Determination of Interfacial Shear Strength in Epoxy/Glass Composites by Multi-Fiber Fragmentation Test (MFFT)

E.D. McCarthy, J.H. Kim, N.A. Heckert, S.D. Leigh, G.A. Holmes*, J.W. Gilman

1 Materials Science and Engineering Division, 2 Statistical Engineering Division,

National Institute of Standards and Technology, Gaithersburg, MD, 20899-8541

* Corresponding author (


Keywords composites, interface, interfacial shear strength, E-glass, epoxy resins


The mechanical strength and toughness of a structural composite is strongly affected by the strength and toughness of the interface achieved between the continuous matrix phase, or resin, and the reinforcing phase, normally consisting of multiple arrays of carbon or glass fibers. Interfacial shear strength (IFSS) is the accepted parameter for quantifying the strength of the matrix-fiber interface. However, the value of IFSS is not directly accessible by measurement and must be approximated indirectly from other data.

In this project we extend the SFFT technique to multiple fiber arrays (multi fiber fragmentation test MFFT) to more closely study the transfer of stress from matrix to reinforcement. We use MFFT data obtained from a conventional epoxy / E-glass system to show that the spatial distribution of fiber breaks along the axes of fibers in close bundles is fitted best by a uniform rather than a Weibull distribution. This knowledge can improve the accuracy of calculations for local and global IFSS in micromechanical specimens, and so inform more effective design of composites in key sectors such as aerospace.