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Laser surface-contouring and spline data-smoothing for residual stress measurement

Abstract

We describe non-contact scanning with a confocal laser probe to measure surface contours for application to residual stress measurement. (In the recently introduced contour method, a part is cut in two with a flat cut, and the part deforms by relaxation of the residual stresses. A cross-sectional map of residual stresses is then determined from measurement of the contours of the cut surfaces.) The contour method using laser scanning is validated by comparing measurements on a ferritic steel (BS 4360 grade 50D) weldment with neutron diffraction measurements on an identical specimen. Compared to lower resolution touch probe techniques, laser surface-contouring allows more accurate measurement of residual stresses and/or measurement of smaller parts or parts with lower stress levels. Furthermore, to take full advantage of improved spatial resolution of the laser measurements, a method to smooth the surface contour data using bivariate splines is developed. In contrast to previous methods, the spline method objectively selects the amount of smoothing and estimates the uncertainties in the calculated residual stress map.

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Prime, M.B., Sebring, R.J., Edwards, J.M. et al. Laser surface-contouring and spline data-smoothing for residual stress measurement. Experimental Mechanics 44, 176–184 (2004). https://doi.org/10.1007/BF02428177

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Key Words

  • Residual stresses
  • contour method
  • coordinate measuring machine
  • wire EDM
  • TIG weld
  • model error