Dear all,
I want to measure the Kc value of 2024-T3 sheet. But the sheet with 80x100x2.5 mm is so small that Kc value can not be measured out. Maybe the sheet for measuring the Kc value shall be 400x1000x2.5mm. And in experimental scale, that so large sheet of 400x1000x2.5 mm is difficult to processing.
And are there another value to substitute the Kc value to weigh the fracture toughness of the alloy sheet with 80x100x2.5 mm? May I measure the Jc value of that material and then convert it to Kc value?
Thanks for your time.
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The method for measuring the Kc value of 2024-T3 sheet
Firstly, KC, KIC or JIC are NOT material properties – no matter what textbook tells you. Any specimen and test can be used to obtain a Kc value by applying a load until fracture. Kc obtained this way is the “critical stress intensity factor” for the material having this particular specimen geometry and under these specific test conditions. Therefore, the “fracture Toughness KIC” commonly referred to by the ASTM testing standard is at its best the “critical stress intensity factor” or Kc under the test condition specified in the ASTM standards. Theoretically, any test procedure to generate Kc value is good for comparing the fracture resistance of material A with material B for ranking purpose. The indentation technique is a good example. When one wants to use the Kc (or fracture toughness) value determined in laboratory for structural failure assessment, one needs to look into the transferability issue. One solution to this end is to consider the constraint level of the specimen and the structure. I hope this helps.
Kc value for 2024-T3:
Bill
Are you looking for Kc value of large size specimens? You can get the Kc data from MMPDS (previously called MIL HDBK) but they are not representative of smaller width specimens. I had some data from 4 in (~ 100 mm) width specimen, of 0.063 in (~ 1.6 mm) thick specimens, all specimens are 12 in (~ 300 mm) in length and are close to 46 ksi√in (~ 50 MPa√m). I used only LEFM, so they yielded only apparent Kc values. If I had used elasto-plastic methods, I could have achieved improved measures but still some width effect is expected. Higher width specimens may come closer to 108 ksi√in as published by Broek (Elementary Engineering Fracture Mechanics, Kluwer Academic Publishers, chapter 8). Your proposed dimensions (400 x 1000 x 2.5 mm) will yield ideal values. Broek used similar specimens.
In your case, there is not only a width effect, but also a problem of distribution of remote stress (or assumption of a uniform remote stress is invalid for shorter (lengthwise) specimens (in case you are doing experimental testing). As far as you satisfy the length > 2.5 width -- not sure, please check the ASTM standards, I guess you will be fine.
If you don't want to do testing but only want the values, you can contact the ALCOA product team, they may help you in providing the Kc values.
Hope it helps.
Regards,
Gopinath
Graduate Student
University of Oklahoma
PS: The values above are for T-L oriented specimens.