A Numerical Method for the Determination of an Effective Modules for Coated Glass Fibers Used in Phenolic Composites

It is well known that the mechanical properties of fiberglass reinforced "phenolic moulding compounds" are significantly enhanced if the glass particles are coated with silane coupling agents before compounding. It has been shown that improvements obtained by using scanning electron microscopy techniques are due to better bonding of phenolic resin to the surface of treated glass fibers. These observations prove that coated glass fibers effectively exhibit properties which are different from those of the glass itself. Thus from a modelling point of view, they can be regarded as materials having moduli different from the modulus of glass. However, considering the very small width of the coating layers used, it cannot be expected that by using direct experimental measurements of relatively large specimens, significantly different moduli for uncoated and coated glass fibers will be found. In this paper, the notion of an effective moduli for coated fibers is introduced. It is shown that such values can be numerically determined using experimentally measured bulk mechanical properties of coated glass filled composites. A trial and error procedure is developed for obtaining optimum moduli for the reinforcing phase. This scheme is based on the comparison of simulation results obtained by a previously validated finite element technique and data collected from flexural tests and fracture surface observations for different types of glass reinforced phenolic composites.