Measurement of Cohesive Parameters of Crazes in Polystyrene Films

Crazing is one of the dominant failure mechanisms in amorphous polymers. The micro-mechanics of crazing is often incorporated by embedding Cohesive Zone Models (CZM) into continuum models. In CZM, a traction separation law for the cohesive zone is specified with a maximum traction and a critical opening as the parameters. The main focus of the present study is to determine the cohesive parameters of crazes in thin polystyrene films. Polystyrene granules were dissolved in Toluene on a glass slide which was then transferred to a spin coater. By changing the spinning speed, polystyrene films of the desired thickness were prepared. Single Edge Notch Tension (SENT) specimens were cutout of the prepared sheets and fracture tests were conducted inside a Scanning Electron Microscope (SEM) using a tensile tester at a loading rate of 0.1 mm/min. The critical opening of the cohesive zone was directly measured from the SEM images while the

J

-Integral was calculated from the load-displacement curve. The opening traction was calculated by differentiating the

J

-Integral with the measured critical craze opening.