Non-uniform fiber-resin distributions of pultruded GFRP profiles

Pultruded fiber reinforced polymer (FRP) composite profiles are usually regarded as the transverse-isotropic material based on the assumption that the fiber and resin are uniformly distributed across the profile sections. However, this is practically not the case due to the limitations of the pultrusion technology. The non-uniform fiber-resin distribution (NUFRD), as a type of inherent initial imperfection for pultruded glass fiber reinforced polymer (GFRP) profiles, was investigated. The resin contents of 49 different pultruded GFRP sections were tested and analyzed. The standard calcination method was used to measure the resin content. The sections were provided by three different manufactures and included the I-sections, box-sections, angle-sections, circular tubes, channel-sections and flat plates. Multiple sampling locations were specified for each type of section. The test results showed that the degree of NUFRD for each type of section is different. In particular, the I-sections showed the most significant material non-uniformity. The largest COV (coefficient of variation) of the measured resin contents is 0.16. Additionally, the influence of NUFRD on the mechanical properties of GFRP members was addressed. The material non-uniformity would increase the initial section eccentricity. Finite element models were built to simulate the compressive GFRP members. It was found that the critical buckling loads of GFRP compressive members will be reduced due to NUFRD.