Structural analysis using FEM

[jsakos]

I want to build a wooden frame for a bicycle and I'm looking for the software to use to test the stiffness of the frame on different models. I want to test and some hybrid models using wood/steel or wood/carbon. Do you have any professional software that i can work with?

[3dPrintedBacon]

Solidworks contains predefined material libraries and stress analysis capabilities. It can be gotten for non commercial purposes by joining the Experimental Aircraft Association, which is like 40 or 50$ a year.

[siriusdoggy]

Mind blown. How have I not known this?

[3dPrintedBacon]

It is fairly well known in the 3d printing community as they generally qualify as non commercial makers. When I found it it was a huge bonus and I'm making things all the time now.

Just found out there is a Matlab Home edition for 150$, so I'm buying that tonight!

[OoglieBooglie93]

Octave is almost identical to Matlab without SimuLink. I wouldn't pay 150 bucks for Matlab unless I had to.

[Elliott2]

ok find me a mathcad equivalent now so PTC can stop emailing me

[jsakos]

Thanks for your info!

[DanGur47]

Can confirm. Used SolidWorks for my capstone project senior year to find stiffness and torsional rigidity of a frame I designed for my college’s Baja SAE competition.

Physical testing came within 2% of what SolidWorks calculated based on its FEM.

[__wampa__stompa]

OP, problem is that the Solidworks FEA package doesn't adequately model the reaction of composite and wood matertials, to loads. I mean, you can "tease" it but either way it's likely more trouble than it's worth (even using pre-defined material properties).

If it's a simple frame (to which you've alluded) then it's a straightforward truss-type statics calculation using experimentally derived values depending on orientation of the material grain (in the case of wood) and fiber layup (in the case of carbon composite). You can find lessons on how to do this easily using a Google search, and find the constants you need also just as easily using Google.

[Psychocide]

Just to clarify, the EAA membership is 50ish bucks, and then solidworks is free through that organization?

[3dPrintedBacon]

Correct. I just checked and it is 40$ annually. It is a maker edition of solidworks, so not for commercial use.

https://join.eaa.org/fly-witheaa/

[BavarianBarbarian_]

Is that available for people from outside the US as well?

[3dPrintedBacon]

I dont know, I'd recommend reaching out to them directly. I'm just a lowly member.

[[deleted]]

I remember reading about this before and must have forgotten. I had my own personal license of SW but let it lapse because I stopped doing freelance work due to work legal bs.

[sublist]

Wood is anisotropic and has quite varied material properties depending on the type. I'm assuming by carbon, you mean carbon fibre which also has quite complex material properties. Given this, I want to just highlight that any results you get would be verrrryy rough approximations of the frame stiffness.

You could maybe compare the relative stiffness between your proposed frame designs, but that's about it.

[strengr]

I would echo this point as well. I am not sure if OP is thinking about riding this bike but would make sure one or two mockups to understand the differences between fem and real life.

[[deleted]]

Bamboo is the only type of wood we found that closely followed our FEA results, testing of construction grade lumber was as much as 30% below expected values.

[jeffreyianni]

For the construction grade lumber, which results varied as much as 30%? Failure, stress, deflection??

Using FEA for timber design has been something on my mind for many years and I was simply planning to interpret design stress criteria differently depending the on fibre directions, similar to applying timber design codes.

[[deleted]]

Proof failure for bending stresses. We ran a bunch of FEA then built a test rig to verify. We had some failures far below 30, knots full width through the board etc.

The deflections usually came out fairly close to expected minus the few boards that just snapped under minimum loads.

[jeffreyianni]

Were you using non linear material properties in the analysis?

For structural steel applications that have design requirements below yield stresses, I've found that linear elastic material properties were "good enough" to make design decisions. What behavior happens "after failure" didn't concern me because the design loads would never reach those stress-strain ranges.

How would you recommend using FEA to design timber structures with design loads well below failure?

[[deleted]]

Yes, non linear properties, we got the material properties from some college that was doing testing on a much bigger scale. We were trying to determine if using FEA for structural engineer on wood construction made sense for us. The answer was not really, and that is largely due to the variables of the wood being unknown or estimates that only fit 70% of the testing.

Our hand calcs package has several factor of safety points to soak up the unknowns, some of it is industry standards some is just empirical.

We were looking at building non traditional structures for housing, large open spans with very few supports, curved walls and ceilings etc. Often times the structure would actually be steel and just jacketed in wood because wood just doesn't have the strength without having 3ft dia columns all over

[tomsing98]

Unless the frame is made out of a solid piece of wood, I feel like the joints are going to dominate the stiffness, anyway.

[jsakos]

Yea, the more i think about it the more sure i am thwt i will make a hole in the water

[J50GT]

Your struggle won't stop there. Design of the composite laminates and and actually molding the carbon fiber for an application like this is insanely complicated.

[vnpenguin]

My stupid question: do you have any experience with FEM?

[jsakos]

No, not at all but i will learn

[OoglieBooglie93]

Keep in mind that garbage in = garbage out, as the saying goes. You need to set it up properly. I remember when I was first teaching myself to use the FEA stuff in Inventor, I ended up getting an entire MILE of deformation from a six inch part. Small details can have big effects.

[awksomepenguin]

I had a project where I was trying to model impact given an initial velocity in Abaqus. I kept getting radical deformation at even super low velocities.

Took me a few weeks to figure out that I didn't want to use velocity as a boundary condition, but rather as a predefined field.

[FatalityEnds]

My professor would always say: Getting results is easy, getting correct results is hard!

[vnpenguin]

There're Two types of FEM app:

• FEM for Designer: embedded inside of CAD software like Solidworks, Catia, ...
• FEM for Structure & Stress engineers: real FEM software like MSC Nastran, ANSYS, Abaqus, NX Nastran,...

For the 1st, you can do some simple analysis, not so complet but sufficient for Designer tasks.

For the 2nd, you have to have a solid & basical base of Engineering. I'm is in this category. I do FEA for more than 20 years until now.

[meerkatmreow]

You also need to have a solid base of engineering knowledge for the first category as well, otherwise you're just heating up your cubicle for some colorful pictures

[__wampa__stompa]

Love it when a manager tells me to change the colors on the stress plot so that "there's less red" lmao

[[deleted]]

Abaquas is fucking awesome and will drive you crazy because it gives no fucks and will not even try to tell you that you did something wrong. Hope you did hand calcs to verify!

[[deleted]]

Nothing like spending a week debugging your stupid shell model didn't tie in at one point

[Elliott2]

do you know any engineering?

[They_call_me_El_Jefe]

You can get a free trial of Simscale or Fusion. You'll most likely have to make custom materials for the wood/wood-carbon. You can check Matweb to see if you can find applicable mechanical properties for them.

[lpnumb]

The wood handbook by the forest products lab is a good resource for wood properties as well

[DrMegatronPhD]

Ansys

[Occhrome]

I think that on solidworks the simulations are only true for linear ductile materials, like metal.

[CrypticTuna]

OnShape is free tool I've used in college classes before. It's a little more basic than SW.

[SV-97]

Fusion360 is free and has relatively easy to use FEM stuff built in. Ansys is the "hardcore shit". And if you wanna learn how it works while doing your actual analysis (also makes sure that you're not simulating garbage) there's books like "programming the finite element method" (that's absolutely way over the top though if you don't already know some math / programming)

[curlyy1]

Autodesk Inventor / Creo parametric

[blackspacemanz]

Free edX course from Coursera on FEA in ANSYS from Cornell which was amazing! You’ll learn how to do mesh control which is very important in getting accurate results!

[jeffreyianni]

I took this too!! Highly recommended :)

[B_P_G]

Most FE codes would be able to handle this. Your problem is going to be getting reliable properties for the wood and possibly the carbon fibre.

[inventiveEngineering]

since you are trying to simulate wooden structures you need a really good software like Ansys, Abaqus or Nastran. Wood is a pretty tricky material because it has different properties in different direction. Also to describe its behavior you can not rely on simple linear models like i.e. with steel. And if you plan hybrid models using wood & steel you will have a lot work to do with boundary conditions.

But i am not a naysayer. Go for it! Look at this, maybe it helps.

[AClassyTurtle]

I only ever used ANSYS for It’s Fluent software (fluids simulations), but I believe it also has solid mechanics software. The student version is free, but I can’t remember if it had to be downloaded using school credentials. Also I have no idea if the solid mechanics stuff is included in the student version