Visualization of crack blunting using secondary fluorescence in soft polymers

A fluorescence-based technique was developed to visualize crack blunting and propagation in soft polymers. The technique, as demonstrated on poly-di-methyl siloxane, can also be applied on intrinsically non-fluorescent polymers after inducing secondary fluorescence with a suitable dye during the specimen preparation. The experimental results indicate enhanced performance of the technique in terms of spatial resolution and contrast compared to white-light microscopy. A dynamic plastic cohesive zone was observed ahead of the blunting crack tips in mode I loading, which was correlated to the computed emitted light intensity gradients. The fractured specimen surfaces were analyzed with scanning electron microscopy to discuss the validity of the interpretations of the experimental data.