On the determination of Fracture Toughness of PP polymers

FRONTINI, PATRICIA; FASCE, LAURA; SALAZAR, ALICIA; RODRIGUEZ, JOSÉ

Ottawa

Conferencia; 12th International Conference on Fracture (ICF 12); 2009

Natural Resources Canada - CANMET Materials Technology Laboratory (NRCan-CANMET) and the National Research Council of Canada (NRC)

The fracture behavior of Polypropylene polymers is rather controversial since  is neither completely brittle nor entirely ductile. Scatter in toughness results and difficulty in distinguishing the amount of stable crack growth impair the situation. Consequently, conventional methods based exclusively either on linear elastic fracture mechanics theory (LEFM) or on non-linear elastic fracture mechanics theory (NLEFM) are not suitable.  It was demonstrated by Cocco et al in 2005, that Weibull statistical method could be successfully used to determine the toughness of polymers displaying ductile-to-brittle behavior. On the other side, when  the amount of stable crack growth was not easy to distinguish on fracture surface, it was also argued in literature that a Jc value may be determined using the stress whitening method suggested by Zhang et al in 1989. The present study compares the PP  toughness values determined by the statistical approach and  the stress whitening method. It also discusses  the reliability of both values and the advantages and drawbacks of  each methodology.