Crazing and strain localization of polycarbonate glass in creep

We apply a constant tensile load (i.e., fixed engineering stress) at different temperatures to examine the mechanical and structural responses of polycarbonate (PC) glass. Unlike the more common displacement-controlled extension, the tensile creep test allows the glass to develop structural failures on its time scales. At room temperature, surface crazes over time at sufficiently high tensile loads, and shear yielding as well as stable necking take place above an engineering stress of 48 MPa. However, none of these two types of strain localization occurs when the same PC is first melt-stretched and quenched back to room temperature. The suppression of crazing and necking by melt stretching can be anticipated based on the picture of a hybrid structure for polymer glasses under large deformation and emphasizes the geometric condensation as an effective way to enhance the chain network.