Numerical and experimental investigation of the fracture behavior of shock loaded alumina

Abstract

Plate impact expeiments are conducted to investigate the dynamic behavior of alumina by using one stage light gas gun. A velocity interferometer system for reflectors (VISAR) is used to obtain Hugoniot elastic limit and the free surface velocity profile, which consists of an elastic wave followed immediately by a dispersive inelastic wave. The stress histories under different impact velocities are measured by in-material manganin gauges. Based on the experimental data a Hugoniot curve is fitted, which shows the compressive characteristics that alumina changes typically from elastic to "plastic", and under higher pressure it will be transferred to similar-fluid state. The turning point of the Hugoniot curve from a high pressure region to a low pressure region is about 11.4 GPa. The fracture process of alumina is simulated by way of finite element code. After the analysis of the fracture mechanism, the numerical results show an important role played by the nucleation and the growth of the cracks in the macroscopic fracture of the alumina target. The numerical predictions of stress histories are compared with the experimental results, which indicates consistency between them. plate impact experiment, hugoniot curve, fracture characteristics, numerical simulation Advanced ceramics are increasingly used in armor, bladed turbine engine and other structural components due to their mechanical properties, such as light weight, high compression strength, high Hugoniot elastic limit. Generally speaking, these materials are very strong in compression and weak in tension. They are also very brittle, but strong after fracture under compression. The materials both intact and fractured are pressure dependent where the strength increases as the confining pressure increases. Excellent ballistic performance against penetrator comes from its unique dynamic mechanical properties. Dynamic mechanical response, dynamic damage and fracture characteristic of ceramic composite armor are all important factors for analyzing ballistic performance against the penetrator.Short duration is characteristic of shock loadings while explosive loadings are devastating in action, which confines the experimental measurement and observation. In addition, the dynamic experimental process involves uncertainty and interferential factor. Therefore, it is difficult to investigate the mechanical behavior, particularly under shock loadings by using single experimental method. However, numerical simulation has the advantage of little interference from the surrounding environment and easy control of simulation conditions. By analyzing the numerical results under different conditions and the trend of changes in important parameters, the numerical simulations will guide the subsequent experiments and the choice of the key parameters. Moreover, numerical simulation explores the unobservable fracture process of the alumina target under high strain rate, and complements the experimental results. In recent years computational explosion mechanics as a new branch of expl...

A constitutive model based on the evolution and coalescence of elliptical micro-cracks for quasi-brittle materials

“…By substituting π 2     into eq. (34), the crack distribution condition for coalescence of wing cracks can be obtained: 1 2 2 w a  , w 2 could be arbitrary Figure 8 Geometric location of cracks in the specimen [25]. value, and the wing crack propagation length depends on the value of w 2 .…”

“…Many experimental studies have shown that micro-crack damage was the significant features of the fracture of brittle materials [1,2]. Currently, a lot of researches focus on the growth and interaction of micro-cracks.…”

Computational explosion mechanics and related progress

“…Ren et al [12] investigated the dynamic behavior of alumina by plate impact experiments and obtained Hugoniot elastic limit, the free surface velocity profile and stress histories. Based on the experimental data a Hugoniot curve was fitted, from which a high pressure state equation was derived.…”