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A. K. Miller

Bio: A. K. Miller is an academic researcher from Stanford University. The author has contributed to research in topics: Constitutive equation & Creep. The author has an hindex of 19, co-authored 43 publications receiving 1817 citations.

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TL;DR: In this paper, the authors developed an equation to predict the creep rate as a function of sub-grain size, stress, diffusion coefficient, and elastic modulus, and found that the subgrain size is a unique function of the current modulus-compensated flow stress, but if fine subgrains can be introduced and stabilized, large increases in creep strength may result.
Abstract: Well defined subgrain boundaries dominate the microstructural changes occurring during plastic flow of polycrystalline metals at elevated temperature. The quantitative influence of subgrain size on elevated-temperature plastic flow is considered. Based on the results of tests under constant-stress and constant-structure conditions, an equation is developed which predicts the creep rate as a function of subgrain size, stress, diffusion coefficient, and elastic modulus. In general, the subgrain size is a unique function of the current modulus-compensated flow stress, but if fine subgrains can be introduced and stabilized, large increases in creep strength may result. The applicability of the phenomenological relation developed to the behavior of dispersion-strengthened materials (where the second-phase particles may predetermine the effective subgrain size) is discussed. When subgrain effects are included, it is shown that the creep rate is less dependent on stacking fault energy than has been previously thought.

379 citations

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TL;DR: In this article, the activation energy for steady-state creep (Qss) was found to be equal to about 87 kj mole−1 which corresponds quite closely to the activation energies for dislocation pipe diffusion as measured by Volin, Lie and Balluffi using a void shrinkage analysis.

199 citations


Cited by
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TL;DR: In this article, the current status of particle reinforced metal matrix composites is reviewed and the different types of reinforcement being used, together with the alternative processing methods, are discussed, and different factors have to be taken into consideration to produce a high quality billet.
Abstract: Particle reinforced metal matrix composites are now being produced commerically, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together with the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into consideration to produce a high quality billet. With powder metallurgy processing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing they are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The factors controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produced by powder metallurgy, since they are required to consolidate the composite fully. Other methods, suc...

1,961 citations

Journal ArticleDOI
TL;DR: A mathematical representation of the multiaxial Bauschinger effect of materials at high temperatures was presented in this paper. But the model was not considered in this paper, nor in the paper.
Abstract: (2007) A mathematical representation of the multiaxial Bauschinger effect Materials at High Temperatures: Vol 24, No 1, pp 1-26

1,583 citations

Journal ArticleDOI
TL;DR: In this paper, the cyclic constitutive equations developed and used at ONERA and LMT-Cachan are presented in detail in terms of a hierarchy of various models, including the Ohno-Kachi time-independent plasticity theory, two unified viscoplastic models by Walker and by Krempl and Yao, the new developments of the endochronic theory by Watanabe and Atluri.

1,446 citations

Journal ArticleDOI
TL;DR: In this paper, the main ingredients and assumptions of developing macroscopic inelastic constitutive equations, mainly for metals and low strain cyclic conditions, have been discussed, with some comparisons with the previous ones, including more recent developments that offer potential new capabilities.

1,414 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the kinetics of the substructure evolution and its correspondence to the strain hardening evolution of an Fe-22 wt.% Mn-0.6 wt% C TWIP steel during tensile deformation by means of electron channeling contrast imaging (ECCI) combined with electron backscatter diffraction (EBSD).

677 citations