MICROMECHANICAL MODELING OF CRACK-TIP RUBBER PARTICLE CAVITATIONAL PROCESS IN POLYMER TOUGHENING

A simple micromechanical modeling of the rubber particle cavitational process at the crack tip was conducted using the combination of Irwin' s crack tip stress intensity factor analysis, slip-line field theory, and Dewey's closed-form elastic solution. This unique micromechanical modeling provides fruitful insights concerning the possible role(s) th e rubber particles play in front of a constrained (plane-strain) crack tip. The cavitation of the rubber particles at the tip of the crack c auses the redistribution of the stress and strain fields around the ca vitated rubber particles. This, in turn, alters the stress state the s urrounding matrix experiences. Consequently, the fracture process is a ffected by the rubber particle cavitational event. The results of the micromechanical analyses suggest that both the preexisting holes and t he occurrence of cavitation in Me rubber particles in front of the cra ck serve (i) to relieve the plane-strain constraint, (ii) to promote s hear yielding of the matrix, and (iii) as stress concentrators. The ma jor difference between the preexisting holes and the rubber particle c avitational event lies on the sudden buildup of the octahedral stress component upon the cavitation of rubber particles in the crack tip reg ion. Experimental observations of toughening mechanisms of various rub ber-modified polymers support this micromechanical analyses.