Michael A. Sutton

Image Correlation for Shape, Motion and Deformation Measurements

Image Correlation for Shape, Motion and Deformation Measurements provides a comprehensive overview of data extraction through image analysis. Readers will find and in-depth look into various single- and multi-camera models (2D-DIC and 3D-DIC), two- and three-dimensional computer vision, and volumetric digital image correlation (VDIC). Fundamentals of accurate image matching are described, along with presentations of both new methods for quantitative error estimates in correlation-based motion measurements, and the effect of out-of-plane motion on 2D measurements. Thorough appendices offer descriptions of continuum mechanics formulations, methods for local surface strain estimation and non-linear optimization, as well as terminology in statistics and probability. With equal treatment of computer vision fundamentals and techniques for practical applications, this volume is both a reference for academic and industry-based researchers and engineers, as well as a valuable companion text for appropriate vision-based educational offerings.

Estimation of stress intensity factor by digital image correlation

Abstract A method of determining stress intensity factors using digital image correlation is presented. The experimental and analytical method is described with results for different specimen geometries given. Effects of using higher order terms in the series expansion are also investigated and presented.

Full-field representation of discretely sampled surface deformation for displacement and strain analysis

A detailed evaluation of the feasibility of determining displacements and displacement gradients from measured surface displacement fields is presented. An improved methodology for both the estimation and elimination of noise is proposed. The methodology is used to analyze the gradients for three tests: (1) uniform rotation, (2) uniform strain, and (3) crack-tip displacement fields. Results of the study indicate that the proposed methodology can be used to extract the underlying two-dimensional displacements and their corresponding gradients from the noisy data with reasonable accuracy. Specifically, it is shown that (a) the digital correlation method for acquiring displacement fields has an error in strain of approximately 150 μ strain at each point, (b) the average strain in a region of uniform strain has much less error, typically on the order of 20 μ strain, (c) the displacement ‘nolse’ present in digital correlation is very small, approximately 0.01 pixels, (d) the proposed methodology for reducing noise in the data is essential to the accurate evaluation of displacement gradients and (e) the successful evaluation of displacement and displacement gradients for all three cases indicates that the proposed methodology can be used both to quantify the displacement fields and to reasonably estimate the overall gradient trends.

High-temperature deformation measurements using digital-image correlation

The ability of the computer-vision technique of digital-image correlation to measure full-field in-plane surface deformations at elevated temperatures was evaluated by a series of experiments. Samples were subjected to pure translation, free thermal expansion and uniform tensile loads. Results are presented which show that the digital-image-correlation technique remains fully capable of accurate measurement of the displacements and strains on the surface of a planar object at temperatures up to 650°C.

Drift and spatial distortion elimination in atomic force microscopy images by the digital image correlation technique

The characterization of nanomaterials and nanostructures on the nanoscale has been a tremendous challenge for many existing testing and measurement techniques. With the rapid development of microfabrication and nanofabrication technologies, appropriate and accurate tools for nanometrology and nanomechanical testing must be developed. In this study, a recently developed methodology for scanning electron microscopy (SEM) image correction has been successfully adapted to correct the drift and spatial distortion of atomic force microscopy (AFM) images. Using this approach with a standard AFM sample stage, the errors in AFM images, artificial strains for zero deformation, have been reduced to 150×10−6 ± 1300×10−6. When using a sample stage with closed-loop control, the method reduces errors to 200×10−6 ± 1000×10−6, confirming that the SEM-based approach is capable of removing much of the distortion present in typical AFM images.

Towards the standardization of in vitro load transfer investigations of hip prostheses

Abstract The effect of optical refraction at an interface between optically dissimilar media is modelled in order to apply the principles of three-dimensional digital image correlation (DIC) to measure deformations on submerged objects accurately. Using an analytical formulation for refraction at an interface, a non-linear solution approach is developed to perform stereo calibration. The proposed method incorporates a simplified parametric representation for the orientation and position of an interface(s), accounting explicitly for the effects of refraction at all such interfaces in the path of each stereo camera. Separating the calibration process into two parts, a modified bundle adjustment process with an updated Levenburg–Marquardt (LM) non-linear optimization algorithm is employed to determine (a) intrinsic and extrinsic stereo camera parameters without interface refraction and (b) orientation and position of each planar interface. Detailed simulations demonstrate the efficiency, accuracy, and stability of the methodology when using multiple images of a grid pattern undergoing general rigid body motion, even in the presence of Gaussian noise in the sensor plane measurements, providing a robust framework for practical implementation of the methodology for submerged object measurements.

Robust Stereo Vision and Calibration Methodology For Accurate Three-Dimensional Digital Image Correlation Measurements on Submerged Objects

The effect of optical refraction at an interface between optically dissimilar media is modelled in order to apply the principles of three-dimensional digital image correlation (DIC) to measure deformations on submerged objects accurately. Using an analytical formulation for refraction at an interface, a non-linear solution approach is developed to perform stereo calibration. The proposed method incorporates a simplified parametric representation for the orientation and position of an interface(s), accounting explicitly for the effects of refraction at all such interfaces in the path of each stereo camera. Separating the calibration process into two parts, a modified bundle adjustment process with an updated Levenburg—Marquardt (LM) non-linear optimization algorithm is employed to determine (a) intrinsic and extrinsic stereo camera parameters without interface refraction and (b) orientation and position of each planar interface. Detailed simulations demonstrate the efficiency, accuracy, and stability of the methodology when using multiple images of a grid pattern undergoing general rigid body motion, even in the presence of Gaussian noise in the sensor plane measurements, providing a robust framework for practical implementation of the methodology for submerged object measurements.

Nanoscale Deformation and Cracking Studies of Advanced Metal Evaporated Magnetic Tapes using Atomic Force Microscopy and Digital Image Correlation Techniques

Abstract A custom designed microtensile tester was integrated with an atomic force microscopy (AFM) to perform in situ tensile tests on two advanced metal evaporated (ME) magnetic tapes – ME/polyethylene terephthalate (PET) (with PET as a substrate) and ME/polyethylene naphthalate (PEN) (with PEN as a substrate) where the tape surfaces were imaged simultaneously by AFM during tensile loading. The digital image correlation technique was used to process the AFM images and quantitatively measure local, nanoscale deformation for both front coat and back coat of the ME tapes subjected to uniaxial tensile loading. The surface morphology change, strain distribution evolution and crack initiation and propagation during tensile loading are discussed with the structures and mechanical properties of the ME tapes.

Radial flexibility factors of nozzles in pressure vessel heads

Abstract An analytical study is performed to investigate the flexibility of nozzless in pressure vessel heads. Classical thin shell theory is employed. Radial flexibility factors for nozzles in hemispherical and ellipsoidal pressure vessel heads are presented as graphs of non-dimensional shell parameters.

Radial flexibility of welded-pad reinforced nozzles in ellipsoidal pressure vessel heads

Abstract A thin shell analysis was performed to investigate the radial flexibility of welded-pad reinforced nozzles in ellipsoidal pressure vessel heads. A comparison of the flexibility of such a nozzle to that of an integrally reinforced nozzle was made. The effect of size and thickness on flexibility was studied. A parametric study was performed for welded-pad reinforced nozzles in ASME 2:1 pressure vessel heads. Results are presented as flexibility factors which are functions of nondimensional nozzle-vessel geometries.