Florian Klunker

Fast method to monitor the flow front and control injection parameters in resin transfer molding using pressure sensors

The quality of composite parts manufactured by resin transfer molding is sensitive to material and process variations during the preform impregnation. In order to improve the process robustness in two-dimensional injection cases, this work proposes a fast method for tracking and controlling the resin flow through the preform, using only a small number of pressure sensors embedded in the mold. The approach combines pressure signals and flow modeling in a quick algorithm that returns on-line estimations of the flow front profiles. Virtual and real injection tests demonstrated the accuracy of the methodology and provided information for designing the sensing system. Moreover, the investigation proved the feasibility of a simple and effective procedure of flow rate control. Based on a computer-controlled pressure regulator acting on the inlet gate, a feedback mechanism was implemented in the system and allowed keeping the flow front velocity within a target range of values. Such a control procedure may be used to limit the formation of voids and enhance the final part quality.

Fiber deformation as a result of fluid injection: modeling and validation in the case of saturated permeability measurements in through thickness direction:

The knowledge of the through thickness permeability is important for the design of modern liquid composite molding processes. In through thickness permeability measurements, the textile undergoes flow-induced compaction, changing the distribution of fiber volume content. As a consequence, results of permeability measurements show a dependency on the applied injection pressure, further denoted as apparent permeability. In the study presented in this paper, saturated permeability measurements were conducted for different fiber volume contents, varying the injection pressure. At the lowest fiber volume content used, the apparent permeability strongly varied with pressure. With increasing fiber volume content the dependency on injection pressure decreased, but it was not negligible. We used a simulation model for coupling of flow and fiber deformation in liquid composite molding in order to predict the apparent permeability in saturated through thickness permeability measurements. The input data for the simulation model were determined by measurements of saturated permeability, using a very low injection pressure, and textile compaction properties. With the proposed methodology, a good agreement of simulation and experimental results was achieved.

Simulation of the cure of paste adhesives by induction heating

This study, part of the European JTI ‘Clean sky’, presents a simulation model designed to predict the evolution of the degree of cure of the paste adhesives used in carbon fiber reinforced polymer bonded systems cured by induction heating. The simulation combines induced Eddy currents in electrical conductive materials, which cause the heating of the carbon fiber reinforced polymer adherents by Joule effect, and the consequent chemical reaction which gives the relation between temperature, time and degree of cure of the adhesive. The model is validated and used to analyze the impact of different parameters on the degree of cure of the paste adhesive.

Evaluation of nanoalumina and nanosilica particle toughened high glass-transition temperature epoxy for liquid composite molding processes:

In this study, nanoalumina (Al2O3) and nanosilica (SiO2) particles are evaluated as tougheners for a high glass-transition temperature (Tg) epoxy system in correlation with liquid composite molding (LCM) processability. The aim of this paper is to directly compare the effectiveness of nanoalumina and nanosilica of the same nominal particle size as epoxy tougheners on the same neat resin system. The epoxy resin system used in this study was Dow D.E.R. 330 amine cured epoxy with a Tg of 150℃. Both particle types are observed to be Tg neutral and increase fracture toughness of the base epoxy system. Between the two particle types, nanoalumina is found to be more effective than nanosilica in terms of achievable fracture toughness at a given particle loading. As resin viscosity increases with particle addition, the addition of fewer particles with the use of nanoalumina is also beneficial to LCM processing where a lower viscosity is preferable.

Experimental validation of through-thickness resin flow model in the consolidation of saturated porous media

In this paper, a reliable and reproducible experimental procedure for the study of the through-thickness flow induced by the compaction of a saturated porous media is presented. Experimental fluid pressure data are exploited in the validation of a fully coupled fluid-mechanical model and the verification of the related material parameters. The experimental results show overall good agreement with the numerical solution, for all three configurations tested. In addition, up-scaling rules have been identified, which relate the consolidation time with the fluid viscosity and the number of layers.

Modeling of void formation during the curing process of paste adhesives

In this study, the void formation of the paste adhesives used for bonding of aerospace components is investigated. When high temperatures are applied to accelerate the curing process, volatiles evaporate; therefore the mechanical performance of joints is affected as a result of an increased void content. Today, mass reduction models only consider the degradation of fully cured samples, not taking into account the influence of the curing process on the quality of the paste adhesive. The fundamental idea of this paper is that the amount of mass reduction as a result of evaporation of the paste adhesive decreases with higher curing progression. For quantification, a model is defined approximating the mass reduction in a paste adhesive as a function of temperature, time and the degree of cure. Thermo gravimetric analysis is used to obtain the experimental data of the evaporation process for curing cycles with a single dwell at different temperatures applied to the paste adhesive. These data are used to define a theoretical model, which is validated by comparing the experimental and simulated data for non-isothermal heating processes. Finally, a relation between evaporated mass and void generation during the curing process is established in order to assess the bonding quality of the joint in terms of final void content as a result of the curing cycle.