Internal geometry of a pultruded product

Pultrusion is a complex manufacturing process due to the diverse interactions between involved multiphysics such as resin flow, heat transfer, chemical curing, and transient stress and shape distortions. As a result of residual stresses and excess chemical shrinkage, manufacturing-induced defects, such as transverse matrix crack in the UD layer and delamination at the interface between UD roving and CFM layer, are present in the profile. Fibre misalignment and porosities can also form during the process due to poor fibre impregnation and nonoptimised process parameters. In addition, the UD layer usually has local resin-rich areas with nonuniform fibre volume fraction distribution. The excessive curing shrinkage at these resin-rich areas may cause matrix cracking. To have reliable and robust manufacturing, there is a need to understand the internal structure and quantify the severity of defects existing in the final pultruded product. In this chapter, we present a characterisation of the internal geometry of an industrial pultruded glass/polyester profile using the X-ray micro-computed tomography (micro-CT) technique with focus on the UD roving layer. It is important to understand the microstructure of the layer, in which transverse cracks or porosities may occur during the process. We quantitatively analyse the resin-rich areas and the misalignment between rovings. In addition, we systematically quantify the 3D continuous and discontinuous porosities in the pulling direction. The analysis is carried out using the VoxTex software. The characterisation of the internal geometry of the pultruded profile parts is necessary to predict the fibre misalignment and process-induced porosity formation using the numerical process models. Understanding and description of the internal geometry of pultruded profiles enable critical assessment of the effect of defects on damage initiation during service loading conditions, e.g., pultruded composites used in wind turbine blades.