Meaning
Optical non-contact measurement tracks surface deformation by observing patterns on a specimen during mechanical testing. Digital image correlation monitors movement across a grid of subsets to calculate displacement and strain fields. This technique requires a high contrast stochastic pattern applied to the surface to ensure pixels remain trackable throughout the load cycle.
Precise hardware calibration determines the relationship between image space and physical coordinates.
Processing Sequence
Image acquisition occurs through synchronized cameras capturing the sample from different angles during deformation. Software then matches subset patterns across sequential frames to extract coordinate shifts. Sub-pixel interpolation algorithms refine the position data to achieve high resolution.
Computational overhead grows with the resolution of the cameras and the complexity of the subset mesh. Data output includes two-dimensional or three-dimensional displacement maps and strain tensors for material characterization.
Performance Limitation
Optical distortion or light fluctuation induces noise into the correlation process. Surface preparation quality governs the accuracy of the tracking. Out-of-plane motion introduces measurement bias unless stereo vision configurations provide depth correction.
Specimen vibration interferes with the ability of the algorithm to maintain tracking continuity. High strain gradients require smaller subset sizes to prevent loss of signal coherence between frames.
Calibration Metric
Camera alignment relative to the specimen determines the spatial resolution of the displacement vector. Rigid body motion tests confirm the baseline accuracy of the measurement system before experimental data collection begins. Sensitivity depends on the ratio of the pixel size to the field of view.
Proper focal depth ensures the entire region of interest remains within the sharp capture volume during the experiment. Quantitative reliability depends on the quality of the image correlation software in minimizing systematic registration error.