Evaluation of surface treatments for fibers in composite materials

Abstract An embedded single filament test has been developed that measures the cumulative distribution of critical fibers lengths for a given fiber‐polymer system. The mean value of critical lengths and the dispersion of values are a function of both the shear transmission characteristics of the interface and the strength characteristics of the fibers. A computer model of the stochastic fracture process has been developed that incorporates a mixed‐element, weakest‐link model to describe the strength properties of the fibers, a random generator to describe the stochastics of multiple fiber fracture, and a shear‐lag analysis to describe the shear transmission across the interface. From the measurement of critical fiber lengths, a value for the magnitude of the shear transmission across the fiber‐polymer interface, τ, can be determined. From measured values fiber strength, the ability of a surface treatment to protect a given fiber can be determined. A variety of surface treatments for E‐glass are evaluated in a number of thermoplastic polymer materials. The experimental technique and the associated analysis are shown to be valuable in separating the coupling and sizing effects of the fiber surface treatment formulations. This should be of particular value in the optimization of commercial fiber treatment formulations.