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  1. #1

    Join Date
    Nov 2020
    Posts
    90

    Question FEA for epoxy granite.

    Hey

    Does anyone have any ideas how to 'reliably' run FEA on epoxy granite?

    Granite is non-isotropic
    Epoxy, I don't really know

    Together? No idea, a mix of both I guess?

    FEA doesn't really work for non-isotropic materials, for concrete, big companies have their own algorithms that they use.

    Any ideas?

  2. #2
    Member
    Join Date
    Jul 2018
    Posts
    2564

    Re: FEA for epoxy granite.

    Hi Ard,
    Granite and epoxy can be considered isotropic for the purposes of FE. Its mix will be isotropic as well. The issue is establishing an accurate youngs modulus to use. Typically the rule of mixtures is used to estimate an E. Its Poisson ratio will be 0.25 - 0.3 and this will not make a real delta either. The strains in machine parts are so small these things don't matter. Machines are designed to be very stiff. Stresses are in the order of 1-2Mpa so strains are tiny. Granite varies from 40-60GPa stiffness. Epoxy is about 2-3GPa. Have a look at CSA cement I think its superior. I'm about to make some parts using this. Epoxy is expensive but not stiff. CSA is 2200kg/m3 and 23-30GPa stiffness. Look up the Milli thread it gets discussed there. Peter

    FE is used for non-isotropic materials all the time. I do alot of composite analysis for yacht structures. Orthotropic solvers just aren't on desktop CAD yet as most people work in metals.

  3. #3

    Join Date
    Nov 2020
    Posts
    90

    Re: FEA for epoxy granite.

    Thanks for the info. I did read through the entirety of your thread. I know the feeling of going in circles with machine design. That's what's been happening to me for the past 7 months too. When all components are co-dependant on each other etc. I did find a solution in the end, for going in circles. You start with the spindle, then you design an appropriate z_axis for it then x...etc. Most diy starts at the bed though. I think that's just inviting trouble.

    As for CSA, I'm a little on the fence when it comes to longevity, concrete in general develops cracks, sooner or later, it's just the nature of it. I'll be paying a close attention to your thread and your experience with CSA. Good luck.

  4. #4
    Registered
    Join Date
    Mar 2010
    Posts
    32

    Re: FEA for epoxy granite.

    FEA of good quality epoxy/quartz castings is very reliable.

  5. #5
    Registered
    Join Date
    Aug 2006
    Posts
    29

    Re: FEA for epoxy granite.

    Quote Originally Posted by castinite View Post
    FEA of good quality epoxy/quartz castings is very reliable.
    How do you do that in practice? What software etc? I would really like to get into this....

    /Thomas

  6. #6
    Member
    Join Date
    Jul 2018
    Posts
    2564

    Re: FEA for epoxy granite.

    Hi Thomas - I do FE work commercially and use Strand7 and Simsolid. Most CAD systems these days come with basic FEA capabilities. Look at Fusion 360 for instance. FreeCAD has FE as well. Peter

  7. #7
    Member
    Join Date
    Jul 2018
    Posts
    2564

    Re: FEA for epoxy granite.

    Hi Thomas - Rampf publish their material properties. Typical of mineral cast materials. Peter

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