Fracture Toughness by ASTM D6671

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. 

Scope:
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.

Procedure:
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.

Specimens:
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.

Data:
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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