4 On the In-Plane Displacement Measurement by 3D Digital Image Correlation Method 25 Fig. 4.8 Different from nominal in-plane displacement before/after proposed geometrical correction model 24 mm away from its original location. Before correcting, the evaluated in-plane displacement is monotonously increased as the nominal in-plane displacement increased and the maximum difference is up to 2.3 mm larger than the nominal one which leads to 9.7%; controversy, the modified in-plane displacement is a little below the nominal in-plane displacement and the difference is monotonously decreased as the nominal in-plane displacement increased and the maximum difference is about 1.7% which is equivalent to 0.41 mm. 4.4 Conclusions In this study, an in-plane displacement of a three-step aluminum block is determined by using 3D DIC method. The measured in-plane displacement in magnitude is much higher than the nominal in-plane displacement which is performed by moving the aluminum block with a precious linear stage. The difference between the 3D DIC determined in-plane displacement and nominal in-plane displacement was reported to be monotonously increased as the nominal in-plane displacement increased and the maximum difference is about 9.7% at nominal in-plane displacement is 24 mm. In addition, thanks to the aluminum block consists of three surfaces at different depths, the change of in-plane displacement at different depths can be determined at the same time. The results in this study present that the displacement determined by front- surface which is close to the camera-pair is highest for small displacement and the corresponding in-plane displacement of rear-surface, far away from the camera, is smallest. The results indicate the 3D DIC determined in-plane displacement is sensitive to the distance between the object and camera-pair. Meanwhile, from the 3D DIC evaluated displacement field, out-of-plane displacement was also reported. Again, the out-of-plane is monotonously increased as the nominal in-plane displacement increase. The ratios of the 3D DIC determined in-plane displacements and out-of-plane displacements at different nominal in-plane displacements are almost constant, in this study, which implied that the precious linear stage might be unparallel with respect to the frame used to support camera-pair for capturing the stereo-images or a no revealed characteristic of 3D DIC method. To identify the possible reason, a laser triangulation method was implemented with left- and right- camera was used to imaging the laser patterns on the aluminum block. The results obtained by using laser triangulation method indicate that the aluminum block is moved along precious linear stage without introduced out-of-plane displacement with respect to the geometrical setup of the camera-pair, therefore, according to current evidence, the out-of-plane displacement could be a characteristic 3D DIC method and the way to correct the 3D DIC determined in-plane displacement is essential. Based on a single camera model, a method to correct 3D DIC determined in-plane displacement was presented. The maximum difference between the determined in-plane displacement and the nominal in-plane displacement is improved from 9.7% to 1.7% in ratio and the corresponding displacements are 2.30 and 0.41 mm. Acknowledgements The study is performed thanks to the financial support provided by the Ministry of Science and Technology of Taiwan, R.O.C. (Grant No. NSC-102-2221-E-492-014 and MOST-103-2221-E-492-017) is greatly appreciated.
RkJQdWJsaXNoZXIy MTMzNzEzMQ==