Abstract

In this work, the oblique impact response of sandwich structures, with carbon/epoxy face-sheets and aluminium honeycomb core, is analysed by implementing a 3D numerical model in Abaqus/Explicit finite element code. The numerical model was validated with data taken from the scientific literature for a normal impact, and numerical results showed good correlation with experimental data. The validated model was used to study the variation of the ballistic limit and the residual velocity with the impact angle of the projectile.  In order to determine the contribution of the core in the impact process, another finite element model was developed, corresponding to that of a laminated spaced plates a distance equivalent to the thickness of the composite sandwich core. It was found that both ballistic limit values ​​and residual velocity are affected by the presence of the core in the sandwich plates and by the obliquity of the impact angle.

Abstract

High-velocity impact is one of the most common load states to which composite material structures can be subjected during their service life and can cause a sudden loss of properties favouring its catastrophic failure. Impact loads are usually caused by external elements such as debris, particles carried by the wind, hail, fragments derived from an explosion, etc. All these cases can be represented as high-velocity impacts; however, in general, these impacts are not usually reduced to the action of a single projectile on the structure but can be represented as multiple projectiles that impact simultaneously, or sequentially, on it. This is known as multiple impact phenomenon. In this work a numerical model is developed, using a commercial finite-element software, that allows to analyse the phenomenon of multiple impact in composite material laminates, focusing attention on the wave’s interaction between projectiles. The model is validated with experimental results from the scientific literature for a single high-velocity impact. The interaction among waves generated by the action of two projectiles impacting at the same velocity, and that are separated at a certain distance from each other (simultaneous high-velocity multiple impact), is studied in terms of out-of-plane displacement, and relative movement between projectiles.

Abstract

New energy-based theoretical models that predict the ballistic behaviour of thin and thick woven composite laminates are presented. These models are formulated for high-velocity impacts, where the boundary conditions do not play a relevant role. This can be assumed as the local structural behaviour is responsible for the ballistic performance. A non-dimensional formulation is used to analyse the influence of material properties and geometrical parameters in the ballistic response of the laminate. The models are physically-based on the energy contribution of different energy-absorption mechanisms. Moreover, a 3D finite element model is also developed by means of  a continuum damage mechanics model that takes into account the different failure mechanisms described in the theoretical models to simulate the performance of the laminate under high-velocity impacts and to validate the hypotheses of the theoretical models.  A comparison between FE and theoretical models is performed by means of energy absorption mechanisms. The predictive capability of the proposed models is verified against experimental results, which were originally conducted in this work. The results obtained show the dependencies between the ballistic response and the non-dimensional physical parameters of the model. Furthermore, the proposed models can be used to see the relative importance of the different energy-absorption mechanisms involved and the comparison of these mechanisms between the theoretical and the FE models can reflect the different roles played by them, depending on the material properties and geometrical characteristics of the laminate. These results highlight the relevance of the in-plane and out-of-plane energy-absorption mechanisms, which rule the penetration process depending on the plate thickness.