Interfacial stress transfer in nylon-6/E-glass microcomposites: effect of temperature and strain rate

In this study, the interfacial properties between E-glass fibers with different commercial sizings have been investigated on model composites with a nylon-6 matrix. In particular, the fiber critical length was measured by means of the single-fiber fragmentation test over a wide range of temperatures (from 25 to 175 °C) and strain rates (from 0.008 to 4 min-1). The general trend observed is that the fiber critical aspect ratio increases as the temperature increases and it decreases as strain rate is increased. The fiber critical aspect ratio for unsized fibers resulted to be reasonably well linearly related to the square root of the fiber to matrix modulus ratio. This results is in accordance with the Cox's shear-lag theoretical model and the Termonia's numerical simulations. Sized fibers display an higher deviation from the theoretical prevision probably because of the presence of interphases whose properties are different from the bulk matrix. As a consequence, the interfacial shear strength values resulted to be dependent on the fiber sizing. In particular, the fibers coated with an epoxy sizing showed a superior thermal stability of the fiber matrix-interface with respect to the unsized or nylon compatible sized fibers.