Determining polyamide dynamic fracture resistance under plane strain conditions by High‐Speed Double Torsion tests

Abstract

Abstract Polyamide 12 (PA12) has emerged as a high‐performance alternative to high‐density polyethylene (HDPE) for gas pipeline applications, particularly under high‐pressure conditions exceeding 10 bar. A critical challenge in polymer pipelines is rapid crack propagation (RCP), which highlights the importance of accurate characterization of dynamic fracture resistance. In this study, the high‐speed double torsion (HSDT) test was employed to evaluate the dynamic fracture resistance under plane strain conditions (Gd1) of PA12 at 0°C. Experiments were performed at impact speeds of ~13, 20, and 31 m/s, and results showed that Gd1 decreases as impact and crack speeds increase, consistent with semicrystalline polymer behavior. Compared with reported Gd1 values for pipe‐grade HDPE, PA12 demonstrated superior fracture resistance, with Gd1 values of 10.13 kJ/m2 at an impact speed of ~31 m/s. Predictions from a dynamic‐linear‐elastic model supported the reliability of the estimated values. Scanning electron microscopy (SEM) analysis revealed distinct fracture zones, and crack front shapes transitioned from flat to curved with increasing impact speed, confirming plane strain behavior. These findings reinforce the suitability of PA12 for high‐pressure applications and demonstrate the effectiveness of HSDT for characterizing dynamic fracture resistance under plane strain conditions in thermoplastic materials. Highlights HSDT test effectively measures plane strain dynamic fracture resistance (Gd1). PA12 exhibits higher dynamic fracture resistance than reported HDPE values. Gd1 decreases as impact and crack speeds increase, following polymer behavior. PA12 crack front shape during HSDT confirms plane strain behavior.

Keywords

• dynamic fracture resistance
• high‐speed double torsion (HSDT)
• plane‐strain conditions
• polyamide 12
• rapid crack propagation (RCP)
• torsional impedance