High-Rate Fracture Dynamics of Polymer Glasses through Laser Ablation

Understanding the failure mechanisms of polymer materials under extreme conditions is crucial for applications ranging from impact mitigation to advanced manufacturing. However, the fracture behavior of glassy polymers is highly rate-dependent, and traditional quasistatic testing does not necessarily translate to the high-strain-rate conditions (10⁶ to 10¹⁰ s^-1) most relevant to ballistic impact events. In this work, we apply pulsed laser ablation to investigate the high-rate fracture of glassy poly(methyl-methacrylate) (PMMA) membranes. Laser ablation of the gold substrate generates inertial stress waves at the impact site that propagate through the PMMA film, resulting in the formation of a characteristic pattern of radial and circular cracks. Within the deformation zone, these cracks develop to accommodate the rapid membrane expansion and serve as a record of the internal stress state. With increasing strain rate, we observe a ductile-to-brittle transition signified by an abrupt decrease in film fracture toughness, a significant reduction in the number of radial cracks, and the ejection of fragmented material. We find that the transition point strongly depends on the molecular mass, indicating the importance of chain entanglements in determining the polymer response rate and mechanism. This measurement approach offers a new platform for characterizing the fracture mechanics of polymers at high-strain rates, aiding in the design of polymer materials for various impact-related applications.