Good mourning, in metallic materials it is commun when people talk about the fracture toughness that they use the so called plane strain compact tension Ct test, and the standards (ASTM for example) are under relatively special conditions dictated by the standard to determine the Fracture Toughness (Kic), and amoung the most important conditions is the existance of a sharp crack in the vicinity of the notch, this is made in a fatigue testing machine and this requered sharpness is important to avoid any plastic instability (according to ASTM standards) during the monotonic-load testing of the CT specimen to determin a precise Kic.
My queries are:
1. Let's take the case of a high stength steels and with a sharp crack in the notch of the specimen, so how much is the maximum load for a specimen with a width of about 25 mm. could you pleas give a referance.
2. Let's now suppose that there doesn't existe a sharp crack in the vicinity of the notch (round notch with verry smal radius of about 0.1 mm), could you give us an estimation of how high would be the Load at the onset of the notch during the test.
thank you very much
Cood morning. The pre-cracking before fracture toughness tests is based on ASTM E647. There is no clear estimation of the maximum load duiring pre-cracking in ASTM standard and it needs try. The chinese standard GB/T 21143-2007 recommends the estimation equation of maximum load. You cna reference.
Thanks Mr Meng for your answer, i'll take a look in the chineese standard that you mensioned.
As mentioned above, pre cracking is done in Fatigue. You should chose a maximum load (maximum K) for fatigue precracking 50% or lower than the expected Frature tougnness - if not your test is not valid. Typically a lod ration of 0.1 is chosen.
For a valid fracture test, crack should be sharp. If this is not the case, the fracture toughness values will be very high. The is a critical tip radius below which there is no effect of tip radius on the fracture toughness. Please refer Fundamentals of Fracture Mechanics - J.F. Knott.
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