Mode I fracture

The double cantilever beam specimen (pictures) has been widely used to measure the mode I interlaminar fracture toughness, of composites. The DCB specimen is a laminate with a non-adhesive insert placed at the mid-plane, at one end prior to curing or consolidation, to simulate a delamination. Generally, unidirectional parallel sided specimens are used. Typically, loads are applied to the DCB via loading blocks or hinges adhesively bonded to the surface of the DCB. During test, the specimen is subjected to displacement controlled loading and usually experiences stable delamination growth allowing several values of , to be determined along the specimen's length. As the delamination grows, fibre bridging usually occurs increasing the energy required to propagate the delamination further. Therefore, only the first value of obtained from delamination growth from the insert is unaffected by fibre bridging and can be considered a generic interlaminar fracture toughness.

Different methods exist for reducing the experimental data but a common method is known as the Modified Beam Theory