Short overview of how to use Digimat to calculate engineering constants for fiber reinforced materials. Digimat is an Advanced Materials Modeling application from MSC Software that is available within MSC One Token licensing solution -there's a number of different modules. Things for simulating additive manufacturing; things for mapping material properties over from, for example, injection moulding simulation to an FE model. What we're going to look at today is difference between Digimat MF using mean field homogenization method & Digimat FE which uses an FEA analysis to generate material constants.
Firstly we're looking at Digimat’s fairly simple GUI and add an analysis to it. Because it's a 2 phase composite we need to define 2 materials. Material one is epoxy that is elastic & isotropic and we validate there and then. I need to add a second material - glass - also elastic and isotropic.
Next step is to microstructure, and what I'm going to model this as a 60% glass filled, long fiber unidirectional material. To do that, I stick with generic microstructure, & first phase is going to be the matrix. So, first type is matrix, choose material that I predefined, Create then add another phase - “GF” for glass fiber, continuous fibers. Validate, and make it 60% by mass. Enter 0.6 mass fraction.
Because what I'm trying to do is get equivalent stiffness, all I need to do is define a loading here. I can pretty much accept defaults and hit “Create”. Then run my simulation, answer simple questions and as quickly as that it has done the calculation.
So, if I click on stiffness in the results, go to engineering constants, you can see it's calculated the three principal stiffnesses, calculated six Poisson’s ratios, and it's calculated three shear terms and the global density.
So, as quickly as that, I've generated material properties that I can take forward to use in either a 3D Orthotropic Solid FEA model, or thick shell model, & these are solver agnostic. It could be used for Nastran, Marc or It could be useful for ANSYS, Abacus or Hyperworks, or 1 of the other solvers.
If you want to get into more detail about the way in which your materials are defined, for example, using a fabric, then, you need to look at Digimat FE. I'm just going to walk you through one that I've already defined - the GUI is basically identical, and we add an analysis, and work our way down - I define Glass and Epoxy in exactly the same way.
My microstructure in this instance - defining a fabric where you choose the matrix and yarn, so you can have different yarns in different directions. Yarns are defined in terms of linear density & cross-sectional dimensions, & individual fiber dimensions; we can define braiding angle and can play around with weave pattern to decide how this thing is woven together.
That will take us forward next to building a geometry model. So it actually produces 3D parasolid bodies that it will then go on to mesh. To show you the matrix and the fibers, how it's generated, we can look at the mesh.
There's 2 options for the mesh. There's a conforming tetra mesh where it throws a tetrahedral mesh on the fibers and on resin that gets harder & harder to do more complicated your microstructure is. if I go into Visualization settings, hide the matrix there, you can see what it's done - basically calculated which elements intersect with which bodies & applied material for largest proportion. Moving down under loadings, choose which properties to evaluate. It will build 6 separate FE jobs with appropriate boundary conditions; run 6 separate FE analyses to generate output.
We then use solution to create a new job - it spawns 6 different FE jobs to use MSC Marc, FEA Solver then Digimat extracts key results to calculate stiffness properties. Each of these takes just over a minute to run - total runtime for all 6 jobs is about 10 -12 mins.
Once run, results are imported automatically & we look at engineering constants calculated.
It’s a longer route to get an answer, but it's a higher fidelity answer because it's using FEA to represent changes in direction locally of the fabric. Again, these materials can be taken and plugged into any FE code of your choice and used for 3D orthotropic material representation.
If you do something that needs a 3D ortotropic material, the properties are often not readily available or uncommon terms are approximated, or guessed at & not always available from material suppliers. The testing can be quite expensive to fully characterize such a material. So having Digimat in your bag of tricks with MSC One means you have a tool where you can produce pretty good material representations very quickly to use in more advanced FEA analysis
If you have any questions about this or you'd like to see more or understand more, please get in touch with DTE and we'll see what we can do to help you. www.dte.co.uk