Thread: C4.1 Chassis
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  #170  
Old 28-11-2011
Fabs Fabs is offline
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Join Date: Jan 2007
Posts: 1,133
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Ok.

First of all 1000, 2000 series etc does not relate to mechanical properties but to the main alloy. Example a 2024 is stronger than a 6082 given the same heat treatment.

Second the heat treatment (which the T6, T4 etc relates to) has no effect on stiffness. Only on strength.

Now read these:

http://en.wikipedia.org/wiki/Strength_of_materials

http://en.wikipedia.org/wiki/Stiffness

http://en.wikipedia.org/wiki/Young%27s_modulus

The key words here are failure, plastic deformation and elastic deformation.

Now what is important to understand is this:

There is no relation between the strength of a material and its stiffness.

The strength depends on many things : type of material (steel, aluminium, plastic etc), the composition of this material (which alloys, what direction for the carbon fibres, the quantity of fibres in the plastic), and in the case of metals, how it was made (how long it took to cool it down, what heat treatment etc). So, for aluminium the range of tensile strength varies between less than 100 MPa and over 500 MPa, the material with the highest tensile strength being 7075 T6.

The stiffness of the material depends on only one thing: what type of material it is. All steels have the same modulus of elasticity, all aluminiums have the same modulus of elasticity, this is true for all metals. This isn't true for carbon fibre and other composite materials.

Which brings us to our subject of interest: a chassis stiffness!

Given that during normal use, the chassis should deform but not in a permanent manner, we can safely assume that the material will stay in the zone of elastic deformation. And given that elastic deformation means direct relation to Young's Modulus only, then we can safely assume that all aluminium chassis will behave the same on the track no matter what grade of aluminium.

Now Andy, to answer your question:

When bending a chassis you go over the tensile yeld strength, into the zone of plastic (permanent) deformation. Given that not all aluminium have the same tensile yeld strength, it is normal and logical that the force varies depending on the material.

Now hope that clears it up and we have no more of this sillyness? If you haven't got a clue what I'm on about, just trusssssssssst me
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