Analysis of the local fiber volume fraction variation in pultrusion process

In order to increase the structural reliability of the pultruded parts used in load-bearing applications, e.g. wind turbine blade components, the local stresses generated by the nature of the process need to be quantified. Fiber volume fraction, Vf, is one of the primary microstructural features in the determination of mechanical properties. Process-induced residual stresses are also affected by the local Vf in the pultruded parts. In the present work, the influence of local Vf distribution on the process-induced residual stresses is investigated for the pultrusion process of a glass/polyester profile (50×50 mm). The actual microstructure is obtained using an optical microscopy. An image segmentation is performed based on the histogram of the gray value which is used to distinguish the fiber and matrix and estimate the actual Vf which is then used in the thermo-chemical-mechanical process model. The enmeshment of the model is adjusted according to the image segmentation. The temperature and degree of cure distributions are interpolated in the local mesh to calculate the local residual stresses and shape distortions. The stress localization due to the actual local Vf distribution is quantified using the proposed numerical process modelling approach.