Session W18 - Computer Simulation II.
ORAL session, Thursday morning, March 15
Room 308-308, Washington State Convention Center
The toughness G is the energy per unit area needed to rupture an adhesive bond, and represents the resistance to crack propagation. Most of the toughness of polymer glasses comes from growth of a micron thick craze zone around the crack tip. We present molecular dynamics simulations with a simple bead-spring model of entangled polymers that allow the toughness to be calculated using a fracture model proposed by H. R. Brown (Macromol. 24, 2752 (1990)). Polymer is deformed from a dense initial state into a craze network at a constant plateau stress. Calculations of the anisotropic elastic moduli of the craze are used to determine the stress intensity factor at the crack tip. The craze stops thickening when the stress at the crack tip reaches the maximum stress that the craze can withstand before chain scission or disentanglement causes the crack to advance. The competition between these processes is studied as a function of chain length. Combining our results in Brown's model gives values for the craze thickness and G that are consistent with experimental results.