Prediction of the ballistic limit of an aluminium sandwich panel

This paper presents research on modelling the impact of a 150g projectile on a 35mm thick aluminium sandwich panel. The objective of the work is a predictive modelling capability for the ballistic limit of the panel. A predictive modelling capability supports the design of capture and deorbit missions for large items of space debris such as satellites and rocket upper stages. A detailed explicit finite element model was built using the LSDYNA software and results were compared with experimental data for the projectile exit velocity to establish key parameters. The primary parameters influencing the model behaviour were the strength and failure of the aluminium face sheets and the friction between projectile and panel. The model results showed good agreement with experimental results for ogive nose projectiles, but overestimated the exit velocity for flat nose projectiles.This work was funded by the European Space Agency under a contract with Airbus Defence and Space

Numerical modelling of the effect of using multi-explosives on the explosive forming of steel cones

Modelling and analysis of underwater explosive forming process by using FEM and SPH formulation is presented in this work. The explosive forming of a steel cone is studied. The model setup includes a low carbon steel plate, plate holder, forming die as well as water and C4 explosive. The effect of multiple explosives on rate of targets deformation has been studied. Four different multi-explosives models have been developed and compared to the single explosive model. The formability of the steel plate based on forming limit failure criteria has been investigated. Aspects such as shape of plates deformation and thickness of the plate during the forming process have been examined. The model results indicate that a multi-explosives model does not always guarantee a faster rate of target deformation without central explosive. On the other hand the model results indicate that the multi-explosives setup is capable of preventing crack failure of the steel plate during the forming process which would occur if a single explosive model was used

Transform-domain analysis of packet delay in network nodes with QoS-aware scheduling

In order to differentiate the perceived QoS between traffic classes in heterogeneous packet networks, equipment discriminates incoming packets based on their class, particularly in the way queued packets are scheduled for further transmission. We review a common stochastic modelling framework in which scheduling mechanisms can be evaluated, especially with regard to the resulting per-class delay distribution. For this, a discrete-time single-server queue is considered with two classes of packet arrivals, either delay-sensitive (1) or delay-tolerant (2). The steady-state analysis relies on the use of well-chosen supplementary variables and is mainly done in the transform domain. Secondly, we propose and analyse a new type of scheduling mechanism that allows precise control over the amount of delay differentiation between the classes. The idea is to introduce N reserved places in the queue, intended for future arrivals of class 1

A study of the effect of projectile orientation on the results of ballistic impact tests as described in the EASA CS-25 regulations for fuel tank access covers

This paper presents the results of an investigation of the ballistic limits and failure modes of AA2024-T351 sheets impacted with cubical projectiles. The experiment/test setup was based on EASA CS-25 regulations for fuel tank access covers. The effect of cube orientation on the ballistic limit and failure modes was considered in detail. A 25% variation in ballistic limit was observed with the lowest ballistic limit (202 m/s) observed for the cubical projectile edge impacted on the target. In the cube face impacts, the ballistic limit was higher (223 m/s), and the highest ballistic limit (254 m/s) was observed for the corner impact. The observed differences in the ballistic limit were due to differences in failure mechanism, which resulted in different localised deformations near the projectile impact point, but also led to differences in global dishing deformation

Modelling of Strain Softening Materials Based on Equivalent Damage Force

The main aim of the work presented in this paper was addressing localisation problem observed in the analysis of strain softening materials using finite element methods (FEM) combined with local continuum damage mechanics (CDM) approach. Strain softening is typically observed in damaged quasi brittle materials such as fibre reinforced composites and application of the CDM approach with the classic FEM features a number of anomalies, including mathematical (change of the type of partial differential equations leading to ill-posed boundary value problem), numerical (pronounced mesh dependency) and physical (infinitely small softening zone with the zero dissipated energy). These features of the classic FEM solutions have been already demonstrated in (Vignjevic, Djordjevic et al. 2014). The model proposed here is still based on the local CDM approach, but introduces an alternative definition of damage effects in the system of equilibrium equations. The constitutive equation in the model is defined in terms of effective stress, whilst the damage effects in the conservation of momentum equation are calculated as equivalent damage force (EDF), which contributes to the equilibrium on the right hand side of the momentum equation. The main advantages of this model are that the problem remains well posed, as the type of partial differential equations remains unchanged when the material enters softening, numerical stability, which is preserved without a need for regularisation measures, and significantly reduced mesh dependency. In addition, the EDF model can be combined with existing local CDM damage evolution functions and does not violate symmetry of the stiffness tensor. The EDF model was implemented in in-house developed coupled FEM - MCM code, where explicit FEM (Liu 2004) is coupled with a stable TotalLagrange form of SPH (Vignjevic, Reveles et al. 2006, Vignjevic, Campbell et al. 2009). Its performance is demonstrated in the analysis of a dynamic one dimensional stress wave propagation problem, which was analytically solved in (Bazant, Belytschko 1985). For a range of loading rates that correspond to the material softening regime, the numerical results shown nonlocal character with a finite size of the damaged zone, controlled with the damage characteristic length, which can be experimentally determined and is an input parameter independent of the discretisation density.European Commissio

Friction Modelling in Particle-to-Particle Contact

Previous work developed a particle-to-particle contact algorithm to treat frictionless sliding between two bodies discretised by SPH particles without the requirement to construct surfaces or approximate a surface normal. This algorithm was then extended to contact between finite element and SPH domains and has subsequently been extensively applied to a range of problems. This paper extends the particle-to-particle contact algorithm to include a friction model to broaden the applicability of the contact algorithm. A simple friction model based on a Coulomb formulation has implemented. This generates a lateral contact force between individual particle pairs, with the friction force vector being orthogonal to the local contact force vector. 2D and 3D sensitivity studies show that the friction model works effectively with the overall contact algorithm.Part-funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 636549