5.1 Susceptibility to delamination is one of the major design concerns for many advanced laminated composite structures. Knowledge of a laminated composite material's resistance to interlaminar fracture is useful for product development and material selection. Furthermore, a measurement of the mode I interlaminar fracture toughness that is independent of specimen geometry or method of force introduction is useful for establishing design allowables used in damage tolerance analyses of composite structures. Knowledge of both the non-precracked and precracked toughness allows the appropriate value to be used for the application of interest.

5.2 This test method can serve the following purposes:

1.1 This test method describes the determination of the opening mode-I interlaminar fracture toughness, G_Ic, of unidirectional fiber-reinforced polymer matrix composite laminates using the double cantilever beam (DCB) specimen (Fig. 1).

FIG. 1 Double Cantilever Beam Specimen

1.2 This test method is limited to use with composites consisting of unidirectional carbon-fiber and glass-fiber-reinforced laminates with brittle or tough single-phase polymer matrices. This limited scope reflects the experience gained in round-robin testing. This test method may prove useful for other types and classes of composite materials; however, certain interferences have been noted (see 6.6).

1.3 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.

1.4 This standard may involve hazardous materials, operations, and equipment.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.