Fracture toughness by using a mixed-mode bending test.
Understand susceptibility to delamination by determining the interlaminar fracture toughness of a polymer composite with an initiated delamination.
ASTM D6671 measures mixed-mode (Mode I and Mode II) fracture toughness - the strain energy release rate for delamination in mixed mode. The test applies load to split laminate specimens at various ratios of Mode I and Mode II loading. Fracture Mode I is crack opening mode. Fracture Mode II is sliding mode with delamination occurring as faces slide over each other.
Insert the specimen in the Mixed Mode Bending Fixture and set desired mode mixture. A Universal Testing machine is used to apply a force to the specimen at a rate of 0.5 mm/min (0.02 in/min). Record force and displacement.
Panels prepared per test standard including piano hinge loading tabs. Typical specimen size is 137 mm (5.5 in) long x 50 mm to 25 mm (0.8 in to 1.0 in) width x 3 mm to 5 mm (0.12 in to 0.2 in) thick. 5 specimens are tested.
GI - Mode I strain energy release rate (kJ/m2)
GII - Mode II strain energy release rate (kJ/m2)
Gc - Mixed Mode Fracture Toughness (kJ/m2)
GII/Gc – Mode Mixture
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