11th week unanswered terms - Gani Can Öz

Double cantilever beam tests (DCB)

This popular test (ASTM 3433) is used to obtain the mode I fracture energy of the adhesive bonds, which is a measure of the fracture toughness of the adhesive in the presence of flaws. Similar to a wedge test, a crack is initiated first by inserting a wedge. The specimen is then loaded by pulling apart the two beams at a certain rate, this increasing load resulting in increased deflection of two beams. At a certain critical load, the crack begins to propagate resulting in a slight drop in the load (due to the increased compliance). At this point, the beams are stopped from moving apart, thus keeping the deflection constant. The drop in load (due to increasing crack length) and the crack length are carefully followed. Following the equilibration of the crack, the specimen is consecutively unloaded and then loaded. Ideally, the compliance of the fixture should remain the same during these two cycles if there is no further propagation of the crack. This overall procedure is repeated several times leading to total cleavage of the specimen. The data finally collected at various times consists of load, deflection, crack length and the compliance.

Crystallization, Morphology, Thermal Stability and Adhesive Properties of Novel High Performance Semicrystalline Polyimides Chapter 7: Wedge and Double Cantilever Beam Tests on a High Temperature Melt Processable Polyimide Adhesive, RATTA, VARUN