Holographic strain measurement with hole-drilling strain relaxation

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Dr. Rakos Balázs
Department of Automation and Applied Informatics

With holographic interferometry very small deformations can be measured around a newly drilled blind hole. This is caused by the relaxation of the material as the residual stress gets freed up. In this project I present a possible method to calculate stress values based on the deformations around the blind hole. I used finite element simulations to determine the stress-deformation scale in case of plane-surfaced objects and calculated the necessary constants needed to separate x and y directional stresses. I also presented the method in case of measurement.

To validate the stress-deformation scales I compared the ones I made using ANSYS to the empirical scale which was based on measurements done by Technoorg Linda Ltd. Co. The result of this comparison showed that using simulations to determine the scales is advantageous, the result is similar to the experimental scale and it is easier to carry out simulations instead of real measurements.

In the next step I simulated a pressure vessel which is slightly curved along the hole diameter in ANSYS. The load is an internal pressure and compared it to a similarly sized which is loaded the same way as the vessel around the hole. The two simulation results are compared to each other. I checked the displacement fields and gage circles and decided whether the vessel simulations can be substituted by a similar plate.

The last part of this thesis is about the comparison of an aluminium cable simulation set to a similarly sized and to a larger plate. The curvature of a cable thread along the hole diameter is significant compared to the other. Then we measured an aluminium cable in different places using the same hole diameter and depth to determine the stresses in every thread of the cable based on the stress-deformation scale I simulated.


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