J. Kargerkocsis et al., COMPARISON OF THE FRACTURE AND FAILURE BEHAVIOR OF INJECTION-MOLDED ALPHA-POLYPROPYLENE AND BETA-POLYPROPYLENE IN HIGH-SPEED 3-POINT BENDING TESTS, Journal of applied polymer science, 64(11), 1997, pp. 2057-2066
The fracture and failure mode of alpha- and beta-isotactic polypropyle
ne (alpha-iPP and beta-iPP, respectively) were studied in high speed (
1 m/s) three-point bending tests on notched bars cut from injection-mo
lded dumbbell specimens and compared. The fracture response of the not
ched Charpy-type specimens at room temperature (RT) and -40 degrees C,
respectively, was described by terms of the linear elastic fracture m
echanics (LEFM), namely fracture toughness (K-c) and fracture energy (
G(c)).K-c values of both iPP modifications were similar, while G(c) va
lues of the beta-iPP were approximately twofold of the reference alpha
-iPP irrespective of the test temperature. It was demonstrated that be
ta-iPP failed in a ductile and brittle-microductile manner at RT and -
40 degrees C, respectively. By contrast, brittle fracture dominated in
alpha-iPP at both testing temperatures. Based on the fracture surface
appearance, it was supposed that beta-to-alpha (beta alpha) transform
ation occurred in beta-IPP. The superior fracture energy of beta-iPP t
o alpha-iPP was attributed to a combined effect of the following terms
: morphology, mechanical damping, and phase transformation. Results in
dicate that their relative contribution is a function of the test temp
erature. (C) 1997 John Wiley & Sons, Inc.