Quantifying the Influence of Lightning Strike Pressure Loading on Composite Specimen Damage

Abstract

Experimental work has shown that a component of lightning strike damage is caused by a mechanical loading. As the profile of the pressure loading is unknown a number of authors propose different pressure loads, varying in form, application area and magnitude. The objective of this paper is to investigate the potential contribution of pressure loading to composite specimen damage. This is achieved through a simulation study using an established modelling approach for composite damage prediction. The study examines the proposed shockwave loads from the literature. The simulation results are compared with measured test specimen damage examining the form and scale of damage. The results for the first time quantify the significance of pressure loading, demonstrating that although a pressure load can cause damage consistent with that measured experimentally, it has a negligible contribution to the overall scale of damage. Moreover the requirements for a pressure to create the damage behaviours typically witnessed in testing requires that the pressure load be within a very precise window of magnitude and loading area.

Coupled Thermal-Mechanical Progressive Damage Model with Strain and Heating Rate Effects for Lightning Strike Damage Assessment

“…[1,[3][4][5][6][7]. Research is on-going to model the plasma developed during a strike using Finite element or CFD simulations and the resulting loading to the specimen [8,9,[18][19][20][21][10][11][12][13][14][15][16][17]. The majority of simulation authors have modelled specimen behaviour only and assumed a surface load, employing FE models to characterise the thermal damage [8,10,11,14,16,20] or damage as a result of pressure loading [11][12][13].…”

Modelling of mechanical failure due to constrained thermal expansion at the lightning arc attachment point in carbon fibre epoxy composite material

“…From measurements taken on test aircraft flown purposely into active lightning storms [1][2][3] standardised lightning intensity and current waveforms have been established for laboratory certification testing [4][5]. Examination of composite specimens under these standardised test conditions suggests that mechanical loading contributes to some aspects of lightning strike damage [6][7][8]. Experimental results on composite specimens typically exhibit three damage modes; material ablation and decomposition, fractured fibres and cracked matrix material, and delamination of the laminate [8][9][10][11][12][13][14][15][16][17][18].…”

“…Numerical simulations have the potential to generate further understanding of the behaviour during experiments and reduce the volume of testing typically required for new design certification. To date numerical studies have mostly focused on modelling resistive heating from the electrical load [22][23][24] but other loading mechanics have also been studied (electromagnetic and acoustic pressure, internal explosive loads [6][7]18]) but with significantly less attention. Thus the objective of this paper is to investigate the potential contribution of the internal specimen mechanical forces due to thermal expansion.…”

“…This inconsistency is due to the variation in the individual specimen designs (materials, material stacking sequence, lightning protection system), differing intensity and current waveforms, and test setup (varying distance between the specimen and the discharge probe, varying specimen fixturing and boundary conditions). In general the damage can be divided into three zones [7,25]:…”

“…The mechanical analysis did not predict failure according to the Tsai-Wu failure criteria, however Munoz et al [18] concluded that 'although the elements did not fail, some matrix cracking might occur through the thickness of the laminate'. Foster et al [7] models the range of pressure loads described in the literature, including [8,9,14,26], and compares the explicit Finite Element (FE) simulation predictions with measured test specimen damage. The results demonstrate that the proposed pressure loads have a negligible contribution to the overall scale of experimental damage.…”