Photoelastic Technique Research Articles

The stress intensity factors (SIFs) of cracked half-plane specimen in contact with semi-circular object

In this paper, photoelasticity technique was used to analyze the stress intensity factors (SIFs) of semi-infinitive plate with an edge crack in contact with the semi-circular wedge. The effects of different parameters such as crack angle, crack length, semi-circular wedge diameter and distance between the crack and the wedge tip on the second mode of stress intensity factor were investigated using experimental tests and numerical simulations. The crack length, crack angle, magnitude of the applied load, the distance between crack tip and loading position were varied in the tests. Image processing and linear elastic fracture mechanic (LEFM) method were used to compute SIFs from fringe patterns acquired from the experimental tests. Finally, a large number of finite element analyses have been carried out, and then numerical and experimental results were compared. The amount of the relative differences between numerical and experimental results was less than 9.8% indicating the high accuracy and good agreement.

Shear modulus and dilatancy softening in granular packings above jamming.

We investigate experimentally the mechanical response to shear of a monolayer of bidisperse frictional grains across the jamming transition. We inflate an intruder inside the packing and use photoelasticity and tracking techniques to measure the induced shear strain and stresses at the grain scale. We quantify experimentally the constitutive relations for strain amplitudes as low as 10(-3) and for a range of packing fractions within 2% variation around the jamming transition. At the transition strong nonlinear effects set in: both the shear modulus and the dilatancy shear soften at small strain until a critical strain is reached where effective linearity is recovered. The scaling of the critical strain and the associated critical stresses on the distance to jamming are extracted. We check that the constitutive laws, together with mechanical equilibrium, correctly predict to the observed stress and strain profiles. These profiles exhibit a spatial crossover between an effective linear regime close to the inflater and the truly nonlinear regime away from it. The crossover length diverges at the jamming transition.

Absorption kinetics and swelling stresses in hydrothermally aged epoxies investigated by photoelastic image analysis

The present work proposes an experimental optical methodology able to measure the transient swelling stresses induced by the water uptake ageing of polymers. In particular, the work describes the implementation of a Photoelastic technique to quantify internal stresses arising during the hydrothermal ageing of cast epoxy samples. The material investigated is a model DGEBA/DDS epoxy system. Curing and post-curing cycles have been optimised in order to obtain a fully cured, high Tg, and completely stress free initial condition. Rectangular beam samples were then left in a hydrothermal bath at 90 °C, and regularly monitored by gravimetric and photoelastic analyses. The quantitative evolution of stresses induced by water ingress was obtained by a Photoelastic Stress Analysis technique applied during water absorption, and successive desorption in controlled conditions. The evolution of stresses is correlated with gravimetric data, allowing to gain a new insight to investigate the complex swelling and diffusion kinetics of water ingress into thermoset polymer networks.

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

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 stress analysis assisted evaluation of fracture toughness in hydrothermally aged epoxies

The present work has investigated the fracture toughness of a model DGEBA epoxy system subject to Hidro-Thermal aging. A Photoelastic Stress Analysis technique has been implemented, showing the evolution of stresses arising throughout the water uptake process due to the non-uniform swelling of the material. Gravimetric and Dynamic Mechanical Thermal Analyses have further complemented the characterization, showing the onset of plasticization effects with aging. The correlation of all previous characterizations has allowed to conclude that an increase of KIC fracture toughness is obtained at the fully saturated condition. In particular Photoelasticity has also revealed the onset of relevant swelling induced stresses during the first stages of water absorption, leading to an increase of fracture toughness due to compressive stresses settling near the crack tip. A stress free condition is instead reestablished at the later stages of absorption, suggesting that the increased toughness of the saturated material is an effect of the modifications induced by aging on the polymer structure.

Use of stress analysis methods to evaluate the biomechanics of oral rehabilitation with implants.

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 of 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. 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 shapes 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 the researcher to localize and quantify the stress magnitude. Strain gauges can be used to assess in vivo and in vitro stress in prostheses, implants, and teeth. Some authors use the strain gauge technique with photoelasticity or FEM techniques. These methodologies can be widely applied in dentistry, mainly in the research field. Therefore, they can guide further research and clinical studies by predicting some disadvantages and streamlining clinical time.

Photo-Elastic Effects near the Centroid of Epoxy Specimens

The stress concentration of the circular hole within the mechanical mart can easily derived by the photo-elastic technique if the testing specimen is sufficiently developed. The testing specimen using the characteristic of the photo-elastic coefficient, with actual form like the mechanical part by rapid prototyping forming is thus used in this paper. The rapid mold for prototype is made by the RTV-2 silicone gel associated with the vacuum chamber to remove the air within it. The testing scheme is by way of the simply supported beam where the load is imposed on the middle of the specimen. Results show that the smaller diameter of hole on specimen provides a larger stress concentration effect. When the diameter of the hole is small, the stress concentration effects caused by the machined hole and the forming hole have almost no difference. However, the stress concentration effects of the larger diameter of the machined hole and of the formed hole give significant difference, the stress concentration caused by the machined hole is much greater than one of the formed hole. In this paper, the actual shape of the specimen which is as same as the original mechanical components can be quickly obtained by the rapid prototyping technology for the photoelastic technique to reveal the experimental mechanics of real applications.

A new method of evaluating interfacial properties of a fiber/matrix composite

Interfacial debonding frequently initiates composite failure in a fiber/matrix composite. A single-fiber fragmentation test and its modifications can be used to evaluate interfacial properties. However, they still have accuracy problems due to fiber impurities and friction work. This paper presents a new method of evaluating interfacial properties using a stress contour of composite matrix. A single-fiber fragmentation test model was developed to simulate the stress contour. The interface was modeled as a cohesive zone model. Four characteristic lengths on the stress contour were found after conducting simulations with many interfacial properties values. The stress contour was then captured from the single-fiber fragmentation test employing a photo-elasticity technique and the four characteristic lengths were measured. Iteration in simulation involved changing interfacial properties until corresponding characteristic lengths from experiment and simulation were obtained. The results were compared with those obtained with existing methods and found to be reasonable.

21003 光弾性法による微小成型された紫外線硬化樹脂の応力解析

21003 光弾性法による微小成型された紫外線硬化樹脂の応力解析

G0310503 応力と温度の同時計測による硬化過程の紫外線硬化樹脂の評価(材料力学部門一般セッション:画像・計測)

The stress and temperature of ultraviolet (UV) curable resin during curing were measured using a simultaneous measurement system of stress and temperature and their relationship was investigated. The specimen consisted of a mold and UV-curable rein in liquid form. The mold consisted of glass plates, acryl plates and a potassium bromide (KBr) plate. The specimen was illuminated with UV rays downwards from the upper side of the specimen. The stress and temperature were measured using a photoelastic and thermographic techniques, respectively. Results indicated the stress and temperature during curing were closely related.

Hierarchical modelling of in situ elastic deformation of human enamel based on photoelastic and diffraction analysis of stresses and strains

Human enamel is a typical hierarchical mineralized tissue with a two-level composite structure. To date, few studies have focused on how the mechanical behaviour of this tissue is affected by both the rod orientation at the microscale and the preferred orientation of mineral crystallites at the nanoscale. In this study, wide-angle X-ray scattering was used to determine the internal lattice strain response of human enamel samples (with differing rod directions) as a function of in situ uniaxial compressive loading. Quantitative stress distribution evaluation in the birefringent mounting epoxy was performed in parallel using photoelastic techniques. The resulting experimental data was analysed using an advanced multiscale Eshelby inclusion model that takes into account the two-level hierarchical structure of human enamel, and reflects the differing rod directions and orientation distributions of hydroxyapatite crystals. The achieved satisfactory agreement between the model and the experimental data, in terms of the values of multidirectional strain components under the action of differently orientated loads, suggests that the multiscale approach captures reasonably successfully the structure–property relationship between the hierarchical architecture of human enamel and its response to the applied forces. This novel and systematic approach can be used to improve the interpretation of the mechanical properties of enamel, as well as of the textured hierarchical biomaterials in general.

The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI): a new tool for aerosol and cloud remote sensing

Abstract. The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) is an eight-band (355, 380, 445, 470, 555, 660, 865, 935 nm) pushbroom camera, measuring polarization in the 470, 660, and 865 nm bands, mounted on a gimbal to acquire multiangular observations over a ±67° along-track range. The instrument has been flying aboard the NASA ER-2 high altitude aircraft since October 2010. AirMSPI employs a photoelastic modulator-based polarimetric imaging technique to enable accurate measurements of the degree and angle of linear polarization in addition to spectral intensity. A description of the AirMSPI instrument and ground data processing approach is presented. Example images of clear, hazy, and cloudy scenes over the Pacific Ocean and California land targets obtained during flights between 2010 and 2012 are shown, and quantitative interpretations of the data using vector radiative transfer theory and scene models are provided to highlight the instrument's capabilities for determining aerosol and cloud microphysical properties and cloud 3-D spatial distributions. Sensitivity to parameters such as aerosol particle size distribution, ocean surface wind speed and direction, cloud-top and cloud-base height, and cloud droplet size is discussed. AirMSPI represents a major step toward realization of the type of imaging polarimeter envisioned to fly on NASA's Aerosol-Cloud-Ecosystem (ACE) mission in the next decade.

Experimental investigation of spur gear tooth mesh stiffness in the presence of crack using photoelasticity technique

Gear mesh stiffness plays a very important role in gear dynamics and it varies in the presence of gear fault such as crack. The measurement of stress intensity factor can lead to the determination of gear tooth mesh stiffness variation in the presence of crack in a spur gear system. In this paper, the technique of conventional photoelasticity has been revisited to explore the possibility of using it as a supplementary technique to experimentally measure the variation of gear mesh stiffness. An attempt has been made to calculate the variation of mesh stiffness for a pinion having a cracked tooth and a gear tooth with no crack of a spur gear pair. An analytical methodology based on elastic strain energy method in conjunction with total potential energy model has been adopted and implemented within the mesh stiffness calculations. To visualize the state of stress in a structure using finite element and other currently available methods, photoelasticity is considered to be one of the oldest and most developed experimental technique. An experimental methodology based on conventional photo-elasticity technique for computing stress intensity factor (SIF) for cracked spur gear tooth is presented for different single tooth contact position and crack length. The relation between contact position, crack length, crack configuration, SIF and the variation of total effective mesh stiffness have been quantified. Finally, a comparison has been made and the results obtained from finite element method (FEM) based on linear elastic fracture mechanics (LEFM), analytical method and proposed experimental method has been outlined.

Separation of Isochromatics and Isoclinics Phasemaps for the Photoelastic Technique with use Phase Shifting and a Large Number of High Precision Images

Abstract Digital photoelasticity is an important optical metrology follow-up for stress and strain analysis using full-field digital photographic images. Advances in digital image processing, data acquisition, procedures for pattern recognition and storage capacity enable the use of the computer-aided technique in automation and facilitate improvement of the digital 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 phaseshifting, 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 pattern and a measurement of the stresses present in the object. A decrease in the mean errors was obtained by increasing the number of observations. 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. The proposed method with many images and high accuracy is a good alternative to the photoelastic techniques.

Leaky Interface Waves Optical Detection at Solid-Solid Interface

The experimental investigation on transparent solid/solid (Aluminum and Plexiglas) interface leaky waves generated by a pulse laser and detected with a photo elastic effect technique is reported. Three waves Lateral wave, Leaky Rayleigh (LR) wave and Leaky Interface wave (IW) are detected successfully; The velocity of the detected interface wave is in good agreement with theoretical calculation and the attenuation characteristic of the two Leaky waves is also in accordance with the theoretical prediction. The Leaky waves propagate along the weak bonding interface is also measured, it was found with the continue Epoxy solidifying, the wave amplitude gradually decrease and the two Leaky waves are more difficult to distinguish. The successful measurement should improve the scientific and technological potential for the research of solid/solid interface waves.

Measurement of Stress and Displacement Fields in Particle Assembly subjected to Shallow Foundation Loading via Photoelasticity Technique

본 논문의 목적은 얕은 기초 하중을 받는 입상체 내의 응력의 분포와 변위를 측정하는 광탄성 기법의 적용 방안을 제시하는 데 있다. 광탄성 측정기법은 입자 집합체의 힘 전달을 시각화하기 위해 사용 되었다. 실내 모형시험은 스틸 프레임으로 경계면을 만들고 폴리카보네이트 탄성중합체로 만들어진 이차원 원형 입자들을 적층하여 구성하였다. 광탄성 시트를 원형 입자에 코팅함으로써 힘 전달의 패턴을 밝은 빛의 줄무늬 형태로 확인할 수 있었고, 광탄성 측정 기법을 통해 접촉되어 있는 입자들에서의 주 응력차의 크기, 방향 또한 측정 할 수 있었다. 변위장은 디지털 이미지 해석 기법을 사용하여 측정 하였다. 하중 재하 초기 상태와 파괴 근처의 상태에서 서로 다른 접촉력의 분포를 정량적으로 분석하였다. 파괴 이전 단계에서 관측된 광탄성 패턴과 변위장은 접촉력 사슬의 좌굴 발생 이후 즉시 사라짐을 확인하였다. The purpose of this paper is to present an photoelasticity technique for measuring the displacement and stress distribution in particle assembly subjected to shallow foundation loading. Photoelastic measurement technique was employed to visualize the force transmission of a particle assembly. A model assembly bounded by a steel frame was built by stacking bi-dimensional circular particles made of polycarbonate elastomer. Each particle was coated by a thin photoelastic sheet so that the force transmission represented by bright light stripes can be visualized. In a contacted particle, both magnitude and orientation of principal stress difference can also be measured via the photoelasticity technique. The different distributions of the contact stresses at the initial loading and near the failure were quantitatively compared. The photoelastic patterns and displacement fields observed in the pre-failure state disappears immediately after the buckling of confined force chains.

Study on Photoelastic Method for Measuring Elastohydrodynamic Lubrication Pressure in Line Contact

In the present paper, a new method for measuring elastohydrodynamic lubrication (EHL) pressure in line contact is proposed, which is based on the photoelastic technique. The pressure distribution of EHL film and the inner stresses in the friction pairs are fundamental issues to carry out EHL research. The film thickness, pressure and temperature have been successfully obtained with solving the basic equations such as Reynolds equation and energy equation simultaneously or separately, with numerical model of EHL problem. The film thickness can be also measured with the optical interference technique. However, the pressure measurement is still a problem which has not been well solved yet, so as the inner stresses inside the friction pairs. With the experimental mechanics, the photoelastic technique is a possible method to be used for measuring the pressure distribution of EHL film and inner friction pair in the line contact. Therefore, A flat plastic disk and a steel roller compose the frictional pairs of the photoelastic pressure measuring rig with combining the monochromatic LED light source, polarizer CCD camera and stereomicroscope to form the whole pressure measuring system of the line contact EHL. The experimental results with the rig display the typical features of EHL pressure. This shows that the method is feasible to be used for measuring the pressure of EHL film and the inner stresses of the friction pairs in the line contact.

Photoelastic study of bi-material notches: Effect of mismatch parameters

The effects of mismatch parameters on isochromatic fringe patterns were studied using the technique of photoelasticity. First, the mathematical equations of isochromatic fringes were derived for singular stress field near a bi-material notch. These equations were used to study the effects of mismatch parameters on the shape of isochromatic fringes theoretically. Analytical results indicated that the mismatch parameters have a significant effect on the shape of the isochromatic fringe patterns around the bi-material notch tip. In order to assess the accuracy of the analytical results, a photoelastic test program was conducted on the V-notched bi-material Brazilian disc specimens. A very good agreement was shown to exist between the experimental results and the analytical reconstructions.

10401 紫外線硬化樹脂の硬化過程における流動と応力の同時測定(OS1-1【実験力学とその応用(1)】)

This study deals with the simultaneous measurement of the flow and stress of ultraviolet (UV) curable resin illuminated at UV ray. The flow is observed as particle trajectory patterns obtained using a particle tracking velocimetry technique, and stress as isochromatics, principal-stress directions and shear 45° obtained using a photoelastic technique, respectively; The specimens consist of glass plates, acrylic plates and UV curable resin in liquid form with acrylic powder. The specimens are illuminated with UV rays downwards from the upper side of the specimens, and the visual and photoelastic images of the resin in curing process are captured at a constant time interval using a digital and CCD cameras, respectively. Results indicated that the stresses in the resin during the curing, process depended on the degree of contact between the mold and the cured part of the resin and were almost independent on the flow of the uncured resin.

10402 光弾性法による微小成型された紫外線硬化樹脂の残留応力解析(OS1-1【実験力学とその応用(1)】)

The residual stress generated in a diffractive grating formed by ultraviolet (UV) curable resin was analyzed using a photoelastic technique. The stress was expressed as isochromatics and principal-stress directions, which are obtained using a four-step phase-shifting technique based on a plane polariscope. The specimens consisted of a steel mold with a diffraction grating pattern, glass plates and UV curing resin in liquid form. The specimens were illuminated with UV rays downwards from the upper side of the specimens, and the photoelastic images of the resin after curing were captured using a digital camera. Results indicated that the residual stress generated in the resin was complex.