Fatigue Failure of a Carbon-TPU Running Outsole Under Real-World Running Conditions: A Self-Experiment with Kinematic Logs, Video Evidence, and Thickness Dependency

This study reports a self-experiment investigating the fatigue failure behavior of a thick carbon-infused TPU (thermoplastic polyurethane) running outsole under real-world running conditions. A custom outsole with a thickness of approximately 10 mm was fabricated and tested during a 2 km outdoor run at a moderate pace (~5:00 min/km), followed by post-run walking. Kinematic data were recorded using a wearable GPS watch, and video documentation was captured during use. Notably, no visible fracture occurred during the running phase itself; instead, catastrophic fracture became apparent during subsequent walking. This observation indicates a fatigue-driven failure process rather than instantaneous overload. The results suggest that thick carbon-TPU structures are vulnerable to cumulative fatigue damage under cyclic loading, with failure potentially manifesting during low-intensity post-exercise activities. These findings highlight a critical design risk in thick TPU-based footwear components that may not be evident through short-duration or static testing alone.