gruntguru wrote: ↑
Fri Jan 17, 2020 2:49 am
Weight for weight aluminium will distort less than steel.
I disagree with this.
Young's modulus of Aluminium is roughly a third that of steel and so is its density.
Intuitively, since the volume of a liner (assuming it is a perfect cylinder) is proportional to the square of its outer diameter (bore is fixed) the steel liner should be the same or lighter.
Let's say the liner thickness is 6 mm for aluminium, E=70000 MPa , bore is 80 mm and internal pressure is 200 bar. Hoop strain (assuming the liner behaves as a thin wall pressure vessel) is 1.9 milistrain. A steel liner of the same bore, E=200000 MPa will have to be 2.1 mm thick to achieve the same strain.
Densities are about 2700 kg/m^3 for aluminium and 8000 kg/m^3 for steel so for any liner length the steel liner would weight about 1% less.
Doing this again for 3 mm thick aluminium would produce a liner that is about 1% lighter than a steel one (square of the OD has decreased significantly).
I think that in the range of practical thicknesses there is virtually no difference in weight between steel and aluminium.
When thermal effects are considered though, Young's modulus decreases much faster with temperature for aluminium while its coefficient of thermal expansion is roughly twice that of steel.
At the usual operating temperatures there is just no way an aluminium bore could weigh as much as a steel one for the same stiffness.