Abstract
Residual stresses occur in many manufactured structures and components. Great number of investigations have been carried out to study this phenomenon. Over the years, different techniques have been developed to measure residual stresses; nowadays the combination of Hole Drilling method (HD) with Electronic Speckle Pattern Interferometry (ESPI) has encountered great interest. The use of a high sensitivity optical technique instead of the strain gage rosette has the advantage to provide full field information without any contact with the sample by consequently reducing the cost and the time required for the measurement. The accuracy of the measurement, however, is influenced by the proper choice of several parameters: geometrical, analysis and experimental. In this paper, in particular, the effects of some of those parameters are investigated: misknowledgment in illumination and detection angles, the influence of the relative angle between the sensitivity vector of the system and the principal stress directions, the extension of the area of analysis and the adopted drilling rotation speed. In conclusion indications are provided to the scope of optimizing the measurement process together with the identification of the major sources of errors that can arise during the measuring and the analysis stages.
Highlights
The stress field existing in some materials without application of an external source of stress, such as loads or thermal gradients, is known as residual stress
Electronic Speckle Pattern Interferometry (ESPI) was successfully used to measure displacement field in anisotropic specimen made by selective laser melting [16,17,18], or orthotropic materials [19] as laminated wood [20] and in combination with hole drilling method to evaluate the residual stress relieving [21] avoiding rigid-body motions [22]
The stress field was initially measured adopting the values of the inner radius (Rint) and the outer radius (Rext) commonly used in this kind of experiments. This values are usually defined in terms of ratio with the radius of the drilled hole (Rhole), and it is common use to adopt rint
Summary
The stress field existing in some materials without application of an external source of stress, such as loads or thermal gradients, is known as residual stress. ESPI was successfully used to measure displacement field in anisotropic specimen made by selective laser melting [16,17,18], or orthotropic materials [19] as laminated wood [20] and in combination with hole drilling method to evaluate the residual stress relieving [21] avoiding rigid-body motions [22]. In defining the set-up it is necessary to have a good control of all the geometrical parameters involved, such as the angles that define the illumination and detection directions If their values are not accurately evaluated this introduces an error in the determination of the displacement field which introduces an error in the calculation of the stress field [23].
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