I'm talking about the sort of carbon fiber that's used in the auto industry (mostly in supercars).If an object made of steel were to be copied by an exact same object, but made of carbon fiber - how lighter would the carbon fiber object be?For example, if a table is made of steel and it weighs X, how much will it weigh if it were made of carbon fiber?Thanks.
In most applications, you do not want to make the graphite fiber composite object the same size as the steel object. You want it to have the same strength. So... the benefit of using the composite is not just the difference in density. What you really want to compare is the specific strength and you can define this slightly differently depending on your application. As a simple example, suppose you need to hang a weight of 100 pounds from a beam with a bar (so the load is pure tension) and not have the weight permanently stretch the bar (so stress in the bar is less than the yield stress). You can calculate the cross sectional area of steel and compare that to the cross sectional area of the graphite fiber composite required. If your application is more complicated, say it has to support the load and flex up to 10 degrees and survive some impact loading and operate at a max temperature of 200C, then you have more homework to do to select the best material. And... if you are not rich enough so that money is no object, you also need to consider the cost.
Carbon fiber doesn't really refer to a single material (steel doesn't either, but most steels have similar densities). Pure carbon fiber is just that, fibers made of 90+% carbon. Carbon fiber in the context of cars usually refers to carbon fiber-reinforced polymers rather than plain woven fibers. The polymer adds rigidity to what would otherwise just be like a sheet of fabric. The density depends on the polymer used and the ratio of polymer:fiber. For 50% fiber by volume in epoxy, it has a density of 1.6 g/cm^3. Steel has a density of ~7.8 g/cm^3. So, by volume, steel is almost 5 times heavier.
