Testing for Toughness



Maybe you haven't given much thought to the growth of interlaminar cracks, or cracks in between layers, in laminated composite materials. Perhaps you should though, because such materials are everywhere and interlaminar cracks can cause serious damage to many types of structures and products, from sports equipment to spacecraft. This is why a new ASTM standard D7905/D7905M, 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, is important.

"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.

A list of products that contain laminated, continuous fiber-reinforced composites proves Davidson's point:

  • Sporting goods, including tennis rackets, golf clubs and skis;
  • Electronics, including many circuit boards;
  • Civil infrastructure, including bridge decking, gas pipelines and beams and columns in buildings;
  • Automotive structure, body panels and interiors; and
  • Airplanes, helicopters and spacecraft, in which said composites are used extensively.

While fracture toughness tests exist for Mode I and mixed-mode, no test currently exists for Mode II. The Mode II test described in 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.

Davidson notes that 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." Determining a material's resistance to delamination growth is a key component to this work.

D7905/D7905M was developed by Subcommittee D30.06 on Interlaminar Properties, part of ASTM International Committee D30 on Composite Materials. To purchase ASTM standards, visit www.astm.org and search by the standard designation, or contact ASTM Sales (tel +1.877.909.ASTM; sales@astm.org).

CONTACT Technical Information: Barry D. Davidson, Ph.D., Syracuse University • Syracuse, New York • tel +1.315.443.4201 | ASTM Staff: Ashley Wiand • tel +1.610.832.9551

Industry Sectors: 
Transportation
Safety
Metals & Materials
Issue Month: 
January/February
Issue Year: 
2015