The ASTM standard D7905/D7905M is entitled Test Method for Determination of the Mode II Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites Using the End-Notched Flexure (ENF) Test.

While fracture toughness tests exist for Mode I and mixed-mode, no test currently exists for Mode II. The Mode II test described in ASTM D7905/D7905M will be used by industry and government for qualitatively comparing composite materials as well as determining values to be used in design, analysis and acceptance/rejection criteria. Interlaminar cracks can cause serious damage to many types of structures and products, from sports equipment to spacecraft.

“Although we don’t really think about it, laminated composites are fairly ubiquitous,” says ASTM member Barry D. Davidson, Ph.D., the Laura J. and L. Douglas Meredith Professor in the department of mechanical and aerospace engineering at Syracuse University.

Critical failure

According to Davidson, delaminations can occur in several different ways: during manufacture, from damage during usage, from unexpected overloads of a structure or simply from normal service loadings over extended periods of time.

“Delamination growth represents a critical failure mode in structures fabricated from fiber reinforced polymer matrix composites, so there is a concerted effort in the community to develop the tools and techniques to make sure that this does not occur,” he added.

ASTM D7905/D7905M was developed by Subcommittee D30.06 on Interlaminar Properties, part of ASTM Committee D30 on Composite Materials.