Online Cure Monitoring and Modelling of Cyanate Ester-Based Composites for High Temperature Applications

A cure kinetics investigation of a high temperature-resistant phenol novolac cyanate ester toughened with polyether sulfone (CE-PES blend) was undertaken using non-isothermal differential scanning calorimetry. Thin ply carbon fiber prepreg, based on the CE-PES formulation, was fabricated, and plates for further in-situ cure monitoring were manufactured using automated fiber placement. Online monitoring of the curing behavior utilizing Optimold sensors and Online Resin State software from Synthesites was carried out. The estimation of the glass transition temperature and degree of cure allowed us to compare real time data with the calculated parameters of the CE-PES formulation. Alongside a good agreement between the observed online data and predicted model, the excellent performance of the developed sensors at temperatures above 260 °C was also demonstrated.

Challenges of complex monitoring of the curing parameters in coupons for LRI manufacturing

In the aerospace industry, Liquid Resin Infusion (LRI) is gaining more and more importance as an out-of-autoclave alternative manufacturing technique to traditional pre-impregnated (prepreg) fabrics. The research in this field has been focused on understanding the cure and the process parameters of these materials, aiming to optimize the manufacturing process and reduce costs. A major problem derived from these technologies is the distortions induced by LRI process, affecting to composite parts due to non-uniform distribution of residual stresses. Such distortions can lead to non-uniform parts with shape distortions, which is a critical issue when trying to assembly with other parts due to mismatches in shape, leading to the rejection of such components. In this context, ELADINE project aims to understand and quantify the key manufacturing parameters that cause shape distortions on composite coupons (such as spring-in of curved parts) using an integrated numerical-experimental approach. The manufacturing process will be accurately monitored through Fiber Optic Sensors (FOS) and Dielectric sensors (DC) to understand how the process variables affect the distortion phenomena. The monitored data will feed a simulation tool for spring-in prediction for large integral composite wing structures. This article covers the preliminary results of cure monitoring and process parameters of thermoset composites implementing monitoring strategies for manufactured coupons by LRI.

Effects of post-infusion dwell on vacuum infusion of thermoset composites toughened by thermoplastic interlaminar veils

The effects of post-infusion dwell on vacuum infusion of thermoset composites toughened by non-woven thermoplastic interlaminar veils were investigated. Permeability measurements and simulation of the resin infusion process demonstrated that the toughening interlayers can effectively act as interlaminar flow distribution media. Local variations in permeability induced non-uniform flow fronts, resulting in high porosity. However, introduction of a low-temperature post-infusion dwell allowed more time for the resin to equilibrate pressure and redistribute during the post-filling stage, achieving full saturation of dry regions. The process parameters of the post-infusion dwell were determined using cure kinetics and viscosity models, while in situ process adjustments were implemented using dielectric cure monitoring system in conjunction with resin cure maps. Laminates fabricated with the modified cycle exhibited reduced porosity and greater peak load during impact testing. This work highlights potential advantages of the post-infusion dwell, which can similarly be applied to other vacuum infusion processes requiring a protracted post-filling stage.