Project Details
Projekt
Modelling porosity in composite liquid infusion processes
Subject Area
Polymeric and Biogenic Materials and Derived Composites
Materials in Sintering Processes and Generative Manufacturing Processes
Materials in Sintering Processes and Generative Manufacturing Processes
Term
from 2019 to 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 432847151
Composites manufacturing to combine reinforcing fibres and liquid resin can be undertaken in different ways. The most popular method involves infusing the resin under pressure so that it is forced to permeate though a dry fabric that is held in closed tooling (Resin Transfer Moulding – RTM) or under vacuum membranes (Vacuum Infusion - VI). Subsequent curing then takes place before the part is removed for final machining. Regardless of the infusion method an essential requirement is full impregnation of the composite preform without defects. In practice this is difficult to realise, and a major problem is the generation of voids and porosity. Some porosity is always present; however, it should be limited to under 1-3% since even this amount can reduce composite strength properties by up to 20% and is especially detrimental to long term fatigue properties. Porosity in infusion processes is almost entirely due to the formation of air bubbles as the resin flows through the fibre reinforcement. At the flow front dual phase flow occurs involving combined fast flow of resin through gaps in the open fabric architecture, combined with delayed infiltration of the individual compact yarns, causing air entrapment and the creation of bubbles. Air may be permanently trapped or may evacuate the yarns and cling to the yarn by surface tension forces. With high pressure gradients bubbles may flow with the resin through channels in the fabric architecture, either to be trapped at some point, or to be evacuated at an outlet vent. Furthermore, bubbles may coalesce, or possibly collapse (diffusion). Finally, their size will change depending on their internal pressure at formation and final applied pressure during resin cure. The final size and distribution of these bubbles determines the porosity distribution.This project will investigate experimentally the processing conditions that create bubbles, the mechanisms of bubble migration and the processing conditions that determine final void sizes and porosity in cured composites. The work will be supported by numerical methods for prediction using finite element (FE) and analytical solutions to obtain criteria for porosity generation. A final task will develop FE and surrogate models using artificial intelligence (artificial neural network - ANN) solutions to predict porosity of two demonstrator parts. The ANN approach is of special interest, since such a technique is computationally fast and could, conceivably, be used in ‘real time’ to monitor sensors in infusion manufacture of a part and control flow rates in for minimum void content.
DFG Programme
Research Grants
