Copper very much work hardens, and will snap off with very little force if kinked sharply back and forth more than a few times.

Embrittlement at a sharp kink is almost certainly the failure mode where it snaps at the pliers, rather than ultimate tensile failure - which would be pulling in a straight line until it necks down and snaps. In the cold drawn state, oxygen free copper, as used for all good wiring, has an ultimate tensile stregnth of  ~40,000 PSI (1 PSI is 0.000703  kilos per square mm, so 1mm2 copper will snap at 28kg force) - for 1mm 2 core that is about the weight of a bag of cement - but you'd have to lift it with the wire perfectly straight, perhaps held rod-like  in some sort of drill chuck arragement, so the force was perfectly balanced on brand new wire with no twists or kinks, and even then,  bring the force on gently.

At the tension it snaps, it has stretched in length  by 17 % or so, and so at the break point the useful area is typically reduced to 75 to 80% of the original.

Note that the breaking strain can reduce by more than a factor of ten after  work hardening, and sets off already being that weak in cheap knock off cables if impurities are present.


Round nose pliers exist to form wires into controlled curves to avoid the kinking issue. Good ones (not these) have plastic sleeves to protect the insulation. For semi- rigid coaxial cables we use something like a small plumber's pipe bender. (small bender for full sized plumber...) bigger tools for bending earthing straps.


Mike

M.

Copper very much work hardens, and will snap off with very little force if kinked sharply back and forth more than a few times.

Embrittlement at a sharp kink is almost certainly the failure mode where it snaps at the pliers, rather than ultimate tensile failure - which would be pulling in a straight line until it necks down and snaps. In the cold drawn state, oxygen free copper, as used for all good wiring, has an ultimate tensile stregnth of  ~40,000 PSI (1 PSI is 0.000703  kilos per square mm, so 1mm2 copper will snap at 28kg force) - for 1mm 2 core that is about the weight of a bag of cement - but you'd have to lift it with the wire perfectly straight, perhaps held rod-like  in some sort of drill chuck arragement, so the force was perfectly balanced on brand new wire with no twists or kinks, and even then,  bring the force on gently.

At the tension it snaps, it has stretched in length  by 17 % or so, and so at the break point the useful area is typically reduced to 75 to 80% of the original.

Note that the breaking strain can reduce by more than a factor of ten after  work hardening, and sets off already being that weak in cheap knock off cables if impurities are present.


Round nose pliers exist to form wires into controlled curves to avoid the kinking issue. Good ones (not these) have plastic sleeves to protect the insulation. For semi- rigid coaxial cables we use something like a small plumber's pipe bender. (small bender for full sized plumber...) bigger tools for bending earthing straps.


Mike

M.