Ceramic materials possess a unique combination of structural material properties that make them attractive for use in ballistic impact protection systems. However, their unique characteristics also make their design and evaluation particularly challenging when compared to conventional materials. The high pressures and complex failure mechanisms observed in a typical ceramic impact event make the use of numerical analysis techniques such as the Finite Element Method important tools to further understand their behaviour.
One of the most commonly used continuum constitutive models for simulation of ceramics under dynamic loading is the Johnson-Holmquist II (JH-2) model, which aims to capture the full range of ceramic behaviour from pristine to fully comminuted. To fully populate the model for a given material, a combination of elastic and inelastic material properties are required, in addition to a set of at least six model specific parameters. Reliable material data can be difficult to find in the literature because, despite its strong influence over the structural properties of granular materials, typically no microstructural description is provided. Full characterization of the material is therefore required involving experiments under both static and dynamic conditions.
Here, an alternative is proposed, utilising a hierarchical multiscale modelling approach. A microstructural FEM model of the material is used to simulate different load cases on the material, providing the necessary continuum material parameters for populating the JH-2 directly. Inputs to the microstructural model include the single-crystal material properties and grain-size distribution, allowing for continuum properties of a specific sample of Alumina to be extracted as a result of the upscaling process. The details of the multiscale modelling process will be discussed and the veracity of the achieved parameters assessed.