Residual stress assessment using optical techniques
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abstract
The goal of this work is the development of different experimental techniques to measure
residual stresses, as alternative to the hole-drilling method with strain gages. The proposed
experimental techniques are based on the use of Moiré Interferometry and in-plane Electronic
Speckle Pattern Interferometry (ESPI). Both are field techniques allowing the assessment of
in-plane displacements without contact and high resolution. Grating replication techniques
were developed to record high quality diffraction gratings onto the specimen’s surfaces. An
optical set-up of laser interferometry was, developed to generate the master grating (virtual).
An in-plane ESPI set-up was also designed and implemented to measure displacements in one
direction. The stress relaxation was promoted by the blind hole drilling and the obtained
fringe patterns (Moiré and speckle) were video recorded. Image processing techniques were
applied to assess the in-plane strain field. A finite elements code (ANSYS®) was used to
simulate the stresses relaxation process whose values were compared with the experimental
data and to calculate the hole-drilling calibration constants.
The goal of this work is the development of different experimental techniques to measure residual stresses as alternative to the hole-drilling method with strain gages. The proposed experimental techniques are based on the use of Moiré Interferometry and in-plane Digital Speckle Pattern Interferometry (ESPI). They are field techniques that allow measure in-plane displacements without contact and with high resolution. Grating replication techniques are developed to record high quality diffraction gratings onto the specimen’s surfaces .It is also, developed an optical assembly of laser interferometry used to generate the master grating (virtual). It was designed and implemented an in-plane interferometer to measure displacements in one direction. It was also developed a drilling equipment to provoke the stress relaxation in the specimens. During residual stresses measurements the obtained fringe patterns (Moiré and speckle) are video recorded. Image processing techniques are used to assess the in-plane strain field. A finite elements code (ANSYS®) is used to simulate the process of relaxation of stresses whose values will be compared with the experimental ones and to calculate the hole-drilling calibration constants.
