ASTM WK75167

    Revision of E1820 - 20b Standard Test Method for Measurement of Fracture Toughness

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    Active Standard: E1820 - 20b

    Developed by Subcommittee: E08.07 | Committee E08 | Contact Staff Manager



    WK75167


    Keywords

    crack initiation; crack-tip opening displacement; CTOD; ductile fracture; elastic-plastic fracture toughness; fracture instability; J-integral; JIc; KJic; Jc; δc; plane-strain fracture toughness; resistance curve; stable crack growth;;

    Rationale

    For historical reasons, an algorithm is proposed in Section A9.6.6 and A11.6.6 to solve a non-linear equation. The standard requires achieving an accuracy of 2 %. This level of accuracy can also be obtained by finding the intersection graphically, although nowadays probably no laboratory would use that approach. In the next section, it is shown that the ASTM proposed algorithm is not the most efficient and that very marginal effort is needed to increase the accuracy from 2 % to 0.01 % or machine precision (10-15). Currently, many non-linear solver tools exist that are embedded in various software packages. Using any of these tools, the mathematical effort to converge to an accuracy much better than 2 % is ridiculously low (less than 11 function evaluations, or iterations, to achieve machine precision). In order to ensure that the result of the analysis of standard data sets is not affected by the mathematical resolution of the linear equation, it is proposed to reduce the allowable error to less than 0.1 %. It is also proposed to leave the selection of the algorithm to the user, as such algorithms are currently embedded in many software packages and include many safeguards against numerical instabilities.

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    Work Item Status

    Date Initiated:
    12-11-2020

    Technical Contact:
    Enrico Lucon

    Item:
    002

    Ballot:
    E08 (21-01)

    Status:
    In Balloting