Photoelastic Technique Research Articles

New numerical method for the photoelastic technique

The objective of this research is to find new equations for a novel phase-shifting method in digital photoelasticity. Some innovations are proposed. In terms of phase-shifting, only the analyzer is rotated, and the other equations are deduced by applying a new numerical technique instead of the usual algebraic techniques. This approach can be used to calculate a larger sequence of images. Each image represents a measurement of the stresses present in the object. Every photographic image has errors and random noise, but the uncertainties due to these effects can be reduced with a larger number of observations.

Linear Analysis of Crack Propagation in a Solid Rocket Propellant

The Solid Rocket Propellant in its crude form is a rubber like material. This rubber like material performs very interestingly when used to study crack propagation. Blunting of crack tips occurred in the composite when the load is applied, which is generally non-linear phenomenon. The crack propagation analysis for such case is generally taken for double edge cracks but the presence of central cracks in the composites cannot be ignored. This trend is nonlinear and complex. In order to simplify things, optical grade polyurethane material is used instead. The polyurethane material we used for our experimental work was PSM-4. In this research work, an extensive study is made regarding crack propagation analysis using the basic principles of fracture mechanics and its different techniques for finding out the parameter necessary for tracing crack propagation. Mode 1 (Opening Mode) is considered for the central crack propagation analysis. The objectives set in this context are the determination of Stress Intensity Factor of central crack in the specimen using photoelastic experimental data and simulation of central crack in softwares (ANSYS, Pro-e). For this purpose a rectangular plate with Central Crack was used to be experimented upon using the techniques of Photoelasticity. A comparative analysis technique is adopted to compare the effectiveness of results from experiments as well as software simulations.

New numerical methods for the photoelastic technique with high accuracy

The objective of this research is to find new equations for a novel phase-shifting method in digital photoelasticity. Some innovations are proposed. In terms of phase-shifting, only the analyzer is rotated, and the other equations are deduced by applying a new numerical technique instead of the usual algebraic techniques. This approach can be used to calculate equation of phase with a larger sequence of images. Each image represents a pattern and a measurement of the stresses present in the object. A reduction in the difference between the theoretical and experimental values of stresses was obtained by increasing the number of images in the equations for calculating phase. Every photographic image has errors and random noise, but the uncertainties due to these effects can be reduced with a larger number of observations.

Leaky Interface Wave Measurement at a Solid-Solid Interface with Laser Ultrasonics

The experimental investigation on transparent solid/solid (aluminum and plexiglas) interface leaky waves generated by a pulse laser and detected with a photoelastic effect technique is reported. Three waves, i.e., longitudinal head wave, leaky Rayleigh wave and leaky interface wave, are detected successfully. The leaky waves propagating along the ‘weak bonding’ interface are also measured. It is found that with the continuing epoxy solidification, the wave amplitude gradually decreases and the two leaky waves are more difficult to distinguish. The velocities of the detected interface wave are in good agreement with the theoretical calculation and the attenuation characteristics of the two leaky waves are also in accordance with the theoretical prediction.

Finite Element Analysis of Elastic Stresses around Holes in Plate Subjected to Uniform Tensile Loading

The author reported stress analysis of infinite isotropic plate with a cylindrical circular hole and oblique hole. The present work deals with infinite isotropic plate under uniform tensile load. Three components of different material with different obliquity angle were used for analysis. These components having holes circular & oblique at angles 0, 30 and 60 degree are considered for study. The long twisted blades of gas turbine blade will be treated as infinite plate with oblique holes/cooling holes constituting a geometrically complex, three- dimensional body that is subjected to the action of systems centrifugal force. Stress concentration and stress field around oblique holes is a major challenge area in design of aerofoil in aerospace applications for safety because of their highly specialized applications in aerospace field under severe operating conditions. In design, Stress Concentration Factor (SCF) can be used as multiplication factor, and using that maximum stress can be predicted, thus it shows the stress field around local region. The experimental methods used are photo elastic and strain gauge techniques. When a infinite plate containing a cylindrical oblique hole is subjected to remotely applied uniform tensile load, the circumferential stresses along the boundary of the hole are produced which have been successfully used to predict stresses around holes. The resulting Stress Concentration Factor (SCF) obtained by Finite Element (FE) analysis are compared with experimentally obtained values. The results of FEA technique are in good agreement with experimental values, thus providing a means of analysing more effectively realistic Gas turbine blades. For analysis FEA software MSC/PATRAN, MSC/ NASTRAN-NX v7.0 has been used.

Use of FEM and photo elasticity for shape optimization of S type load cell

In modern technological environment, the conventional methodology of design cannot compete the modern trends of computer aided engineering techniques. Continuously the research is going on for new innovative design in the engineering field. To build a highly optimized product is the basic requirement of today's global market. All around efforts were put forward in this direction. Various software professionals and technologies have developed various design packages. It is a challenging task to shape optimize 'S' type load cell with best functional requirements and at lowest weight. In this project an attempt is made to model an 'S' type load cell and optimization of the same using the finite elements analysis software 'ANSYS'. A simple model of 'S' type load cell is considered for FEM modeling and optimization. This paper illustrates the model of 'S' type load cell before optimization and finally obtained optimized model. Using Photo-elasticity technique, results are crosschecked which gives results very close to FEM technique. With the aid of these tools the designer can develop and modify the design parameters from initial design stage to finalize basic geometry of Load Cell.

The use of stress analysis methods to evaluate the biomechanics of oral rehabilitation with implants

Abstract Because the biomechanical behavior of dental implants is different from that of natural tooth, clinical problems may occur. The mechanism of stress distribution and load transfer to the implant/bone interface is a critical issue affecting the success rate of implants. Therefore, the aim of this study was to conduct a brief literature review about the available stress analysis methods to study implant-supported prosthesis loading, and to discuss their contributions in the biomechanical evaluation of oral rehabilitation with implants. It was found that several studies have used experimental, analytical and computational models by means of finite element models (FEM), photoelasticity, strain gauges and associations of these methods to evaluate the biomechanical behavior of dental implants. The FEM has been used to evaluate new components, configurations, materials and shape of implants. The greatest advantage of the photoelastic method is the ability to visualize the stresses in complex structures such as oral structures, and to observe the stress patterns in the whole model, allowing to localize and to quantify the stress magnitude. The strain gauges can be used to assess in vivo and in vitro stress in prosthesis, implants and teeth. Some authors use the strain gauge technique associated with either photoelasticity or FEM techniques. These methodologies can be widely applied in Dentistry, mainly in the research field. Therefore, they can guide further researches and clinical studies by predicting some disadvantages and streamlining the clinical time.

Substrate effects from force chain dynamics in dense granular flows

Granular materials are composed of solid, discrete particles and exhibit mechanical properties that range from fluid to solid behavior. Some of the complexity exhibited by granular systems arises due to the long‐range order that develops due to particle‐particle contact. Inter‐particle forces in granular materials often form a distributive network of filamentary force‐accommodating chains (i.e., force chains), such that a fraction of the total number of particles accommodates the majority of the forces in the system. The force chain network inherent to a system composed of granular materials controls the macroscopic behavior of the granular material. Force transmission by these filamentary chains is focused (or localized) to the grain scale at boundaries such as the granular flow substrate. This investigation addresses the effects of force localization on the substrate by dynamic force chain processes and the implications for bed entrainment in dense, unconfined, two‐dimensional, gravity‐driven granular flows. Our experimental system employs photoelastic techniques and provides an avenue for quantitative force analysis via image processing and provides a data set that can be used validate discrete element modeling approaches. We show that force chains cause extreme bed‐force localization in dynamic granular systems, and that these localized forces can propagate extensively into the substrate, even ahead of the flow front.

광탄성 위상이동법을 이용한 인장판 경사균열 선단주위의 프린지 해석

광탄성법은 실험역학에서 응력 또는 변형률을 해석하기 위한 여러 실험방법 중의 하나이며, 다양한 종류의 구조물의 응력 분포를 실험적으로 결정하는 기법이다. 광탄성법은 광탄성 영상의 등색 프린지와 등경 프린지로부터 광탄성 시편에 나타나는 전체의 응력장 분포를 정밀하게 측정할 수 있다. 본 논문에서는 여러 가지 광탄성 기법중 8단계 위상이동법(8-step phase-shifting method)에 관한 이론을 살펴보고, 경사균열이 있는 평판 시편에 인장을 가하여 나타난 광탄성 프린지로부터 경사균열 선단주위의 응력분포를 8단계 위상이동법으로 결정한 후, 이들 결과를 유한요소법(FEM)에 의한 결과와 비교하였다. 8단계 위상이동법을 이용한 실험에 의해 측정된 프린지 차수는 유한요소법에 의한 계산된 프린지 차수값에 근접하였다. Photoelasticity is a technique of experimental methods and has been widely used in various domains of engineering to determine the stress distribution of structures. Without complicated mathematical formulation, this technique can conveniently provide a fairly accurate whole-field stress analysis for a mechanical structure. Here, stress distribution around an inclined crack tip of finite-width plate is studied by 8-step phase-shifting method. This method is a kind of photoelastic phase-shifting techniques and can be used for the determination of the phase values of isochromatics and isoclinics. According to stress-optic law, the stress distribution could be obtained from fringe patterns. The results obtained by polariscope arrangement combined with 8-step method and ABAQUS FEM simulations are compared with each other. Good agreement between them shows that 8-step phase-shifting method is reliable and can be used for determination of stress by experiment.

Investigation of the Sound Field of Phased Array Using the Photoelastic Visualization Technique and the Accurate FEM

In this study, we tried to obtain an accurate ultrasonic sound field of the commercial phased array system. For this purpose, the experimental photoelastic ultrasonic visualization system was improved to evaluate a phased array system and the analytical special large-scale finite element method (FEM) code for ultrasonic transmission was applied. As the results, an actual sound field of phased array system was much more complicate than that of the conventional industrial assumption based on a simple superposition. One of the causes of the difference might be the accuracy of the directivity for each element in the array transducer. Thus, the combination of photoelastic visualization method and FEM analysis was useful for the accurate sound field investigation of the phased array measurement. [doi:10.2320/matertrans.I-M2012806]

Analysis of a Complex Shape Chain Plate Using Transmission Photoelasticity

The stresses and its distribution in complex shape chain plate geometry play a critical role in the fatigue life performance of a chain assembly. However, it is difficult to identify the stress distribution and stress concentration zones precisely using only the conventional industrial friendly tools such as routine quality control test, breaking load test and numerical computations. In this context the transmission photoelastic technique has made it possible to identify the stress distribution, its concentration and also to quantify the stress and strain at any point in the chain plate. This paper explains how transmission photoelastic technique is used to estimate the stress distribution and its concentration zones in a complex chain plate when it is loaded.

ADAPTIVE FINITE ELEMENT METHOD TO DETERMINE KI AND KII OF CRACK PLATE WITH DIFFERENT EINCLUSION/EPLATE RATIO

An adaptive finite element method is presented to determine the KI and KII stress intensity factors of crack plate with different inclusions. The paper starts from describing two-dimensional fracture mechanics theory, an adaptive finite element formulation and the reflection photoelastic technique. An adaptive finite element method is evaluated by analyzing two examples. A single edge cracked plate made from polycarbonate. The second example is the slant edge 45° cracked plate subjected to a uniform uniaxial tensile stress. The KI and KII results are found to be function of the crack length per width and the inverse function of E ratio. These examples demonstrate the efficiency of the adaptive finite element method to provide accurate solutions as compared to those from the reflection photoelastic technique.

In Situ Optical Investigations of Hypervelocity Impact Induced Dynamic Fracture

One of the prominent threats in the endeavor to develop next-generation space assets is the risk of space debris impact in earth’s orbit and micrometeoroid impact damage in deep space. To date, there is no study available which concentrates on the analysis of dynamic crack growth from hypervelocity impacts on such structures, resulting in their eventual catastrophic degradation. Experiments conducted using a unique two-stage light-gas gun facility have examined the in situ dynamic fracture of brittle polymers subjected to this high-energy-density event. Optical techniques of caustics and photoelasticity, combined with high-speed photography, analyze crack growth behavior of Mylar and Homalite 100 thin plates after impact at velocities ranging from 3 to 7 km/s (7,000–15,500 mph). Results indicate that even under extreme impact conditions of out-of-plane loading, highly localized heating, and energetic impact phenomena involving plasma formation and ejecta, the dynamic fracture process occurs during a deformation regime dominated by in-plane loading.

Experimental and Numerical Study of Double Containment Joint Having Circular Cross-Section Support

Bonded structure are commonly of three types, purely adhesive bonded, weld-bonded and adhesive/mechanical structures. Present work concern with experimental set-up of double containment joint with circular cross-section support using photoelasticity techniques. The experimental results were found to be within 5% when compared with the numerical analysis.

Sensitivity of isoclinic data using various phase shifting techniques in digital photoelasticity towards generalized error sources

Photoelasticity is a whole field experimental technique to obtain stress fields in both 2-D and 3-D elasticity problems. The accuracy of parameter evaluation by digital photoelastic techniques depends on the choice of the optical arrangements for parameter estimation, the inherent error in optical elements and any misalignments introduced during experimentation. A generic approach to simulation of error in digital photoelasticity by Jones calculus is presented in this paper. Of late it has been shown that the quarter-wave plate mismatch error is varying and is not a constant value. The present simulation accounts for inherent variable error in quarter-wave plates and also accommodates the error arising due to the optical misalignment of the various optical elements. The applicability of the new methodology is shown for different phase shifting techniques. A comparative study among various techniques is done regarding sensitivity to general error sources and it is found that the ten-step method is the least sensitive among them all. Therefore usage of the ten-step method is thus recommended while using manual polariscope for digital photoelastic applications.

Finite element and photoelastic modelling of an abdominal aortic aneurysm: a comparative study

Rupture prediction of abdominal aortic aneurysms (AAAs) remains a clinical challenge. Finite element analysis (FEA) may allow for improved identification for intervention timing, but the method needs further substantiation. In this study, experimental photoelastic method and finite element techniques were compared using an idealised AAA geometry. There was good agreement between the numerical and experimental results. At the proximal and distal end of the AAA model, the maximum differences in principle strain for an internal pressure of 120 mmHg had differences ranging from 0.03 to 10.01%. The maximum difference in principle strain for the photoelastic and the finite element model at a pressure of 120 mmHg was 0.167 and 0.158, respectively. The current research strengthens the case for using FEA as an adjunct to the current clinical practice of utilising diameter measurement for intervention timing.

Experimental determination of stress field parameters in bi-material notches using photoelasticity

The experimental technique of photoelasticity has been utilized for calculating bi-material notch stress intensities as well as the coefficients of higher order terms. Employing the equations of multi-parameter stress field allows data collection from a larger zone from the notch tip and makes the data collection from experiments more convenient. Moreover, the effects of higher order terms in the region near the notch tip are taken into account. For the photoelasticity experiments, a laboratory specimen known as the Brazilian disk with a central notch, consisting of Aluminum and Polycarbonate, has been utilized. Using this specimen, different mode mixities could be easily produced by changing the loading angle. The bi-material notch stress intensities and the first non-singular stress term (called I-stress) were then calculated for different test configurations. In order to utilize the advantages of whole-field photoelasticity and minimize the experimental errors, a large number of data points were substituted in the multi-parameter stress field equations. Then the resulting system of nonlinear equations was solved by employing an over-deterministic least squares method coupled with the Newton–Raphson algorithm. It has been shown that considering the I-stress term improves, to a large extent, the accuracy of the stress intensities calculated through the photoelasticity technique. Moreover, by reconstructing the isochromatic fringes, the effects of the I-stress term on the shape and size of these fringes around the notch tip were investigated for a 30° notch. Finally, the experimental photoelasticity results were compared with the corresponding values obtained from finite element analysis and a good correlation was observed.

Experimental Investigation of Load Sharing in Multiple Gear Tooth Contact Using the Stress‐Optical Method of Caustics

Abstract: In this paper, a comprehensive methodology for calculating load sharing in multiple tooth contact is presented based on the experimental stress‐optical method of caustics. The technique is applied to a set of poly‐methyl‐methacrylate gears at various meshing positions covering a complete meshing cycle, including single and multiple gear tooth contact. The load sharing factor (LSF) is calculated using well‐established mathematical formulae from the photographs of the transmitted caustics and the obtained results are compared with the pertinent International Organisation for Standardisation and American Gear Manufacturers Association standards with which good agreement is verified. The proposed method is a reliable alternative for measuring load distribution in gear teeth compared with photoelasticity and other experimental techniques.

The effect of crystal hardness on radial pressure at the wall of a tabletting die.

Abstract The force transmitted to the die wall during the tabletting of seven crystalline pharmaceutical materials has been measured using a photoelastic technique. The Vickers hardness of these materials has also been measured. The compounds examined were aspirin, urea, hexamine, salicylamide, potassium chloride, sodium chloride and sucrose. The pressure on the die wall increases as the hardness value decreases. The Vickers hardness of the resultant tablets was also measured; aspirin and sodium chloride both showed the occurrence of work hardening in that the tablets had a greater hardness value than the parent crystalline substance.

The application of photoelastic techniques to a rotary tabletting machine.

Abstract Powders have been compacted on a rotary tabletting machine, using a Perspex die mounted above the die table, with an extended lower punch and a shortened upper punch. By high speed cine photography in polarized light, the fringes due to the radial stress in the die wall were recorded during compaction. At the same time, the upper and lower punch forces were monitored by instrumented pressure rollers coupled to a recording oscilloscope. The total information thus obtained was sufficient to enable compression cycles to be determined for the first time on a rotary machine.