Showing papers on "Photoelasticity published in 2010"
TL;DR: In this article, an overview of some of the applications of DIC for crack tip characterisation such as K, T-stress and crack tip opening angle (CTOA) measurements as well as data obtained from 3D measurements of a propagating crack.
206 citations
TL;DR: In this article, a 10-step phase-shifting methodology is proposed and a new strategy for obtaining the isochromatic phasemap free of ambiguity is demonstrated.
Abstract: With advancements in digital image processing and data acquisition, a separate branch of photoelasticity namely digital photoelasticity came into existence. Here, intensity information of the acquired image is used for the evaluation of whole-field photoelastic parameters. Digital photoelasticity provides only wrapped phasemaps of isoclinics and isochromatics and they have to be unwrapped in different ways for getting the continuous-phase values. In the case of the isochromatic phasemap, ambiguity removal prior to unwrapping is essential. In this paper, a 10-step phase-shifting methodology is proposed and a new strategy for obtaining the isochromatic phasemap free of ambiguity is demonstrated. Isoclinic unwrapping is performed by a new adaptive quality guided algorithm. Adaptive in the sense that isoclinic phase unwrapping is done autonomously even in the presence of isotropic points/π jumps occurring in the isoclinic phasemap. The isochromatic phasemap is also unwrapped using the quality guided path follower. The methodology is validated for the problem of a ring under diametral compression and later shown for three other models which have complex stress fields. Wherever possible, the parameters obtained by the new methodology are compared with analytical or numerical methods and the comparison is quite good.
55 citations
TL;DR: In this article, the main developments of RGB photoelasticity with reference to the maximum measurable retardation were considered and a new procedure based on the standard error function evaluated on a subset of the calibration array is also proposed and experimentally tested.
Abstract: This paper considers the main developments of RGB photoelasticity with reference to the maximum measurable retardation. In this paper, a new procedure based on the standard error function evaluated on a subset of the calibration array is also proposed and experimentally tested. The experiments show that the filament lamp makes it possible to find retardations until approximately 4 fringe orders while the fluorescent lamp makes it possible to determine higher fringe orders (12 fringe orders in this paper) owing to the discrete spectrum of the source. The paper shows that, by using the incandescent lamp, the primary limiting factor is the lack of modulation of the R, G and B signals whereas, by using the fluorescent lamp, the limitation of the maximum fringe order derives mainly from the gradient of the fringes and the procedure of search of the retardation.
52 citations
TL;DR: In this article, the authors show how to produce elastic materials containing thin inclusions and provide photo-elastic investigation of these structures, until a distance from the inclusion tip on the order of its thickness, corresponding to a stress concentration up to seven.
Abstract: Can the thickness of a thin inclusion (in a matrix material) be made so small (though retaining sufficient stiffness and matrix adhesion) to generate ‘in practice’ a stress state in agreement with the analytical (square-root singular) solution for a rigid line inclusion (so-called ‘stiffener’) embedded in a linear elastic plate? Can this inhomogeneous stress state be generated for tensile loading parallel to the stiffener? We provide a direct and positive answer to these questions, by showing how to produce elastic materials containing thin inclusions and by providing photoelastic investigation of these structures. The experiments fully validate the stress state calculated for an elastic plate containing a rigid (finite-length) line inclusion, until a distance from the inclusion tip on the order of its thickness, corresponding to a stress concentration up to seven.
52 citations
TL;DR: Within the limitation of the experimental methods of this study, the FRC post was advantageous in lower premolars, especially with two or more walls in terms of the fracture resistance and stress distribution.
44 citations
TL;DR: A general overview of the different stress-separation techniques, and their current state of development and usage can be found in this article, where the authors present the publications and the authors who have contributed to the development of new techniques.
Abstract: Photoelasticity has been used for decades in the experimental measurement of stresses and strains. As data-acquisition techniques only identify the differences between principal stresses and strains, stress-separation techniques exist to identify each of their values separately. A variety of techniques have been developed since the early days of photoelasticity, aiming to automate the measurement process, to exploit the full potential of photoelastic methods, and to facilitate its application. The purpose of this paper is to provide a general overview of the different stress-separation techniques, and their current state of development and usage. The paper presents the publications and the authors who have contributed to the development of new techniques.
43 citations
TL;DR: In this article, the authors compare the orientations of branching fractures at strike-slip relay zones between en echelon stylolites and en-chelon joints both reactivated in shear with both photoelastic and 3D numerical models that consider the remote stress conditions and the role of the geometry of the strike slip segments.
42 citations
TL;DR: In this paper, transmission photoelasticity on scale models is shown to disclose the stress distribution within dry masonry walls, where unilateral joints between elements, where randomness constrained within a geometrical scheme of contact points occurs, so that stress percolation results highly localized, evidencing "unloading islands" in a "stress stream".
Abstract: Transmission photoelasticity on scale models is shown to disclose the stress distribution within dry masonry walls. This distribution is found to be complicated by unilateral joints between elements, where ‘randomness constrained within a geometrical scheme’ of contact points occurs, so that stress percolation results highly localized, evidencing ‘unloading islands’ in a ‘stress stream’. These findings are theoretically explained in Part II of this paper from both micromechanical and continuous modelling perspectives.
36 citations
TL;DR: In this paper, a portable scattered light polariscope SCALP has been developed, which permits measurement of the residual stress profile through the thickness of glass panels, and the results of the fragmentation test were extremely scattered and had almost no correlation with the values of residual stress at the surface.
Abstract: A portable scattered light polariscope SCALP has been developed, which permits measurement of the residual stress profile through the thickness of glass panels. At a glass factory strength assessment of glass panels of different thermal treatment was carried out using both residual stress measurement with SCALP and the traditional four-point bending tests. Linear correlation between the residual surface stress and the bending strength was observed. At another glass factory residual stress in glass panels was measured before performing the traditional fragmentation test. The results of the fragmentation test were extremely scattered and had almost no correlation with the values of the residual stre ss. It is concluded that sufficiently reliable assessment of the strength of glass panels is obtained by measuring the residual stress at the surface.
30 citations
TL;DR: In this paper, a micromechanical model based on a form of random cascade transmission of forces between bricks, which includes random coalescence additionally to random branching, was proposed to explain the highly localized stress distribution found within dry masonry walls through transmission photoelasticity.
Abstract: The highly localized stress distribution found within dry masonry walls through transmission photoelasticity in Part I of this article is explained both proposing a micromechanical model (based on a form of random cascade transmission of forces between bricks, which includes random coalescence additionally to random branching) and applying a phenomenological description (based on the extreme orthotropy of the equivalent homogeneous material).
28 citations
TL;DR: In this paper, the authors demonstrate that polarisation-sensitive optical coherence tomography (PS-OCT) is suitable for mapping the stress distribution within materials in a contact-free and non-destructive way.
Abstract: We demonstrate that polarisation-sensitive optical coherence tomography (PS-OCT) is suitable for mapping the stress distribution within materials in a contact-free and non-destructive way. In contrast to transmission photoelasticity measurements, the samples do not have to be transparent but can be of scattering nature. Denoising and analysis of fringe patterns in single PS-OCT retardation images are demonstrated to be the bases for a quantitative whole-field evaluation of the internal stress state of samples under investigation.
TL;DR: In this article, the authors considered the calculation of maximum dimensionless stress at gear tooth root when the meshing gears are loaded at their most favorable contact point (HPSTC), using both numerical and experimental methods.
Abstract: Problem statement: Toothed gears are some of the most used machine elements for motion and power transmission between rotating shafts. Thi s fact induces the need for improved reliability an d higher endurance, which require precise and clear k nowledge of the gear tooth stress field during meshing. Approach: This study considered the calculation of maximum s tress at gear tooth root when the meshing gears are loaded at their most unfavora ble contact point (highest point of single-tooth contact-HPSTC), using both numerical and experimental methods. Finite Element Method (FEM) is used for the numerical stress analysis and photoela sticity is applied for the experimental investigati on of the stress field. Results: The experimental results of the maximum dimensionless stress derived from the photoelasticity experiments are compared t o the respective theoretical stress results of the finite element analysis. Conclusion: It was found that the deviation between the result s of the applied methods falls between reasonable limits whereas it rises with increasing number of teeth of the large gear.
TL;DR: In this paper, a polariscope was designed for urethane elastomer vasculature models, the photoelastic coefficient of UEL was measured, and a camera system was calibrated to quantify and reduce error in the measurement system.
Abstract: Real-time and accurate stress calculation in walls of vasculature is a desired goal in order to provide feedback control for catheter insertion robots without changing catheter stiffness and lumen This feedback source also has applications in endovascular surgery simulation In order to address this need, we consider photoelastic effect, as birefringence produced by light retardation relates to the stress inside photoelastic materials In this research, a polariscope was designed for urethane elastomer vasculature models, the photoelastic coefficient of urethane elastomer was measured, and a camera system was calibrated to quantify and reduce error in the measurement system An average error of 39% was found in stress measurements for the pressure range of 60-189 mmHg inside the urethane elastomer model This result was applied to correct stress distribution images, using the average stress value as a reference and preserving local maxima and minima of stress This enabled us to accurately calculate stress in vasculature models during human blood pressure simulation (HBPS), and enables the comparison, in a closed loop, of stress produced by HBPS and by catheter motion when driven by a robot, as well as to measure the stress produced by medical tools on the vascular model wall
TL;DR: In this article, the residual strain and its variation in multicrystalline Si substrates for solar cells have been quantitatively characterized from the absolute difference of refractive indices |Δn| and the principal direction ψ of strain-induced birefringence measured by scanning infrared polariscope, and the effective photoelastic coefficients calculated numerically at each grain, the crystallographic orientation of which was determined by the electron backscatter diffraction technique.
Abstract: The residual strain and its variation in multicrystalline Si substrates for solar cells have been quantitatively characterized. The strain was evaluated from the absolute difference of refractive indices |Δn| and the principal direction ψ of strain-induced birefringence measured by scanning infrared polariscope, and the effective photoelastic coefficients calculated numerically at each grain, the crystallographic orientation of which was determined by the electron backscatter diffraction technique. It has been shown that the residual strain increases at grains with multitwin boundaries and in the vicinity of small-angle grain boundaries, reaching the order of 10−4, corresponding to 10 MPa in terms of stress.
TL;DR: In this paper, a framework is developed to solve the inverse problem effectively, using synthetic displacement field data obtained from finite element analysis (FEA) are used to extract the cohesive relation by fully utilizing the measured displacement field.
Abstract: The cohesive zone model (CZM) is a key technique for finite element (FE) simulation of fracture of quasi-brittle materials; yet its constitutive relationship is usually determined empirically from global measurements. A more convincing way to obtain the cohesive relation is to experimentally determine the relation between crack separation and crack surface traction. Recent developments in experimental mechanics such as photoelasticity and digital image correlation (DIC) enable accurate measurement of whole-field surface displacement. The cohesive stress at the crack surface cannot be measured directly, but may be determined indirectly through the displacement field near the crack surface. An inverse problem thereby is formulated in order to extract the cohesive relation by fully utilizing the measured displacement field. As the focus in this article is to develop a framework to solve the inverse problem effectively, synthetic displacement field data obtained from finite element analysis (FEA) are used. Fi...
TL;DR: In this article, a loading device was developed to perform these functions, which was confirmed through the stress distribution, the configuration change and the contact length of the O-ring, when the internal pressure was applied to the Oring, while under a uniform squeeze rate the upper contact length increases slightly with increase in internal pressure, while the lower contact length was constant with an increase of internal pressure.
Abstract: Typically, O-rings are used to prevent penetration of dust and alien substances from entering a cylinder during motion. Moreover, Orings are used to create an air tight seal around a stationary shaft. The stresses developed in O-rings depend on the squeeze rate, gap between the external diameter of the groove and internal diameter of the cylinder as well as internal pressure. In application, the stress distributions in O-rings can be very complicated and are almost always studied through experiment. Photoelastic experiment has been applied to the study of 3-dimensional stress distributions in O-rings. The loading device used in photoelastic experiment is important. Its function is to apply a uniform squeeze rate and internal pressure on the O-ring and to allow uniform squeeze rate to be controlled. In this research, a loading device was developed to perform these functions. The validity of this loading device was confirmed through the stress distribution, the configuration change and the contact length of the O-ring. When the squeeze rate was constant, the upper and lower contact lengths of the deformed O-ring were almost equal. When internal pressure was applied to the O-ring, while under a uniform squeeze rate the upper contact length increases slightly with increase in internal pressure, while the lower contact length of the O-ring is constant with an increase in internal pressure.
TL;DR: In this paper, the authors studied the interfacial shear stress transfer behavior on both sides of the specially designed fiber when it was being pulled out; in which automatic analysis of three-dimensional photoelasticity is employed and the finite element method is adopted.
Abstract: Specially designed fibers are widely used in engineering practice because the specially-designed shape can help to improve the bonding strength of the fiber and the interface. Studied in this paper is the interfacial shear stress transfer behavior on both sides of the specially designed fiber when it is being pulled out; in which automatic analysis of three-dimensional photoelasticity is employed and the finite element method is adopted. The results show that the stress transfer occurs mainly in the region near the fiber’s embedded end where the stress reaches its critical point, leading to debonding of the interface. Before debonding, as the pullout loading increases, the peak value of shear stress transfers along the fiber from the embedded end to the interior of the matrix, and then stops at the hooked part of the fiber because of its impediment. When the interface begins to debond as the load increases, the shear stress can be transferred to the hooked part.
11 Apr 2010-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the residual internal stresses in PbWO 4 (PWO) scintillating crystals grown by the Bridgman method have been systematically studied, and the analysis revealed defects occurring during the crystallization process, attributed to dislocations, lattice disorientation and poly-crystallinity.
Abstract: Residual internal stresses in PbWO 4 (PWO) scintillating crystals grown by Bridgman method have been systematically studied. Residual stresses induced during growth play an important role in production yield. Cracking probability during mechanical processing as well as stable mechanical properties in finished crystal are closely related to internal stress levels. A regular production of good-quality crystals requires a fast and easy feed-back on growth parameters. Samples from a pre-serial production were analyzed in order to give the producer a quality feed-back for process optimization. By means of photoelasticity, we measured residual stress distribution in several sections along the growth axis and for typical positions in every section. The stress analysis revealed defects occurring during the crystallization process, attributed to dislocations, lattice disorientation and poly-crystallinity. This work had been prompted by the need for quality monitoring of a pre-serial production of PWO for the CMS experiment at CERN's LHC. Mapping stress levels inside the ingot volume and proposing a synthetic parameter to be used as a quality indicator, the resulting analysis should contribute to parameter optimization and improve the growth performance. The proposed method may be useful in conventional crystal production.
TL;DR: In this paper, a new application of this model is developed through a numerical simulation of the experimental tests, which were previously performed, aimed to analyze the shielding effect related to constant amplitude cycling loading and a single overload peak, considering numerical simulation.
TL;DR: In this paper, a full-field polariscope has been built to measure the relative retardation of a light beam transmitted through a model built from glass grains and a liquid with a matching refractive index in the pores.
Abstract: Photoelastic measurements provide a means to obtain a meaningful representation of the stress state in a granular material over the full area of a plane-strain sample without the need to place stress transducers inside the sample. This method uses the property of non-crystalline materials to become optically anisotropic when put under stress. To measure the resultant relative retardation of a light beam transmitted through a model built from glass grains and a liquid with a matching refractive index in the pores, a full-field polariscope has been built. This setup is able to characterize the stress state in the full-field of the sample with only seven intensity measurements. A plane-strain pile penetration test is used as an example.
TL;DR: The paper discusses efficacy of both RGB calibration and phase shifting techniques in sensing applications and proposes a neural network based approach in an expert system environment that can extract load information from photoelastic images in real time.
TL;DR: In this article, a Trefftz-element numerical method for the reconstruction of stress trajectories and the determination of full stress tensors in two-dimensional elastic bodies from discrete data on principal directions is presented.
Abstract: This paper presents a Trefftz-element numerical method for the reconstruction of stress trajectories and the determination of full stress tensors in two-dimensional elastic bodies from discrete data on principal directions. The conventional techniques cannot be used because neither displacements nor tractions are specified on the boundary. The proposed approach involves the subdivision of the domain into smaller subdomains and the introduction of the Cauchy integrals with unknown densities on element boundaries in order to approximate complex potentials within the elements. For polynomial approximations of the densities, this leads to piecewise polynomial approximations for the complex potentials within the entire domain and, therefore, all elasticity equations are automatically satisfied as in the Trefftz method. Continuity of the complex potentials is forced at the collocation points, which forms the first group of equations. The second group is formed by satisfying the data on principal directions known in some locations. All these equations are homogeneous; therefore, it is assumed that the average value of the maximum shear stresses at data points is unity. This guarantees the existence of a non-trivial solution of the system; however it addresses the non-uniqueness of the reconstruction of the full stress tensor. The technique is validated by reconstructing stress trajectories and determining maximum shear stresses from synthetic and photoelasticity data. It has been applied to reconstruction of tectonic stresses in the Australian region and the results were compared with previous approaches.
TL;DR: In this paper, a simple method is applied to calculate the optical path difference (OPD) of a plane parallel uniaxial plate with an arbitrary optical axis direction, and the theoretical expressions of the OPD and lateral displacement (LD) of Savart polariscope under non-ideal conditions are obtained exactly.
Abstract: A simple method is applied to calculating the optical path difference (OPD) of a plane parallel uniaxial plate with an arbitrary optical axis direction. Then, the theoretical expressions of the OPD and lateral displacement (LD) of Savart polariscope under non-ideal conditions are obtained exactly. The variations of OPD and LD are simulated, and some important conclusions are obtained when the optical axis directions have an identical tolerance of ±1°. An application example is given that the tolerances of optical axis directions are gained according to the spectral resolution tolerances of the stationary polarization interference imaging spectrometer (SPIIS). Several approximate formulae are obtained for explaining some conclusions above. The work provides a theoretical guidance for the optic design, crystal processing, installation and debugging, data analysis and spectral reconstruction of the SPIIS.
TL;DR: In this article, the distribution of expansion stress measured in initial cracking and partial cracking stages is examined, based on optical linear elastic fracture mechanics, the relation between the stress intensity factors and increment extensions are generated in different corrosion times.
Patent•
17 Jun 2010TL;DR: In this article, a GaN single crystal substrate has a main surface with an area of not less than 10 cm2, the main surface has a plane orientation inclined by not more than 65° with respect to one of a (0001) plane and a (000-1) plane.
Abstract: A GaN single crystal substrate has a main surface with an area of not less than 10 cm2, the main surface has a plane orientation inclined by not less than 65° and not more than 85° with respect to one of a (0001) plane and a (000-1) plane, and the substrate has at least one of a substantially uniform distribution of a carrier concentration in the main surface, a substantially uniform distribution of a dislocation density in the main surface, and a photoelasticity distortion value of not more than 5×10−5, the photoelasticity distortion value being measured by photoelasticity at an arbitrary point in the main surface when light is applied perpendicularly to the main surface at an ambient temperature of 25° C. Thus, the GaN single crystal substrate suitable for manufacture of a GaN-based semiconductor device having a small variation of characteristics can be obtained.
TL;DR: In this paper, the coefficients of reflection and refraction on the interface of crystal in the Savart polariscope are obtained for ordinary ray (o-ray) and extraordinary ray (e-ray).
TL;DR: In this paper, a photoelastic technique was used to measure the interfacial shear stress distribution in the matrix resin along a reinforcing E-glass fiber of ∼25 μm in diameter at its end and at a fibre-break.
TL;DR: In this article, the dispersion between the ordinary ray and extraordinary ray when light passes through the modified Savart polariscope was theoretically calculated and numerically simulated separately using the extension of Snell's law, and the relationship curve between incident angle and dispersion was obtained by simulation.
Abstract: The static large field of the view polarization interference imaging spectrometer is based on the modified Savart polariscope. There appears a dispersion between the ordinary ray and extraordinary ray when light passes through the modified Savart polariscope. The dispersion greatly influences the intensities and the results of the interferogram and target image in the static large field of the view polarization interference imaging spectrometer. At the same time, the incident angle determines the dispersion. When the light goes through the modified Savart polariscope, the dispersion occurs in the left plate, the half-wave plate and the right plate of the modified Savart polariscope. Using the extension of Snell's law, the dispersion in the crystal is theoretically calculated and numerically simulated separately. The relationship curve between incident angle and the dispersion is obtained by simulation.