# Desining a aluminium rod

#### Philip Wong

Hi guys,
I'm studying my first semester in engineering, I was giving the first assignment in my material science class which I'm not so sure on how to get started on.

The assignment was to ask us to design a aluminum rod which has the following specification:
1) Withstand an applied force of 200kN
2) Maximum allowable stress on the rod is limited to 170Mpa with a strain of 0.0025mm.mm^-1
3) Rod must be at least 3.8m long but deform elastically no more than 6mm when force is applied

I was thinking of a "I" shape rod, but am not sure were I on the right track or what should I include (e.g. width, depth, and shape) to sufficiently uphold the conditions.

Secondly can someone please tell me how do I convert load-guage length to engineering stress and strain?

Thanks,
Phil

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#### Jobrag

How is the force to be applied, along the length of the rod, or at 90 degrees?

#### Philip Wong

the question is just say "An aluminium rod is to withstand an applied force of 200 kN".
I guess its at orthogonal

#### Chestermiller

Mentor
the question is just say "An aluminium rod is to withstand an applied force of 200 kN".
I guess its at orthogonal
If the load is applied perpendicular to the rod (orthogonal), then you need to know the boundary conditions on the ends, and solve the problem as a beam bending problem. It sounds like, in this problem statement, a tensile load is applied on the ends. Try out some different shapes and see what you get. Start with a circular cross section for simplicity. Why? If you can't solve that, you are not going to be able to do more complicated cross sections.

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