4 On the In-Plane Displacement Measurement by 3D Digital Image Correlation Method 21 Table 4.1 Calibrated parameters of camera-pair Parameters Cx Cy fx fy Skew ›1 ›2 ›3 Left camera 783.22 525.51 8709.47 8707.76 1.4528 0.2015 0 0 Right camera 819.33 512.09 8718.95 8717.76 1.7855 0.2026 0 0 Fig. 4.3 In-plan displacement derivations with respect to nominal displacement-raw data surfaces, named as front, middle and rare surface, and averaged over the each area of each surface. The displacements were determined by using a commercial DIC system VIC 3D, the camera-pair has calibrated by proposed calibration procedures and the associated parameters were shown in Table 4.1. 4.3 Results and Discussions In this study, the in-plane displacement was first determined by using 3D DIC with 27 27 pixels subset. Different from previous studies, a three-step specimen is used instead of a plate. Because of the surfaces are located at different depths, therefore, 3D DIC determined in-plane displacements can be obtained across the depths at the same time. Considering rotation along y-axis might be introduced while moving the test specimen along x-axis, a laser triangulation method was implemented in this study and the two available cameras captured the images from left- and right- views to monitor the movement. The detail measurement results are presented and discussed by the following sections. 4.3.1 In-Plane Displacements at Different Depths The determined in-plane displacements at different surfaces were illustrated in Fig. 4.3, the results showed that the deviations between the determined in-plan displacements and nominal displacements are always lager than 9%, and the deviations are increasing as the in-plane displacement enlarged. The illustrated Fig. 4.3 also revealed very interesting informations; the deviations from nominal in-plane displacement in magnitude are ordered as ujfront surface > ujmiddle surface > ujrear surface when the object was moved from 0 to 21 mm; in fact, the deviation difference among three surfaces at a given nominal in-plane displacement also decreases when the object is moved from 0 to 21 mm and the deviation is almost the same for all three surfaces as the nominal in-plane displacement is 21 mm in this study.
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