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Charpy impact test

Cutting method in which an electrically charged wire is fed through a workpiece creating an electric discharge that cuts a contour in its horizontal plane.

Illustration of Charpy impact test

The process

From a wire spool [1], a metal wire [2] is guided by guide pulleys [3] and wire guides [4]. To resist wear, the wire guides are usually made of diamond. The thread is finally collected by a collection spool [5] or cut into smaller pieces when it is exhausted and cannot be reused.

A power source is connected to the wire and the workpiece and they act as cathode and anode respectively. When the electrode, in this case, the wire is brought close to the workpiece, sparks are created across the gap, which causes removal of material from both the workpiece and the wire.

The discharge is assisted by a dielectric fluid [6], which helps to cool the process and carry away the removed material. This process can also be completely immersed in a dielectric fluid.

The spark gap [7] causes the contour to be slightly larger than the diameter of the wire [8]. The outline is usually controlled by the workpiece movement in the horizontal plane.

Advantages and disadvantages
In comparison with alternative methods
Easy to prepare, easy to implement
Results obtained quickly
Can be implemented in a wide range of ambient temperatures
Can be used to study the difference and influence of alloys and heat treatments
Some results are only comparative
The results are difficult to use in design