Is wood possible for a material with sns?

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Permalink Reply by Vadim Shapiro on February 16, 2011 at 6:39pm

Not yet,  but it is on our list. 

Version 1.0 of S&S will have only isotropic materials (material properties do not change depending on orientation).    But thank you for bringing this up,  because we really would like to know how *you* (the users) would like to specify the material properties for wood?    It is usually considered an orthotropic material (with different properties in x, y, and z directions).    But how would a user indicate what happens in which  directions?  ... and of course, choosing x,y,z directions may not work so well for bent wood ...   

What kind of wood models are you considering? 

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Permalink Reply by Brian Kraut on March 7, 2011 at 11:45am

I was excited to see a lower cost product for FEA available, but for me not having wood and unidirectional composites makes it a non-starter.  I was looking for something to analyze wood and composite aircraft structures.

 

Yes, I understand that a more advanced analysis by a structural engineer with tools designed for this is prudent, but I need a simple and low cost tool for doing the initial design work before that happens.

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Permalink Reply by Vadim Shapiro on March 7, 2011 at 11:56am

Could you please help us by describing a non-trivial example of a "uni-directional composite" and how you would want to describe the preferred direction in the user interface?

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Permalink Reply by Brian Kraut on March 15, 2011 at 9:12am

One example would be something like a wing spar.  Common methods of building them would be in an I beam type of form of unidirectional carbon fiber or a box type spar made up of spruce caps top and bottom with plywood webbing on both sides.  Not sure how to describe the direction as I have not used FEA software before.

 

Another example I can think of would be a landing gear leg made up of unidirectional fiberglass or carbon fiber and being able to analyze how much it flexes at different weights on it (or G loads on landing) and at what loading it will break and where it would break.  This is needed to determine how thick it needs to be made for the correct flex and strength.

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Permalink Reply by Nariman Mousavi on April 2, 2011 at 10:53pm

Another example would be wood to wood joints which are appearing more often in building thanks to cnc fabrication methods.  There's great potential here since designs explore complex joints which can make it difficult to predict where a component would fail.  Since with wood strength is relative to the grain direction user input does not need to be complicated but does have to be set for each component individually. I'm thinking two clicks (using osnap) on a curve existing on the geometry to decide the longitudinal direction of the grain and a third optional click for the root end vs crown end. I'm very interested in this and can provide more information if it helps. Thanks.

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Permalink Reply by Michael Roberts on May 1, 2011 at 3:48am

I have just started to use SnS to analyse certain heavily stressed parts of a 62 foot catamaran hull.  The hull is a sandwich of epoxy laminates and foam and even some plywood.  Like wood, the sandwich is not isotropic but it does not matter.  What I need to know (and SnS shows me) are the stress 'hot spots', points of maximum positive and negative stress and a visualisation of deflection.  Provided the cross sectional areas are the same,  the actual stress values do not depend on the material properties.  Having identified the critical values it's up to the designer to see if the max stress exceeds the known values of his composite construction material.

 

I am looking forward to being able to solve all sorts of structures, like the carbon fibre wing mast, SnS is a really useful design tool, I love it!

 

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• SnS stress picture.jpg, 902 KB

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Permalink Reply by Michael Freytag on May 3, 2011 at 9:50am

A word of caution: one should exercise extreme care in extrapolating stress results with isotropic materials to mixed materials and composites.  It is true that in simple cases, stress=(force/area) independently of material choice, and one can get a pretty good idea where the potential hotspots may be even when the material is not quite right.    In general, however, this independence from material does not always hold true.  As an example, imagine an extreme case of changing the core material from foam to solid aluminum.  Principal stresses in the composite skin would drop dramatically as the aluminum carries the load, yet the geometry of the assemblage remains the same.

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