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    Volume 11, Issue 2 (June 2021)

    Special Issue Paper

    Accelerated Creep Testing of Inconel 718 Using the Stepped Isostress Method (SSM)

    (Received 31 October 2020; accepted 2 April 2021)

    Published Online: 21 June 2021

    CODEN: MPCACD

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    Abstract

    This paper demonstrates the stepped isostress method (SSM), an accelerated creep test (ACT) for the rapid assessment of metallic materials. The SSM test is based on the time-temperature-stress superposition principle in which temperature, stress, or both, are step increased to accelerate the time to rupture. The SSM test has proven successful for the ACT of polymers and polymeric composites but has yet to be proven for metallic materials. In this study, new test matrix design rules for the SSM of metals are established based on deformation mechanism, time-temperature transformation, and time-temperature precipitation maps. A test matrix of SSM and conventional creep tests (CCTs) are executed for alloy Inconel 718 at 750°C (1,382°F) with stress levels ranging from 100 to 350 MPa. Validation CCT data are gathered from the Japan National Institute of Material Science. Material constants for the Sine-hyperbolic (Sinh) constitutive model are calibrated using the SSM data and employed to predict the conventional creep response. When blindly compared with the CCT data, the SSM-calibrated Sinh model can accurately predict the conventional creep response across logarithmic decades and, thus, accelerate the capture of conventional creep data. Fractography indicates ductile fracture by transgranular microvoid coalescence with the same fracture mode observed in both SSM and CCT specimens. Creep cavitation is indicated by the population, smoothness, and size of microvoids.

    Author Information:

    Stewart, Calvin M.
    Department of Mechanical Engineering, The University of Texas at El Paso, El Paso, TX

    Hossain, Md Abir
    Department of Mechanical Engineering, The University of Texas at El Paso, El Paso, TX

    Pellicotte, Jacob
    Department of Mechanical Engineering, The University of Texas at El Paso, El Paso, TX

    Mach, Robert
    Department of Mechanical Engineering, The University of Texas at El Paso, El Paso, TX

    Alexander, David
    Department of Mechanical Engineering, The University of Texas at El Paso, El Paso, TX

    Siddiqui, Sanna F.
    Department of Mechanical Engineering, Florida Polytechnic University, Lakeland, FL


    Stock #: MPC20200174

    ISSN:2379-1365

    DOI: 10.1520/MPC20200174

    Author
    Title Accelerated Creep Testing of Inconel 718 Using the Stepped Isostress Method (SSM)
    Symposium ,
    Committee A01