Investigating the nano-scale creep behavior of BOPA6 films via nanoindentation

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In this study, the nano-scale creep behavior of biaxially oriented polyamide 6 (BOPA6) films was investigated via instrumented nanoindentation. A modified empirical equation was proposed to characterize the evolution of strain rate during the loading stage, showing excellent agreement with the experimental data (R 2 > 0.99). It was observed that an elevated loading rate resulted in higher strain rates and smoother strain-displacement curves, indicating a transition from thermally activated localized deformation to stress-driven cooperative mechanisms, as described by the Eyring activation model. In the holding stage, a power-law equation was used to analyze the creep behavior and determine the creep stress exponent n. It can be found that the value of n increased significantly with the elevated maximum holding load, suggesting enhanced stress sensitivity and the activation of viscoplastic mechanisms. These time-dependent deformation mechanisms were further interpreted within the framework of the Eyring activation model, which clarified the transition from local thermally activated molecular rearrangement to stress-driven cooperative deformation. Overall, these results deepen the understanding of nano-scale creep behavior in semi-crystalline polymers and offer theoretical guidance for enhancing the mechanical properties of BOPA6 films in advanced packaging and flexible electronics.

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