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We explore piezooptic and photoelastic properties of Ca3Ga2Ge4O14 (CGG) crystals. A Mach–Zehnder interferometry technique is utilized to determine a complete set of the piezooptic tensor constants πim, with particular attention to the measurement accuracy, reliability, and uncertainty resolution in the piezooptic measurements. For these reasons, independent piezooptic constants or their combinations were determined by performing interferometric measurements for different geometries of piezooptic coupling using samples of both principal (direct) and non-principal (X/45°) crystallographic cuts. Basing on the results of piezooptic measurements, a complete set of photoelastic tensor constants pim and the acousto-optic performance (figure of merit M2) of CGG crystals were evaluated. The obtained piezooptic, photoelastic, and acousto-optic characteristics of CGG crystals are compared with those of other crystals of the langasite group, langasite and CTGS (Ca3TaGa3Si2O14). A comparative analysis reveals a correlation between the values of the piezooptic or photoelastic constants and the lattice parameters for this group of crystals. High optical quality and optical transparency in the UV region of the spectrum up to 260 nm together with extremely high mechanical resistance to uniaxial compression (≤2000 kg/cm2) opens up the possibility for specific application of CGG crystal as an optical material for piezooptic sensors of high uniaxial compression. The presented piezooptic interference technique along with methodological and metrological approaches paves the way for accurate and unambiguous characterization of photoelastic crystal materials of trigonal symmetry. [ABSTRACT FROM AUTHOR]

In this study, the concept of rheo-optics was applied to explore the flow birefringence induced by the stress components along the camera’s optical axis since it is often overlooked in the traditional theories of photoelastic flow measurement. A novel aspect of this research is that it involved conducting polarization measurements on simple shear flows, specifically from a perspective in which a shear-velocity gradient exists along the camera’s optical axis. A parallel-plate-type rheometer and a polarization camera are employed for these systematic measurements. The experimental findings for dilute aqueous cellulose nanocrystal suspensions demonstrate that the flow birefringence can be expressed as a power law based on the power of the second invariant of the deformation-rate tensor. This suggests that flow birefringence can be universally characterized by the coordinate-independent invariants and a pre-factor determined by the direction of polarization measurement. By adjusting the nonlinear term in the stress-optic law, its applicability could be expanded to include three-dimensional fluid stress fields in which the stress is distributed along the camera’s optical axis. [ABSTRACT FROM AUTHOR]

Geometric optimization for the optimal use of material and the weight reduction of gear is possible by removing material from the gear teeth. The current research focuses on the stress analysis of gear with radial holes drilled through the gear tooth to reduce the weight of standard gear. The radial holes from the tip of the gear tooth for different depths are introduced. A standard gear with holes is analyzed using ANSYS, and the magnitude of stresses near the root of the gears for similar loading and boundary conditions are studied. New efforts have been made to study the stress distribution by photoelastic technique to supplement FEA results and confirm the stress distribution of gear with and without radial holes. This process achieves a volume reduction of up to 6.1% compared to an AGMA standard spur gear without affecting much of the stress distribution. These holes may be helpful for adequate lubrication and cooling of gears by fluid circulation. [ABSTRACT FROM AUTHOR]

After analyzing the stress characteristics of the bolt, we determined that it can be regarded as experiencing a planar stress state due to the absence of circumferential stress. Consequently, a photoelastic bolt specimen was fabricated by taking a slice across its diameter. Using a photoelastic bench, we collected interference fringe images of the photoelastic specimen under different loads. This method enabled us to visually and continuously measure the stress distributions within the specimen in real-time. Additionally, the load distribution ratio of each tooth was derived. By comparing these results with those obtained through numerical simulation, we were able to validate the reasonability of the theoretical assumption regarding the load distribution of each tooth in the bolt. Our method establishes a solid foundation and can be effectively utilized for precise thread connection design. [ABSTRACT FROM AUTHOR]

To compare the stress produced on the walls of simulated canals by rotary instruments with varied tip and taper sizes. Ninety isotropic transparent blocks, each containing a 60-degree curved canal, were distributed into 18 groups (n = 5) based on the instrument tip (sizes 10, 15, 20, 25, 30, and 35) and taper (sizes 0.02, 0.04, and 0.06). The blocks were fixed in a circular polariscope setup for dark field analysis. A digital camera was employed to capture the real-time birefringence patterns generated by each instrument. Digital image frames, corresponding to the instrument reaching the end of each canal third, were extracted and evaluated by 2 independent observers for the stress generation on canal walls. The data analysis employed a semi-quantitative scale ranging from 0 to 5. Cohen's Kappa coefficient test was used to determine the inter-observer agreement while the results were compared using Kruskal–Wallis test followed by an all-pairwise posthoc procedure (α = 5%). Inter-observer agreement was 0.95. A significant influence of the tip size on stress was observed across the coronal (P =.011), middle (P =.006), and apical (P =.026) thirds. In contrast, taper size did not affect the stress induced at the coronal (P =.509), middle (P =.958), or apical (P =.493) thirds. The variations in tip and taper sizes did not result in a significant stress differences among the thirds (P =.181). The stress significantly increased across all canal thirds with larger tip sizes of rotary instruments, whereas the taper sizes did not influence the stress when compared to the canal thirds. [ABSTRACT FROM AUTHOR]

Abstract In this study, the concept of rheo-optics was applied to explore the flow birefringence induced by the stress components along the camera’s optical axis since it is often overlooked in the traditional theories of photoelastic flow measurement. A novel aspect of this research is that it involved conducting polarization measurements on simple shear flows, specifically from a perspective in which a shear-velocity gradient exists along the camera’s optical axis. A parallel-plate-type rheometer and a polarization camera are employed for these systematic measurements. The experimental findings for dilute aqueous cellulose nanocrystal suspensions demonstrate that the flow birefringence can be expressed as a power law based on the power of the second invariant of the deformation-rate tensor. This suggests that flow birefringence can be universally characterized by the coordinate-independent invariants and a pre-factor determined by the direction of polarization measurement. By adjusting the nonlinear term in the stress-optic law, its applicability could be expanded to include three-dimensional fluid stress fields in which the stress is distributed along the camera’s optical axis.

An alternative method to obtain the internal stress distribution in photoelastic materials using digital holography (DH) is presented. Two orthogonally polarized holograms were used to obtain the phase maps and analyzed using the proposed approach. This method directly determines the stress distributions from the phase differences obtained in the reconstructed phase maps, unlike methods obtained by photoelasticity. Optical information, such as index of refraction, phase differences, etc., are not measured directly in traditional photoelasticity. However, this approach was validated with both the finite element method and the RGB (red, green, and blue) photoelasticity method that is traditionally used. [ABSTRACT FROM AUTHOR]

The stress distribution in sealing glass is one of the most concerning issues for glass‐to‐metal (GtM) seals. In this study, photoluminescence spectroscopy was applied by exploiting the piezospectroscopic effect of Cr‐doped α‐Al2O3 (ruby), and the overall stress distribution along the radius of a concentric seal was detected and analyzed. It was discovered that the compressive stress first increased and then decreased at the edge of the seal. The maximum compressive stress of 91 MPa was detected at ∼20 µm from the interface and was ascribed to the interaction between the glass and surface oxide film of the metal. Stress distributions in pore regions were also investigated and obvious stress fluctuations were observed clustering around pores. A circle of compressive stress was observed around the pores in a single glass without a metal housing; for the pores in the center of the concentric seal, the stress distribution was dominated by the inner contraction of the metal housing; and for the pores near the edge of the seal, the concentration of tensile stress located perpendicular to that of the compressive stress. This study demonstrates a high‐resolved and nondestructive method to detect the stress field and explores the potential for future tailorability of stress distribution in GtM seals. [ABSTRACT FROM AUTHOR]

Background: The interaction of stress fields between cracks or cracks with discontinuities like holes, etc., has been widely studied. Another crucial class of problems include cracks interacting with contact stresses but there has been no work to study them systematically. Objective: This study aims to understand the role of contact stress in influencing the crack-tip stress field which is essential for reliable estimation of stress intensity factors (SIFs) experimentally. Method: The contact stress influence on crack-tip isochromatic features is initially discussed using an experimental result for a moderately-deep beam with a small crack. SIFs are evaluated using the over-deterministic nonlinear least squares method. The crack-contact stress interaction is then studied by a superposed crack-contact analytical solution. Photoelastic experiments are conducted for a cracked moderately-deep beam subjected to three-point bending. The SIFs evaluated using the multiparameter solution compare well with finite element predictions. Subsequently, multiple interaction configurations are experimentally examined in a cracked moderately-slender beam by varying the magnitude and position of the contact load relative to the crack. Results: Even a small crack shows a noticeable change in isochromatics due to influence of contact stress and a two-parameter solution is inadequate here. A multiparameter crack-tip solution is observed to capture the isochromatic fringe field very effectively towards SIF evaluation. Conclusion: The changes in isochromatics at a crack-tip due to contact stresses are significant. A systematic analysis shows that with appropriate data collection, the multiparameter solution provides SIFs with very little uncertainty in the presence of contact stresses with varying complexities. [ABSTRACT FROM AUTHOR]

The interaction mechanism of oppositely propagating cracks is an important basis for the study of rock fracture under dynamic loading. In this article, the stress field superposition and crack tip stress evolution are deeply investigated during the interaction of oppositely propagating cracks by using dynamic photoelastic experiment method and numerical simulation analysis. Obtained results indicate that the cracks interaction process is accompanied by the deflection of the crack, and the deflection of the cracks is mainly affected by the shear stress field at the crack tip. According to the difference of the crack deflection characteristics, the interaction process of the oppositely propagating cracks can be divided into two stages. The Stage I: the non-interlaced stage and Stage II: the interaction stage after the mutual staggered. It includes the period of Stage I that the oppositely propagating cracks are not interlaced with each other; the Stage II is the interaction period after the oppositely propagating cracks are interlaced with each other. The effects of stress intensity factor KI, stress intensity factor KII and far-field T stress on crack propagation process should be comprehensively considered when predicting the crack growth trajectory. The interaction of the stress field between cracks is the main factor determining the crack propagation trajectory. In addition, the vertical spacing between cracks also has a significant effect on the fracture behavior of oppositely propagating cracks. When the vertical distance between the two cracks is large, the local stress fields at the crack tip cannot overlap and interfere with each other, and the oppositely propagating cracks will expand independently of each other. [ABSTRACT FROM AUTHOR]

The evaluation of the stress field based on digital photoelasticity is of interest in many engineering fields because of the full-field and non-destructive capabilities of this optical technique. Regardless of the approach used, reconstructing the stress field using photoelasticity involves processing information encoded in images with fringe patterns. The visual information in these images depends on the interaction between the light source and the sensor used to acquire or generate such images. In this work, a new descriptor is presented to quantify the effect of the light source - sensor interaction, on the quality of the visual information available in photoelastic fringe patterns, and on the ability to resolve higher fringe orders in the stress field. [ABSTRACT FROM AUTHOR]

Stress analysis, a fundamental aspect of engineering and design, is critically dependent on experimental methods, with photoelasticity being a key technique. Despite its effectiveness, photoelasticity is often limited by subjective human interpretation, leading to variable stress measurement results. To address this, we have concentrated on the practical applications of this method, employing a circular disc analyzed under various compressive loads. Our research introduces a novel algorithm specifically developed for processing photoelastic images. This algorithm enhances the clarity of thinned fringes, enabling more precise measurement of the principal stress differences. Our findings indicate that the digitally processed photoelastic images align closely with analytical solutions, suggesting a more reliable and consistent approach to stress analysis. This advancement mitigates the subjectivity inherent in traditional photoelastic methods, thus improving the accuracy of stress measurement. The implications of this study are significant for the broader field of engineering. The developed methodology can be applied to diverse scales of instruments and facilities, offering a versatile tool for identifying stress patterns. Overall, our work also improves the accuracy of such a tool and technique, making it more useful for failure analysis scenarios understanding. [ABSTRACT FROM AUTHOR]

We investigated the conversion of optical energy into mechanical energy during nanosecond laser ablation in an underwater regime. Our study analyzed the energy distribution between the shockwave, cavitation bubble, and work done by plasma impulse on the solid target, while also examining how laser intensity and absorptive coating affect this distribution. We monitored the evolution of the shockwave and cavitation bubble using the photoelasticity imaging technique and a high-speed laser stroboscopic videography system in the photoelasticity mode. Based on the experimental data, we determined the energy allocated to each process. Our result showed that shockwave energy contributed the most to the energy balance, followed by the cavitation bubble energy. The ratio of shockwave energy to cavitation bubble energy was independent of the laser pulse energy. Coating material helps to convert more optical energy to the thermal energy of the plasma plume, thus increasing the overall optical-to-mechanical energy conversion efficiency. [ABSTRACT FROM AUTHOR]

A precise estimation of the bending and contact stresses, as well as the true friction value during the gear mesh, are critical aspects of a cost-effective and safe gear design. Previous studies have usually neglected friction by assuming a frictionless contact. Additionally, the impact of friction on the bending stress of spur gears has rarely been addressed. Moreover, to the authors' best knowledge, the impact of friction on the weakest section, stress concentration factor, and Lewis form factor remain unexplored for both symmetric and asymmetric gears. This study presents an analytical model incorporating friction at different contact locations to calculate the variables related to the tooth's weakest section. This model facilitates the evaluation of the stress concentration factor, Lewis form factor, and maximum tensile stress for symmetric and asymmetric gears. The proposed model is especially beneficial for assessing the load-carrying capacity of spur gears operating in challenging conditions. The results showed that the asymmetric spur gear is superior to its equivalent symmetric counterpart in terms of tooth form factor; however, this superiority decreases as the coefficient of friction increases. In addition, friction has been found to have a greater effect on fillet stress than contact stress. For μ = 0.2, at the HPSTC, the contact load and tooth form factor decreased by 7 % and 12 %, respectively, and the fillet stress worsened by 13 % compared to the frictionless assumption. Meanwhile, at the LPSTC, the stress concentration factor and contact stress increased by 9 % and 3 %, respectively.

Recently moving towards the usage of sustainable and renewable construction materials, the badminton strings are identified as alternate material for commercial fibers. These recycled badminton strings once discarded from the racquets become a waste and cannot be reused. Hence investigation of the interphase bond behavior of these fibers with the cement and epoxy polymer matrix plays a major role. Therefore, the pullout mechanism between the fibers with the epoxy matrix is examined using the photoelasticity technique with a 40 mm embedment length. Whereas the pullout mechanism between the fibers with the cementitious matrix is examined for a single string of fiber using a pullout test with varied embedment lengths of 10, 20, 30, 40, 50, 60, 70, and 80 mm. From the study, the minimum and maximum bond stress between the fiber and epoxy interface is 3.23 MPa and 11.59 MPa respectively. Whereas between the fiber and cementitious interface, the minimum and maximum bond stress is 1.02 MPa and 2.15 MPa respectively. The experimental results are validated by the Weibull modulus approach which shows less variability. Thus, the results of the pullout test in composite matrix recommend the usage of waste badminton strings in fiber-reinforced concrete applications. [ABSTRACT FROM AUTHOR]

Porous materials have been extensively used in electronic communications, aerospace, bio-medicine and petrochemical, etc. due to their attractive attributes such as low relative density, thermal and acoustical insulation and good permeability. Ultrashort laser pulses have a series of unique advantages including high energy density, ultrashort interaction time and high accuracy, which are widely used in the fields of precision machining and microelectronic manufacture. For porous materials heated by an ultrashort laser pulse, revealing the interplay between deformation field and temperature field is crucial to guide their engineering application and optimization design. The present work devotes to investigating the transient response of a porous half-space heated by a non-Gaussian laser beam on its boundary surface based on the newly established linear thermoelastic theory with strain and thermal relaxations. The coupled governing equations are formulated and solved through the Laplace transform and its numerical inversion. The distributions of the non-dimensional temperature, displacement, stress as well as volume fraction field are obtained and illustrated graphically. In calculation, the effects of the thermal relaxation factor, the strain relaxation factor on the temperature field, volume fraction field, displacement field as well as stress field are examined and discussed in detail. [ABSTRACT FROM AUTHOR]

In this study, the fabrication of microfluidic chips through the bonding of poly (methyl methacrylate) (PMMA) boards featuring designed patterns to create a three-dimensional sandwich structure with embedded microchannels was explored. A key focus was optimization of the interface quality of bonded PMMA pairs by adjusting the solvent, such as such as acetone, alcohol, and their mixture. Annealing was conducted below 50 °C to leverage the advantages of low-temperature bonding. Because of the differences in the chemical reactivity of PMMA toward acetone, alcohol, and their combinations, the resulting defect densities at the bonding interfaces differed significantly under low-temperature annealing conditions. To achieve the optimal sealing integrity, bonding pressures of 30 N, 40 N, and 50 N were evaluated. The interface was analyzed through microstructural examination via optical microscopy and stress measurements were determined using digital photoelasticity, while the bonding strength was assessed through tensile testing. [ABSTRACT FROM AUTHOR]

The linear optical response of lithium niobate under compressive as well as tensile stress is calculated from first principles. For this purpose, the elastic constants are computed with different exchange‐correlation functionals and compared with available experimental values. A good agreement with the measured quantities is obtained. A full set of the piezo‐optic and photoelastic coefficients is determined from the dependence of the dielectric permeability in the linear regime on the considered stress. The calculated coefficients agree with the experimental values as well. In contrast to the numerous experimental investigations, the coefficients are not only given for a single excitation wavelength but also within the technically relevant optical range. From the dispersion of the piezo‐optic and photoelastic coefficients, conclusions can be drawn about the refractive indices and the birefringence under strain for different excitation energies. It can be concluded that the birefringence in the long wavelength range increases under stress in the z direction. For uniaxial stress in x and y directions, the lattice symmetry is broken and the crystal becomes biaxial in the x and y directions as well. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare two testing methodologies employed for assessing the polymerization shrinkage stress of dental resin composites. Ten commercial resin composites were investigated (EverX Posterior & Flow; G-ænial Anterior, Posterior, A’CHORD & Universal Injectable; Filtek One Bulk Fill & Universal Restorative; SDR flow+ and Aura Bulk Fill). Photoelastic and contraction forces measurement methods were performed. The slope of the linear trendline and C-factor of specimens were calculated. The shrinkage stress values (range between: 6.4–13.4 MPa) obtained by the photoelastic method were higher for all resin composites than the values obtained by contraction forces measurements (range between 1.2–4.8 MPa). However, there was a strong linear correlation between these methods (r=0.8). The use of both investigated methods revealed important information about the shrinkage behavior of the restorative resin composites. [ABSTRACT FROM AUTHOR]

As a lightweight material with high performance, carbon fiber‐reinforced thermoplastic plastic (CFRTP) is being implemented increasingly in aerospace, automotive, new energy, and so forth. The connection between CFRTP and metals, which are still used in these areas, is an inevitable problem. Among the various connection techniques, laser welding of CFRTP to metal is attractive due to high efficiency, excellent strength, and no contact. This paper presents the most recent research on laser welding CFRTP and metals in three aspects: (a) the principle of laser welding CFRTP to metals and the influence of process parameters on joint quality including laser power, defocus distances, scanning speed, clamping pressure, and beam shape, (b) the joint enhancement mechanisms and methods, and (c) numerical simulations of temperature and stress fields of laser‐connected CFRTP to metals. The findings show that joint strength is significantly influenced by process parameters and that the maximum joint strength can be achieved by choosing the right parameters. Apart from the conventional techniques of texturing the metal surface, applying a suitable layer of resin, and applying chemical treatment, other novel joint improvement measures have also been used, including the use of blue laser and CFRTP embedded in the metal. The temperature field and residual stresses can be successfully simulated by finite elements, which can be useful when studying new processes and choosing parameters for metal laser welding and CFRTP. Highlights: We review the progress from parameters, simulations, and enhancements.The main parameters have essential effects on the dimensions and strength of joints.FEM (Finite Element Method) is applied to simulate the temperature and stress of the laser welding.Joints can be reinforced by surface pre‐texturing, adding resin, and grafting. [ABSTRACT FROM AUTHOR]

Numerical analysis of complex problems invariably requires the use of inputs from experimental methods like photoelasticity to validate the boundary conditions as well as the numerical modelling. In this era where the engineering community follows open-source culture to solve numerical problems, this brief note brings out a procedure to plot the photoelastic contours from FE results. The methodology is verified using a benchmark problem of a disk under diametral compression with experimental results and applied to a plate with an edge crack problem. [ABSTRACT FROM AUTHOR]

Acoustic–plasmonic coupling in metallic nanoparticles can significantly alter their optical absorption and scattering characteristics. However, almost all previous investigations on acoustic–plasmonic coupling so far have been focused on the spectral response of particles in a vacuum. In this report, a spatial photon scattering mode taking count in the acoustic–plasmonic coupling of individual gold nanoparticle (GN) on a silicon substrate under ultrasonic influence was presented. The acoustic–plasmonic is visualized with parametric images with spatial scattering patterns of the particle under the excitation of polarized light along the Poincare's equatorial trajectory. The ultrasonic sources can be sensitively extracted from the parametric sinδ images, providing clear evidence of the extremely weak influence of ultrasound wave directivity on the spatial characteristics of the scattering of the particle through acoustic–plasmonic coupling. Experiment and simulation results reveal that, in general, the coupling is the strongest, when the maximum electric field (plasmon vibration mode) aligns with the ultrasonic propagation direction. This study provides a new angle to observe and deepen the understanding of the acoustic–plasmonic effect of nanoparticles, in addition to the conventional manner of investigation on their scattering spectra. It emphasizes the possibility of determining the spatial distribution of nanoparticles via photon state scattering when they are in a weakly oscillating environment, providing valuable guidance for future potential applications exploiting the acoustic–plasmonic effect of nanostructures. [ABSTRACT FROM AUTHOR]

We investigated laser-induced shock excitation of elastic surface waves at a free surface and a soft solid–liquid interface using a custom-designed photoelasticity imaging technique. Epoxy-resin and pure water were selected as the solid and liquid media. The elastic surface waves were excited via a shock process induced by focusing a single nanosecond laser pulse on the solid surface. To confirm the experimental observations, the roots of the Rayleigh and Stoneley equations were calculated. For a free surface, we present an entire-field observation of elastic surface waves, which includes a super-shear evanescent wave (SEW) that propagates faster than the shear wave but slower than the longitudinal wave. For a soft solid–liquid interface, we demonstrate the presence of a non-leaky Rayleigh wave that corresponds to a real root of the Stoneley equation. We also evidence the existence of a SEW that propagates 1.7 times faster than the shear speed in the solid and corresponds to a complex conjugate root of the Stoneley equation. These results correct the previously accepted notion that the Scholte wave is the only surface wave that can be generated at a soft solid–liquid interface. [ABSTRACT FROM AUTHOR]

The influence of the contact between specimen and machine jaw in Brazilian disc testing method is investigated by the reflection photoelasticity technique. To this end, six brackets with various angles from 5° to 30° are employed. A polycarbonate plate cut by a water-jet cutting machine is employed as the reflection specimen. To figure out which contact is the best alternative for the flat one, stress distributions in contact with various angles under various applied forces are correlated. Results show only in contacts with 5° angle the distributions of stresses remain completely similar to the usual Brazilian disc. In the second step, polycarbonate specimens with various notch lengths from one-eighth of the disc diameter to half are tested. The distribution of stresses around notches resulting from photoelasticity fringes is similar to flat contacts only for contacts with 5° slope. It is also notable that using inclined brackets the concentration of the stress at contacts dramatically declines to around half of the flat contacts. [ABSTRACT FROM AUTHOR]

Overflow is usually used to keep fluid continuously flowing to avoid the fluid from changing flow direction and subsequently inducing large stresses. To explore the mechanism of flow‐induced stress evolution, a flow model was established in terms of compressible, non‐isothermal, and viscoelastic flow. Based on the Leonov model and the mid‐plane approach, a pseudo‐Poisson type equation for pressure was derived to decouple the interdependence between velocity and pressure. To improve computational efficiency, a numerical approach involving double iterations was proposed to solve the flow problem. Two kinds of mold cavities, with and without overflow, were designed and manufactured. Molding experiments were conducted, and corresponding simulations based on the proposed model and algorithm were performed. The results show that the simulated contours of flow‐induced stress are in good agreement with the photoelastic streaks. The use of overflow can significantly reduce flow‐induced stresses. If the slot thickness is set to a proper value, the flow‐induced stress can be reduced by more than 80%. On the other hand, a slot that is too thick does not have significant reducing effects. Therefore, using overflow to reduce flow‐induced stresses during transparent part production is a promising approach if the material cost is worthy of the quality. Highlights: A double iteration method is proposed for viscoelastic flow problem.Overflow can reduce the stress as much as 80% if the dimension is properly set.The simulated stress streaks are in good agreement with photoelasticities. [ABSTRACT FROM AUTHOR]

• Proposal of photoelastic method for a stress analysis in granular terrains. • Visualization and observation of dynamic changes in internal stresses of a granular terrain beneath a traveling wheel. • Comparative investigation of force chain structures (stress propagation angles and propagated range) in granular terrains. • Quantitative evaluation of the force chains based on an orientational order. This paper presents a photoelastic method for the stress analyses of granular terrains beneath a traveling wheel. Recently, wheel terramechanics have been studied using various advanced techniques such as particle velocimetry and machine learning. However, the dynamic profiles of the stress distributions in soil have not been directly observed. In this paper, we propose a photoelastic method to experimentally demonstrate the two-dimensional stress analysis of a granular terrain. This method uses photoelastic disks as terrain particles; thus, the internal stress and propagation of the granular terrain can be visualized using the interference fringe of light. This study aimed to observe the dynamic behavior of grains, typically simulating circular or spherical objects of the granular terrain. To demonstrate the photoelastic method for simulated ground, we developed a single-wheel testbed using photoelastic materials. Moreover, the effects of mixing with non-photoelastic materials were investigated to simulate steady states with small and large wheel-slip conditions. This paper presents a force chain analysis of the photoelastic particles beneath a single traveling wheel. The force chain structure was geometrically compared with the propagation angle and length. In addition, the orientational orders of the force chains were quantitatively evaluated under both small and large wheel slip conditions. The experimental results confirmed that the photoelastic method can reveal dynamic changes in the internal stress structures of granular terrain beneath the wheel under various slip conditions. [ABSTRACT FROM AUTHOR]

To measure the energy of the source of acoustic pulses in the absolute scale of units (J) from the registered pulses, an analysis of the energy balance "source of pulses"–"transmitting medium"–"receiver of pulses" was carried out using a spectral analysis device. Comparison of two independent methods for determining the energy of elastic interaction (capacitive method and photoelasticity method) gave a discrepancy between the results of less than 12%. The spectral composition of the interaction energy is determined. The results make it possible to determine both the parameters of the signal source and the structure of the transmitting average signal conversion. To measure stresses in an elastic wave, a piezoelectric receiver, in which a piezofilm served as a sensitive element. This receiver differs from receivers made on the basis of piezoceramic elements, has a significantly lower non-linearity of the amplitude–frequency characteristic, since it has only two natural frequencies. [ABSTRACT FROM AUTHOR]

The optical polarization method with ring-shaped photoelastic sensors, digital photography of isochromatic patterns and their clarification using neural networks is developed for the stress measurement in rock mass. The case-studies of the photoelasticity application in solving various problems of elasticity and rock pressure analysis are reviewed. As a result of a lab-scale experiment, a data set of 15000 isochromatic images is collected. The machine learning algorithm was a convolutional neural network, the Inception module. The authors recommend using downhole sensors for the continuous stress monitoring in underground mines and integrating the obtained data in a digital model with the help of IoT. [ABSTRACT FROM AUTHOR]

Aim: The aim of this study is to compare the stress produced on the internal walls of simulated canals by nine rotary and four reciprocating systems. Methodology: Sixty‐five isotropic transparent blocks containing a 60° curved and tapered simulated canal were selected and distributed into 13 groups (n = 5) according to the preparation system: BioRace, HyFlex EDM, iRaCe, Mtwo, One RECI, ProTaper Next, RaCe EVO, Reciproc, Reciproc Blue, R‐Motion, VDW.ROTATE, XP‐Endo Rise Shaper, and XP‐Endo Shaper. Each resin block was mounted in a vice and a digital camera recorded the entire sequence of each preparation system through a circular polariscope set for dark field analysis. The video frames when each instrument reached the end of the coronal, middle, and apical thirds of the canal were extracted from the recordings and analysed by two independent observers regarding the stress generated on the canal walls using a semi‐quantitative evaluation on a 0–5 scale. Intra‐ and inter‐observer agreement were subjected to the Cohen's Kappa coefficient test, whilst the experimental results were compared using Kruskal‑Wallis test post hoc pairwise comparisons with Bonferroni correction (α = 5%). Results: The inter‐ and intra‐observer agreement were 0.98 and 1, respectively. Most instruments demonstrated acceptable performance (scores ≤ 2) in all thirds. Other instruments, such as the HyFlex EDM 25.12 (coronal and middle thirds), Reciproc Blue R25 and Reciproc R25 (coronal and apical thirds), R‐Motion 30.04 (apical third), and VDW.ROTATE 20.05 (apical third) showed scores higher than 3. Statistical analysis revealed a significant difference amongst the tested systems at the coronal, middle, and apical thirds (p <.05). Conclusion: None of the canal instrumentation protocols were stress‐free, showing varying levels of stress concentrations. Various factors seemed to influence the magnitude of stress and its distribution pattern on the canal walls. Overall, instruments characterized by a larger taper, lower speed, reciprocating motion, and made of heat‐treated NiTi alloy exhibited higher patterns of stress distribution. [ABSTRACT FROM AUTHOR]

The problem of a completely debonded short fiber (rigid line inclusion/anticrack) embedded in a 2D isotropic elastic soft matrix subjected to the remote loading condition is of fundamental interest. The current work investigates completely debonded anticrack embedded in a soft (isotropic) matrix using Kolosov Muskhelisvili's complex potential framework. Here two configurations are studied: debonded inclusion oriented (i) parallel and (ii) perpendicular to the loading direction. In particular, the potentials take the form of a non-homogeneous Riemann--Hilbert equation for the given problem. Upon solving analytical forms of potentials, the stress fields were obtained. The stress field for the fully debonded anticrack exhibited oscillatory singular behavior between r-3/4 and r-1/4 with the dependence on the oscillatory index e and material constants. The correctness of the analytical solution was validated using numerical simulation and experiments based on the digital photoelasticity technique. The analytical results were in good agreement with the experimental and numerically obtained stress fields confirming the accuracy of it. The magnitude of singularity is quantified by defining a complex stress intensity factor at the tip of the discontinuity and compared with the experimentally estimated value. So far in the literature, no full-field analytical solution exists for the completely debonded rigid inclusion embedded in an isotropic soft matrix. The solution obtained in the present work is of fundamental importance in developing the constitutive properties of short fiber reinforced thermoplastic (SFRT) composites. [ABSTRACT FROM AUTHOR]

Featured Application: This research has pivotal applications in geotechnical and civil engineering fields, particularly for improving the reliability and precision of stress and strain analysis in granular materials, which can lead to more accurate predictions of soil behavior and further optimize the design and safety of the infrastructure. This study investigates the impact of various experimental parameters on the reflective photoelastic coating technique used to measure the stress and strain in model soil particles. The focus is directed towards three pivotal parameters: the choice of adhesive for the photoelastic coating, the inherent properties of the light source, and the configuration of the camera for color image analysis. Through a series of uniaxial compression tests on consistently crafted model soil particles, a notable relationship emerges between the adhesive's shear strength, its viscosity, and the uniformity of the photoelastic response. While the light source's characteristics and camera adjustments hold significance, their influence on the consistency of the response is comparatively subtle. Consequently, the adhesive's role is underscored as instrumental in influencing the photoelastic response, offering valuable insights for subsequent research endeavors utilizing the reflective photoelastic technique. [ABSTRACT FROM AUTHOR]

Free-Form-Gear (FFG) is a recently published title for a gear that has a curved path of contact and offers contact between a convex addendum and a concave dedendum during the meshing cycle. Based on this method of designing a gear pair, the path of contact can be altered to improve the way the gears mesh and slide against each other by only adjusting the maximum pressure angle and the involute curve parameter. The analytical investigations into this gear pair indicated that, when compared to the standard involute gear pair, the sliding velocity, meshing efficiency, contact, and fillet strengths are improved while the contact ratio is decreased. In this study, experimental stress analysis is conducted on various configurations of the tooth profile and tooth fillet shape for the proposed FFG and the standard involute gear to validate the analytical results. Since it is difficult to measure the contact stress for the gear specimens, the contact stresses at critical points are estimated using an effective computational technique based on photoelastic data and a numerical approach utilizing the nonlinear least squares method. At the fillet zone, isochromatic fringe patterns are used to directly measure the maximum fillet stress. Using addendum modification coefficients, the reduction in contact ratio for the proposed FFG is eliminated, and the results are then verified experimentally. Based on the experimental estimations, the finite element analyses are conducted using ABAQUS to simulate the examined gear specimens. Under the same loading conditions, the experimental, analytical, and numerical results have all been in good agreement. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of dynamic monitoring from a bird's eye view for typical rapidly changing processes such as mechanical rotation and photoresist exposure reaction, we propose a vertical high-speed Mueller matrix ellipsometer that consists of a polarization state generator (PSG) based on the time-domain polarization modulation and a polarization state analyzer (PSA) based on division-of-amplitude polarization demodulation. The PSG is realized using two cascaded photoelastic modulators, while the PSA is realized using a six-channel Stokes polarimeter. On this basis, the polarization effect introduced by switching the optical-path layout of the instrument from the horizontal transmission to the vertical transmission is fully considered, which is caused by changing the incidence plane. An in situ calibration method based on the correct definition of the polarization modulation and demodulation reference plane has been proposed, enabling the precise calibration of the instrument by combining it with a time-domain light intensity fitting algorithm. The measurement experiments of SiO2 films and an air medium prove the accuracy and feasibility of the proposed calibration method. After the precise calibration, the instrument can exhibit excellent measurement performance in the range of incident angles from 45° to 90°, in which the measurement time resolution is maintained at the order of 10 μs, the measurement accuracy of Mueller matrix elements is better than 0.007, and the measurement precision is better than 0.005. [ABSTRACT FROM AUTHOR]

The Gaussian laser mode can be converted into a hollow-ring laser mode through beam conversion system, realizing the conversion of circular and solid spot into a hollow-ring spot, which changes the energy distribution form of the laser spot. In order to study the effects of the Gaussian and hollow-ring laser modes on temperature and stress fields in cladding layers, the numerical simulation and experimental investigation were performed. The results showed that molten pool experienced once temperature peak and generated sharp temperature change under the Gaussian laser, while the molten pool experienced twice temperature peaks and temperature changed relatively gentle when using hollow-ring laser. Comparing with the Gaussian laser, the maximum temperature gradient along the depth of cladding layer decreased by 72.3% from 1.79 × 106 to 4.95 × 105 ℃/m, and the maximum residual stress decreased from 272 to 251 MPa under hollow-ring laser. Meanwhile, the simulation results were validated by experiments with the same process. Furthermore, the sample microstructure was studied from the experiment. The microstructure was finer and more uniform using hollow-ring laser. This paper can provide guidance and advantage for laser cladding and direct metal deposition based on the hollow-ring mode and expand the application of laser field. [ABSTRACT FROM AUTHOR]

The degree of quality of thermoplastic injection-molded parts can be established based on their weight, appearance, and defects. However, the conditions of the injection process may induce effects on the mechanical performance of the injected parts, and the residual stresses can cause cracks or early failures when an external load or force is applied. To evaluate these mechanical behaviors, different experimental techniques have been reported in the literature, where digital photoelasticity has stood out both for being a non-contact technique and for achieving quantitative results through sophisticated computational algorithms. Against this background, our proposal consists of analyzing the overall residual stress distribution of parts injected under different molding conditions by using digital photoelasticity. In this case, the specimens are subjected to bending strength tests to identify possible effects of the injection process conditions. The findings show that, at mold temperatures of 80 °C, flow-induced residual stresses increase with packing pressure. However, these internal stress levels do not affect the external load applied by the mechanical bending test, while the mass injected at higher levels of packing pressure helps to increase the bending strength of the injected part. At lower mold temperatures (50 °C), the mechanical strength of the injected part is slightly reduced, possibly due to a lower effect of the packing pressure. [ABSTRACT FROM AUTHOR]

The absolute difference between two photoelastic coefficients p 11 - p 12 and its wavelength dispersion have been experimentally studied in commercially available (0001) 4H silicon carbide substrates by using originally developed imaging polariscopes (xIPs) with different light-source wavelengths (λ = 630 nm, 940 nm, and 1200 nm). The simple three-point bending test was adopted to measure the distribution of birefringence Δ n in a small beam under an external load. Additionally, numerical simulation was performed to accurately estimate the distribution of σ 1 - σ 2 in the beam, even with its size restriction. The value of p 11 - p 12 was evaluated by regression analysis on the value pairs of σ 1 - σ 2 and Δ n examined under various external loads. In order to avoid the effect of residual strain in the sample, the regression analysis was performed at many positions over the sample rather than a few representative points as is adopted conventionally. The value of p 11 - p 12 was obtained as 0.040, 0.090 and 0.13 at wavelengths of 630 nm, 940 nm, and 1200 nm, respectively. The wavelength dispersion revealed inverse correlation with photon energy and suggested that p 11 - p 12 may become close to zero at a certain wavelength shorter than 630 nm, implying a technical trade-off between the sensitivity of the photoelastic effect and the signal-to-noise ratio in polariscopic photometry, which is useful for considering the optimal wavelength in quantitative strain imaging with photoelastic technique. [ABSTRACT FROM AUTHOR]

Transparent polymeric materials have gained significant popularity as replacements for glass in various industries due to their low cost, lightweight nature, and high processing efficiency. Injection molding is the primary method for producing transparent polymer parts. However, residual stress often poses a challenge, leading to various defects. Traditional approaches utilize photoelasticity and polarizers to determine stress in transparent parts, which costs time and cannot be easily used for online monitoring and real time quality inspection. The digital image processing (DIP), combined with photoelasticity, offers a promising solution for detecting residual stress and assessing product quality in real-time during manufacturing. In this study, we propose a photoelastic digital image processing (PDIP) approach that combines photoelasticity and DIP techniques to identify residual stress and evaluate part quality using a single digital polarized image without the need for a rotation process. By collecting and analyzing the gray values and variations from the photoelastic images through PDIP, we compared and correlated the gray values of the entire image, a specific area on one side lens, a warp line, and a weft line. Additionally, numerical simulations were performed to validate the proposed method. The results demonstrated the feasibility of this instant identification method. The PDIP technique should be applied to a specific area or line within the parts. By obtaining the average gray value, the instantaneous identification of residual stress can be achieved. The determination of the specific area or line can be tailored according to the quality requirements of the parts.

Characterization of lattice properties of monocrystalline semiconductors (MS) has been rapidly advanced. Of particular interest is the use of shear strains induced by optoacoustic-bulk-waves. However, this technique has been hindered owing to the lack of quantitative correlations between optoacoustic-bulk-waves-induced shear strains and anisotropic photoelasticity of MS. Motivated by this, a multiphysics model is developed to interrogate the coupling phenomena and interaction between optical polarization and shear strains in MS. With the model, perturbation to the polarization of a monochromatic laser beam, upon interacting with optoacoustic waves in MS, is scrutinized quantitatively. Experimental results are in agreement with those from the model, both revealing the polarization perturbed by shear strains quantitatively depends on the crystal orientation and crystal-structure-related symmetry, which are jointly governed by mechanical/photoelastic/optical anisotropies of MS. The approach has paved a new way for selectively acquiring high-sensitivity shear components of optoacoustic-ultrasonic-waves for in situ, high-definition characterization of anisotropic MS.

We present a floating element force balance design that uses an optical measurement of the force using photoelastic stress analysis. The force sensing element consists of pins embedded in photoelastic polyurethane pads, which generate an internal stress when the floating element is loaded that is observed via a transmission polariscope. A series of known loads and their corresponding fringe patterns allow a calibration matrix to be derived using a polynomial model solved by least squares regression. Finite element analysis (FEA) simulation is carried out to validate the proposed method. The balance then measured a lift curve of the NACA0015 wing at low speed. A comparison of the photoelastic balance and a commercial, 6-axis strain-gauge load cell showed typical differences of less than 6 % . This optical approach enables accurate measurements with inexpensive and simple components inside the sensor. This work demonstrates that a photoelastic balance is a simple, inexpensive, and sensitive force transducer. [ABSTRACT FROM AUTHOR]

The light field at the output of the Mach–Zehnder interferometer, where one of its arms contains a birefringent sample and a rotating polarizer is placed at the output, has been investigated both theoretically and experimentally. Initially unpolarized light, after passing through the interferometer, becomes partially polarized and carries information about the sample points with equal sums of principal stresses, forming the isopachic field. Depending on the relative path difference at the considered point in the output light field, the degree of polarization varies from 0 to 1. Analyzing this phenomenon allows us to establish the relationship between the intensity of the outgoing light and the azimuth of the rotating polarizer, thereby enabling the determination of the directions of the main optical axes at each point of the birefringent sample, known as the isoclinic field. [ABSTRACT FROM AUTHOR]

Most studies on bearing stress analysis have considered single row rolling elements. In this study, the stress behavior of a spherical roller bearing with two rows of rolling elements is investigated. Photoelastic experimental hybrid method, is applied to investigate the interior and contact stresses of high-speed train bearings under combined axial and radial loads. The experimental results show that the bearing under investigation has the capability of sustaining high loads. The sharing of the loads between the two rows of rollers was found to contribute to excellent load bearing capabilities. It is also shown that the barrel-shaped roller has an influence on the stress concentrations and their distributions on the bearing races. At low radial and axial loads, the stresses on the races result from the bulging out section of the roller. As load is increased, the roller deforms and race stress occur at the ends of the roller, which now act like a punch. Only half of the bearing structure was found to be highly stressed. At position 3, the few isochromatic fringes on rollers and inner race shows that low stress concentrations occur on them. A comparison of the results from spherical roller bearing (SRB) and tapered roller bearing (TRB) showed that the stresses induced at the bearing races of the TRB bearing have higher magnitudes than those of SRB. This observation can be attributed to the two rows of rollers in SRB. High stress concentrations often lead to crack initiation and spall growth. Therefore, the low stresses on the SRB makes them more suitable for applications involving heavy loads. [ABSTRACT FROM AUTHOR]

The present article proposes an evolutionary development of the photoelasticity method for measuring stresses based on annular photoelastic sensors application along with stress pattern recording with the aid of a digital camera and its recognition using artificial neural networks. The analysis of the modern application of the photoelasticity method for various problems within the theory of strength is presented. The principle of operation of photoelastic sensors based on the photoelasticity effect is considered. Optical patterns in an annular photoelastic sensor are presented for various values of the horizontal stress. The calculation of the stress state of the sensor for the following full-scale experiment has been performed, the estimate of the threshold conditions under which the sensor can be applied has been performed. As a result of a laboratory experiment, a dataset of 1500 isochromatic images has been assembled. A subspecies of a neural network, namely a convolutional neural network, has been applied as a machine learning algorithm. Different combination of models and optimizers have been employed. The application of downhole sensors for continuous monitoring of alterations in the rock mass stress state and the integration of this data into a digital field model based on Internet of Things technologies has been proposed. [ABSTRACT FROM AUTHOR]

Some results of experimental studies on the deformation of a rail under the force impact of a moving railway vehicle were presented. The studies were performed by using a supersensitive strain sensor with an ultimate relative strain of . The capabilities of optical tensometry in the problems of monitoring the technical state of wagon bogies and the upper structure of railways were analyzed. [ABSTRACT FROM AUTHOR]

Laser cladding is a directed energy deposition process and can lead to high residual stresses, which can compromise the quality of the specimen. As a result, it is crucial to accurately predict and investigate the residual stress distribution in cladded parts and understand the formation mechanisms. In this study, a thermo-mechanical metallurgical simulation model of the laser cladding process was developed for three different deposition sequences for a thin wall hexagon with inner junctions to investigate the formation of residual stress and distortion. The study was performed for single and multilayer scenarios. Two types of computational techniques, the detailed transient approach and the imposed thermal cycle approach, were performed and comparisons conducted. Consistent results were observed when comparing the resultant stress patterns for the single layer; subsequently, the imposed thermal cycle method was applied for the five-layer models. A preheat scenario is explored. This reduced the computational cost significantly, but the stress patterns were not similar. This indicates that building up worn regions at the top of a thin-walled component, such as a roll die, needs to be investigated further as unique issues have been highlighted. The differences between the implemented computational techniques are described as well as the advantages and disadvantages of each. Knowledge obtained from these case studies provides a foundation for efficient and rapid optimization of laser cladding processes, with the aim of minimizing residual stress in both simple and complex laser cladding structures. [ABSTRACT FROM AUTHOR]