Endurance Testing of Bus Bar for Electric Vehicles

Importance of the Topic

Fatigue testing of bus bars is crucial for ensuring the long-term reliability of power distribution components in electric vehicles. Bus bars carry high currents and are subject to mechanical stresses from vibrations and thermal cycling. Assessing their endurance under cyclic loads helps prevent premature failures and enhances safety and performance in EV applications.

Objectives and Study Overview

This study aimed to evaluate the fatigue strength of a small bus bar intended for electric motorcycles under two load directions: in-plane and out-of-plane relative to the conductor cross-section. Using bent copper specimens plated with nickel and coated for insulation, endurance tests simulated realistic loads based on inverter weight.

Methodology and Instrumentation

• Specimens: Tough-pitch copper bus bars (9 mm × 2 mm), nickel-plated and nylon-coated.
• Test Equipment: EMT-1kNV-50 electromagnetic dynamic and fatigue tester.
• Fixture: Custom jigs with a trunnion mechanism for in-plane (Z-axis) and out-of-plane (Y-axis) load application.
• Loading Conditions:
  • In-plane tests: Sine wave force control, amplitudes of 10 N and 30 N, frequency sweep from 10 Hz to 20 Hz after 1×10^6 cycles.
  • Out-of-plane tests: Sine wave force control, amplitudes of 30 N and 60 N, frequency sweep from 20 Hz to 50 Hz after 1×10^6 cycles.

Main Results and Discussion

• Stable control and well-formed sine waves were maintained throughout both in-plane and out-of-plane tests up to 50 Hz.
• In-plane fatigue at 30 N reached failure after approximately 1.4×10^6 cycles, whereas out-of-plane at 30 N did not fail even after 10^7 cycles.
• Out-of-plane at 60 N resulted in failure at about 1.7×10^6 cycles, demonstrating roughly double the fatigue strength compared to the in-plane direction.
• Force–displacement curves and displacement peak evolution indicated uniform crack growth in the out-of-plane loading, while in-plane cracks propagated predominantly in one direction.
• Fracture surface analysis revealed characteristic beach marks aligned with loading directions: planar propagation for in-plane and bidirectional twisting for out-of-plane.

Benefits and Practical Applications

• Provides a reliable method for assessing directional fatigue strength of bus bars under realistic load conditions.
• Enables rapid high-frequency testing, reducing total test time for qualification.
• Supports the development and quality control of EV power distribution components by identifying optimal designs and materials.
• Fractography insights aid in understanding failure modes and improving bus bar resilience.

Future Trends and Possibilities

• Integration of temperature-controlled environments to simulate Joule heating effects during operation.
• Scaling up testing capacity for full-size bus bars used in larger EV platforms.
• Combining with advanced sensors and real-time monitoring for in situ crack detection.
• Application of new materials (e.g., aluminum or composites) and novel coatings to enhance fatigue life.

Conclusion

Fatigue durability tests using the EMT-1kNV-50 machine demonstrated clear directional dependence of bus bar strength, with out-of-plane loading showing superior endurance. The approach offers a practical framework for evaluating and improving EV bus bar performance, contributing to safer and more reliable power systems.

References

No external literature references were provided in the original text.