Monitoring the damage evolution of flexural fatigue in unidirectional carbon/carbon composites by electrical resistance change method

• ERC methods were introduced into C/C composites to detect fatigue damages.
• Electrical resistance change can reflect different types of fatigue damages.
• The role of initial conductivity is similar to the stress level for fatigue tests.
• Electrical properties can be used to evaluate the degree of fatigue damage.

This paper reported simultaneous monitoring damage evolution of flexural fatigue in unidirectional carbon-fiber-reinforced carbon composites (C/C composites) by electrical resistance change (ERC) methods. The degree of irregularity in electrical resistance changes increased with stress levels increasing. The shapes of electrical resistance change rate–fatigue cycle curves can reflect stress levels and damage types of tested samples: sawtooth shapes reflected delamination at a higher stress level; and “peak” shapes reflected inner damages in one fiber bundle at the fatigue limit stress level. In addition, the similarity of initial electrical resistance–fatigue life curve and S–N curve was observed clearly. In summary, ERC methods can monitor the damage evolution and qualitatively estimate the fatigue life of unidirectional C/C composites.