Polymer matrix composites are widely used in a variety of civil engineering projects, including highway construction and concrete pavements. Subcommittees D30.05 on Structural Test Methods and D30.06 on Interlaminar Properties are both working on proposed new standards that involve fiber-reinforced polymer matrix composites. The subcommittees are part of ASTM International Committee D30 on Composite Materials.
Transverse Shear Strength
Subcommittee D30.05 is currently developing a proposed new standard, WK22348, Test Method for Transverse Shear Strength of Fiber-Reinforced Polymer Matrix Composite Bars.
“Concrete pavements have joints in them to accommodate thermal movements,” says Russell Gentry, Ph.D., 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 WK22348 will be manufacturers of composite material rebar, research laboratories, highway engineers, glued-laminated lumber producers and structural engineers.
Interlaminar Fracture Toughness
Delamination growth, or the growth of cracks in between layers in laminated composite materials, can occur during usage (for example, low velocity impact), from unexpected overloads of a structure or from an extended lifetime of normal service loadings.
A proposed new ASTM standard will be part of a series of test methods developed by D30.06 that characterize the delamination toughness of laminated composites.
Two test methods already developed by D30.06 that deal with this type of testing are D5528, Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites, and D6671/D6671M, Test Method for Mixed Mode I-Mode II Interlaminar Fracture Toughness of Unidirectional Fiber Reinforced Polymer Matrix Composites.
According to Barry Davidson, Ph.D., 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 was 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 Fiber Reinforced Polymer Matrix Composites Using the End-Notched Flexure (ENF) Test.
“Delamination growth represents a critical failure mode in structures fabricated from fiber 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 material’s resistance to delamination growth, or toughness.”
Davidson says that toughness assessments using 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.
Technical Information: (WK22348) Russell Gentry, Ph.D., Georgia Institute of Technology, Atlanta, Ga.
(WK22949) Barry Davidson, Ph.D., Syracuse University, Syracuse, N.Y.
ASTM Staff: Jennifer Rodgers