A methodology for microstructural evaluation of unsaturated flow phenomena by in‐situ UV‐flow freezing

Abstract Microstructural analysis of resin flow in liquid composite molding is impeded by the absence of a characterization method that possesses both the required spatial and time resolution to capture the ongoing phenomena. An optimized UV‐flow freezing methodology is presented to rapidly capture dynamic flow behavior, followed by high‐resolution micro‐computed tomography (μCT) imaging to extract the flow front morphology. Optimisation of the resin strongly enhances the photopolymerisation kinetics, reducing the gelation time by up to 56%, while an adequate postcuring procedure at moderate temperature is proposed by introducing radical induced cationic polymerization. Additives are identified to facilitate facile variation of the capillary number while distortions of the flow front morphology are minimized by finetuning the experimental procedure. μCT imaging allows for a micron‐scale through‐thickness assessment of unsaturated flow at range of flow regimes corresponding to both capillary‐ and viscous‐dominated flow regimes while the corresponding saturation curves were derived by segmentation of the resulting images. Highlights An optimized method for evaluating microstructural flow in fibrous preforms. Optimisation of the resin composition allows for fast UV‐photopolymerisation. Additives identified for facile variation of the capillary number. Visualization of “frozen” microstructural flow by micro‐CT analysis. Applicable to broad range of flow conditions that normally cannot be captured.