Numerical modelling of plasma current density & pressure impact on composite damage during lightning strike testing

Research output: Contribution to conferenceAbstractpeer-review

Abstract

Experimental testing of lightning strikes on materials is very expensive hence the drive to move towards simulations to quantify and understand the damage behaviour of aircraft composites. Experiments have shown that lightning strikes can cause significant damage to the composite including surface erosion, fibre breakage and ply-lift. Lightning strike simulations have focussed on modelling various individual features of lightning strikes on composite materials. 
Simulations have considered the external plasma conditions and the composite material internal damage mechanisms caused by direct application of current or pressure loads. State-of-the-art approaches have typically focussed on thermal loading scenarios to-date. These methods have applied the relevant current waveform profile, directly to the surface of the composite. Ogasawara et al. presented the first coupled thermal-electric simulation in literature to follow the experimental work of Hirano et al. In this simulation the current was applied to a single node on the top surface of the composite but this resulted in extremely high temperature predictions. No temperature-dependent material properties were considered in this analysis. Abdelal and Murphy developed this approach by including those properties along with expanding the loading area to a 5mm arc radius, surface load. However, this simulation underestimated the damage produced and generated a highly unstructured mesh. 
Pressure loading simulations have used different lightning shock wave equations to predict the pressure applied to the composite surface within the arc radius and radially outwards from the edge of the arc. Different authors have proposed broadly similar equations but with differing division factors. Lightning has been idealised into four waveforms which have been standardised for testing purposes. These current waveforms are referred to as A, B, C and D-waveforms.

A numerical thermal plasma model for waveform B was developed previously in COMSOL Multiphysics and was built using the finite element method, magnetohydrodynamics (MHD) and similitude theory. This approach used Navier-Stokes equations for fluid motion, Maxwell equations of electromagnetism and thermal conduction equations for heat transfer. This model can predict the pressure, current and thermal loads generated on the top surface of the composite. To-date, work has focussed on linking the plasma model with an FE solid mechanics model in ABAQUS, with subroutines, scripts and scale factors to transfer the key outputs at the top surface, from one simulation to the next. The sensitivity of damage predictions to the coupling strategy and order has been considered for two of the three primary outputs.

The present work will link the third primary output, current density, and analyse its effects on the composite structure. This provides an opportunity to compare this method with the current state-of-the-art mode of applying a current load. This new approach produces loading over a wider profile to accommodate expansion of the arc and expansion of the resulting current and pressure profiles. It also enables the comparison of damage generated by Waveforms A and B which have significantly different current loads and time periods. In addition the pressure predicted by the plasma simulation will be applied with this new approach in a different manner to that of the previous publication.

The output data from COMSOL varies radially and with time. Typically this type of loading can only be applied by subroutines. However, a novel python script is demonstrated to analyse the output data from COMSOL and segment the surface of the composite in ABAQUS in such a way that the applied loads best matched the output data and could be applied as non-uniform, time varying loads. The specimen measured 150x100 mm and contained 32x0.147mm plies with a ply layup of [45o/0o/-45o/90o]4s using IM600/133 material properties. Boundary conditions were applied to replicate the experimental setup of Hirano et al. within the simulations and allow the comparison of damage prediction with experimental measured results.

The results of this work will, for the first time in literature, present a thermal-electrical model applying the outputs of a thermal plasma model to assess damage due to waveform B along with a typical thermal-electric simulation for the same waveform. The developed loading strategy presents a novel method to link the currently discrete phases of a lightning strike test and will enable future examination of the influence of varying lightning strike conditions and resulting composite specimen damage.

Original languageEnglish
Publication statusPublished - 25 Apr 2018
Event3rd Composites@Manchester Research Workshop - Sackville Street Building, Manchester, United Kingdom
Duration: 14 Jun 201815 Jun 2018

Workshop

Workshop3rd Composites@Manchester Research Workshop
CountryUnited Kingdom
CityManchester
Period14/06/201815/06/2018

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