High Throughput Determination of Creep Parameters Using Cantilever Bending: Part I - Steady-State
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High Throughput Determination of Creep Parameters Using Cantilever Bending: Part I - Steady-State Syed Idrees Afzal Jalali1,a), Praveen Kumar1,b), Vikram Jayaram1,c) 1
Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] c) e-mail: [email protected] a)
Received: 28 September 2019; accepted: 27 January 2020
Variation of stress across the length and thickness of a cantilever during creep allows obtaining multiple pairs of strain rates and stress under steady-state condition. This work applies digital image correlation (DIC) and conjugate analytical models to obtain several such “strain rate–stress” pairs during steady-state creep by testing a single cantilever at a constant applied load. Furthermore, these strain rate–stress pairs are used to accurately determine the stress exponent of the material (e.g., Al and Pb). In addition, an empirical observation of plotting strain rate as a function of stress at fixed strain during primary creep for estimating stress exponent is extended to bending creep, wherein strain rates of the points in the cantilever lying on an iso-strain contour were plotted against the moment at the point to determine stress exponent. This study, thereby, proves that the “bending creep–DIC” combination is a high throughput test methodology for studying steady-state creep.
Introduction
several months to years [2]). Hence, considerable time is spent
Understanding creep, which is a diffusion-controlled timedependent deformation process, is critical in assessing structural integrity of components, especially, at high temperatures, e.g., at temperatures greater than 0.35Tm, where Tm is the melting temperature of the material [1]. The dominant creep mechanism can be unambiguously studied during steady-state creep, where the dislocation substructure remains under a dynamic equilibrium because of balancing of the hardening and the recovery processes [1]. In practice, the creep life of a component can also be understood, at least qualitatively, based on the steady-state creep response. Hence, the majority of creep studies focus on obtaining the steady-state creep response of a material. Conventionally, the creep studies which aim at obtaining the critical creep parameters by understanding the steady-state creep response use uniaxial testing. Here, tests are performed at various uniaxial stresses at a fixed temperature to calculate the stress exponent, n, and at different temperatures at a constant uniaxial stress to calculate the activation energy for creep, Qc. As per the standards prescribed by the American Society for Testing and Materials (ASTM) [2], these protocols require testing more than 10 specimens, and each of these tests may span very long durations (sometimes
in material selection before a newly developed material
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qualifies for field trials. In the current era when big data analysis-based material discovery is rap
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