USE OF DIGITAL IMAGE CORRELATION TO INVESTIGATE THE BIOMECHANICS OF THE VERTEBRA

Digital image correlation (DIC) is being introduced to the biomechanical field. However, as DIC relies on a number of major assumptions, it requires a careful optimization in order to obtain accurate and precise results. The first step was the preparation of the speckle pattern by an airbrush spray gun following a factorial design to explore the different settings: the different speckle patterns created were analyzed to achieve the optimal speckle size, with minimal dispersion of speckle sizes. A benchmark test, with an aluminum specimen prepared with the speckle pattern, was conducted in which the errors affecting the computed strain were measured in a zero-displacement, zero-strain condition. The software parameters (facet size, step, and local regression) were singularly analyzed in order to understand their behavior on the final output. Moreover, the hardware parameters (camera gain, exposure, lens distortion) were analyzed. The output showed that a careful optimization allowed the reducing the systematic and random errors, respectively, from 150 to 10 microstrain and from 600 to 110 microstrain. Finally, the acquired know-how was applied to a biological specimen (human vertebra).

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Characterization of LIGA Microsystems Using Digital Image Correlation Technique and SEM Imaging

Aerospace ◽

10.1115/imece2005-81123 ◽

2005 ◽

Author(s):

Helena (Huiqing) Jin ◽

Wei-Yang Lu ◽

Jeff Chames ◽

Nancy Yang

Keyword(s):

Digital Image Correlation ◽

Digital Image ◽

Speckle Pattern ◽

Image Correlation ◽

Specimen Surface ◽

Correlation Technique ◽

Sem Images ◽

Full Field ◽

Speckle Patterns ◽

Dic Technique

A new experimental technique was developed to characterize the mechanical properties of LIGA (an acronym from German words for lithography, electroplating, and molding) materials. An advanced imaging capability, scanning electron microscopy (SEM), with an integrated loading stage allows the acquisition of in situ microstructural images at the micro scale during loading. The load is measured directly from a load cell, and the displacement field is calculated from the SEM images based on the digital image correlation (DIC) technique. The DIC technique is a full-field deformation measurement technique which obtains displacement fields by comparing random speckle patterns on the specimen surface before and after deformation. The random speckle patterns are typically generated by applying a thin layer of material with high contrast to a specimen surface. Alternatively, DIC can also be applied using the microstructural features of a surface as texture patterns for correlation. DIC technique is ideally suited to characterize the deformation field of MEMS structures without the need to generate a random speckle pattern, which can be very challenging on the micro and nanoscale. In this paper, the technique is experimentally demonstrated on a LIGA specimen. The digital images showing LIGA surface features acquired during the loading can serve as random patterns for the DIC method. Therefore, full-field displacement and strain can be obtained directly on the specimen and the errors incurred by the testing system can be eliminated.

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Analysis of Strain Field Heterogeneity at the Microstructure Level and Inverse Identification of Composite Constituents by Means of Digital Image Correlation

Materials ◽

10.3390/ma13020287 ◽

2020 ◽

Vol 13 (2) ◽

pp. 287 ◽

Cited By ~ 1

Author(s):

Witold Ogierman ◽

Grzegorz Kokot

Keyword(s):

Digital Image Correlation ◽

Digital Image ◽

Strain Field ◽

Optimization Procedure ◽

Image Correlation ◽

Inverse Identification ◽

Full Field ◽

Speckle Patterns ◽

Measured Strain ◽

Speckle Size

The present paper is devoted to the theoretical study on the estimation of the full-field strain at the microstructural level of composite materials by means of Digital Image Correlation (DIC). The main aim of the paper is to investigate the influence of speckle size on the accuracy of the strain field measurement at the microscale. The DIC analysis was conducted based on artificial speckle patterns generated numerically and the deformation behavior of the composites was simulated by using the finite element method (FEM). This approach gives the opportunity to compare the results of the DIC in terms of speckle size with the reference FEM solution. Moreover, the paper focuses on the inverse identification of the material constants of the composite constituents by using information associated with the measured strain field. The inverse problem is solved by using a novel two-step optimization procedure, which reduces the problem complexity. The feasibility and accuracy of the proposed approach are presented by analysis of two exemplary microgeometries representing the microstructures of fiber reinforced composites.

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Using text as a native speckle pattern in digital image correlation

The Journal of Strain Analysis for Engineering Design ◽

10.1177/03093247211045602 ◽

2021 ◽

pp. 030932472110456

Author(s):

Weston D Craig ◽

Fiona B Van Leeuwen ◽

Steven R Jarrett ◽

Robert S Hansen ◽

Ryan B Berke

Keyword(s):

Digital Image Correlation ◽

Rigid Body ◽

Measurement Uncertainty ◽

Digital Image ◽

Speckle Pattern ◽

Image Correlation ◽

Bending Test ◽

Line Spacing ◽

Speckle Patterns ◽

Surface Patterns

In certain applications, native surface patterns can be used in place of speckle patterns in digital image correlation (DIC). This paper explores the feasibility of using text as a native speckle pattern in DIC. Five text speckle patterns are tested in three different scenarios: a rigid body translation test, a rigid body rotation test, and an out of plane bending test. The patterns are benchmarked against a sixth, random speckle pattern applied using traditional DIC speckling methods. Rigid body translation tests are additionally performed on text patterns with varying font types and line spacings. In general, text patterns have good contrast, but low density as line spacing increases. Measurement uncertainty for the text patterns was comparable to measurement uncertainty in the random speckle pattern. Results from these tests show that while text patterns cannot be expected to perform better than a traditional DIC speckle pattern, text patterns can be effective speckle patterns in situations where already present on a specimen and applying a traditional speckle pattern is difficult.

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