Showing papers on "Photoelasticity published in 2014"

Effects of an absorptive coating on the dynamics of underwater laser-induced shock process

Abstract: The effects of an absorptive coating on the dynamics of underwater laser-induced shock process have been observed from the end of laser pulse to hundreds of microseconds after irradiation by time-resolved imaging techniques. A laser pulse of 13 ns at 1,064 nm was focused by a 40-mm focal length lens onto the surface of epoxy-resin blocks immersed in water to induce the shock process in the confining regime. A custom-designed time-resolved photoelasticity imaging technique and a high-speed laser stroboscopic videography technique in photoelasticity mode were used to analyze the evolution of shock waves in the water phase, the strength of stress waves in the solid phase, the oscillation of cavitation bubbles, and the generation of bubble-collapse-induced shock waves. We showed that black paint coating enhances the strength of laser-induced stress wave inside the solid, drives faster shock waves traveling in the water phase, and produces higher-energy cavitation bubbles. We propose that even at power densities of 1 GW/cm2 and above, an absorptive coating can intensify the shock process by enhancing the absorption of laser energy by plasma.

Experimental and numerical study of the load distribution in a ball-screw system

Abstract: In this work, load distribution on ball-screw systems (BSS) is determined by experimental techniques. Two optical techniques are used: photoelasticity for stress-field measurement and the mark-tracking method for displacement-field determination. In parallel to the experimental study, finite element method (FEM) and analytical solutions are used to calculate the loads applied on each ball of the BSS. Experimental results are used to validate the choice of boundary conditions and contact conditions between ball-screw and ball-nut in the FEM solution. The validation criterion is the correspondence between numerical and experimental fringes representing the differences of principal stresses. In addition to the study of load distribution, this paper presents the influence of the angle of contact direction on the stress distribution in BSS.

Comparison of the correlation of photoelasticity and digital imaging to characterize the load transfer of implant-supported restorations.

Abstract: Statement of problem Whether splinting or not splinting adjacent implants together can optimize the stress/strain transfer to the supporting structures remains controversial. Purpose The purpose of this study was to compare the photoelasticity and digital image correlation (DIC) in analyzing the stresses/strains transferred by an implant-supported prosthesis. Material and methods A polymethylmethacrylate model was made with a combination of acrylic resin replicas of a mandibular first premolar and second molar and threaded implants replacing the second premolar and first molar. Splinted (G1/G3) and nonsplinted (G2/G4) metal-ceramic screw-retained crowns were loaded with (G1/G2) and without (G3/G4) the presence of the second molar. Vertical static loads were applied to the first molar implant-supported crown (50 N-photoelasticity; 250 N-DIC). The resulting isochromatic fringes in the photoelastic models were photographed, and a single-camera 2-dimensional DIC system recorded the deformation at the surface of the resin models. Results Residual stresses were present in the photoelastic model after screw fixation of the crowns. The following average photoelastic stress results (MPa) were found around the loaded implant: G1 (20.06), G2 (23.49), G3 (30.86), G4 (37.64). Horizontal strains (e xx , %) between the molars averaged over the length of the loaded implant were found by DIC: G1 (0.08 ±0.09), G2 (0.13 ±0.10), G3 (0.13 ±0.11), G4 (0.16 ±0.11). Splinted crowns transferred lower stresses to the supporting bone when the second molar was absent. The second molar optimized the stress distribution between the supporting structures even for nonsplinted restorations. Conclusions Both methods presented similar results and seemed capable of indicating where issues associated with stress/strain concentrations might arise. However, DIC, while apparently less sensitive than photoelasticity, is not restricted to the use of light-polarizing materials.

A critical assessment of automatic photoelastic methods for the analysis of edge residual stresses in glass

Abstract: The measurement of residual stresses is of great importance in the glass industry. The analysis of residual stresses in the glass is usually carried out by photoelastic methods since the glass is a photoelastic material. This article considers the determination of membrane residual stresses of glass plates by digital photoelasticity. In particular, it presents a critical assessment concerning the automated methods based on gray-field polariscope, spectral content analysis, phase shifting, RGB photoelasticity, “test fringes” methods and “tint plate” method. These methods can effectively automate manual methods currently specified in some standards.

Critical Evaluation of a Constitutive Model for Glassy Polycarbonate

Abstract: Polycarbonate (PC) is an important amorphous glassy polymer whose intrinsic uniaxial response exhibits all the features like strain softening and hardening at large deformations characteristic of this class of materials. Polycarbonate is significantly ductile and is capable of sustaining large plastic deformation. Constitutive models of PC, in order to be useful, should be able to faithfully model its elastic as well as plastic behaviour with as few undetermined parameters as possible. We assess the efficacy of a particular model of glassy polymers by fitting its parameters through usual uniaxial tensile and compressive tests and then using those parameters to model a fracture specimen in 3-dimensions. A range of experimental techniques like digital image correlation, photoelasticity and x-ray tomography are used to make careful quantitative comparisons with computer simulations. Our results indicate that in view of the small scale yielding situation prevalent in PC specimens even at high loads, a faithful prediction of the elastic parameters are sufficient for reproducing most global responses and deformation fields away from the crack. However, to predict fracture initiation, the deformation state within the small but significant fracture process zone needs to be reproduced. This cannot be done unless the entire uniaxial response is modelled to a reasonable degree of accuracy.

Stress analysis of a pinned wood joint by grey-field photoelasticity

Abstract: Pinned (bolted) joints/connections are a widely used, but difficult to analyze, component. Their bolt/hole interface stresses are typically unknown a priori . Structural failures often initiate at connections and their contact stresses can be the “Achilles’ heel”. Although such connections are extremely prevalent in wood structures, ability to determine the individual stresses in mechanical wood joints is aggravated by the material’s orthotropy. Solutions to such non-linear problems that account for finite geometry, pin/hole friction and clearance are non-trivial. Many mechanical-joint analyses ignore friction for simplicity, but some contact friction is virtually always present. By applying a thin birefringent coating to the wood, the individual stresses and strains in the coating (and hence in the wood) are determined by synergizing grey-field photoelasticity, a stress function and boundary information. Full-field individual stresses are obtained in the wood, including at the contact boundary. Predicted strength based on the determined stresses is compatible with the connection failure.

Photoelastic Analysis of Partially Occluded Objects With an Integral-Imaging Polariscope

Abstract: Polariscopes are the basic instruments used for the analysis of the stress state of transparent materials. Polarized light passing through a 3D object carries the integrated effect of the stress field along the light path. Therefore, conventional polariscopes are not able to discern the stress state of objects involving multiple plates with mutual occlusions. In this paper we propose a novel experimental system for three-dimensional stress analysis based on the combination of a polariscope and Synthetic Aperture Integral Imaging technique. Experimental results show the system's ability to recover the information of the stress distribution of a set of plates located at different depths having mutual occlusions.

Residual stress, thermomechanics & infrared imaging, hybrid techniques and inverse problems

Abstract: Analysis of Thrust Production in Small Synthetic Flapping Wings.- Coarse-resolution Cone-beam Scanning of Logs Using Eulerian CT Reconstruction. Part I: Discretization and Algorithm.- Coarse-resolution Cone-beam Scanning of Logs Using Eulerian CT Reconstruction. Part II: Hardware Design and Demonstration.- Crack Nucleation Threshold Under Fretting Loading by a Thermal Method.- Crack Growth Study of Fibre Metal Laminates Using Thermoelastic Stress Analysis.- Crack Detection in Large Welded Components Under Fatigue Using TSA.- Hybrid Thermoelastic Analysis of an Unsymmetrically-loaded Structure containing an Arbitrarily-shaped Cutout.- Quantitative Themographic Characterization of Composites.- Thermal Deformation of Micro-structure Diffuser Plate in LED Backlight Unit.- Polariscopy Measurement of Residual Stress in Thin Silicon Wafers.- Curvature From Residual Stress in Rapidly Quenched Amorphous Metals Using Abrasive Layer Removal.- Slitting Method Measurement of Residual Stress Profiles, Including Stress Discontinuities, in Layered Specimens.- Repeatability of the Contour Method for Residual Stress Measurement.- Repeatability of Incremental Hole Drilling and Slitting Method Residual Stress Measurements.- Drilling Speed Effects On Accuracy Of HD Residual Stress Measurements.- Ultrasonic Nonlinear Guided Waves and Applications to Structural Health Monitoring.- Defect Detection in Composite Structures Using Lock-in Infrared Thermography.- Digital Image Correlation for Identification of Vibration Modes.- Application of VFM for the Simultaneous Identification of Visco-pseudo-hyper Elastic Constants of Rubbers.- Anisotropy Evaluation of Paperboard With Virtual Fields Method.- Investigation of Fatigue Properties of Titanium Alloy Applying Variational Infrared Thermography.- Monitoring Materials Under Impact With Infrared Thermography.- Damage Induced Evolution of the Thermal Diffusivity of SiC/SiC Composite.- Identification of Welding Heat Sources From Infrared Temperature Measurements.- Nondestructive Evaluation of Fiber Reinforced Polymers With Lockin Thermography.- Realistic 3D FE Modelling of Peening Residual Stresses of Strain-rate Sensitive Materials With Oblique Incident Angles.- Water Cavitation Peening by Ultrasonic Vibration for Improvement of Fatigue Strength of Stainless Steel Sheet.- Effect of Residual Stress on Spallation of NiCrBSi Coating.- Multiaxial Fatigue Resistance of Shot Peened High-strength Aluminium Alloys.- Quantifying Residual Strains in Specimens Prepared by Additive Layer Manufacturing.- Parameter Determination of Anisotropic Yield Criterion.- Performance Assessment of Inverse Methods in Large Strain Plasticity.- Optical - Numerical Determination of the Flow Curves of Anisotropic Steels and Failure Prediction.- Advanced Biaxial Cruciform Testing at the NIST Center for Automotive Lightweighting.- An Enhanced Plasticity Model for Material Characterization at Large Strain.- Residual Stress and Phase Transformation map for Impact Fatigued Zirconia.- Characterization of Silicon Photovoltaic Wafers using Infrared Photoelasticity.- Acoustic Emission Analysis Of Aluminum Specimen Subjected To Laser Annealing.- Optical Analysis of Weld-induced Residual Stress by Electronic Speckle-pattern Interferometry.- Shape Is Not Enough to Test Hypotheses for Morphogenesis.- FBG Based Insitu Characterization of Residual Strains in FDM Process.- Polynomial Fitting Techniques for IRT Inspection.- In-flight Infrared Thermography for Studies of Aircraft Cabin Ventilation.- Study of Elastomeric Membranes for Vibration Dampers in Non-stationary Conditions.- Structural Dynamic Modification to Predict Modal Parameters of Multiple Beams.

Characterizing Frictional Contact Loading via Isochromatics

Abstract: Isochromatic patterns in the vicinity of frictional contacts furnish vital clues for characterizing friction. Though friction effects are evident in a diametrally loaded circular disk, three-point loading provides better results towards highlighting friction. In this paper, a new method of characterizing friction at loading contacts using photoelastic isochromatics patterns is presented. Location of isotropic points (IPs) formed in three-point and four-point loadings of circular disk is used as a main tool to quantify the friction component using theoretical analysis. Bifurcation of isochromatic fringe loops near the distributed loads is explained by the presence of anti-symmetric Hertzian shear traction in addition to Hertzian normal traction. The classical solution by Flamant for point load at the edge of half plane is used to derive stresses in circular disk for all required loading configurations. A semicircualr ring under three-point loading is examined using photoelasticity to understand the isochromatics pattern theoretically by considering normal and shear traction components at loaded regions.

Fringe Analysis for Photoelasticity Using Image Processing Techniques

Abstract: In research of photoelasticity, photoelastic fringe patterns are obtained through a circular polariscope with different optical arrangements and they are processed with image processing techniques in a personal computer. Image processing techniques are reviewed and discussed for stress analysis of the photoelastic fringes in this paper. The image processing techniques include fringe sharpening, fringe multiplication, and 8-step phase measuring technique. Gradient descent process is used for fringe sharpening. In fringe multiplication, fringes are multiplied twice for limited fringe order. 8-step phase measuring technique is used to separate isoclinics and isochromatics. The results of image processing techniques show that they are quite useful for stress analysis in photoelasticity.

The Optical Methods of Caustics and Photoelasticity: A Comparison

Abstract: The optical methods of photoelasticity and caustics have extensively been used for the determination of stress intensity factors (SIFs) in static and dynamic crack problems. Both methods present their potentialities and limitations. In crack problems the state of stress in the neighborhood of the crack tip changes from plane strain near the tip to plane stress away from the tip through an intermediate three-dimensional region. This affects the determination of SIFs using experimental methods. In the present work the methods of photoelasticity and caustics applied to crack problems are briefly presented and compared regarding the following criteria: the optical set-up, the efficiency in the determination of stress intensity factors, the effect of crack tip radius, the effect of plate boundaries, the location of the crack tip and the changing state of stress near the crack tip.

Analysis of stress induced by screws in the vertebral fixation system

Abstract: Objective: To compare, using photoelasticity, internal stress produced by USS II type screw with 5.2 and 6.2 mm external diameters, when submitted to three different pullout strengths. Methods: Two photoelastic models were especially made. The simulation was performed using loads of 1.8, 2.4 e 3.3 kgf.The fringe orders were evaluated around the screws. In all the models analyzed the shear stress were calculated. Results: Independently of the applied load, the smaller screw showed higher values of shear stress. Conclusion: According to the analysis performed, we observed that the place of highest stress was in the first thread of the lead, close to the head of the screws. Experimental study.

Photoelasticity in Dentistry: a literature review

Abstract: Resumen en: Introduction and Objective: Photoelasticity consists of an experimental technique of stress analysis. This technique is very used in most different areas...

Analysis of Stress Distribution in Dry Masonry Walls Using Three Fringe Photoelasticity

Abstract: Masonry being a composite system is very complex to study with analytical methods alone. Quantitative digital photoelastic analysis using Three Fringe Photoelasticity (TFP) is carried out on a model of a dry masonry wall with bricks made up of epoxy, loaded with a concentrated load. The result obtained provides insight into the micromechanics of force transmission and interactions between bricks in masonry. The result shows that force transmission through the wall occurs at discrete points. A tree like hierarchical pattern of stress flow is observed. It is also observed that the stress percolation results in the existence of stress-free zones in the model domain.

Effect of the molding temperature and cooling time on the residual stresses of crystal polystyrene

Abstract: The use of crystal polystyrene for high performance components requires knowledge of the distribution of residual stresses. The aim of this research was to analyze the influence of the molding temperature and cooling time on the residual stresses present in parts of two types of crystal polystyrene PS1 and PS2, processed by injection molding. The results obtained using photoelasticity showed that at low temperatures the residual stresses increase due to the processes of formation and destruction of intermolecular forces. Internal stresses were reduced in the polymer specimens with greater thickness because the molecular relaxation of chains of polystyrene is facilitated by the space increase between the walls of the mold. It was concluded that the photoelasticity technique can be applied effectively in the measurement of residual stresses in injection molded crystal polystyrene parts.

Photoelastic properties of oxide and non-oxide glasses

Abstract: An unperturbed piece of glass is optically isotropic. Birefringence can be induced by breaking this symmetry, for example by applying a uniaxial stress to the glass. An empirical model exists which predicts when oxide glasses will exhibit positive, negative or zero birefringence under stress. This model has been used to determined new zero-stress optic oxide glass compositions; however, it has not been tested on non-oxide systems, nor does it take into account the wavelength of the incident light. The stress-optic response in chalcogenide glasses was investigated using stoichiometric GeS2-P2S5 and GeS2-Sb2S3, and non-stoichiometric Ge-P-S. The trends of the stress-optic response in stoichiometric non-oxide glasses correlated well with predictions based on the empirical model for oxide glasses. Small differences between the predictive parameter of the model, 〈d/Nc〉, were explained by expanding the treatment of metallicity. The wavelength dependence of the stress-optic coefficient for a large variety of oxide glass formers and modifiers was measured. Glasses composed of positive modifiers (e.g. BaO, CaO, Na2O) exhibited positive dispersion of the stress-optic coefficient, while those with negative modifiers (e.g. PbO, SnO) showed negative dispersion. Mixing positive and negative modifiers in a glass resulted in compositions exhibiting wavelength independent stress-optic coefficients. The photoelastic response of a material can also be described by its elasto-optic tensor (pij). Isotropic materials have three elasto-optic tensor elements, two of which are independent. These two independent elements were measured for lead and barium borate, phosphate and silicate glasses using Brillouin spectroscopy. Both elements were found to correlate with the empirical parameter 〈d/Nc〉, while the third dependent element showed no relationship to the empirical model. Finally, an alternative model of photoelasticity is discussed. The normalized polarizability of a material is found to correlate with both the sign and magnitude of the stress-optic coefficient.

Measurement of residual birefringence in thin glass plates using digital photoelasticity

Abstract: Residual stresses in glass causes it birefringent, affecting its optical properties. Annealed P-LASF47%trade; glass plates of 75 × 20 × 5 mm are subjected to two different thermal cycles. An automatic polariscope is used to employ Phase Shifting Technique (PST) to determine the residual integrated retardations over the thickness. Smaller field of view of the polariscope necessitates analysing the glass plate separately for the upper and lower regions of the glass plate. A code is developed in MATLAB to stitch the retardation data for the upper and lower region. The integrated retardation for the whole field is plotted as a contour plot using OriginPro software. Maximum retardation is observed in small regions at the free surfaces of the glass plate. It is noted that the nature of the thermal cycle has an influence on the retardation distribution.

Application of photo elasticity for the measurement of internal stresses in indeterminate structures

Abstract: Photoelasticity, an optical technique for experimental stress analysis, is widely used for 2-D and 3-D analysis of components for getting the information of principal stress difference and principal stress direction at every point in the domain. The recent developments in digital image processing have given birth to a separate branch of photoelasticity called digital photoelasticity. This method can be successfully employed to determine the stresses in structures with complicated shapes and loading. This paper gives a review of integrated photoelasticity and of its application for residual stress measurement in indeterminate structures. Significant reported methods on Photoelasticity for stress determination of indeterminate structures for the last 30 years has been analysed.

Integral photoelasticity relations for inhomogeneously strained di electrics

Abstract: A model for interaction of polarized light with inhomogeneously strained non-magnetizable dielectric solid is considered in the paper. The model establishes ray photoelasticity integrals connecting distributions of strain tensor components on any direction on the body volume with measurable optical parameters of polarized light beam propagating in this direction. The model can be used for developing mathematical methods for polarized-optical computational tomography of stress-strained states of dielectric solids.

Polarization tomography for residual stress measurements in a hexagonal single crystal

Abstract: The application of tensor field tomography for non-destructive reconstructions of residual stresses in a long hexagonal single crystal is studied. The residual stresses are considered to be of a tempering character. Thus, it is assumed that there exists a temperature field T(x,y,z), the so-called fictitious temperature, which causes a stress field that is equal to the stress pattern. Transformation of the polarization of light is measured in a plane orthogonal to the optical axis of a crystal. Stresses are determined within the framework of the Maxwell piezo-optic law (linear dependence of the permittivity tensor on stresses) and the small rotation of principal stress axis. This paper generalizes a method of integrated photoelasticity for the case of a hexagonal single crystal.

Polariscopy Measurement of Residual Stress in Thin Silicon Wafers

Abstract: Near-infrared (NIR) Polariscopy has been used to find residual stresses in thin silicon wafers using phase shifting techniques. This paper describes the usage of the ten-step phase shifting method to measure the in-plane residual stresses in single- and multi-crystalline silicon wafers. We show how this technique can be applied to wafers without the application of external loading. The system is calibrated with a beam of monocrystalline CZ silicon loaded in an in-plane four-point bending fixture. The residual maximum shear stresses of the unloaded wafers are then determined. The shear difference technique is used for obtaining the normal stress values. Results are compared before and after smoothing of the isoclinic parameter, and its impact on the separated stress values is explained.