Effects of Fiber Architecture on Flexure Properties of Pultruded GFRP Plates and Sections

Flexural properties of pultruded glass fibre reinforced polymer (pGFRP) materials vary considerably and, unlike longitudinal properties, are affected by fibre architecture which, itself, is typically a function of plate thickness. Thin plates may have only a single longitudinal glass roving located near the plate midline while thicker plates will have multiple rovings arranged at a distance from the midline. As a result, thicker plates will be disproportionately stiffer and stronger in their flexural response than thinner plates. While the rule of mixtures is appropriate for assessing axial and shear properties, additional information on the fibre architecture is required to assess flexural properties which the rule of mixtures alone will overestimate. Variation of the location of the roving through the plate thickness will also significantly affect longitudinal flexural properties. Thus the authors argue for a member stiffness approach: determining flexural stiffness as the product of modulus and moment of inertia (EI) rather than determining E and I separately. The paper presents a parametric study of idealised plate geometry that demonstrates the impact of fibre architecture and that the rule of mixtures formulation results in an upper bound solution for stiffness. Subsequent experimental and imaging data is presented that illustrates the significant variation of fibre architecture and its effect on the flexural stiffness of the plate. Conclusions and recommendations are made having direct relevance to ongoing international pGFRP design standards development