Shear modulus of standard pultruded fiber reinforced plastic material

Research to determine the shear modulus of standard pultruded fiber reinforced plastic (FRP) material is reviewed and appraised. It is found that different test methods have given shear moduli data in the range from 1.3 to 5.1 GPa, with varying degrees of scatter. Pultruded material is comprised of alternate layers of two distinct glass reinforcement types. By applying micromechanical modeling, it is shown that the in-plane shear modulus of the continuous unidirectional rovings layer is similar to that of the continuous filament (or strand) mat layer, and that these layer moduli, generally, lie in the range 3.5 to 4.8 GPa (depending on fiber volume fraction). This finding indicates that the significant difference (>1.3 times) between the in-plane (3 GPa or less) and the St. Venant torsion (always >4 GPa) shear moduli is likely to be due to the experimental test procedures and the physical interpretation of shearing, rather than the layer construction of the material. For structural profiles, it is seen that the shear modulus of 3 GPa in company design manuals is often less than measured. Researchers require correlated elastic constant data if elastic deflections and instability loads for structural members can be accurately predicted using elastic theory. Further work is, therefore, recommended to establish standard test and analytical methods for the determination of shear moduli of pultruded FRP material