Fracture toughness studies of rubber-toughened polycarbonate
Polycarbonate was toughened with preformed core/shell particles. The fracture toughness at different toughener levels and temperatures was measured according to a J-integral procedure using compact tension test specimens. An extensive critique of the J-integral procedures was made and compared in this study. The fracture toughness J[sub IC] of unmodified polycarbonate in Mode I is 2.68 kJ/m[sup 2] at a crosshead speed of 5.08 mm/min with the specimen thickness ranging from 3.175 to 9.525 mm, at temperatures ranging from [minus]20 to 23[degrees]C. Under the same conditions, the J[sub IC] of rubber-toughened polycarbonates were 4.88, 5.68, 7.70, and 7.46 kJ/m[sup 2], at toughener levels of 2.5, 5, 7.5, and 10 parts, respectively, by weight per hundred parts (phr) of polycarbonate. The maximum toughness was realized at 7.5 phr of toughener and began to decrease at 10 phr. Tensile stress-strain curves indicated that the modulus is retained at all toughener levels. The ultimate stress and strain, however, steadily decreased. Fracture surfaces of test specimens were examined by scanning electron microscope (SEM) and analyzed to elucidate the toughening mechanism. This indicated polycarbonate deforms through shear-yielding with or without the second phase. The fracture surface of broken tensile bars showed limited cavity volume compared to the compact tension specimens. The reason for this appears to be the higher crack speed accompanying fracture in the bars. The failure mechanism and the degree of toughening from the rubbery domains are different in the compact tension specimen and tensile bar specimen: with the compact tension specimens, dilatational deformation involving cavitation is dominant. The cavitation is initiated by interfacial debonding around the particles. In this, shear-yielding is limited. In the fracture of the tensile bar specimens, shear-yielding is dominant with limited dilatational deformation involving cavitation.
- Research Organization:
- Massachusetts Inst. of Tech., Cambridge, MA (United States)
- OSTI ID:
- 6915858
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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