Liquid Resin Infusion Process Validation through Fiber Optic Sensor Technology

In the proposed work, a fiber-optic-based sensor network was employed for the monitoring of the liquid resin infusion process. The item under test was a panel composed by a skin and four stringers, sensorized in such a way that both the temperature and the resin arrival could be monitored. The network was arranged with 18 Fiber Bragg Gratings (FBGs) working as temperature sensors and 22 fiber optic probes with a modified front-end in order to detect the resin presence. After an in-depth study to find a better solution to install the sensors without affecting the measurements, the system was investigated using a commercial Micron Optics at 0.5 Hz, with a passive split-box connected in order to be able to sense all the sensors simultaneously. The obtained results in terms of resin arrival detection at different locations and the relative temperature trend allowed us to validate an infusion process numerical model, giving us better understanding of what the actual resin flow was and the time needed to dry preform filling during the infusion process.

Development of Detailed FE Numerical Models for Assessing the Replacement of Metal with Composite Materials Applied to an Executive Aircraft Wing

This work provides a feasibility and effectiveness analysis, through numerical investigation, of metal replacement of primary components with composite material for an executive aircraft wing. In particular, benefits and disadvantages of replacing metal, usually adopted to manufacture this structural component, with composite material are explored. To accomplish this task, a detailed FEM numerical model of the composite aircraft wing was deployed by taking into account process constraints related to Liquid Resin Infusion, which was selected as the preferred manufacturing technique to fabricate the wing. We obtained a geometric and material layup definition for the CFRP components of the wing, which demonstrated that the replacement of the metal elements with composite materials did not affect the structural performance and can guarantee a substantial advantage for the structure in terms of weight reduction when compared to the equivalent metallic configuration, even for existing executive wing configurations.

Effect of Core Architecture on Charpy Impact and Compression Properties of Tufted Sandwich Structural Composites

This study presents a novel sandwich structure that replaces the polypropylene (PP) foam core with a carbon fiber non-woven material in the tufting process and the liquid resin infusion (LRI) process. An experimental investigation was conducted into the flatwise compression properties and Charpy impact resistance of sandwich composites. The obtained results validate an enhancement to the mechanical properties due to the non-woven core and tufting yarns. Compared to samples with a pure foam core and samples without tufting threads, the compressive strength increased by 45% and 86%, respectively. The sample with a non-woven layer and tufting yarns had the highest Charpy absorbed energy (23.85 Kj/m2), which is approximately 66% higher than the samples without a non-woven layer and 90% higher than the samples without tufting yarns. Due to the buckling of the resin cylinders in the Z-direction that occurred in all of the different sandwich samples during the compression test, the classical buckling theory was adopted to analyze the differences between the results. The specific properties of the weight gains are discussed in this paper. The results show that the core layers have a negative effect on impact resistance. Nevertheless, the addition of tufting yarns presents an obvious benefit to all of the specific properties.

Evaluation of the crosslinking steps of an unsaturated polyester resin during the infusion process of polymer-matrix composites using embedded PZT transducer

The originality of this study lies in the real-time monitoring of the crosslinking steps of the polyester resin during the Liquid Resin Infusion (LRI) process of polymer-matrix composites (PMC) by a simple measurement of the electrical capacitance variation of a PZT (Lead Zirconate Titanate) transducer embedded into the heart of the fibrous stack. Three mass rates of a Methyl Ethyl Ketone Peroxide (MEKP) hardener were tested (1wt%, 1.5wt% and 2.5wt%). The electrical capacitance showed a very sensitivity to the crosslinking kinetics while identifying the key steps of the physicochemical transitions of the thermosetting matrix. To identify the promising potential of the PZT transducer as a real-time curing assessment tool of the thermosetting resins, and understand its capacitance signature, the LRI device was multi-instrumented by various non-destructive testing (NDT) techniques such as acoustic emission (AE) and infrared thermography (IRT). The obtained NDT results are confronted with the ones conducted using the oscillatory rheology tests. The agreement between the two types of results (NDT and rheological) allows determining the gelation and vitrification phases of the polyester resin impregnating six plies of 2/2 twill glass fabrics.

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.

Experimental and Numerical Study of Vacuum Resin Infusion of Stiffened Carbon Fiber Reinforced Panels

Liquid resin infusion processes are becoming attractive for aeronautic applications as an alternative to conventional autoclave-based processes. They still present several challenges, which can be faced only with an accurate simulation able to optimize the process parameters and to replace traditional time-consuming trial-and-error procedures. This paper presents an experimentally validated model to simulate the resin infusion process of an aeronautical component by accounting for the anisotropic permeability of the reinforcement and the chemophysical and rheological changes in the crosslinking resin. The input parameters of the model have been experimentally determined. The experimental work has been devoted to the study of the curing kinetics and chemorheological behavior of the thermosetting epoxy matrix and to the determination of both the in-plane and out-of-plane permeability of two carbon fiber preforms using an ultrasonic-based method, recently developed by the authors. The numerical simulation of the resin infusion process involved the modeling of the resin flow through the reinforcement, the heat exchange in the part and within the mold, and the crosslinking reaction of the resin. The time necessary to fill the component has been measured by an optical fiber-based equipment and compared with the simulation results.