ASTM works on new composites standards

Transverse shear strength

ASTM Subcommittee D30.05 on Structural Test Methods is currently developing a proposed new standard, ASTM WK22348: Test Method for Transverse Shear Strength of Fibre-Reinforced Polymer Matrix Composite Bars. “Concrete pavements have joints in them to accommodate thermal movements,” says Russell Gentry, Georgia Institute of Technology, and a co-chair of D30.05. “Large diameter dowel bars are used to bridge across these joints to prevent transverse movement of pavements. The proposed test method captures this sort of loading on the bar.”

Gentry notes that there are many other applications for composite material bars loaded in this way. According to Gentry, primary users of ASTM WK22348 will be manufacturers of composite material rebar, research laboratories, highway engineers, glued-laminated lumber producers and structural engineers.

Interlaminar fracture toughness

A proposed new standard will be part of a series of test methods developed by ASTM Subcommittee D30.06 on Interlaminar Properties to characterise the delamination toughness of laminated composites. Two test methods dealing with this type of testing have already been developed by D30.06:

  • ASTM D5528, Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fibre-Reinforced Polymer Matrix Composites; and
  • ASTM D6671/D6671M, Test Method for Mixed Mode I-Mode II Interlaminar Fracture Toughness of Unidirectional Fibre Reinforced Polymer Matrix Composites.

According to Barry Davidson, a professor in the mechanical and aerospace engineering department at Syracuse University, and a D30 member, the need for a standard dealing exclusively with Mode II loading is a high priority. The Subcommittee is now addressing Mode II loading with the development of proposed standard WK22949, Test Method for Determination of the Mode II Interlaminar Fracture Toughness of Unidirectional Fibre Reinforced Polymer Matrix Composites Using the End-Notched Flexure (ENF) Test. “Delamination growth represents a critical failure mode in structures fabricated from fibre reinforced polymer matrix composites, so there is a concerted effort to develop the tools and techniques to make sure that this does not occur,” says Davidson. “A key component of the approach is the determination of a materials resistance to delamination growth, or toughness.” Davidson says that toughness assessments using ASTM WK22949 will be used in the development of new materials, for selecting among materials for structural applications, for screening the quality of new batches of material to be used in production and to support structural design and analysis efforts.

Subcommittees D30.05 and D30.06 are under the jurisdiction of ASTM International Committee D30 on Composite Materials.

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