High-Speed Imaging of Arc Behavior in Lightning Strike Tests

Significance of the topic

Lightning strikes produce extremely rapid thermal and mechanical loads that can cause localized damage to aircraft structures and composite materials. Accurate, time-resolved observation of arc initiation, propagation, and plasma formation is essential for understanding damage mechanisms, validating simulation models, and developing mitigation strategies used in aircraft design, maintenance, and certification.

Objectives and overview of the study

This study aimed to visualize the ultrafast sequence of events during a laboratory arc-entry lightning test using a high-speed video camera. The focus was to capture the onset of discharge between a fine aluminum wire and an aluminum plate, follow the propagation of the simulated lightning current along the wire, and determine the timescale for wire vaporization and plasma formation.

Methodology

Imaging was performed using optical self-emission from the discharge. The tests employed a simulated lightning-current delivery method in which a Φ 0.2 mm aluminum wire was attached to the tip of an electrode via an insulating sphere and allowed to hang along the sphere surface toward an aluminum target plate. Recording used a HyperVision HPV-X3 high-speed camera at 20 million frames per second (20 Mfps), providing the temporal resolution necessary to resolve microsecond-scale events. Sequential frames were analyzed to extract the timing of discharge onset, brightening along the wire, and expansion of the luminous region consistent with plasma formation.

Instrumentation used

• HyperVision HPV-X3 high-speed video camera (recording at up to 20 Mfps)
• Electrode assembly with insulating sphere and Φ 0.2 mm aluminum wire
• Aluminum target plate as the specimen
• Optical imaging relying on self-emission (no external illumination)

Main results and discussion

High-speed imaging resolved the following sequence: an initial faint discharge appeared between the wire tip and the plate; within approximately 0.4 microseconds the wire itself exhibited visible emission; emission intensity increased over subsequent frames and then expanded rapidly in a plume-like manner over the next microseconds. Post-test inspection indicated the aluminum wire had been consumed, consistent with rapid vaporization to plasma. The measured ~0.4 µs interval from discharge onset to visible plasma on the wire underscores the ultrafast nature of lightning-related arc processes and highlights the need for multi-Mfps temporal resolution to capture key phenomena. The HPV-X3’s increased spatial resolution (threefold improvement over the previous model) combined with 20 Mfps temporal capability enabled clearer visualization of current propagation along the fine wire and the short-timescale transition to plasma.

Benefits and practical applications of the method

High-speed optical recording of arc-entry tests provides direct, time-resolved evidence of where and when energy is deposited during simulated strikes. Practical applications include:

• Improving understanding of lightning damage initiation and progression in metallic and composite aircraft structures
• Validating and tuning computational models of arc attachment, heating, and material response
• Supporting design and testing of lightning protection systems and material layups
• Providing diagnostic data for failure analysis, QA/QC in materials testing, and standards development

Future trends and potential applications

Further advances will combine ultra-high-speed imaging with complementary diagnostics and data analytics to deepen process understanding and enable predictive capability. Expected developments include:

• Integration with time-synchronized electrical measurements (current and voltage probes) to correlate optical events with electrical transients
• Time-resolved optical spectroscopy to identify species, temperatures, and ionization states during plasma formation
• Higher spatial resolution sensors and larger sensor arrays for improved localization of attachment points
• AI-driven image analysis for automated event detection, feature extraction, and statistical evaluation across many tests
• Three-dimensional and tomographic imaging approaches to reconstruct arc geometry and plume evolution

Conclusion

Using the HPV-X3 at 20 Mfps, the study successfully captured the rapid progression of a simulated lightning strike from faint discharge to plasma formation along a 0.2 mm aluminum wire. The observed ~0.4 µs timescale for plasma formation demonstrates the necessity of extreme temporal resolution for meaningful diagnostics. The technique offers direct, high-fidelity data valuable for materials testing, model validation, and design of lightning protection approaches in aerospace applications.

Reference

Kamiyama S., Okada T., Miyaki H., Hirano Y., Ogasawara T.: Effect of Inter-laminar Toughened Layer on Lightning Strike Damage to CF/epoxy Composites, Journal of the Japan Society for Composite Materials, 50(2), pp. 70–76, 2024.

Imaging cooperation: Aviation Technology Directorate, Japan Aerospace Exploration Agency