Why is thick steel wire stronger than thin steel wire?
The material will yield when stress reaches a critical value.
Stress = Load / Area
Thick steel wire is stronger than thin steel wire because there is more cross sectional area in the thick wire. Although the material's strength in load per unit area would be the same, the ultimate load that the wire can sustain would be more in the thick wire. A simple way of looking at it is to imagine a thick wire as a number of thin wires stuck together. If a thin wire can support a mass of 1kg then 2 thin wires can support 2kg. A wire which is twice as thick (twice the cross sectional area) can also support 2kg.
This is a poorly defined question, because the difficulty of biting through steel depends upon how thick the steel is, as well as the kind of steel (some steel alloys are much harder than others), and in addition, there are many different kinds of sharks, and some have stronger jaws than others. I will note that if the steel is sufficiently thin (steel foil) even we human beings can bite through it. I will also…