| Summary: | 碩士 === 國立中正大學 === 機械工程學系暨研究所 === 100 === Electronic speckle pattern interferometry (ESPI) and moiré interferometry belong to non-contact measurement techniques. Full-field displacement can be measured by ESPI and moiré interferometry while distribution the conventional hole-drilling strain gage method could only provide strain and stress information at the point of measurement.
Although we had successfully developed that hole-drilling strain gage method combined with moiré interferometry to measure residual stress, due to the limited preparation of specimen and the complex steps of optical grating attaching, moiré interferometry was not very convenient for stress measurement on real components. This research was therefore focused on developing a method which uses ESPI to combine with hole-drilling strain gage method measure in-plane displacements.
A biaxial loading device was designed and developed for this research. The feature of this device is that additional sliding device provides the horizontal and vertical clamp fixtures with one more degree of freedom. In this situation, as horizontal loading is applied on specimen, the vertical axial fixtures can move freely to avoid the cruciform specimen from distortion when it is constrained with the fixtures. In addition, a hole in the central of the loading device allows hole-drilling at the cruciform specimen center from reverse side of the device. The rosette strain gage is applied on the reverse side of the cruciform specimen. This arrangement also avoids the hole-drilling system obstructing the optical paths of the ESPI.
The biaxial loading device combined with hole-drilling device ESPI optical system which provides the cruciform specimen different in-plane stress combinations and allows the recording of strain and stress as well as the ESPI pattern as different stress conditions. We compared the theoretical ESPI fringe patterns with the experimental ones in fringe order and fringe type. The stresses obtained from the fringe patterns were also compared with those obtained from the hole-drilling method. The interference and noises in experimental fringe patterns were reduced by Gaussian low-pass filter transform, by comparing the theoretical displacement with the experimental displacement the feasibility of ESPI combing with strain gage hole-drilling method in measuring the in-plane displacement and stress field was verified
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