Impact Toughness of Materials: Charpy Testing Explained

[garygooboo]

Can someone please give me a bit of advise. I was dealing with impact toughness of materials today, which I haven't dealt with since uni days. I was involved in charpy testing. I understand the concept of finding the impact toughness from the test [ m x g x (h2 - h1) ].
But what I can't get my head around is, say my result is 100J, is this impact value related to thickness? e.g. the CSA of the standard test specimen is 10mm x 10mm so if the specimen was 20mm x 20mm then the impact toughness will be higher?

 

[Lok]

Depends on the type of fracture/bend/split. It has to do with the amount of deformation and surface of crack. If for example a 100J impact would create a 10mm crack in the first it might not even start a crack in the 20x20mm. There are many more variables in toughness to take into account. Usually the Area is "ok" for brittle materials yet for plastic ones the Volume comes into play with an uneven importance. I hope what I said makes a small bit of sense.

The Charpy test is mostly useful for comparing materials in different conditions (temp, treatment etc.) and it is not a reliable computational tool.