The tensile strength of steel is the maximum stress that the steel can undergo before breaking – in other words, how much the steel can stretch before it breaks. This can be calculated by performing tensile tests on wire. First, the ultimate tensile strength of wire (UTS) can be found by measuring the most force needed to break (fracture) the steel being tested under tension. Second, by adding gauge marks before a tensile test, the length of the stretch during the tension can be calculated. Some tests are done by bending the wire as far as it will go before breaking (this is called the stress-strain curve). The results can then be compared with the relevant Australian Standards for wire, to assess the compliance (how far it can bend).
The ductility of steel is its ability to be drawn out into thin wires or flat sheets without pulling apart or breaking. Materials that are extremely ductile are those which can be stretched thin without cracking and losing their strength. This is what manufacturers want – materials that will not break, even when thin pieces are required. To find out the ductility of the steel, a common method used is called the ‘bend test’. The wire is placed in a machine that applies force to a certain spot at a certain angle. This force is applied for a certain amount of time. Afterwards, it is checked to see how well it did during the test. So, the more ductile the wire, the better it will do on the test.
Chainwire fencing wire is extremely strong as it needs to withstand extreme forces and a great deal of pressure. When you understand the tensile strength and ductility of the wire, you’ll realise that the wire has endured a huge amount of pressure to be twisted into the various shapes that form the chainwire mesh.
The wires run vertically and are bent into a zig-zag pattern so that each “zig” hooks around the wire immediately on one side and each “zag” hooks around the wire immediately on the other. This forms the characteristic diamond pattern seen in chainwire fencing.
Selvedge Styles – the ‘diamonds’ are twisted at the top and bottom (the selvedges), and are formed as follows: a single twist selvedge is called a ‘knuckle’ selvedge; a series of tight twists is called a ‘barbed’ selvedge. They are twisted in either: Barb – Barb (twisted into a barbed selvedge at both ends); Knuckle – Barb (knuckled at the bottom and twisted into a barbed selvedge at the top); or Knuckle – Knuckle (knuckle twist at both ends).