Extrusion dimensions: 11.5x19.5x1.5x800 mm
Material: Uncoated aluminium, no other data
Test length: 710 mm
Test weight: 1.6 kg
Tension element: M3 threaded rod
Load (kg) Camber (mm) Total deflection (mm)
------------------------------
0.0 0.00 0.00
1.6 0.00 1.18
1.6 0.05 1.15
1.6 0.10 1.18
1.6 0.15 1.22
1.6 0.20 1.22
1.6 0.25 1.24
where:
δ = the deflection of the beam
F = force acting on the centre of the beam
L = length of the beam between the supports
E = modulus of elasticity
I = area moment of inertia
Area Moment of Inertia: (mm4): (X) 1.58 x 104 (Y) 6.07 x 104
Ultimate Tensile Strength: 30 ksi
Modulus of Elasticity: 70 GPa
Cre8ivdsgn wrote:I had been considering the stiffening of the makerslide by bolting a rectanglar solid slab of aluminum and so I =(b*h^3)/12 made sense. But this equation also assumes that the ends are rigidly fixed so that the neutral surface (where the compression forces and the tension forces cancel) is basically the centroid of the part. I=(b*h^3)/12 applies. Intuitively (a dangerous thing!!!) Bart's moment of inertia is about 4x greater than I would have thought.
Cre8ivdsgn wrote:I was wondering if the cad program provided a moment of inertia at Y=0 or did it provide it at the neutral axis of the part. If Y=0, then I-(b*h^3)/3 or a value 4x greater, making deflection 4X less.
Its been 25 years since I went through this last! I have noticed in my mechanics of materials book that it gives moments of inertia at both the neutral axis and Y=0, but I am drawing a blank for when Y=0 comes into play - maybe when figuring out yield strenghth? It really has been too long!!! If anyone could clarify this for me, its beginning to gnaw at my mind (and makes me feel a bit like an idiot for even posting this)!!!
Cre8ivdsgn wrote:And of course what happens if the ends are simply supported versus rigidly mounted like they would be for a machine. When simply supported the beam has a single curve but when rigidly mounted it has three.
Ultimately I might just set up a quick experiment on my bench and see what I get for deflection.
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