Chosen Material

The chosen material for the crane is Aluminium alloy 7075. It is commonly used in bikes and aerospace as a light metal with high strength and moderate toughness.

It is also important to note: The yield stress has been used to compare the calculated values not the ultimate tensile stress as by the time the stresses had built up so much to reach the ultimate tensile stress the material will have completely plasticly deformed and the crane would be unusable. The yield stress is the point at which the material begins to plasticly and permanently deform which is very undesirable.

For untreated 7075 aluminium:

Specific Density: 2810 Kg/cb.m
Youngs Modulus: 72 Gpa
Yield Stress: 145 x10^6 pa
USD/LB: 0.97

Compared to steel:

Specific Density: 7850 Kg/cb.m
Youngs Modulus: 210Gpa
Yield Stress: 300x10^6 pa
USD/LB: 0.55

It isn't as strong with a Youngs modulus of 75Gpa whereas steel has 200Gpa. However it is much lighter with a specific gravity of 2810 compared with 7850. Its yield strength is 145 x10^6 pa which is below steel but should be more than enough for our crane.

Specific Density: 2640 Kg/cb.m
Youngs Modulus: 68 Gpa
Yield Stress: 60 x10^6 pa
USD/LB: 1.04

Compared with pure aluminium:
It is stronger than pure aluminium, as aluminium's value is 68Gpa but it is the yield stress that is greatly different as pure aluminium is only 60 x10^6 pa. It is slightly heavier by around 200kg/cu.m but this shouldn't make that much difference for the small amounts we'll be using.


To conclude Aluminium alloy 7075 is well suited for our crane as it is light (lighter than steel), it is strong so it should easily be able to withstand the loads and it is reasonably priced. As with all metals prices do fluctuate with the market but at current values it is 0.97 USD/LB.