Tensile strength and modulus of FRP pultruded composites at varying load angles relative to the pultrusion direction

Abstract

Tensile strength and modulus are key material properties for the design of pultruded fiber reinforced polymer (FRP) composite members and connections. Pultruded FRP composites are orthotropic materials and thus both the tensile strength and modulus vary with the angle between the pultrusion direction and the applied force. In current design standards, the variation of material properties with load direction is addressed by prescribing the use of longitudinal properties for angles between zero and five degrees, and the use of transversal properties for angles greater than five degrees. To derive a more precise and representative equational relationship between load angle and tensile material properties, 228 coupons extracted from pultruded FRP profiles were tested in tension in accordance with ASTM D638-22 to determine the resulting average tensile strength and tensile modulus values. Coupons were taken from different profiles from different manufacturers, different section locations (e.g., web versus flange), as well as varying angles between the pultrusion direction and the applied force. The characteristic design value of the tensile strength and tensile modulus at each tested angle was determined in accordance with ASTM D7290-22. Using this dataset, a predictive relationship based on a generalized form of Hankinson’s equation was developed for both average and characteristic tensile strength and both average and characteristic tensile modulus as a function of three factors: 1) the differential angle between the pultrusion direction and the applied force, 2) the longitudinal tensile property (i.e., strength or modulus), and 3) the transverse tensile property (i.e., strength or modulus). The average relative difference between tested and predicted values using the developed equations varied between 4.4% and 8.3%, depending on the considered mechanical property.