Charpy Impact Testing

Published: 05th July 2010
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Charpy impact testing services (also known as the Charpy v-notch test) use a standardised form of testing to examine the amount of energy that's absorbed by a material with fracture. Charpy impact testing services measure the energy absorbed in order to reflect the toughness of the material and is an important aspect of mechanical testing services. As a form of mechanical testing services Charpy impact testing has strengths and weaknesses and is at once a very cheap and easy way to test the toughness of a material, while unfortunately only being able to find results comparatively.
Carpy impact testing services were devised in 1905 by a French scientist named Georges Charpy thus explaining the origin of the name. Carpy impact testing was particularly widely used during the first world war for testing the fracture problems of the Navy. Today it is used in mechanical testing services for a range of pressure vessels and bridges.
Charpy impact testing services require a large apparatus devised of a pendulum axe that swings into a notched sample of the material. The energy of transferred is then inferred by the comparison of the difference in height of the hammer before and after the fracture. Thus this explains why Charpy impact testing services can only provide comparative results, with the actually height being arbitrary and only the difference in height being relevant. It is therefore also crucial that the size of the hammer and pendulum be of a standardised size so that the dent is equal size and doesn't affect the results. At the same time the size of the sample is also highly important as this too can otherwise be a confounding factor. There are documented industry guidelines to ensure that Charpy impact testing remains accurate (the standardised size of a sample is 10mm X 10mm X 55mm).
Interestingly however it is also possible to get both qualitative and quantitative results. For those not in the know, the term 'qualitative' means elaborative data and descriptive data such as text or prose, whereas 'quantitative' is any data that is purely quantifiable such as numbers.
In the quantitative results of Charpy impact testing the energy needed to fracture the material is used to calculate a yield test as was described above. Interestingly another form of Carpy impact testing can also test the 'ductile brittle transition temperature' (DBTT). This is calculated by the temperature the at which the energy needed to break the material largely changes (rather than the temperature needed to change the material on its own). However as there is no precise temperature at which the material changes it's hard to find a precise quantitative number. Some Charpy impact testing then tries to measure the precise size and severity of the fracture (such as 50% cleavage) and set that as the precise point at which to measure the exact temperature of the DBTT.
Qualitative in terms of Charpy impact testing can determine the ductility of the material and give it a label such as 'brittle' or 'ductile'. To determine this is a roughly accurate way the material is subjected to a range of different circumstances and tests. For example if the material breaks on a flat plane at a certain impact then this classifies it as brittle. If it breaks with jagged edges then the fracture (rather than the material itself) is 'ductile'.

For a range of mechanical testing services visit the links. Services include failure analysis services and Charpy impact testing services.

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