Full-Field Pressure and Strain Measurement Technique Using a Dual-Layer Luminescent Coating

Abstract Among the full-field optical measurement methods, the Digital Image Correlation (DIC) is one of the techniques which has been given particular attention. Technically, the DIC technique refers to a non-contact strain measurement method that mathematically compares the grey intensity changes of the images captured at two different states: before and after deformation. The measurement can be performed by numerically calculating the displacement of speckles which are deposited on the top of object’s surface. In this paper, the Two-Dimensional Digital Image Correlation (2D-DIC) is presented and its fundamental concepts are discussed. Next, the development of the 2D-DIC algorithms in the past 33 years is reviewed systematically. The improvement of 2DDIC algorithms is presented with respect to two distinct aspects: their computation efficiency and measurement accuracy. Furthermore, analysis of the 2D-DIC accuracy is included, followed by a review of the DIC applications for two-dimensional measurements.

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Noise Reduction Technique for Digital Image Based Full Field Strain Measurement

Volume 2: 32nd Computers and Information in Engineering Conference, Parts A and B ◽

10.1115/detc2012-70704 ◽

2012 ◽

Cited By ~ 2

Author(s):

Yoshitaka Wada ◽

Tomonari Furukawa

Keyword(s):

Noise Reduction ◽

Digital Image ◽

Strain Measurement ◽

Low Noise ◽

Reduction Technique ◽

Distortion Correction ◽

Image Correlation ◽

Full Field ◽

Deformation Problem ◽

Noise Reduction Technique

In recent years several techniques of full-field measurement have been studied by digital image correlation method, moiré interference method and holographic interferometry method and so on. Image based method can be easily applied to large deformation problem and moving specimen at slow speed. Because digital camera capabilities, which are high resolution, low noise and faster data transfer speed, have been improved, very small strain measurement can be achieved by those improvements. The improvement will widen those applications, for example, moving object at high speed and less 0.1% strain measurement which is almost the same accuracy with a precise strain gauge. In order to apply the advanced application, noise reduction for a digital image and lens distortion correction for an optical system should be developed. In this paper we propose noise reduction technique using statistical camera model to be applied to any kinds of digital cameras.

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Non-Contact Technique for Characterizing Full-Field Surface Deformation of Shape Memory Polymers

ASME 2010 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Volume 1 ◽

10.1115/smasis2010-3679 ◽

2010 ◽

Author(s):

A. J. W. McClung ◽

G. P. Tandon ◽

K. E. Goecke ◽

J. W. Baur

Keyword(s):

Elastic Modulus ◽

Shape Memory ◽

Strain Measurement ◽

Shape Memory Polymers ◽

Material Behavior ◽

Image Correlation ◽

Optical Measurements ◽

Transverse Strain ◽

Strain Gages ◽

Full Field

Thermally-actuated shape memory polymers (SMPs) typically display two phases separated by the glass transition temperature (Tg). At temperatures well below the Tg, the polymer exhibits a relatively high elastic modulus. Well above the Tg the elastic modulus drops by several orders of magnitude. In this high temperature region, SMP materials can achieve strain levels well above 100 %. The complex behavior of SMPs (stiffnesses dropping to the order of 1 GPa and extremely high strain levels) precludes the use of traditional strain gages and low-contact force extensometers. The present study presents a detailed expansion of state-of-the-art thermomechanical testing techniques used to characterize the material behavior of SMPs. An MTS environmental chamber with an observation window allows for non-contact optical measurements during testing. A laser extensometer is used for measurement and active control of axial strain. The upper limit on the strain rate capability of the laser extensometer is established. In addition, the photographic strain measurement method known as digital image correlation (DIC) is incorporated, allowing for full field measurement of axial and transverse strains of SMPs over a range of temperatures and strain rates. The strain measurements of the DIC and laser extensometer are compared to each other as well as to clip-on extensometers and strain gages. The comparisons provide insight into the limitations of the traditional strain measurement systems. A series of tensile tests are performed on a commercial SMP from 25 °C up to temperatures of 130 °C and strain levels above 100 %. The laser extensometer provides a robust method for controlling the strain in the gage section of the samples. In addition, results show that the full field measurements of both the axial and the transverse strain are essential for characterizing the constitutive response of SMPs at room and elevated temperatures.

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