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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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01 Jan 2021-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this paper, a variotherm-assisted microinjection molding is used to manufacture a practical microlens array designed for light-field applications in order to achieve satisfactory geometric accuracy, surface quality and stress birefringence of the microlenses.
Abstract: Injection moulding is ubiquitous in the production of plastic optical components, the functionality of which depends on minimising residual stress and on precisely replicating surface forms. In this study, variotherm-assisted microinjection moulding is used to manufacture a practical microlens array designed for light-field applications in order to achieve satisfactory geometric accuracy, surface quality and stress birefringence of the microlenses, all of which are difficult to achieve by conventional microinjection moulding. Based on in-line process monitoring and a comprehensive evaluation regarding the quantitative and qualitative aspects of the aforementioned factors, the replication is shown to correlate well with machine settings and dynamic machine responses. Screw movements are found to be crucial in the replication process. Compared to an optimised conventional microinjection moulding condition, the general residual stress level and uniformity of the microlens array area are improved by 5.08% and 88.11%, respectively, when the warm circuit temperature is 135 °C and enhanced by 2.73% and 84.32%, respectively, by a delayed switch from the warm circuit to the cold circuit. It is concluded that variotherm-assisted microinjection moulding can significantly reduce residual stresses while maintaining excellent geometric accuracy and surface quality.
18 citations
TL;DR: In this article, a method of experimentally visualising and elucidating the 3D structures and stress fields of porous solids using photopolymer materials, 3D printing, the frozen-stress method, and photoelastic tests was presented.
Abstract: The physical visualisation of a three-dimension (3D) stress field is a promising method for quantitatively analysing and revealing the stress distribution and evolution of a porous solid, and it significantly contributes to the understanding of the governing effects of stress fields on the mechanical behaviours of complex porous solids. However, experimental limitations regarding the manufacture of complex porous models and the extraction of the stress distributions in matrices inhibit the accurate visualisation of the 3D stress fields of porous structures. This paper presents a method of experimentally visualising and elucidating the 3D structures and stress fields of porous solids using photopolymer materials, 3D printing, the frozen-stress method, and photoelastic tests. Transparent thick discs containing various randomly distributed pores were produced using photopolymer materials and 3D printing technology. Experimental measures, including the frozen-stress method, photoelastic testing, and the phase-shifting method, were applied to quantitatively characterise the 3D stress fields distributed throughout the porous discs under radial-direction compressive loads. The temperature for ‘freezing’ stresses in the photopolymer materials was experimentally determined. The effects of pore distribution and population on the stress-field characteristics were investigated. The experimental results were used to validate the numerical analysis of the stress-field characteristics of the porous models. The visualisation test results agreed well with those of the numerical simulations. The proposed method can be used to visually quantify the characteristics and evolution of the 3D stress fields of porous solids.
18 citations
Cites methods from "Digital Photoelasticity: Advanced T..."
...In this study, we mainly focus on the experimental method of identifying and extracting the characteristics of principal stress difference in porous models, because the principal stress difference is one of the key factors that fundamentally affect the mechanical behaviours of porous solids, such as shear deformation, hydraulic fracture, contact failure, stress concentration, and coupled fracture [43]....
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TL;DR: The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe order are obtained by comparing the colou
Abstract: The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe orders are obtained by comparing the colou
18 citations
Cites methods from "Digital Photoelasticity: Advanced T..."
...orders, the RGB values in Figure 4(a) are converted to HSV using the standard relations available in Ramesh.(1)Figure 4(b) shows a uniform modulation of HSV for the entire range of fringe orders....
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...In digital photoelasticity, a colour image processing system is basically used as an image acquisition device.(1) Representation of the colour information could be based on red, green and blue (RGB) in which the image is seen as a superposition of RGB image planes or hue, saturation and intensity (HSI) or hue, saturation and value (HSV)....
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...To explore the use of HSV colour model for photoelastic specimens involving higher fringe orders, the RGB values in Figure 4(a) are converted to HSV using the standard relations available in Ramesh.1Figure 4(b) shows a uniform modulation of HSV for the entire range of fringe orders....
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TL;DR: In this article, the explicit equations recently reported in the literature for a flat punch with rounded edges are generalized so that a single set of equations can be used for Hertzian contacts with arbitrary radii of curvatures, and the generality of the governing equations is verified by plotting isochromatics for conformal and non-conformal contact situations.
Abstract: Experimental studies to exploit photoelastic data of conformal geometries to extract contact parameters are non-existent because closed-form stress field equations were not available until recently. In this paper, the explicit equations recently reported in the literature for a flat punch with rounded edges are generalized so that a single set of equations can be used for a flat punch with rounded edges and Hertzian contacts with arbitrary radii of curvatures. The generality of the governing equations is verified by plotting isochromatics for conformal and non-conformal contact situations. A generic method to evaluate unknown contact parameters from the whole-field isochromatic data for conformal and non-conformal geometries is implemented. The methodology is initially verified using theoretically generated isochromatic data and is then used to experimentally evaluate two contact situations. In view of high-fringe gradient zones, the suitability of various digital photoelastic methods is compared. A novel four-step phase shifting technique is proposed in which isochromatic and isoclinic data can be evaluated using the minimum number of images.
18 citations
TL;DR: An adaptive scanning scheme is proposed so that stress separation can be carried out even if there is only one free boundary pixel available in the model.
Abstract: In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference method is one of the widely used techniques for stress separation in digital photoelasticity. Normally a simple raster scanning approach is used in shear difference method in which stress separation is carried out for all the lines within the model domain by either row-wise horizontally or column-wise vertically starting from the boundary pixels. This requires the presence of a free boundary to start the integration scheme for every row of interest, which is not always possible in most of the practical problems. In order to overcome this, in this paper, an adaptive scanning scheme is proposed so that stress separation can be carried out even if there is only one free boundary pixel available in the model. The new scanning scheme is validated using the theoretically generated data for the problem of a ring subjected to internal pressure. Later, the applicability of this scheme is demonstrated by using two other example problems.
18 citations