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Digital Photoelasticity: Advanced Techniques and Applications
01 Jan 2000-
TL;DR: In this article, phase shifting, Polarization Stepping and Fourier Transform Methods are used for phase unwrapping and Optically Enhanced Tiling in digital photoelasticity.
Abstract: Transmission Photoelasticity.- Reflection Photoelasticity.- Digital Image Processing.- Fringe Multiplication.- Fringe Thinning and Fringe Clustering.- Phase Shifting, Polarization Stepping and Fourier Transform Methods.- Phase Unwrapping and Optically Enhanced Tiling in Digital Photoelasticity.- Colour Image Processing Techniques.- Evaluation of Contact Stress Parameters and Fracture Parameters.- Stress Separation Techniques.- Fusion of Digital Photoelasticity, Rapid Prototyping and Rapid Tooling Technologies.- Recent Developments and Future Trends.
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TL;DR: In this article, a new LPC configuration applied in the LPC method is presented, based on a brief introduction on the principle of molecular luminescence, the intensity formula for the new lumen-based LPC is derived according to the theory of photoelasticity.
Abstract: For overcoming the limitation of a low signal-to-noise ratio (SNR) in practical applications of luminescent photoelastic coating (LPC) method, a new LPC configuration applied in the LPC method is presented. Based on a brief introduction on the principle of molecular luminescence, the intensity formula for the new LPC is derived according to the theory of photoelasticity. Through the comparative analysis with the existing coating configurations (dual-layer coating and single-layer coating), the feasibility of this new LPC used in the LPC method for experimental strain analysis is proved theoretically, and the signal intensities of the LPC method can be increased by over two times.
5 citations
Cites background or methods from "Digital Photoelasticity: Advanced T..."
...(2) In contrast to the two kinds of existing coating configurations, dual-layer coating and singlelayer coating, the enhanced emission intensities of the new coating could increase by over four times and two times, respectively....
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...(1) applying high-performance CCD camera with high full-well capacity and/or low cooling temperature to the measurement system, which would lead to the increase in the cost of equipment; (2) increasing the number of the collected images and using the mean image method for the postprocessing, which would provide more time for the image capturing and processing; (3) directly improving the existing coating configurations to enhance the detection signal intensities, which is preponderant over the above two methods....
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...(P), and a wavelength-matched quarter-wave plate (QWP), all of them assemble together for providing needed excitation light; (2) a rotating analyzer (A), interference filter (emission filter), a scientific grade charged-couple device (CCD) camera, a zoom lens, etc....
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TL;DR: This study provides important insights and recommendations regarding the overall replication quality of microlens arrays, while advanced injection moulding solutions may be necessary to further improve the general replication quality.
Abstract: Injection moulding has shown its advantages and prevalence in the production of plastic optical components, the performance and functionality of which rely on the precision replication of surface forms and on minimizing residual stress. The present work constitutes a systematic and comprehensive analysis of practical microlens arrays that are designed for light-field applications. Process parameters are screened and optimized using a two-stage design of experiments approach. Based on in-line process monitoring and a quantitative and qualitative evaluation being carried out in terms of geometric accuracy, surface quality and stress birefringence, the replication is shown to relate directly to machine settings and dynamic machine responses. The geometric accuracy and stress birefringence are both largely associated with screw displacement and peak cavity pressure during the packing stage, while surface quality is closely related to cavity temperature. This study provides important insights and recommendations regarding the overall replication quality of microlens arrays, while advanced injection moulding solutions may be necessary to further improve the general replication quality.
4 citations
01 Jan 2010
TL;DR: In this article, a comparison between phase contrast microscopy and phase coherence tomography (OCT) has been made to illustrate the similarities, differences, and limitations of both techniques.
Abstract: This work is concerned with the topic of phase-sensitive imaging techniques suitable for the investigation of structures in the micron range, and shows the potential for quantitative analysis resulting from an appropriate image processing for the investigated specimens. The probed samples are mostly of technical nature, but the methods are in general not restricted to technical applications. Moreover, several imaging aspects have originated from biological applications, being recently transfered to technical material sciences. Concerning imaging technique, we focus on optical coherence tomography (OCT) and in particular on its phase-sensitive modifications: Polarization-sensitive OCT (PS-OCT) and differential phase contrast OCT (DPC-OCT). The comparison to quantitative imaging in phase contrast microscopy techniques (classical phase contrast microscopy, differential interference contrast microscopy, and advanced versions of phase microscopy) has been done to illustrate the similarities, differences, and limitations of both techniques. We propose two procedures comprehending the measurement, the enhancement and the quantitative analysis of phase-related quantities: In case of PS-OCT we consider the reconstruction of retardation and birefringence distributions, and in case of DPC-OCT imaging, the extraction of the phase gradient fields and the reconstruction of the optical path length maps therefrom. From the point of view of physics we demonstrate how existing phase-sensitive OCT techniques can be modified in their imaging setup to allow an advanced data acquisition. Especially, we consider how one-dimensional measurement schemes in DPC-OCT can be extended to allow a two-dimensional solution of the phase reconstruction problem. From the point of view of signal processing we illustrate the potential given by extending also the analysis of PS-OCT retardation images from one-dimensional signal processing to two-dimensional image analysis. We include demodulation schemes, based on generalized analytic signal theory and originally developed for two-dimensional fringe pattern analysis of conventional interferometry, in PS-OCT imaging applications. From the point of view of mathematics we show how the existing image processing schemes can be adapted and improved to become suitable for the measured PS-OCT and DPC-OCT images. Especially the necessity of an appropriate pre-processing (as image denoising and decomposition), tailored to the features of phase-based OCT imaging, is illustrated. We have demonstrated the performance of the described methods to obtain spatially-resolved and quantitative information about internal material states, as birefringence and stress, or about the topography of embedded phase structures. Suggestions for further improvements of the reconstruction scheme are discussed. We have exemplified the proposed procedures for different test samples in real-world applications and situations being relevant in the field of material testing. The thesis is written deliberately in the field spanned between physics, in particular optics, and mathematics, in particular image processing. The work should illustrate the potential, which can be obtained by the interdisciplinary consideration of optical measurement techniques, mathematical data analysis, and aspects of material sciences.
4 citations
Cites background from "Digital Photoelasticity: Advanced T..."
...Photoelasticity (PE) techniques represent the classical experimental method for the analysis of strain/stress states in materials [127, 128]....
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TL;DR: In this article, the use of two digital photoelasticity methods for collecting these data is discussed and SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation.
Abstract: The main sources of error in the determination of stress intensity factors (SIFs) for an interface crack in a bi-material by conventional photoelasticity are the measurement of the positional co-ordinates of the data point and the fringe order. In the present work, use of two digital photoelasticity methods for collecting these data is discussed. SIFs are evaluated using constant radius method and a least squares approach based on the singular stress field equation. The need for developing a multi-parameter stress field solution for evaluating SIF is highlighted.
4 citations
Cites methods from "Digital Photoelasticity: Advanced T..."
...Following the procedure mentioned in reference [10], phase map given in Fig....
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...A way out to this problem was found by resorting to digital fringe multiplication [10]....
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