ASTM D6671 Piano Test Fixture | GD6671-815p

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ASTM D6671 Test Fixture | GD6671-815p


Model #
GD6671-815p test fixture meets ASTM D6671 requirements. The GD6671-815P Mixed-Mode Bending (MMB) test fixture with piano hinges is used to load split laminate specimens to determine the delamination fracture toughness at various ratios of Mode I to Mode II loading. The composite test specimen is a rectangular, uniformly thick, unidirectional laminated composite specimen, containing a non adhesive insert at the midplane which serves as a delamination initiator. Loads are applied to the MMB specimen via tabs that are applied near the ends of the delaminated section of the specimen and through rollers that bear against the specimen in the non delaminated region.

The base of the MMB apparatus holds the specimen stationary while the MMB lever loads the specimen. The base attaches to the bottom specimen tab and also bears on the specimen near the far end with a roller. The lever attaches to the top tab and bears down on the specimen halfway between the base roller and the tabs. The lever roller acts as a fulcrum so by pushing down on the lever arm opposite the tab, the tab is pulled up. The length of the lever arm can be changed to vary the ratio of the load pulling on the tab to the load bearing through the roller thus changing the mode mixture of the test. The load must remain vertical during the loading process. To reduce geometric nonlinear effects as a result of lever rotation, the lever is loaded such that the height of loading is slightly above the pivot point where the lever attaches to the test specimen.

Piano Hinge Attachment

The mixed-mode bending fixture uses a lever to load the MMB specimen. Using one applied load at the end of the lever, a downward load is applied to the specimen center creating Mode II, while an upward force is applied to the split end of the laminate creating Mode I. The testing machine is equipped with a clevis which can be attached to the loading yoke of the MMB fixture and an anvil on which the base of the MMB apparatus can be placed. The overall length of the specimen is not critical but will normally be around 137 mm (5.5 in.). The width of the specimen is between 20 to 25 mm (0.8 to 1.0 in.). The width of the MMB specimen is not considered a critical parameter.

Load is introduced through tabs made from engineered piano hinges.