Abstract
This paper presents a uniquely designed device combining the hole-drilling technique with two optical systems based on the PhotoStress and digital image correlation (DIC) method, where the digital image correlation system moves with the cutting tool. The authors aimed to verify whether the accuracy of the drilled hole according to ASTM E837-13a standard and the positioning accuracy of the device were sufficient to achieve accurate results. The experimental testing was performed on a thin specimen made from strain sensitive coating PS-1D, which allowed comparison of the results obtained by both methods. Although application of the PhotoStress method allows analysis of the strains at the edge of the cut hole, it requires a lot of experimenter’s practical skills to assess the results correctly. On the other hand, the DIC method allows digital processing of the measured data. However, the problem is not only to determine the data at the edge of the hole, the results also significantly depend on the smoothing levels used. The quantitative comparison of the results obtained was performed using finite element analysis.
Highlights
Residual stresses are present in almost all materials
Attaching a strain gauge rosette with special measuring grids to the examined location; drilling a through-hole at the geometric center of the strain gauge rosette in one step to the specimen whose thickness is much less than the diameter of the hole or a blind hole in a series of steps to the specimen whose thickness is much greater than the diameter of the hole; measuring the resulting relieved strains whose values depend on the residual stresses existing in the material of the hole; determining the residual stresses in the removed material using mathematical relations based on linear elasticity theory
While the results of the measurement by the digital image correlation (DIC) method provide quantitative information about the displacements as well as strains in the center of each facet, for the quantification of the results obtained using PhotoStress method, the use of a digital compensator is necessarily required in each evaluated location of the specimen
Summary
Residual stresses are present in almost all materials They may arise during the manufacturing process or over the life of a material. Determination of residual stresses in the material is usually based on the standardized hole-drilling strain gauge method allowing identification of in-plane residual stresses near the measured specimen surface made from an isotropic linear-elastic material. The methodology of residual stresses quantification using the hole-drilling strain gauge method involves several steps: smoothing of the specimen surface using, e.g., chemical etching (manufacturing technologies such as abrading or grinding have to be avoided); attaching a strain gauge rosette with special measuring grids to the examined location; drilling a through-hole at the geometric center of the strain gauge rosette in one step to the specimen whose thickness is much less than the diameter of the hole (denoted as thin) or a blind hole in a series of steps to the specimen whose thickness is much greater than the diameter of the hole (denoted as thick); measuring the resulting relieved strains whose values depend on the residual stresses existing in the material of the hole; determining the residual stresses in the removed material using mathematical relations based on linear elasticity theory
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