Endurance Test and Dynamic Three-Dimensional DIC Analysis of Outer Case of Electric Vehicle Motors

Importance of the Topic

With the growing adoption of electric vehicles (EVs), lightweight aluminum die-cast components have become critical to reduce vehicle mass while maintaining structural durability. Accurate assessment of dynamic deformation and fatigue behavior under realistic loading conditions is essential to ensure reliability of motor housings and other EV parts. Dynamic three-dimensional digital image correlation (3D DIC) combined with endurance testing offers a non-contact, full-field measurement approach to capture strain distributions and displacement in situ.

Objectives and Study Overview

This study demonstrates the integration of a fatigue testing machine with 3D DIC to evaluate the endurance performance and real-time strain mapping of an EV motor outer case. The goals were to:

• Conduct a cyclic fatigue test under controlled force loading.
• Simultaneously record test force, machine stroke, and full-field deformation.
• Validate DIC measurements against traditional strain gauges.
• Visualize principal strain directions and bending effects on the protrusion.

Methodology and Instrumentation

A Shimadzu Servopulser EHF-UV020KNA-040 fatigue testing system with a 10 kN load cell and dedicated grips applied a 0–1000 N Haversine sine waveform at 0.5 Hz to the specimen protrusion.

• DIC system: VIC-3D software with two BASLER boA5328-100cc cameras (5328×4608 pixels) and synchronized image acquisition at 5 fps.
• Specimen preparation: Speckle pattern spray on the loaded surface; strain gauges attached to the specimen’s backside for reference measurements.
• Data synchronization: Test force, machine stroke, and DIC outputs recorded concurrently to ensure phase-aligned analysis.

Main Results and Discussion

Full-field DIC analysis revealed that under maximum load, the protrusion tip experienced tensile strain at its lower portion and compressive strain at its upper portion, evidencing a bending moment. Displacement maps and strain time histories aligned closely with the machine stroke and force signals without observable phase lag. Comparison at a common location showed near-identical strain readings between DIC and strain gauge data. Principal strain mapping with vector overlays further illustrated counterclockwise rotation of the principal strain direction due to cantilever bending.

Benefits and Practical Applications

• Non-contact, full-field measurement enables strain evaluation at any point without multiple gauges.
• Synchronized DIC and machine data provide comprehensive insight into dynamic deformation during endurance testing.
• Color-coded mapping facilitates rapid identification of critical stress regions for design optimization.

Future Trends and Potential Applications

Advancements may include higher-speed DIC acquisition for transient loading, integration with in-situ temperature and optical sensors, and expansion to other EV components such as battery enclosures and suspension parts. Coupling DIC data with digital twins and predictive fatigue models will further accelerate component design and reduce development cycles.

Conclusion

The combination of a high-capacity fatigue testing machine and 3D DIC provides a robust method for dynamic endurance evaluation of EV motor housings. This approach yields accurate, phase-synchronized displacement and strain data over complex geometries, offering valuable insights for material selection, design improvement, and durability validation in electric vehicle development.