Degradation and Cracking Behavior of Polyamide-Based Backsheet Subjected to Sequential Fragmentation Test

In this paper, a facile test method combining weathering with a sequential fragmentation test is designed to quickly and effectively reproduce the cracking behavior of polyamide (PA)-based backsheets in the field, leading to a new way to evaluate and predict the crack propensity of backsheets. Commercial PA-based backsheets were exposed to ultraviolet (UV) light for 2000 and 4000 h, respectively. The exposed samples were then pulled in tension stepwise with
in situ
monitoring using laser scanning confocal microscopy. Detailed characterizations of the backsheets indicate significant chemical degradation, along with surface erosion and loss of ductility. Moreover, it was found that cracking appeared on the surface of the UV-exposed samples at a small applied strain (<;1%). With increasing strain, more parallel cracks formed at multiple sites, which is similar to the cracking behavior observed in the field. The sample aged for 2000 h showed a relatively shallow crack depth with higher crack density than the sample aged for 4000 h. Different crack patterns and fracture energies of the degraded samples could be further explained by depth-profile characterizations and the Hsueh and Yanaka model.