Towards a novel solid constitutive model for simulating gelatin impacts as a bird strike surrogate

An original constitutive model is proposed for ballistic gelatin, considered as a bird surrogate, to simulate bird strike on structures. The proposed stress–strain relation is an isotropic hyperelastic model with a Mooney–Rivlin strain energy function and an uncoupled volumetric/deviatoric response. Gelatin quasi-incompressibility is treated with a multiplicative decomposition of the deformation gradient. This solid model aims at removing the assumptions and limitations of the commonly used hydrodynamic model, which assumes a fluid-like behaviour, exhibiting little to no shear resistance. Hence, it expands the possibilities of modelling complex impacts and offers a more accurate representation of gelatin’s behaviour. This proposed material model is implemented in LS-DYNA^® R11 as a user-material subroutine. An influence study is conducted on the material constants and on the parameters of the numerical method used: the smoothed-particle hydrodynamics. The goal is to highlight their effects on the responses, stability, robustness, etc. Correlation with real tests are performed, and the results are compared with the previous fluid material model. This proposed solid constitutive model presents interesting results and offers a more physical response of the gelatin compared to the hydrodynamic one. Indeed, this material model adds more cohesion, and to some extent reversible deformation, which may enable a better representation of complex impact simulations, although a proper calibration and identification of its parameters are still required.