How Do I Design an Aluminum Rod to Meet Specific Engineering Requirements?

[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-gauge length to engineering stress and strain?


Thanks,
Phil

 

[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]

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.

 

[alphy]

Hello Phil,

As a scientist and materials engineer, I can offer some guidance on how to approach designing an aluminum rod that meets the given specifications.

Firstly, it is important to understand the properties of aluminum and how it behaves under different loads. Aluminum is a lightweight and strong material, but it has a lower tensile strength compared to other metals like steel. This means that it can withstand less force before it starts to deform.

To begin, you can start by calculating the maximum load that the rod needs to withstand. In this case, it is 200kN. Next, you can use the formula for engineering stress (σ = F/A) to determine the cross-sectional area of the rod that is needed to withstand this force without exceeding the maximum allowable stress of 170Mpa. Keep in mind that the cross-sectional area will depend on the shape of the rod, so you will need to consider this as well.

In terms of the shape of the rod, you are on the right track with considering an "I" shape. This shape provides a good balance between strength and stiffness. However, you will also need to consider the width and depth of the rod. A wider and deeper rod will have a higher cross-sectional area and therefore, a higher capacity to withstand force. But keep in mind that the rod also needs to be at least 3.8m long and deform no more than 6mm, so you will need to find a balance between these factors.

To convert load-gauge length to engineering stress and strain, you will need to use the formula for strain (ε = ΔL/L) and the formula for engineering stress (σ = F/A). Here, ΔL is the change in length of the rod, L is the original length, F is the applied force, and A is the cross-sectional area. By plugging in the values, you can calculate the engineering stress and strain.

I hope this helps you get started on your assignment. Remember to consider the properties of aluminum and how they relate to the given specifications. Good luck!