Low cost pultruded carbon fiber composites development for spar cap applications in wind turbine blades

Development of low cost carbon fibers and implementing their use for carbon fiber composites in applications associated with wind energy is a major current emphasis for the composites community. Authors report results from a seed study here on developing low-cost manufacturing technique associated with pultrusion process using two types of suitably sized carbon fibers available from DowAksa (24K-A42 and 24k-A49) and an epoxy based resin system. Carbon fiber based spar caps for wind turbine blades provide high stiffness at reduced weight and are ideally suited for increasing the length of the blades. Due to high initial cost, carbon fibers have not been used often in low cost and continuous manufacturing techniques such as pultrusion and thus have not received detailed attention related to its development. The recent success at the Carbon Fiber Technology Facility in Oak Ridge, TN in developing low-cost Carbon Fibers using textile PAN based precursors shows further promise for the implementation of carbon fiber composites in wind energy applications. The high alignment obtained in pultrusion process is well suited for spar cap applications to provide necessary compressive and tensile properties. This paper summarizes results associated with tensile behavior of pultruded plates and related challenges in evaluating true failure strength of pultruded carbon fiber composites properties as the thickness of the plate increases. The need for considering non-standard specimen geometry, integrated with spatially resolved strain mapping using 3-D Digital Image Correlation technique to understand the deformation and failure mechanisms is introduced and shows promise for characterizing mechanical properties of thick (> 2 mm) pultrusion based carbon fiber composites at multiple length scales.