Understanding Morphological Signatures of Creep Versus ESC Failure in Common Thermoplastics

Differentiating creep and ESC failure mechanisms is important for understanding how various stresses affect material behavior and product lifetime. In practice, the resulting fracture surfaces from these mechanisms can be very similar. Common approaches rely on knowledge of service conditions and/or solvent extraction of the fracture surface to check for the presence of an ESC agent. However, when the ESC agent is volatile or service history is unknown, it may not be possible to reliably tell the two mechanisms apart based on fracture surfaces alone.

This study aims to provide insights into fracture morphologies of known creep failure and ESC failure to aid in root cause investigations when fracture occurs. Creep performance and environmental stress cracking (ESC) susceptibility of three amorphous thermoplastics: polycarbonate (PC), acrylonitrile–butadiene–styrene (ABS), and chlorinated polyvinyl chloride (CPVC). The time to failure under sustained mechanical loading was quantified and resulting fracture surfaces were analyzed. Additionally, the influence of externally applied ESC agents on failure behavior and resulting fracture morphologies was evaluated.

Parallel test set ups were exposed to an ESC agent applied under constant stress. Time to initial crazing and time to through-thickness cracking were recorded and compared across pure creep and ESC-assisted conditions for each polymer. Fracture surfaces were examined using optical microscopy and scanning electron microscopy (SEM) to characterize crack initiation sites, craze morphology, crack propagation features, and overall fracture modes. Comparative analysis focused on distinguishing ductile versus brittle features, the presence and extent of fibrillation, and shear yielding. Fractographic observations were correlated with measured time-to-failure data to compare mechanisms of creep rupture to mechanisms and surface morphologies associated with ESC failure modes.

The results provide insight into the fractographic morphological differences between creep and ESC failure modes in three commonly used thermoplastic materials.