Surface fracture of glassy materials as detected by real-time atomic force microscopy (AFM) experiments

We have studied the low speed fracture regime for different glassy materials with variable but controlled length scales of heterogeneity in a carefully mastered surrounding atmosphere. By using optical and atomic force microscopy (AFM) techniques we tracked in real-time the crack tip propagation at the nanometer scale, on a wide velocity range (10−3 to 10−10 m s−1 and below). The influence of the heterogeneities on this velocity is presented and discussed. Our experiments revealed also—for the first time—that the crack advance proceeds from nucleation, growth and coalescence of nanometric damage cavities inside the amorphous phase, which generate large velocity fluctuation. Implications of the existence of such a nano ductile fracture mode in glass are discussed.