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Forming a high-strength granular plugging zone is important to lost circulation control success in fractured oil, gas, and geothermal resources. The stability of mesoscale force chain network, which is the way to transferring contact force between particles, determines granular plugging zone strength. However, the effect of granular performance parameters on mesoscale structure stability of plugging zone remains unclear. In this work, a photoelastic method is adopted to visually observe mesoscale structure evolution accounting for fracture occurrence, plugging zone stress condition and failure mode. Results show that force chains display better symmetry along the shear direction and distribute more uniformly in a plugging zone formed with higher friction coefficient particles. Contact force transmission causes lower friction coefficient particles siding and induces plugging zone instability. Symmetry and uniformity of the strong force chain network are the two key optimal distribution parameters to improve plugging zone stability and materials selection. [Display omitted] • Photoelastic images of different friction particles formed over shear loads were observed. • Strong force chains evolution was extracted from the plugging zone. • Force chain distributed more uniformly and better symmetrically in the high-friction plugging zone. • The configuration and distribution of strong force chains determine stability of granular matter system. • Symmetry and uniformity of strong force chains were proposed for plugging zone stability improvement. [ABSTRACT FROM AUTHOR]

An acousto-optic delay line (AODL) is an effective tool for signal processing in the time domain. A smoothly controlled signal delay over a wide time interval allows high-performance radar simulators to be built based on an AODL. This paper considers the AODL's design and marks the parameters that determine the limit of using its capabilities. The features of the photoelastic interaction in an AODL are investigated for the case when the duration of the input pulse is shorter than the time of crossing the optical beam by an elastic wave packet. It is found that under these conditions the duration of the output response is determined by the time taken to cross the optical beam by an elastic wave packet and does not depend on the duration of the input action. It is shown that the AODL response to the input action in the form of a rectangular pulse is determined as the sum of three terms. In this case, the first term is determined by the process of entry of the elastic wave packet into the optical beam; the second, by the process of propagation of the elastic wave packet in the aperture of the optical beam; and the third, by the process of the exit of the elastic wave packet from the aperture of the optical beam. The corresponding equations for calculating the parameters of the pulse at the output of the AODL are obtained. It is shown that for a sufficiently short input pulse duration, the parameters of the output signal contain information on the energy-geometric characteristics of the laser radiation. The established provisions and patterns are confirmed by the numerical calculations. The numerical simulation results are tested on the AODL prototype with direct detection. A comparative analysis of the results of the theoretical and experimental studies show that AODL can also be used at frequencies above the boundary, both in terms of its main functional purpose and for solving a number of other radio engineering problems. [ABSTRACT FROM AUTHOR]

Since the beginning of the Covid-19 pandemic, carrying out of practical applications, it has been a challenge for technical higher education. Several technical disciplines, such as the strength of materials, requires students to access the laboratories and perform specific tests. Among these, the photoelasticity method is established for determination of the isocline and isochromatic families of curves. The method involves the analyze of an optically transparent, homogeneous and isotropic material, in an unsolicited state, through polarized light. This requires that the test specimen to be fixed into the polariscope, which implies the physical access of the students into the laboratory. The result obtained, as an image, is often blurred or hard to interpret. On the other hand, the determination of the above-mentioned families of curve by the finite element method (FEM) may be carried out remotely on any PC on which a specific finite element analysis program is installed, if the result of a tensile test on an identical specimen in shape and dimensions, as that one used for photoelasticity is transmitted to the users. In addition to the advantage of remote work, which can be overseen on a platform such as Microsoft Teams or Google Meat, once the analysis with the finite elements is completed, several additional results are available. In this paper, the authors aim to present the usefulness of using the finite elements method (FEM) as opposed to the photoelasticity method, especially under the circumstances of the Covid-19 pandemic. Also, at the end of the paper, a comparative table is presented containing the results that can be obtained by the two methods. [ABSTRACT FROM AUTHOR]

Using a cross-polarization transmission geometry, stress maps for the normalized birefringence and intrinsic stress direction of polymeric materials may be obtained using terahertz nondestructive evaluation. The analysis method utilizes a deconvolution method to determine the arrival times and amplitude of the cross-polarized terahertz pulses through a birefringent material. Using amber (a naturally occurring polymer) as a material of interest, stress maps show that inclusion-free Lebanese amber samples behave as classic uniaxial birefringent (photoelastic) materials whose principal stress directions, as inferred in the terahertz spectral range, agree well with visible photoelasticity measurements. Since amber samples, depending upon their source, may be either transparent or opaque to visible light, comparing birefringence measurements in the visible and terahertz spectral ranges cross-validates the stress measurements, thereby establishing a strong and unique stress analysis methodology for visibly opaque samples. While the material of interest for this paper is amber, the method is generally applicable for any terahertz-transparent polymer. The cross-polarization experimental configuration enables stress levels within the amber matrix to be visualized while also outlining highly localized regions of stress surrounding inclusions. Birefringence stress maps clearly show localized increases in stress magnitude and directional changes surrounding inclusions.

The bonding structure is affected by environmental loads during use, causing internal stress in the adhesive layer, which leads to the debonding and expansion of the bonding layer. Therefore, it is important to accurately measure the stress distribution of the bonding layer to assess the life of the bonding structure. In this study, based on the transmission and reflection terahertz time-domain spectroscopy (THz-TDS) technique, the stress optical coefficients of a silicone adhesive were measured, and the calculation models of the transmission and reflection stress optical coefficients were derived. In the reflection calculation model, the caliper THz thickness measurement method was proposed to compensate for the thickness change of the silicone adhesive, under tensile stress. Under the transmission THz-TDS stress optical coefficient calculation model, the stress optical coefficient C of the silicone adhesive is 0.1142 ± 0.0057 MPa−1, and the stress optical coefficient C of the reflective system is 0.1135 ± 0.0051 MPa−1. The test results show that the reflective THz-TDS can also be used to measure the optical stress coefficient of the material, which compensates for the shortcomings of the traditional transmission measurement method, and lays a foundation for the characterization of the internal stress of the adhesive layer of the adhesive structure.

Myxine limosa is a burrowing species of hagfish that occurs in the western North Atlantic in areas with muddy substrate and at depths generally greater than 100 meters. Burrowing of M. limosa has been observed from submersibles, but little is known about the behavior of these animals within the substrate or the biomechanical mechanisms involved. Here, we investigated burrowing in M. limosa by observing individuals as they burrowed through transparent gelatin. A photoelastic setup using crossed polarizers allowed us to visualize stress development in the gelatin as the hagfish moved through it. We found that M. limosa created U-shaped burrows in gelatin using a stereotyped, two-phase burrowing behavior. In the first ('thrash') phase, hagfish drove their head and their anterior body into the substrate using vigorous sinusoidal swimming movements, with their head moving side-to-side. In the second ('wriggle') phase, swimming movements ceased, with propulsion coming exclusively from the anterior, submerged portion of body. The wriggle phase involved side-to-side head movements and movements of the submerged part of the body that resembled the internal concertina strategy used by caecilians and uropeltid snakes. The entire burrowing process took on average 7.6 min to complete and ended with the hagfish's head protruding from the substrate and the rest of its body generally concealed. Understanding the burrowing activities of hagfishes could lead to improved understanding of sediment turnover in marine benthic habitats, new insights into the reproductive behavior of hagfishes, or even inspiration for the design of burrowing robots., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

We developed a tactile sensor for robot hands that can measure normal force (FZ) and tangential forces (FX and FY) using photoelasticity. This tactile sensor has three photodiodes and three light-emitting diode (LED) white light sources. The sensor is composed of multiple elastic materials, including a highly photoelastic polyurethane sheet, and the sensor can detect both normal and tangential forces through the deformation, ben sding, twisting, and extension of the elastic materials. The force detection utilizes the light scattering resulting from birefringence.

A new optical method is presented for evaluation of the stress profile in chemically tempered (chemically strengthened) glass based on confocal detection of scattered laser beam. Theoretically, a lateral resolution of 0.2 μm and a depth resolution of 0.6 μm could be achieved by using a confocal microscope with high-NA immersion objective. The stress profile in the 250 μm thick surface layer of chemically tempered lithium aluminosilicate glass was measured with a high spatial resolution to illustrate the capability of the method. The confocal method is validated using transmission photoelastic and Na+ ion concentration profile measurement. Compositional influence on the stress-optic coefficient is calculated and discussed. Our method opens up new possibilities for three-dimensional scattered light tomography of mechanical imaging in birefringent materials. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this pilot study was to evaluate the behavior of stresses surrounding orbital model implants subjected to a load of a silicone oculo-palpebral prosthesis. Materials and Methods: A photoelastic model was constructed mimicking the orbital cavity of an adult patient who underwent left orbital resection. Two 3.75 x 5--mm extraoral implants with 3.75 x 5.25--mm magnetic connectors were placed in the model to anchor a silicone oculo-palpebral prosthesis. The stress generated by prosthesis retention was evaluated using photoelasticity at 15, 30, and 60 minutes. The polariscope images were analyzed qualitatively at five areas surrounding the implants. These same areas were analyzed quantitatively using Matlab software based on the RGB color pattern. Data were compared with the Wilcoxon test. Results: Using fringe localization, the qualitative analysis demonstrated that the area between the implants had the greatest stress. The quantitative analysis showed that the peri-implant stress increased significantly in proportion to the increase in prosthesis retention time. Conclusion: The oculo-palpebral prosthesis generated stress around the implants, and the stress intensity was directly proportional to the duration of use. [ABSTRACT FROM AUTHOR]

The theory is proposed for solving problems of adhesion mechanics that is based on the concept of an anisotropic layer that serves as a contact between the adhesive and substrate. All boundary conditions in contact problems and the original equations are satisfied exactly; i.e., the mathematical Cauchy problem is solved. The possibilities of the theory are demonstrated by solving a specific problem of multiple destruction of a fiber in a polymer matrix during stretching of the Kargin—Malinsky model, which simulates the behavior of a reinforced polymer. The solution results explain the unusual experimental results. [ABSTRACT FROM AUTHOR]

To analyze the stress of functionally graded materials (FGMs) through an experiment, transparent homogeneous FGMs (THFGMs) with similar theoretical and physical properties need to be created. This study developed such THFGMs and proposed a method for determining their stress intensity factors (SIFs) and T-stresses via photoelastic experiments. The Young's modulus and Poisson's ratio of these THFGMs linearly change along the physical variation direction, and the shear modulus varies almost linearly. The SIFs and T-stresses were obtained for the central and edge cracks in finite rectangular FGM plates with linear variations in the shear modulus under constant density along the direction of the crack under mode I loading. The SIFs and T-stresses can be obtained using the exponential and linear variation in the stress fields, even if the physical properties of FGM plates show linear variation in the shear modulus. The characteristics of the experimental SIFs obtained in this study generally agree with those of theoretical SIFs reported in previous research. For center crack tips, the SIFs at the hard right crack tip were greater than those at the soft left crack tip. For edge crack tips, when a/W < 0.35, the SIFs were lower than the homogeneous materials. By contrast, when a/W > 0.35, the SIFs were greater than the homogeneous materials. The experimental T-stresses for the center crack agreed well with the numerical T-stresses reported in previous research. For the edge crack, when a/W ≤ 0.3, the experimental T-stresses agreed with the numerical T-stress, but when a/W ≥ 0.4, considerable differences were observed between the experimental and numerical T-stresses. Where a(a) denotes the crack length for edge cracks or half the crack length for center cracks, and W is the width of the specimen. Experimental results coincide well with those reported in the literature, except for the T-stresses for edge crack when a/W > 0.3. Therefore, the THFGMs, which are new FGMs developed in this study, can be effectively used in experimental fracture analysis. [ABSTRACT FROM AUTHOR]

At present, theoretical analysis, numerical simulation, and other methods cannot be used to properly solve the problems associated with the stability and bearing capacity of the surrounding rock and its supporting system, the interaction between the supporting structure and surrounding rock, and the sharing role of each supporting structure, all of which commonly occur in deep tunnels. The model test method represented by the photoelastic test is still an important approach to study this kind of problem. In view of the deficiency of the current loading system of the photoelastic model test, we developed a geo-stress loading system for the photoelastic model test, which can simulate the in situ geo-stress environment of unidirectional loading, bidirectional equal pressure, bidirectional unequal pressure, and tridirectional unequal pressure. The universal retaining force loading rod can realize the stability and effective compensation of loading, which is an original design. According to the principle of umbrella-shaped expansion and contraction mechanism, an excavation unloading device for the photoelastic model test is developed, which can realize the simulation of various degrees of displacement release in the excavation process of deep tunnels and other underground projects. The loading simulation test and excavation unloading simulation test show that the geo-stress loading system and excavation unloading device developed in this paper are flexible, exhibit good performance, and can fully achieve their respective test functions. The combination of two devices can compensate for the insufficiency of the current photoelastic model test and will promote the application of photoelastic model tests in underground engineering applications such as deep tunnel projects. [ABSTRACT FROM AUTHOR]

In curved liquid crystal display, the glass substrate is in the state of bending, and the bending stress is generated inside the glass. Under the effect of stress photoelastic effect, the display will produce light leakage, which is called stress‐Mura. Based on the theory of stress photoelasticity and the finite element analysis of panel forming, this paper deduces the light leakage intensity of curved LCD (liquid crystal display) by using the Jones matrix, and puts forward a scheme to improve the design of curved curvature of LCD, which is verified by experiments. [ABSTRACT FROM AUTHOR]

Quantitative visualization of the full-field stress and strain in porous structures is of significance to reveal the mechanism of the damage and failure of engineering materials. To quantitatively characterize the full-field stresses and strains, optical measurement methods, such as photoelasticity for determining the stress fields, moiré and digital image correlation (DIC) methods for measuring the strain fields, have been developed in previous works. However, it is challenging to combine these methods to measure stress and strain fields simultaneously because the speckles and gratings for strain measurement will disturb the interference fringes in the photoelasticity. In this study, a method incorporating photoelasticity and DIC techniques was developed to determine the stress and strain fields simultaneously in different porous structures which were fabricated by three-dimensional (3D) printed technique. The tested models were printed with a highly transparent, colourless material and the speckles on the front surface of the tested models were printed with a translucent, magenta material. Under compressive loads, the stress fields in these models were obtained based on the photoelastic patterns and the strain fields were determined by DIC method. The results indicate the proposed method can simultaneously determine the full-field stresses and strains and the comparison of the distribution of the principal stress and strain difference and the distribution of the shear stress and strain verified its good accuracy. In addition, the stress and strain distribution in different pore structures were compared and found that the optimal design of the pore distribution can greatly change the concentration of the stress and strain fields.

Complex stresses are created or applied as part of medical and dental treatments, which are linked to the achievement of treatment goals and favorable prognosis. Photoelasticity is an optical technique that can help observe and understand biomechanics, which is essential for planning, evaluation and treatment in health professions. The objective of this project was to review the existing information on the use of photoelasticity in medicine and dentistry and determine their purpose, the areas or treatments for which it was used, models used as well as to identify areas of opportunity for the application of the technique and the generation of new models. A literature review was carried out to identify publications in dentistry and medicine in which photoelasticity was used as an experimental method. The databases used were: Sciencedirect, PubMed, Scopus, Ovid, Springer, EBSCO, Wiley, Lilacs, Medigraphic Artemisa and SciELO. Duplicate and incomplete articles were eliminated, obtaining 84 articles published between 2000 and 2019 for analysis. In dentistry, ten subdisciplines were found in which photoelasticity was used; those related to implants for fixed prostheses were the most abundant. In medicine, orthopedic research predominates; and its application is not limited to hard tissues. No reports were found on the use of photoelastic models as a teaching aid in either medicine or dentistry. Photoelasticity has been widely used in the context of research where it has limitations due to the characteristics of the results provided by the technique, there is no evidence of use in the health area to exploit its application in learning biomechanics; on the other hand there is little development in models that faithfully represent the anatomy and characteristics of the different tissues of the human body, which opens the opportunity to take up the qualitative results offered by the technique to transpolate it to an application and clinical learning.

Polyethylene terephthalate (PET) is one of the most commonly used substrate materials in the field of flexible electronics, and its stress-induced birefringence often has a detrimental effect on the optical properties of the device. Therefore, a deep and systematic understanding of the stress-optical properties of PET films is crucial for device design and manufacture. The photoelastic method is a direct optical measurement technique based on the stress-induced birefringence effect of materials, which has the advantages of being nondestructive and noncontact. In this work, the photoelastic method was used to quantitatively characterize the anisotropy of the stress-optical properties of PET films under the uniaxial stress state. First, a self-built reflection-transmission coaxial bidirectional photoelasticity measurement system was developed by means of a combination of transmission and reflection photoelasticity. Then, the stress-optical coefficients and isoclinic angles of PET films with different stretching angles were measured. Finally, the linear combinations of the photoelastic tensor components and refractive-index-related parameters were determined by fitting the analytical relationship between the stress-optical coefficients and isoclinic angles.

The visual properties of a large plasmoid rising from a water container into the air for up to 450 ms are brought into correlation with the total energy dissipated into the system, and, in particular, with the energy used for plasma generation. The latter parameters are deduced from the time-resolved discharge current and voltage of the capacitor bank which is used as energy supply. By varying the experimental parameters, the energy dissipated to the system varies between 5 kJ and 30 kJ from which 10% to 30% is transferred to the plasma. Clear correlations are obtained for the size of the plasmoid changing from 15 cm to 35 cm in width, the ascent velocity ranging from 1 m/s to 2 m/s, and the rising height for which up to 85 cm is measured. For the relation of the autonomous phase with the energy transferred to the plasma, two trends are observed: 450 ms duration is achieved in maximum with the present setup being almost independent on the electrode gap, the voltage-on time, the water conductivity, or the type of salt dissolved in the water. On the other hand, an almost linear dependence is obtained by changing the capacitance. [ABSTRACT FROM AUTHOR]

We theoretically investigate the optomechanical (OM) coupling of submicron cavities formed in one-dimensional phoxonic-plasmonic slabs. The phoxonic-plasmonic slabs are structured by depositing periodic Ag strips onto the top surfaces of dielectric GaAs slabs to produce dual band gaps for both electromagnetic and acoustic waves, thereby inducing the coupling of surface plasmons with photons for tailoring the OM coupling. We quantify the OM coupling by calculating the temporal modulation of the optical resonance wavelength with the acoustic phonon-induced photoelastic (PE) and moving-boundary (MB) effects. We also consider the appearance of a uniform Ag layer on the bottom surface of the slabs to modulate the photonic-plasmonic coupling. The results show that the PE and MB effects can be constructive or destructive in the overall OM coupling, and their magnitudes depend not only on the quality factors of the resonant modes but also on the mode area, mode overlap, and individual symmetries of the photonic-phononic mode pairs. Lowering the mode area could be effective for enhancing the OM coupling of subwavelength photons and phonons. This study introduces possible engineering applications to achieve enhanced interaction between photons and phonons in nanoscale OM devices. [ABSTRACT FROM AUTHOR]

Residual stresses and deformation in additive manufactured (AM) are two main barriers which hinder its extensive application seriously. In recent years, pulsed laser additive manufacturing has been widely examined for its advantages such as lower finer microstructure, more excellent mechanical properties, and heat accumulation in comparison with continuous-wave laser additive manufacturing. Few researches about residual stress of pulsed laser additive manufacturing, however, have been studied, and the development law of stain and residual stress is not clear. In this work, a three-dimensional (3D) transient uncoupled thermo-elastic-plastic model for pulsed-wave laser additive manufacturing procedure is carried through to examine the residual stress distribution and thermal history in 316L laser cladding. Excellent acceptance between the experimental measurements and the numerical results is obtained. It is discovered that pulsed-wave laser additive that manufactures attributes melt pools with periodic shape changes, the thermal stress evolution process moves like heartbeat periodically, and the residual stress distribution in laser cladding direction is similar to zigzag inhomogeneity. Furthermore, the influence of laser pulse parameters on residual stress distribution has been studied, and the results indicated that decreasing constant duty cycle and laser pulse length reduces the size and stress gradient of maximum stress' region for x-direction tensile stresses. It provides operation parameters' optimization choice with guidance to control or reduce residual stress. [ABSTRACT FROM AUTHOR]

This article presents the measurement of residual stress distribution in ITER (“The Way” in Latin) diagnostics windows using a circular polariscope. The method being used is based on the measurement of the change in the state of polarization of a circularly polarized light after transmission/reflection from the stressed window under test. The theory based on Mueller calculus for the experimental setup has been presented. The measurement technique is validated for transmission mode by comparing the stress values measured for borosilicate glass (BK7) sample disks under diametrical compression with the theoretical values obtained using linear isotropic theory of elasticity. The method is, then, applied to an undamaged and a damaged ITER trial window, both in transmission and reflection modes, to observe the stress patterns inside the glass material and on the glass to metal seal. The major observations are that the undamaged window shows higher stress in majority of the cross section with lower stress values at localized regions. The glass near the seal shows high values of stress all along the circumference in case of the undamaged window. The damaged window that has got detached from the metal seal shows much lower stress values in majority of the cross section of the window with higher stress values in some regions. The region where the seal seems to have got detached from the glass shows lower values of stress at the seal location, and also the stress values in the glass near those locations are low. In conclusion, by observing the stress patterns inside the window, this technique helps determine the health of vacuum seal, and hence can be used in taking preventive measures. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated the accuracy of models reconstructed from ultrasound image processing by comparing the radial displacement waveforms of a subject-specific artery model and evaluated stress changes in the proximal shoulder, throat, and distal shoulder of the plaques depending on the degree of carotid artery stenosis. Methods: Three groups of subjects (healthy and with less than 50% or more carotid stenosis) were evaluated with ultrasonography. Two-dimensional transverse imaging of the common carotid artery was performed to reconstruct the geometry. A longitudinal view of the same region was recorded to extract the Kelvin viscoelastic model parameters. The pulse pressure waveform and the effective pressure of perivascular tissue were loaded onto the internal and external walls of the model. Effective, circumferential, and principal stresses applied to the plaque throat, proximal shoulder, and distal shoulder in the transverse planes were extracted. Results: The radial displacement waveforms of the model were closely correlated with those of image processing in all three groups. The mean of the effective, circumferential, and principal stresses of the healthy arteries were 15.01±4.93, 12.97±5.07, and 12.39±2.86 kPa, respectively. As stenosis increased from mild to significant, the mean values of the effective, circumferential, and first principal stresses increased significantly (97%, 74%, and 103% at the plaque throat, respectively) (P<0.05). The minimum effective stress was at the lipid pool. The effective stress in calcified areas was higher than in other parts of the artery wall. Conclusion: This model can discriminate differences in stresses applied to mildly and severely stenotic plaques. [ABSTRACT FROM AUTHOR]

In laser cleaving, the thermal stress caused by laser heating and water-jet cooling propagates previously induced cracks in the workpiece material. The laser-cleaving conditions affect the quality of the fracture surface, and therefore, elucidating the relationship between the cleaved surface, cleaving conditions, and crack propagation is essential. Against this backdrop, in this study, we investigated the morphology of the cleaved surface and visualized the crack propagation and stress in situ using a high-speed polarization camera. The distance between the glass edge and cleaved surface was varied. When the laser-cleavage line was close to the glass edge, twist hackles were formed on the cleaved surface. The area in which the twist hackles formed on the cleaved surface coincided with the lagging section of the crack front. Furthermore, the twist hackle reached the specimen surface, and the edge of the surface exhibited a sawtooth shape. Observations with the high-speed polarization camera revealed that the internal stress was asymmetric with respect to the crack when the twist hackles were formed. [ABSTRACT FROM AUTHOR]

Die vorliegende Studie zeigt Grundzüge eines Verfahrens, welches Potentiale zum Ausgleich der Defizite bisheriger additiver Verfahren bezüglich Maßhaltigkeit, Homogenität und Transparenz der Struktur aufweist. Silikatische Gläser werden durch eine CO2‐Laserquelle aufgeschmolzen. Ein Dreiachssystem defokussiert den Laserstrahl, um die Intensitäten zum Aufschmelzen unterschiedlicher silikatischer Gläser einzustellen und die Bewegung von Druckstufe und Substrat zu realisieren. Die flexible Zuführung des Zusatzwerkstoffes ermöglicht die kontinuierliche Anpassung des Aufbauprozesses und die Möglichkeit der Geometrieänderung. Erste Versuche verdeutlichen, dass dieser Prozess eine Alternative zu den bisher angewendeten Verfahren darstellt. Production of individual structures from silicate materials using Wire‐Laser Additive Manufacturing. This study shows the main features of a method, which has the potential to compensate for the deficits of previous additive methods in terms of dimensional accuracy, homogeneity and transparency of the structure. Silicate glasses are melted by a CO2‐laser source. A three‐axis system defocuses the laser beam to adjust the intensities for melting different silicate glasses and to realize the movement of pressure stage and substrate. The flexible feeding of the filler material allows the continuous adaptation of the build‐up process and the possibility of changing the geometry. Initial tests have shown that this process is an alternative to the methods previously used. [ABSTRACT FROM AUTHOR]

• The proposed polariscope is free from the disadvantages of fringe-scanning and phase-stepping polariscopes. • The proposed polariscope is capable of whole-field optical path retardation and principal angle measurements. • The proposed polariscope is particularly useful for examining samples with discontinuous fringe sub-patterns or complex boundaries. • Experimental results exhibit standard deviations of 8 nm and 1.21ο when repeatedly measuring an optical path retardation and a principal angle, respectively. • Experimental results confirm the proposed polariscope's validity and feasibility. Fringe-scanning (or TFP/RGB) and phase-stepping are now the most acceptable techniques for examining stressed photoelastic samples; however the former requires a calibration table, which is sensitive to the geometrical and optical parameters of the corresponding polariscope, and concentrates only on phase retardation measurements; the latter suffer from three potential issues: 1) the principal angle is indeterminate when the corresponding phase retardation is close or equal to an integer multiple of π, 2) the obtained phase retardation and principal angle are wrapped, and 3) the phase retardation and principal angle may couple together in certain situations. Free from the disadvantages of the fringe-scanning and phase-stepping polariscopes, a white light OPD (optical path difference) scanning polariscope composed of a white light laser, an OPD modulator, and a dark-field circular polariscope was proposed for whole-field optical path retardation (proportional to the phase retardation) and principal angle determinations. This paper introduces the theory of the polariscope, demonstrates the experimental setup for implementing the polariscope, and presents the results from the uses of the setup. The results manifest a standard deviation of 8 nm when repeatedly measuring an optical path retardation and 1.21ο when repeatedly measuring a principal angle; moreover, the results confirm the polariscope's validity and feasibility, but showing a limitation while adopting the polariscope to evaluate fringe orders < 3. [ABSTRACT FROM AUTHOR]

• A novel method for accurately quantifying full-field stress in continuously loaded fractured rocks is proposed. • A modified global fringe thinning technique for automatic extraction of fringe skeletons is introduced. • An automatic identification algorithm for regions of near-zero-order fringes is developed. • The applicability in quantifying full-field stress in fractured rocks under both continuous and static loading conditions is demonstrated. Accurately characterizing stress fields in fractured rocks is crucial for understanding fracture propagation and rock failure mechanisms. However, existing methods struggle to quantify stress fields in continuously loaded fractured rocks with complex fracture networks. In this study, we propose a novel method that utilizes 3D printing and digital photoelasticity to quantify full-field stress in complex fractured rocks under continuous loading. Our method incorporates three key components: a modified global fringe thinning technique for automatic extraction of fringe skeletons, a proposed algorithm for automatic identification of near-zero-order fringe regions, and an optimized phase calculation process for efficient phase unwrapping. The effectiveness and accuracy of our method are validated through theoretical analysis and comparison with results obtained from the ten-step phase shifting method. Furthermore, our proposed method can also be applied to quantify stress fields in fractured rocks under static loading. [ABSTRACT FROM AUTHOR]

Topography and tomography are valuable techniques for measuring the corneal shape, but they cannot directly assess its internal mechanical stresses. And nonuniform corneal stress plays a crucial biomechanical role in the progression of diseases and postoperative changes. Given the cornea's inherent transparency, analyzing corneal stresses using the photoelasticity method is highly advantageous. However, quantification of photoelasticity faces challenges in obtaining the stress-optic coefficient due to wrinkles caused by the non-spherical geometry during tensional experiments. In this study, we propose an innovative experimental setup aimed at generating a gradient field of simple shear stress and achieving surface flatness during corneal stretching experiments, enabling the acquisition of the stress-optic coefficient through comparison with numerical results. Our designed setup applies fluid pressure and force couples on the cornea. The internal fluid pressure maintains the corneal shape, preventing wrinkles, while the force couples create a stress field leading to isochromatic fringes. We successfully measured the stress-optic coefficients of the porcine anisotropic cornea in ex-vivo as 1.87 × 10−9 (horizontal) and 1.97 × 10−9 (vertical) (m2/N). Each isochromatic fringe order represents a shear stress range of 6.05 × 104 Pa under a low tension. This study establishes a significant connection between corneal photoelastic patterns and the quantification of corneal stress by enabling direct measurement through advanced photoelastic visualization technology for clinical applications. [ABSTRACT FROM AUTHOR]

In this paper, we studied the effect of the stress on the propagation modes of the thin-wall hollow core fiber based on geometric nonlinearity model by employing the finite element method. For this special fiber, strong dichroism is observed and the leakage losses of the two orthogonal polarization modes are very sensitive to the applied force. We found that the deformation (the reshaped configuration) majorly contributes to this dichroism effect, so that the effect of the nonuniform distribution of the refractive indices induced by the stress can be omitted. The simulation process can be also appropriate in all kinds of the micro- and nano-system with complicated thin-wall or thin-arm configurations. • We studied the stress induced dichroism of thin-wall hollow core fiber based on geometric nonlinearity model by employing FEM. • This schematic simulation process of coupling the nonlinear elastic problems and electromagnetic field problems can also appropriate in all kinds of the micro- and nano-system with complicate thin-wall or thin-arm configurations. • For this special fiber, a small force can introduce obvious dichroism. • We found that the deformation, rather than the nonuniform distribution of the refractive indices induced by the stress, majorly contributes to the dichroism. [ABSTRACT FROM AUTHOR]

This work systematically demonstrates the process of achieving zero-photoelastic constant compositions in the TeO 2 -ZnO-Li 2 O-Bi 2 O 3 quaternary system by carefully adjusting each component step by step. For each component variation, Raman spectroscopy was conducted and a structure/property correlation is proposed. Finally, this work presents two glass compositions with refractive index difference of 0.014 (78TeO 2 -3ZnO-16Li 2 O-3Bi 2 O 3 and 78-TeO 2 -7ZnO-12Li 2 O-3Bi 2 O 3 glasses) which have compatible thermal properties. These materials were fibered together to obtain a single-mode fiber that can be tightly bent after coating. [ABSTRACT FROM AUTHOR]

The stresses induced by a mechanical contact imposed on a birefringent sphere have been studied experimentally and numerically. The birefringent sphere is machined from a birefringent parallelepiped on a high speed numerically controlled machine. The residual stresses developed in the birefringent sphere have been eliminated by a heat treatment relaxation. The technique of freezing and mechanical cutting in thin slices was used. In the case of 3D photoelasticity, the frozen stress techniques, which are very much used, may introduce residual stresses in the cut up slices. Although the means to avoid the introduction of these residual stresses are well established, these techniques remain time consuming. Slices are analyzed on a polariscope using plane polarized light and circular polarized light. The photoelastic fringes are used to determine the principal directions of the stresses as well as the values of the stresses. A numerical simulation using the finite elements made it possible to make a comparison with the experimental results. The analysis shows a good correlation between experimental measurements and numerical simulation.

Photoelasticity method was used to measure strain and stress fields to address the precision problem of determining fringe order of loading and cracking and notch areas. In this study, microscope was used as an additional tool in a photoelastic device for magnification of isochromatic fringe size. An experimental method was used by utilizing optical system and reflective polariscope. A simple compression tool was designed to provide a compression load on the solid disk-shaped specimens. Isochromatic fringe field was observed in the loading zone for different loading and captured image based on the following conditions: 9x, 15x and 20x without magnification and with magnification using SLR type Nikon camera Serie D3000. The image was processed using OpenCV software while C + + was used to produce clearer isochromatic fringe pattern formed on the surface of the specimen in the determination of the maximum fringe order observed. The average of additional fringe could be obtained as the optical magnification result. Data was analyzed using Finite Element Analysis Software. The result showed an increasing trend in fringe order with increasing levels of optical magnification. Its maximum value was obtained on20x optical zoom, which was 2-order fringe.

In the paper, we present the results of an investigation of polymethylmetacrylate’s birefringence induced due to applying high-load. The stress-induced birefringence of the polymethylmetacrylate samples was experimentally investigated by an apparatus combining an in-house made plane polariscope with a machine for fatigue testing of materials. A halogen lamp was used as the source of white light. The polariscope’s basis was formed by two sets of plane polarizers, one designed for visible (470-750) nm and another one for near-infrared (900-1800) nm spectral range, respectively. The investigated sample was placed between the polarizers and light that passed through the polariscope was collected by an optical fiber connected to an appropriate optical spectral analyzer. The spectra of transmitted light were measured as a function of load and their analysis provided information on the load-induced birefringence of the investigated polymethylmetacrylate samples.

In the article we show the possibility of distorting the results of the experiment by photoelasticity path, in case the isochromatic fringe patterns are recorded by the camera. The recording of the color spectrum may be distorted by inappropriate selection of the recording medium, which is reflected by different types of aberrations. Transferring a record to a computer allows you to automate the experiment process, thus saving time to work with isochromatic fringes. As an example, we present the experimental determination of the stresses of the rotor with a symmetrical arm. The analysis was performed using software developed by the authors. This software enables full automation of the experiment process. The rotor is investigated by the method of reflection photoelasticity. The experimental solution is realized as a case of periodically repeating dynamic effects, in which a stroboscopic source of white light is needed. The results of the experiment are compared with the numerical solution and their dependence is represented by diagram.

It is of great significance to measure the residual stress distribution accurately for optical elements and evaluate its influence on the performance of optical instruments in optical imaging, aviation remote sensing, semiconductor manufacturing, and other fields. The stress of optical elements can be closely related to birefringence based on photoelasticity. Thus, the method of quantifying birefringence to obtain the stress becomes the main method of stress measurement technologies for optical elements. This paper first introduces the basic principle of stress measurement based on photoelasticity. Then, the research progress of stress measurement technologies based on this principle is reviewed, which can be classified into two methods: polarization method and interference method. Meanwhile, the advantages and disadvantages of various stress measurement technologies are analyzed and compared. Finally, the developing trend of stress measurement technologies for optical elements is summarized and prospected. [ABSTRACT FROM AUTHOR]

The geometry of the cladding pass cross section cannot be easily predicted in laser melting deposition. Due to the huge difference between the actual and the predicted cross section, it is difficult to conduct numerical simulations. In this paper, the finite element method (FEM) with thermal–mechanical coupling is performed. A novel cladding pass cross section model, isosceles trapezoid model, is proposed. The comparisons between the isosceles trapezoid model and the traditional model (disk model and rectangle model) are performed in terms of geometrical deviation, heat dissipation, temperature field, and stress field. The results show that the geometrical deviation and heat dissipation between trapezoid model and disk model is small, and that between trapezoid model and rectangle model is large. The trapezoid model has an additional degree of freedom for modeling, i.e., contact angle, which helps to conform complex cross section geometry more flexibility. The results of temperature field and stress field show that the deviation between the isosceles trapezoid model and the traditional models is small on the upper surface of the sample, and rectangle model has worse prediction results than the other two models at the interface between cladding pass and substrate. Finally, the validation experiment is carried out and the stress is measured by laser ultrasound technique. The experimental result matches the FEM result based on isosceles trapezoid model. [ABSTRACT FROM AUTHOR]

Background/Aims: Traumatic dental injuries are highly prevalent and are considered an important health problem. The aim of this study was to evaluate the in vitro stress distribution around simulated traumatized teeth subjected to different types of splints by photoelastic analysis. Materials and Methods: For each group, five models of maxillary and mandibular arches were made in photoelastic resin using prefabricated teeth models, which were fixed and adjusted in a semi‐adjustable articulator. All splints were bonded with composite resin on the labial surfaces of the maxillary central incisors, the lateral incisors and the canine teeth, simulating trauma to the 11. The groups were divided according to the type of splint: control—without splint; rigid—brackets and 0.021 × 0.025 inch stainless steel wire; semi‐rigid—brackets and 0.016 × 0.016 inch cobalt‐chromium wire; fiber—fiberglass ribbon; and flexible—nylon thread. The groups were submitted to an occlusal force in a special device attached to a universal test machine in balanced, protrusive, and lateral occlusions. Then, the incisal edge of the 11 was ground to simulate infra‐occlusion, and the tests were performed again. Five points were analyzed around tooth 11 with a polariscope, and the data were submitted to ANOVA and Tukey tests at a 5% level of significance. Results: When centric occlusion was analyzed by comparing normal occlusion to infra‐occlusion, all groups showed high stress values in infra‐occlusion with statistical differences—except for the control group. When lateral occlusion was analyzed, the nylon splint showed lower statistical differences compared with the control, fiberglass, and rigid splint groups, which did not differ between each other. The semi‐rigid splint did not differ from any group. Conclusions: Fiberglass and semi‐rigid splints showed better stress distribution around the traumatized tooth under occlusal loads. The nylon splint showed characteristics of non‐stress distribution. [ABSTRACT FROM AUTHOR]

In view of the near slope blasting in Barun open-pit mine, which has merged sublevel mining, the operation safety conditions of middle-sized and large equipment in the second phase expansion are poor and need urgent improvement. To increase the efficiency of expansion and reduce costs, a 24-m-high bench and large spacing parameter for loosening blasting are proposed. The analysis of the physical mechanism of the stress wave attenuation in the rock indicates that the cylindrical charge is equivalent to several spherical charges. Considering the pressure attenuation, reflection, transmission, and superposition of the spherical charge after the equivalence, a double exponential function correction equation of the stress wave attenuation is obtained based on the Mises strength criterion. The stress of any point in the rock medium with various spacing parameter is obtained by calculation. ANSYS/LS-DYNA was used to simulate and study the stress distribution of a 24-m-high bench with various spacing parameter. Meanwhile, the accuracy of the correction equation was verified. The parameters of the high-bench blasting with good effect and low cost were determined to be 15 m × 5.5 m, and field tests were carried out. Results show that the large spacing parameter for 24-m-high bench loosening blasting in Barun open-pit mine is efficient and economical in medium-hard rock blasting. This study provides a reference for the practical exploration of the expansion of high benches in open-pit mines in China. The calculation error of the corrected double exponential function is near the numerical simulation result. It is suitable for all kinds of professional designers. [ABSTRACT FROM AUTHOR]

The stress state from an eccentric ring made of an elastic material symmetrically loaded on the outer boundary by concentrated forces is deduced. The analytical results are obtained using the Airy stress function expressed in bipolar coordinates. The elastic potential corresponding to the same loading but for a compact disk is first written in bipolar coordinates, then expanded in Fourier series, and after that, an auxiliary potential of a convenient form is added to it in order to impose boundary conditions. Since the inner boundary is unloaded, boundary conditions may be applied directly to the total potential. A special focus is on the number of terms from Fourier expansion of the potential in bipolar coordinates corresponding to the compact disk as this number influences the sudden increase if the coefficients from the final form of the total potential. Theoretical results are validated both by using finite element software and experimentally through the photoelastic method, for which a device for sample loading was designed and constructed. Isochromatic fields were considered for the photoelastic method. Six loading cases for two different geometries of the ring were studied. For all the analysed cases, an excellent agreement between the analytical, numerical and experimental results was achieved. Finally, for all the situations considered, the stress concentration effect of the inner hole was analytically determined. It should be mentioned that as the eccentricity of the inner hole decreases, the integrals from the relations of the total elastic potential present a diminishing convergence in the vicinity of the inner boundary.

Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five‐step phase‐shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non‐uniformity of block geometry even in very regular dry stack masonry. [ABSTRACT FROM AUTHOR]

Studying rock crack-arrest toughness, which determines the arrest behaviours in rock materials with cracks, is important to prevent further damage to rock mass. To investigate the crack-arrest behaviours both qualitatively and quantitatively, dynamic impact experiments (using caustics and photoelastic methods) were performed on rock-like (epoxy resin) single cleavage drilled compression (SCDC) specimens to study the crack-arrest behaviours and the microscopic fracture characteristics. The crack-arrest toughness of the SCDC specimen was obtained and the extended finite element method (XFEM) in ABAQUS software was used to validate the experimental results. The results show that under the interaction between reflected compression and tensile waves, the running crack experiences two crack-arrest periods before the final arrest, and the crack-arrest toughness stabilizes at a value of 0.669 MPa m1/2. Moreover, the peak propagation velocity in each crack initiation process gradually decreases with the development of the crack path. Additionally, the observations by scanning electron microscopy (SEM) and photoelastic methods show that the roughness of the fracture surface is influenced by the crack-arrest behaviours, causing the spalling fragments as well as wing micro-cracks in the fracture surface. [ABSTRACT FROM AUTHOR]