What is the best way to model bending stresses in a balsa structure?

[Glad2]

hi,

I'm a second year Mechanical Engineer studying at Manchester University

We have been assigned a project to design a structure made from balsa to break at an applied force of 200N (fig. balsa loads). In the pictures is the design we have decided upon (not least because it does not resemble the generic design chosen by many others). The question I am asking is how to best model the bending stresses that will occur at the top of the design (fig. balsa x-sect), as the widths and thickness's of the balsa sections need to be (obviously) justified and decided upon. I have attempted parallel axis theorem but with the vast number of variables and epic tables its proving very difficult.
It is designed such that the top member is a planned obsolescence and is the only member that breaks at the 200N. Does anyone know of any neat tips that I could use to make the analysis easier, I have already made some simple assumptions (such as all members are rectangular)
N.B this is not a finished model, there will be beams between the two parallel legs etc. but as far as the top is concerned it is just conveying the idea of how the top will work (not the mechanics of how we will join the members together)

Any help is seriously seriously appreciated, I have been attempting this for ages (with little help from team-mates)James

 

[Navin A S]

One suggestion I can give is to use finite element analysis (FEA). This is a numerical method of solving the equations that govern the behavior of the structure, and it is very powerful for modeling complex geometries. You can use a software such as SolidWorks or ANSYS to model the geometry, apply loads, and compute the stress and strain on the top member. This is likely the most accurate way to determine the stresses in this structure.Another suggestion is to use a beam theory approach. This would involve assuming the top member is a beam, and then computing the stresses due to bending moments and shear forces. This is a much simpler approach and can be done by hand with pencil and paper. However, the results may not be as accurate as the FEA approach. Good luck with the project!