Article

Experimental Mechanics

, Volume 40, Issue 4, pp 345-350

First online:

Measurement of curved-surface deformation in cylindrical coordinates

  • P. F. LuoAffiliated withDepartment of Mechanical Engineerings, Chung Hua University
  • , J. N. ChenAffiliated withDepartment of Mechanical Engineerings, Chung Hua University

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Abstract

Stereo vision is used to measure the strain field of a round tension test specimen in a cylindrical coordinate system. Initially, the displacement fields of the specimen are measured relative to a world coordinate system erected by the stereo vision. Through coordinate transformations, the measured displacement fields expressed in world coordinates are then converted to the displacement fields expressed in cylindrical coordinates. By differentiating the axial and circumferential displacements in the axial and circumferential directions, the axial, circumferential and shear strains are determined. Results indicate that the measured mean value of the axial strains is in good agreement with the measurements of the extensometer and the strain gage. The Poisson's ratio obtained by the circumferential and axial strains is close to .33 in the elastic state. The mean error of the computed shear strain is approximately .03 percent in the smaller elastic deformation and .08 percent in the larger plastic deformation.

Key words

Strain fields cylindrical coordinate computer vision/digital image processing