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While testing the toughness of brittle material by izod or charpy test why do we provide v notch?

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    $\begingroup$ Not tests of "brittle " materials, but any materials. Does anyone use Izod anymore ? $\endgroup$ Aug 8 '18 at 15:02
  • $\begingroup$ FYI, this test gives qualitative results, and not reliable for design related purposes. $\endgroup$ Aug 8 '18 at 17:39
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    $\begingroup$ Charpy V is used for design in US industry: eg. ASME requires certain ASTM materials to be used, The ASTM specs usually require certain levels of Cv. API specs also require certain levels of Cv. $\endgroup$ Aug 9 '18 at 1:16
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The point is to promote the condition of brittle fracture. The notch here acts as a stress riser and favours the crack propagation.

This test is designed for any material, if you already know that the material is brittle then why do you put it through the test ? The absolute values and numbers here are less important and they are not reliable. The impact engineers want to know when a material favours brittle fracture, some materials are ductile in a specific range of temperature, but they still fail like brittle material, why ? presence of stress risers, high rate of strain ... , by bringing the notch they promote the condition of brittle fracture and the notch provides three dimensional stress condition.

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    $\begingroup$ also, by machining the notch in exactly the same way for all test samples, the repeatability of the measurements is improved. $\endgroup$ Aug 8 '18 at 17:30
  • $\begingroup$ @SK05 don't forget to take a look at the comment of niels nielsen here above, great information. $\endgroup$ Aug 8 '18 at 17:34
  • $\begingroup$ What is the use of crack propagation, since failure is brittle in nature because the Charpy test is conducted mostly for brittle materials to find the toughness? Also what if we don't provide the notch? @SamFarjamirad $\endgroup$
    – SK05
    Aug 9 '18 at 9:38
  • $\begingroup$ @SK05 I added more details. $\endgroup$ Aug 9 '18 at 10:17
  • $\begingroup$ How can we measure the toughness(magnitude)? @SamFarjamirad $\endgroup$
    – SK05
    Aug 9 '18 at 16:30

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