Digital image correlation

About: Digital image correlation is a research topic. Over the lifetime, 7842 publications have been published within this topic receiving 132166 citations.

Optical Non-contacting Vibration Measurement of Rotating Turbine Blades II

Abstract: Identifying the structural dynamics of rotating components can be difficult. Often times, structural dynamic measurements are obtained while the structure is in a static configuration. There are differences that exist in the structural behavior when comparing these statically performed tests and the dynamic characteristics when in operation. In order to evaluate the actual system while in operation, slip-rings are used during testing with measurements made at only a very few selected points. But this slip-ring configuration can be problematic, suffer from measurement noise and the attached sensors can obscure the true dynamic response due to mass loading and aerodynamic effects. 3D digital image correlation (DIC) has been used to capture the out-of-plane motion on the surface of a small scale rotating fan blade. This work extends prior efforts, by quantifying the performance of the optical measurement on a 46 in (1.17m) diameter, rotating wind turbine. The optical measurements are made using DIC (10,000+ measurement points) and dynamic photogrammetry (providing dozens of effective measurement locations). The motion of the turbine as measured using DIC, photogrammetry and accelerometers is compared at several discrete points. The proposed measuring approaches via DIC and dynamic photogrammetry enable full-field dynamic measurement and monitoring of rotating structures in operation.

A critical local energy release rate criterion for fatigue fracture of elastomers

Abstract: Using Digital Image Correlation on high-resolution images, the full strain field near the tip of a crack propagating under cyclic loading in an elastomer was characterized. We show unambiguously, and for the first time, the existence of a strongly localized and highly oriented process zone close to the crack tip and propose a simple physical model introducing a local energy release rate glocal = WunloadingH0, where Wunloading is the unloading strain energy density in uniaxial tension at the maximum strain measured at the crack tip, and H0 is the undeformed size of the highly stretched zone in the loading direction. Remarkably, the crack growth rate under cyclic loading is found to fall on a master curve as a function of glocal for three elastomers with different filler contents and crosslinking densities, while the same crack growth rate as a function of the applied macroscopic energy release rate G, differs by two orders of magnitude for the same three elastomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1518–1524, 2011

Digital image correlation used for mechanical tests on crimped glass wool samples

Abstract: Mechanical compression and tearing tests are carried out on crimped glass wool samples. The displacement field is determined by using digital image correlation based on images taken at different stages of the mechanical tests. A multiscale algorithm is used to resolve accurately fine details of the displacement field. This technique reveals strain heterogeneities and further localisation in compression tests well below the peak stress. Crack formations are identified in tearing tests. Reliability and resolution of the displacement and strain fields are validated by using different window sizes in the correlation analysis.

Transient Dynamic Simulation and Full-Field Test Validation for A Slim-PCB Of Mobile Phone under Drop / Impact

Abstract: Product durability due to drop shock is a critical element for assessment of reliability for handheld devices. So far, no simulation model for a board-level drop has been extensively validated by experiments for its predictions of global (full-field) dynamic response. Accelerometers and strain gages which are traditionally utilized to measure the response at selected locations, fail to assess the global strain gradients and complex mode shapes. In this work, a novel non-contact optical technique has been proposed for measurement of full-field impact response. Pair of synchronized high-speed cameras capture the images of board assembly subjected to JEDEC standard impact, at rates up to 15,000 pictures per second. A digital image correlation (DIC) system has been integrated with the cameras to analyze the acquired images to give dynamic deformation, shape and strain over the entire surface of board during impact. A finite element model for the drop test has been developed using ANSYS/LS-DYNA. The numerical solution has been fully validated against experimental measurements of acceleration, strain and warpage at series of instants of time after impact. Effect of tightening torque at PCB mounts has been studied comprehensively with regards to the eigenvalues and mode shapes, and the necessity for accurate modeling of dynamic contact conditions existing at the supports has been demonstrated. Simulation model has been further used to assess the drop impact reliability of components on the board. Excellent correlation of all simulation results with the measured data validates the experimental and numerical propositions made in this work for analyzing a board-level drop impact.