Abstract
Microstructure and fracture mechanical behaviour of injection-moulded, longer glass fibrereinforced polypropylene (Verton* aspect ratio ≈ 320) were studied as a function of fibre volume fraction and compared to that of shorter fibre-filled polypropylene (aspect ratio ≈ 70). Toughness was measured using instrumented notched lzod and falling weight impact tests, as well as compact tension specimens. It was found that the addition of longer fibres generally increased the toughness of the material, although more significant increases were seen in the impact tests than were seen in the compact tension test. For the latter results, a correlation between toughness improvement and microstructural details was performed on the basis of the microstructural efficiency concept, a semi-empirical approach of the formK c,C = (a* +nR)K c,M, where,K c,C andK c,M are the fracture toughnesses of the composite and the matrix, respectively,a* is a matrix stress correction factor,n is a scaling parameter andR is a fibre reinforcement effectiveness factor. The latter corrects for differences in the composite microstructures, and incorporates effective fibre orientation factors, layering of injection moulded parts, and fibre volumes in the different layers.
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Abbreviations
- a :
-
crack length
- a * :
-
matrix toughness correction factor
- A :
-
cross-sectional area
- B :
-
thickness of the sample plaques
- C :
-
thickness of the composite core regions
- E peak :
-
energy adsorbed up to the maximum force in the impact load-displacement curve
- E t :
-
tensile modulus
- F max :
-
maximum force in impact force-displacement curves
- f p :
-
fibre orientation factor
- f pe :
-
effective orientation factor
- f pe,C :
-
effective orientation parameter, core region
- f pe, s :
-
effective orientation parameter, surface region
- F :
-
critical load in the tensile test load-displacement curves
- K c :
-
critical stress intensity factor/fracture toughness
- K L :
-
fracture toughness of the composite materials
- K d :
-
dynamic fracture toughness
- K L :
-
fracture toughness of the matrix
- L :
-
test with crack parallel to the mould filling direction
- M :
-
microstructural efficiency factor
- n :
-
scaling parameter for reinforcement effectiveness factor (energy absorbtion ratio)
- R :
-
reinforcement effectiveness factor
- S :
-
thickness of the composite surface regions
- T:
-
test with crack perpendicular to the mould filling direction
- V f :
-
fibre volume fraction
- V m :
-
matrix volume fraction (= 1 —V f)
- W :
-
specimen width
- W f :
-
fibre weight fraction
- W m :
-
matrix weight fraction (= 1 —W f)
- X n :
-
number average fibre length
- X v :
-
volume average fibre length
- Y(a/ W):
-
polynomial correction for compact tension specimens
- α:
-
variable in effective orientation factor formula
- β :
-
variable in effective orientation factor formula
- ɛB :
-
strain to break
- ϱc :
-
density of the composite
- ϱf :
-
fibre density
- ϱm :
-
matrix density
- σF :
-
fracture strength
- θ:
-
fibre angle with respect to a reference direction
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Spahr, D.E., Friedrich, K., Schultz, J.M. et al. Microstructure and fracture behaviour of short and long fibre-reinforced polypropylene composites. J Mater Sci 25, 4427–4439 (1990). https://doi.org/10.1007/BF00581104
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DOI: https://doi.org/10.1007/BF00581104