Application of digital speckle correlation method to disk surface thermal deformation measurement

To overcome the limitations of thermal deformation measurement conducted by strain gages, the DSCM (digital speckle correlation method) was used to determine the real-time surface thermal deformation of a static hollow disk subjected to thermal load on the outer rim. In the experiment system, electromagnetic induction heating method was applied to simulate the heat boundary of the disk and the real-time temperature distribution of the disk was obtained by infrared thermometer. Meanwhile, for the purpose of improving accuracy of DSCM, measures were taken by considering the range of field of CCD (change coupled device) camera view, the usage of medium focal length micro lens and the arrangement of illumination to lessen the effects of error factors like off-plane displacement and speckle image quality. The comparison between the experimental and theoretical results of thermal deformations shows that a good agreement is achieved, although some deviations still exist, and the maximum absolute deviations and relative deviations are 6μm and 31%, respectively; the absolute deviations of the outer rim are larger while the relative deviations are smaller,and this case is contrary to the inner rim. The results validate that the feasibility of DSCM for disk surface thermal deformation measurement, thus providing an effective experimental tool on turbine thermal deformation investigations.