ALUMINUM ALLOYS TUBE VERSUS STEEL TUBE    SEE OUR SITE FOR STRUCTURAL ALLOY SPECIFICS

Aluminum alloys typically have an elastic Young’s modulus of about 79 G Pascals which is about one third of the elastic modulus of most kinds of steel and steel alloys.  Therefore, for a given load, a component or unit made of an aluminum alloy will experience a greater elastic deformation than a steel part of the identical size and shape.  Through there are aluminum alloys with somewhat higher tensile strengths than the commonly used kinds of steel, simply replacing a steel part with an aluminum alloy might lead to problems.

In general, stiffer and lighter designs can be achieved with aluminum alloys than is feasible with steel.  For instance consider the bending of a thin walled tube: the second moment of area is inversely related to the stress in the tube wall, i.e. stresses are lower for the larger values.  The second moment of area is proportional to the cube of the radius times the wall thickness, thus increasing the radius (and weight) by 26% will lead to a halving of the wall stress.  For this reason, bicycle frames made of aluminum alloys make use of larger tube diameters than steel or titanium in order to yield the desired stiffness and strength.  In automotive engineering, cars made of aluminum alloys employ space frames made of extruded profiles to ensure rigidly.  This represents a radical change from the common approach for current steel car design, which depends on the body shells for stiffness, that is a unibody design.