Evaluation of a Residual Stresses Measurement Device Combining a Radial In-Plane ESPI and the Blind Hole Drilling Method

摘要

A new kind of electronic speckle pattern interferometer was developed by the authors' group using conical mirrors to measure the radial in-plane displacement component. True radial in-plane sensitivity is achieved by double illumination ESPI. A compact version of this interferometer was designed and built and successfully tested outside of an optical table. This paper presents a measurement evaluation of a second generation of this interferometer applied to residual stresses measurement. An ultra high-speed drilling unit was added to the device to drill a small blind hole in the region of interest. Due to the drilling process residual stresses are released in the neighborhood of the hole. The resulting radial displacement field is conveniently measured by the radial in-plane interferometer and fitted to a mathematical model. The principal residual stresses and principal stresses directions are then determined. One main difficulty dealing with evaluation of a residual stresses measurement device is to obtain a standard with a well known reference value. Two mechanical devices where built to provide a reference residual stresses value. The first one is a long specimen under a known uniform stresses field. The second one is a long pipe with known internal pressure. Both were designed, built and calibrated to provide a reference residual stresses value to calibrate the built residual stresses measurement device. Results of the evaluation of this device are also presented in detail in this paper. Both devices where used to check the measurement performance of the developed residual stresses measurement system and the results are presented and discussed in this paper.