HVI-induced stress field and vibrations. Analysis by SPH-FEM coupled numerical method

Abstract

Hyper-Velocity Impacts (HVI) from micrometeoroids and orbital debris pose a significant threat to satellites in low Earth orbit due to the higher density of sources and the resulting increased impact frequency. Understanding the stress field and dynamic behavior around impact points is critical for satellite design, structural integrity, and platform stability assessment. A coupled Finite Element and Smoothed Particle Hydrodynamics (SPH) methodology implemented in LS- DYNA explicit software is used to simulate HVI effects. Without compromising the reliability of the results and ensuring their continuity at the methodological interface, the aim is to take advantage of the strengths of both simulation methods. Although previous studies have used SPH-FEM coupling to model Hyper-Velocity Impacts, the focus of this thesis is on characterizing the stress field surrounding the impact zone. It has been observed that a portion of the stress wave is reflected at the interface between the two numerical methods within the plate. This reflection is not caused by a physical obstacle and is therefore numerical and artificial. A comparative analysis of stress signals collected near this numerical modeling discontinuity demonstrated that the implementation of a SPH-FEM hybrid elements interface exhibited superior performance in mitigating this effect in comparison with a tied type contact. Indeed, stress waves can smoothly move from the impacted region towards the external domain of the structure, exhibiting only minor internal reflection at the interface between the two numerical methodologies. Furthermore, the impact of the SPH lattice on stress wave propagation was explored. It was found that the default modeling approach had a detrimental effect on uniform stress propagation in the plate, as it introduced preferential directions of propagation. This issue was addressed by implementing a custom SPH lattice that ensures the isotropic properties of the material selected for modeling the plate. The propagation of impact-induced effects is ensured to be independent of the direction of study. Initial calibration and validation were conducted on a single flat plate system, followed by an extension to a full Whipple shield simulation. With regard to the latter, not only stress data, but also the HVI-induced vibration field within the plates was studied. This was achieved by collecting the out-of-plane velocity signal at variable distances from the impact site. Nevertheless, further studies are necessary for further refinement and validation.