E.C. Simons | TU Delft Repository

Ceramic material under ballistic loading

A numerical approach to sphere impact on ceramic armour material

Doctoral thesis (2020) - Erik Simons, Lambertus J. Sluys, Jaap Weerheijm

Armour systems for ballistic protection can be made from many materials. One type of material used in armour systems is ceramic. Ceramic materials, such as alumina and silicon carbide, can be beneficial in an armour system because of their high hardness and relatively low weight. The high hardness of the ceramic potentially causes a projectile to deform heavily and fracture upon impact with the armour, thereby reducing or even eliminating the threat. The ceramic itself may also damage during the interaction. Although ceramics can damage under impact, they contribute to the protective capability of the armour system as long as they exert a force on the projectile to deformand deceleration it. In order to improve an armour system one does not only need to know when the ceramic component fails, but also how it fails. Once the failure mechanisms of the ceramic are known the armour design may be modified to delay or in an ideal scenario even prevent catastrophic failure of the ceramic. This will eventually result in stronger and lighter armour systems. ...

An experimental and numerical investigation of sphere impact on alumina ceramic

Journal article (2020) - E. C. Simons, J. Weerheijm, G. Toussaint, L. J. Sluys

In this study, the impact of a steel spherical projectile on an alumina ceramic is considered. New experimental and numerical results are presented and analysed. Numerical results are obtained using the Finite Element Method and the upgraded viscosity regularized Johnson-Holmquist-2 constitutive model to describe the ceramic material behaviour. First, a short investigation is done using 2d Finite Element simulations to establish a proper numerical framework. Second, the numerical framework is extended to 3d and experimental results are used to validate the framework and the ceramic material model. This shows that all relevant ceramic failure mechanisms are captured correctly and the framework and model can be used to simulate sphere impact on ceramic material. Third, the simulations are used to analyse the failure processes in the ceramic material in more detail. Here the focus lies in obtaining information which can currently not be retrieved from experiments. Timing and interaction of propagating conical and radial cracks are investigated and corroborate with the typical failure mechanisms observed in sphere impact on ceramic material. ...

Simulating brittle and ductile response of alumina ceramics under dynamic loading

Journal article (2019) - E. C. Simons, J. Weerheijm, L. J. Sluys

Alumina ceramic is often used in armour systems. This material is known to have a brittle response under tensile loading, while a ductile response is found when sufficiently high pressures are reached. During projectile impact a ceramic material experiences both tensile loading and high pressures, hence fails in both a brittle and ductile way. Properly capturing the ceramic failure in a single material model remains challenging. A viscosity regularized Johnson-Holmquist-2 model has been used to simulate dynamic loading on alumina ceramic. The simulations show that the brittle and ductile nature of the material can not be captured simultaneously in the current material model. A new failure strain formulation is proposed where the behaviour under tensile and compressive loading can be controlled independently. This allows to properly capture both the brittle and ductile response of the material in a single constitutive framework, with a single set of model parameters. ...

A viscosity regularized plasticity model for ceramics

Journal article (2018) - E. C. Simons, J. Weerheijm, L. J. Sluys

Plasticity models are frequently used to describe ceramic materials. Well established and often used ceramic models are those by Johnson and Holmquist. These are softening plasticity models for which mesh dependency is a well known problem. A viscosity or rate dependency can be added to the material model to provide regularization and solve the mesh dependency problems. For the Johnson-Holmquist models a viscosity is proposed to work on the hydrostatic tensile strength. A consistency visco-plastic formulation is used. For the Johnson-Holmquist-2 model it is demonstrated that the proposed viscosity indeed removes the mesh dependency problems. This is shown for both quasi-static and dynamic loading. In addition it is shown that the proposed viscosity can predict an experimentally measured rate dependent spall strength of alumina ceramic, while the original model fails to do so. ...

A fully implicit plasticity model for the characterization of ceramics in ballistic protection

Conference paper (2016) - Erik Simons, Jaap Weerheijm, Bert Sluijs

The Johnson-Holmquist-2 ceramic model is used for quasi-static indentation simulation. A modification is proposed to an associated plasticity formulation. This allows for a fully implicit solution scheme, where dilatation is used instead of the traditional explicit bulking formulation. Dilatation is shown to have an important influence on ring-crack formation during indentation. A mesh refinement study is performed to show the current tensile failure behaviour leads to mesh-dependent results. ...