A Lightning Plasma and Composite Specimen Damage Simulation Framework for SAE Test Waveform B

This paper presents an overview of the research which has been conducted to simulate and understand the direct effects resulting from SAE test Waveform B. The research focuses on an unprotected composite specimen, with aerospace materials, and attempts to demonstrate how simulation can quantitatively link artificial lightning test waveform parameters to test specimen loading from the lightning plasma, through to the resulting specimen material damage. A variety of simulation techniques have been investigated to characterize the lightning plasma and the specimen damage and a framework for simulation is proposed. A 2D-axisymmetric finite element plasma simulation was used in which the waveform properties and specimen materials were modified to establish their impact on the plasma formed between the discharge probe and the specimen surface. Within the specimen a two-step finite element modelling process was assembled; to represent the coupled thermal-electric behavior and to predict the temperature profile as a result of current resistive heating; to represent the coupled temperature, displacement and damage behavior resulting from the strike pressure loading and the thermal expansion due to the resistive heating. Finally a novel material representation has been developed which modifies the local specimen material properties such as moduli, strength and stiffness parameters to reflect the effects of combined strain and thermal loading and also includes both failure initiation and softening. The results demonstrated the sensitivity of plasma properties to the artificial waveform parameters (maximum current, rise times etc.) and the specimen properties (electrical and thermal conductivity). The sensitivity of the specimen damage, including the mechanisms (thermal versus mechanical) and the damage profile (damage depth and surface area) were also calculated. The presented results, for Waveform B, illustrated the volume of thermal damage over mechanical damage due to the long exposure to the current load and the opportunity for greater resistive heating, and the lower peak current and rise time, when compared with other artificial lightning test waveforms.