Fatigue performance is typically evaluated using S-N curves, which represent the relationship between stress amplitude and the number of cycles to failure. Compared with metals, polymer S-N curves are often steeper, meaning a small increase in stress may drastically shorten service life. Therefore, designs relying solely on static strength rarely reflect long-term reliability.
Successful engineering practices often evaluate three parameters simultaneously: static strength, fatigue limit, and creep behavior. For example, some robotic transmission systems use higher fiber-content materials such as PA66 GF50, combined with structural optimization to reduce stress concentration. In addition, fatigue testing exceeding 10⁷ cycles is often performed during development to validate durability.
Experience suggests that in continuous transmission applications, strength parameters alone are insufficient for reliable material selection. Fatigue testing data should be introduced during the early material selection stage, and lifetime evaluation should reflect actual operating conditions. For modified nylon materials, factors such as fiber content, interface compatibility, processing orientation, and environmental humidity can significantly influence fatigue performance.
Ultimately, reliable engineering decisions require understanding how materials behave under long-term cyclic stress rather than relying solely on static strength values.
