Unraveling slow crack growth mode transition in high-density polyethylene pipe

초록

The slow crack growth (SCG) behavior of high-density polyethylene (HDPE) is influenced by the testing temperature and the stress intensity factor KI. At low KI values, cracks grow continuously, whereas discontinuous SCG is observed at moderate KI. Due to the small crack initiation sites in actual HDPE pipes, a mode transition from continuous to discontinuous SCG often occurs within a single SCG process. However, this phenomenon is difficult to explain using existing crack growth models, posing challenges for accurate long-term lifetime estimation in HDPE pipe design. Here, we introduce the first crack layer-based framework that captures the full mode transition by coupling classical crack layer theory with a thermal-activation scheme. This model integrates an auxiliary component into the original crack layer theory, enabling it to reproduce both the continuous-to-discontinuous SCG transition under low loads and the discontinuous SCG behavior at moderate loads. The proposed model successfully reproduces experimental results, providing a more comprehensive understanding of SCG behavior in HDPE. By addressing the limitations of existing models, this study establishes a fundamental framework for improving the accuracy of lifetime predictions in HDPE pipe design and advancing the understanding of crack growth mechanisms.

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