Abstract
Some bending usually occurs in uniaxial testing systems due to small unavoidable misalignment. The resulting elastic strain gradient can lead to significant differences between axial strain and extreme surface bending strains, especially at small strains. A three-point microstrain measurement around a cylindrical sample permits evaluation of the extreme strains and of the precision of alignment. A three-point, parallel-plate capacitance strain gage having a linear output with displacement was designed to evaluate bending of tensile samples in the microstrain range. The resolution of the gage was 3 parts in 10,000 at plate separations of 0.010 in. Varying misalignment resulted in extreme elastic bending strains at the sample surface of the order of tens to hundreds of micro-in. per in. larger than the axial strain. Analysis of the mechanics of bending in uniaxial loading demonstrated that: 1) the average applied stress divided by the average elastic strain always gives a unique number, Young's modulus, and 2) the average microplastic strain is not uniquely related to the average applied stress, but rather depends upon precision of alignment. The influence of bending on the determination of the average stress at which microplastic flow initiates is discussed, and a method for making meaningful comparisons of plastic microstrain data generated with significant misalignment is suggested.
Similar content being viewed by others
References
R. L. Templin:Proc. ASTM, 1929, vol. 29, p. 523.
J. L. M. Morrison:Proc. Inst. Mech. Eng. (London), (1939), vol. 42, p. 198.
(a) B. Chalmers:Proc. Roy. Soc. (London), 1936, vol. 156 (Series A), p. 427. (b) B. Chalmers:J. Inst. Metals, 1937, vol. 61, p. 103.
(a) N. Brown: “Observations of Microplasticity”, p. 52, (b)Microplasticity, edited by C. J. McMahon, Jr., Interscience Publishers, New York, 1968.(b) Microplasticity, edited by C. J. McMahon, Jr., Interscience Publishers, New York, 1968.
B. W. Christ and S. R. Swanson: “Alignment Problems in the Tensile Test”, ASTM Standardization News. In Press.
G. W. Geil and I. J. Feinberg:Trans. TMS, AIME, 1970, vol. 1, p. 1845.
R. D. Cutkosky: Metrology Division, National Bureau of Standards, Washington, D. C. 20234.
F. K. Harris and R. D. Cutkosky:Instrum. Soc. Amer. J., 1961, February, p. 27.
B. W. Christ, I. J. Feinberg, and W. A. Willard: “Pre-Macroyield Behavior of Commercial Titanium Alloys Tested in Uniaxial Tension (Part I), NBS Report No. 10640 to Naval Air Systems Command, Washington, D. C., November, 1971.
A. K. Schmieder: “Measuring the Apparatus Contribution to Bending in Tension Specimens”, ASTM STP 488, p. 15–42, ASTM, 1916 Race Street, Philadelphia, PA. 1971.
F. A. McClintock: “Tensile and Compressive Deformation”, Chapter 8, p. 310,Mechanical Behavior of Materials, edited by F. A. McClintock and A. S. Argon, Addison-Wesley Publishing Co., Inc. Reading, Mass., 1966.
R. B. Clough and G. W. Geil:Trans. TMS AIME, 1970, vol. 1, p. 1850.
M. H. Jones and W. F. Brown, Jr.: ASTM Bull., 1956, (January), p. 53.
Metals Handbook, 8th Edition, 1961, p. 1211, American Society for Metals, Metals Park, Ohio.
Metals Handbook, 8th Edition, 1961, p. 538, American Society for Metals, Metals Park, Ohio.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Christ, B.W. Effects of misalignment on the pre-macroyield region of the uniaxial stress-strain curve. Metall Trans 4, 1961–1965 (1973). https://doi.org/10.1007/BF02665424
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02665424