How to obtain permeability values for vacuum infusion

How to obtain permeability values for vacuum infusion

To achieve the first time right dream, smarter and better solutions are always being researched to improve many of the methods used to create composite products. One of such methods is vacuum infusion. Unsuccessful infusion is one of the risks that come with this production process.  A genius solution invented to prevent failure and minimize waste of time and products is infusion simulation software. These simulation programs are used to imitate an actual vacuum infusion process on a fictional digital model. 

The permeability of composite laminates and viscosity of resins are two important parameters required to carry out a simulation. These parameters are not readily available for each material, and so must be determined before hand. Hadiza Hamza, 3rd year aeronautical engineering student: “I was asked to o create a new method to determine the permeability parameter of fibre material. I accepted this challenge because I love writing code and I’m generally interested in programming. This assignment gives me the opportunity to enhance these skills and to combine it with a practical application. Practicing the vacuum infusion production process and using the smart mould was definitely a bonus.”

This project is a continuation of ROBOCOMPO, also a RAAK research programme looking into automation possibilities for the vacuum infusion production process. The smart mould is a result of ROBOCOMPO and created together with Twenco and Polyworx, both partners of First Time Right.

RTM Worx by Polyworx is the vacuum infusion simulation program available for the First Time Right. Therefore the method used to determine the permeability parameter have to be compatible with the RTM Worx program.

“The permeability calibrator”

The subject of determining these parameters have been researched in the last 10 to 15 years resulting in different approaches. For First Time Right one these approached was selected based on simplicity, the availability of the smart mould with integrated sensors and found and compatibility with RTM Worx.

Hadiza: “The method has no official name but I would like to call it The permeability calibrator”. It is a system that will be able to determine the optimal permeability value of a composite fibre layup through vacuum infusion. The method first involves actual vacuum infusion of a 3-layered laminate of the same fibre material, using water in stead of resin on the smart mould. The smart mould by Twenco has 4 imbedded dielectric sensors at equal intervals. It records real time the arrival of resin, resin flow, at each sensor by recording change in capacitance.

As RTM worx requires the permeability parameters to carry out the simulation, a code is necessary to convert the resin arrival data from the mould into the parameter values. This data is referred to in a SALT code and applied to the optimization algorithm known as DIRECT (Dividing Rectangles). DIRECT is a partitioning algorithm that samples’ points in a given domain and then refines the search domain at each iteration based on the objective function values at the sampled points.

For the SALT code, the domain (lower and upper bounds) given is an estimated guess of the range in which the permeability is most likely to fall within. After much research, the range of 1e-10 m2 to 1e-11 m2 was chosen. This is because it was observed that most composite fibre weaves’ permeability values fall within the same range.

RTM Worx uses the optimized parameter value to imitate the resin flow within a virtual laminate model with the same geometry properties as the real one.

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