Abstract
The results of previous work, in which static fracture tests were applied to propylene-ethylene copolymers, suggest that under circumstances of high constraint the theory of fracture mechanics is useful in the description of the fracture behaviour of such tough materials. In this work similar experiments have been carried out on a series of polypropylene/EPR/HDPE blends in order to compare their behaviour with that of the copolymers. From the evidence it appears that these materials are very similar to the copolymers in terms of fracture behaviour and morphology. The examination of impact fracture behaviour of the blends showed that both instrumented and energy measuring pendulum machines yield similar results when loading times are similar. However, it has been shown that short loading times may lead to high fracture energies, which cause blunting of the crack tip. This behaviour has been modelled using previously developed theory. The effects described demonstrate the care required in impact data interpretation.
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Abbreviations
- a :
-
crack length.
- b :
-
notch width for surface notch specimen.
- B :
-
specimen thickness.
- c :
-
specific heat.
- D :
-
specimen width.
- E :
-
elastic modulus.
- E′ :
-
dynamic storage modulus.
- G c :
-
strain energy release rate.
- G b :
-
apparent strain energy release rate.
- k :
-
thermal conductivity.
- K c :
-
critical stress intensity factor.
- K c1 :
-
plane strain fracture toughness.
- K 1c :
-
instability fracture toughness.
- K′c :
-
apparent toughness (SEN)
- K c2 :
-
plane stress fracture toughness
- L :
-
specimen span in impact
- M w :
-
weight average molecular weight
- M n :
-
number average molecular weight
- M w/M n :
-
polydispersity ratio
- N :
-
notch blunting parameter
- tan δ :
-
loss factor
- t :
-
loading time in impact
- t 1 :
-
limiting loading time
- T 0 :
-
loading time for beginning of thermal blunting
- t 0 :
-
test temperature
- T s :
-
softening temperature
- V :
-
striker velocity in impact
- w :
-
impact fracture energy
- wk :
-
kinetic energy
- x a/D.Y :
-
finite width correction factor
- σ y :
-
yield stress
- σ c :
-
fracture stress
- φ :
-
compliance function
- ρ :
-
density
- [η]:
-
limiting viscosity number
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On leave from Centro Ricerche Giulio Natta, Montepolimeri, S.p.A., Feriara, Italy
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Hodgkinson, J.M., Savadori, A. & Williams, J.G. A fracture mechanics analysis of polypropylene/rubber blends. J Mater Sci 18, 2319–2336 (1983). https://doi.org/10.1007/BF00541836
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DOI: https://doi.org/10.1007/BF00541836