into a semi-infinite target. Then, using structure-selection technique, the penetration force function is inversely obtained, and crucial factors affecting characteristics of the penetration force are identified. The obtained penetration force function is very simple in form. Based on the penetration force function, a penetration depth formula, which can predict penetration depths and decelerations of the projectile accurately, is deduced. Finally, three series of experiments and models are used to validate the presented inverse technology, which shows it can determine penetration force function conveniently and accurately.(3) Using the penetration force function to replace the contact forces between the projectile and target, a rapid computational method for penetration simulation is presented. In the method, the penetration force function is embedded in the finite element model of the projectile as loading conditions. This avoids the meshing of the target and complicated contact calculation, so the computation model simplifies significantly and computational memories and time are reduced. The method can predict penetration depths and decelerations of the projectile quickly. Also, it can include the effects of the yield strength of the projectile and predict the critical impact velocity resulting in plastic deformations of the projectile. The results by the presented method show good agreement with experimental results.(4) The effects of material parameters of ceramic and projectile as well as conllision conditions on penetration characteristics of ceramic/metal composite armor are studied through a series of numerical simulation. The importance of effects of material parameters of ceramic on penetration depths is analyzed. It is found the damaged material strength shows very important effect, while the bulking factor and damage parameter are negligible. The mechanism for effects of projectile strength on the penetration of composite armor is also analyzed. On the one hand, the projectile strength helps to maintain the projectile shape and kinetic energy. On the other hand, it may result in the upset of the projectile nose and increase of penetration resistance. Additionally, we obtained the mechanism of action of the impact velocity and the angle of obliquity to the fore deflection plate, the energy dissipation mechanism of the penetration with attack angle and the variation rules of the acceleration magnitude, the change of velocity direction and the global bending in the penetration process.(5) With the rapid computational method which uses the penetration force function to replace the contact forces between the projectile and target, the depth ranges of five constant-depth control technologies under uncertain collision conditions are analyzed, and the accuracy order of them is given. The main factors affecting the control accuracy are also analyzed. The feasible intervals of penetration with uncertain attack angles for the five control technologies are obtained. It is found the constant-vertical-displacement method and the constant-axial-displacement method show very high accuracies. Among the five control technologies, the constant-axial-displacement method is preferable since it is simple in implementation and accurate.