Comparison of the fracture and failure behavior of injection-molded α- and β-polypropylene in high-speed three-point bending tests
✍ Scribed by J. Karger-Kocsis; J. Varga; G. W. Ehrenstein
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 477 KB
- Volume
- 64
- Category
- Article
- ISSN
- 0021-8995
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✦ Synopsis
The fracture and failure mode of aand b-isotactic polypropylene ( a-iPP and b-iPP, respectively) were studied in high speed (1 m/s) three-point bending tests on notched bars cut from injection-molded dumbbell specimens and compared. The fracture response of the notched Charpy-type specimens at room temperature (RT) and 040ЊC, respectively, was described by terms of the linear elastic fracture mechanics (LEFM), namely fracture toughness (K c ) and fracture energy (G c ). K c values of both iPP modifications were similar, while G c values of the b-iPP were approximately twofold of the reference a-iPP irrespective of the test temperature. It was demonstrated that b-iPP failed in a ductile and brittle-microductile manner at RT and 040ЊC, respectively. By contrast, brittle fracture dominated in a-iPP at both testing temperatures. Based on the fracture surface appearance, it was supposed that b-to-a (ba) transformation occurred in b-iPP. The superior fracture energy of b-iPP to a-iPP was attributed to a combined effect of the following terms: morphology, mechanical damping, and phase transformation. Results indicate that their relative contribution is a function of the test temperature.