MICROCRACKS, SPALL AND FRACTURE IN GLASS - A STUDY USING SHORT PULSED-LASER SHOCK-WAVES

This work reports our meso mechanical study of microcrack behavior, es pecially the process leading from microcracking to macro failure. Usin g laser loading with a duration on the order of nanoseconds, spallatio n in a cylindrical geometry was achieved in soda-lime glass at the mic rocrack evolution stage. Laser induced shock waves were used to conduc t crack initiation experiments for the first time. The specimens were examined after experiments and were compared with those loaded by conv entional static and dynamic methods. A meso scale failure model of nuc leation, growth, and percolation (NGP) is suggested based on the exper iments. The NGP model is characterized by a randomly generated microcr ack field and by simultaneous percolation statistics in time iteration . In most existing damage models, the statistical average of microcrac ks over a finite space is required in order to evaluate the damage var iables. This procedure is not necessary in the NGP model. We show that the connection of microcracks can be very complicated, possibly a sel f-organized process. (C) 1998 American Institute of Physics. [S0021-89 79(98)05407-3].