Showing papers on "Photoelasticity published in 2022"
TL;DR: In this paper , a deep convolutional neural network was proposed for recovering the stress field wrapped into color fringe patterns acquired through digital photoelasticity studies, which achieved an average performance of 92.41% according to the SSIM metric.
Abstract: Quantifying the stress field induced into a piece when it is loaded is important for engineering areas since it allows the possibility to characterize mechanical behaviors and fails caused by stress. For this task, digital photoelasticity has been highlighted by its visual capability of representing the stress information through images with isochromatic fringe patterns. Unfortunately, demodulating such fringes remains a complicated process that, in some cases, depends on several acquisitions, e.g., pixel-by-pixel comparisons, dynamic conditions of load applications, inconsistence corrections, dependence of users, fringe unwrapping processes, etc. Under these drawbacks and taking advantage of the power results reported on deep learning, such as the fringe unwrapping process, this paper develops a deep convolutional neural network for recovering the stress field wrapped into color fringe patterns acquired through digital photoelasticity studies. Our model relies on an untrained convolutional neural network to accurately demodulate the stress maps by inputting only one single photoelasticity image. We demonstrate that the proposed method faithfully recovers the stress field of complex fringe distributions on simulated images with an averaged performance of 92.41% according to the SSIM metric. With this, experimental cases of a disk and ring under compression were evaluated, achieving an averaged performance of 85% in the SSIM metric. These results, on the one hand, are in concordance with new tendencies in the optic community to deal with complicated problems through machine-learning strategies; on the other hand, it creates a new perspective in digital photoelasticity toward demodulating the stress field for a wider quantity of fringe distributions by requiring one single acquisition.
9 citations
TL;DR: In this paper , a general overview of the different full-field methods for measuring retardation in tempered glass and their current state of development and usage is presented, and a comparison based on recent literature is presented.
6 citations
TL;DR: In this paper, a fitting phase-shift method based on the multistep phase shift method was proposed to extract the phase difference and isoclinic angle from a sequence of in situ photoelastic images by iteratively fitting the intensity values under a series of combinations of optical parameters.
5 citations
TL;DR: In this article , the authors 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.
Abstract: 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.
5 citations
TL;DR: In this article , a fitting phase-shift method based on the multistep phase shift method was proposed to extract the phase difference and isoclinic angle from a sequence of in situ photoelastic images by iteratively fitting the intensity values under a series of combinations of optical parameters.
5 citations
4 citations
4 citations
4 citations
TL;DR: In this paper , the authors evaluated and compared the stress distribution and primary stability of three different designs of Neodent® implant blocks and found that G1 and G2 exhibit high primary stability and satisfactory stress distribution.
Abstract: This study aimed to evaluate and compare the stress distribution and primary stability of three different designs of dental implants. 24 implants Neodent® were used (n=8): G1 – Alvim CM; G2 – Drive CM; G3 – Facility, submitted to insertion torque (IT) and pullout test, on 20 PCF (0.24 g/cm3) and 40 PCF (0.64 g/cm3) polyurethane blocks. For the stress distribution, by means of photoelasticity, axial and oblique loads (model at 30° inclination) of 100 N were performed, for reading and quantifying the fringe orders. According to the distribution data, a parametric or non-parametric analysis was performed (α=0.05). The IT was lower in G3 (p<0.05) compared to G1 and G2, in 20 and 40 PCF polyurethanes. In the pullout, no difference (p>0.05) was observed between G1 and G2, in both 20 and 40 PCF polyurethanes. In the comparisons between polyurethanes, higher values (p<0.05) were obtained in the 40 PCF for IT and pullout. In the axial loading, lower stresses were observed in the cervical third and higher stresses in the middle and apical third of the implants. With the oblique inclination of the models, higher stresses were generated in the opposite side of the load, in the cervical third of G1, followed by G3 and G2. The results allow to affirm that G1 and G2 exhibit high primary stability and satisfactory stress distribution. Although G3 generates stresses comparable to other implants, its indication is limited in low density bones.
4 citations
TL;DR: In this paper , a density functional theory approach was proposed to obtain both elastic and photoelastic properties of calcite, considering realistic experimental conditions (298 K, 1 atm).
Abstract: Calcite (CaCO3, trigonal crystal system, space group [Formula: see text]) is a ubiquitous carbonate phase commonly found on the Earth's crust that finds many useful applications in both scientific (mineralogy, petrology, geology) and technological fields (optics, sensors, materials technology) because of its peculiar anisotropic physical properties. Among them, photoelasticity, i.e., the variation of the optical properties of the mineral (including birefringence) with the applied stress, could find usefulness in determining the stress state of a rock sample containing calcite by employing simple optical measurements. However, the photoelastic tensor is not easily available from experiments, and affected by high uncertainties. Here we present a theoretical Density Functional Theory approach to obtain both elastic and photoelastic properties of calcite, considering realistic experimental conditions (298 K, 1 atm). The results were compared with those available in literature, further extending the knowledge of the photoelasticity of calcite, and clarifying an experimental discrepancy in the sign of the p41 photoelastic tensor component measured in past investigations. The methods here described and applied to a well-known crystalline material can be used to obtain the photoelastic properties of other minerals and/or materials at desired pressure and temperature conditions.
3 citations
TL;DR: In this article , a simultaneous measurement system for in situ investigation on dynamic fractures using the photoelastic, digital image correlation (DIC), and strain gauge measurement methods was established for the first time.
TL;DR: In this article , a density functional theory approach was proposed to obtain both elastic and photoelastic properties of calcite, considering realistic experimental conditions (298 K, 1 atm).
Abstract: Calcite (CaCO3, trigonal crystal system, space group [Formula: see text]) is a ubiquitous carbonate phase commonly found on the Earth's crust that finds many useful applications in both scientific (mineralogy, petrology, geology) and technological fields (optics, sensors, materials technology) because of its peculiar anisotropic physical properties. Among them, photoelasticity, i.e., the variation of the optical properties of the mineral (including birefringence) with the applied stress, could find usefulness in determining the stress state of a rock sample containing calcite by employing simple optical measurements. However, the photoelastic tensor is not easily available from experiments, and affected by high uncertainties. Here we present a theoretical Density Functional Theory approach to obtain both elastic and photoelastic properties of calcite, considering realistic experimental conditions (298 K, 1 atm). The results were compared with those available in literature, further extending the knowledge of the photoelasticity of calcite, and clarifying an experimental discrepancy in the sign of the p41 photoelastic tensor component measured in past investigations. The methods here described and applied to a well-known crystalline material can be used to obtain the photoelastic properties of other minerals and/or materials at desired pressure and temperature conditions.
TL;DR: In this paper , a 3D printed photoelastic model with orthogonal grating and sampling moiré was used to determine the full-field stress and displacement fields.
TL;DR: In this article , an automatic algorithm for the complete identification of the crack tip location was proposed, using the first hypersingular functions (i.e., the 1st negative term of William's series).
TL;DR: In this article , the interaction between the oblique incident blast stress wave and the prefabricated crack is studied using the dynamic photoelastic method and numerical simulation method, and the experimental results show that incident angle has a great influence on the way the stress wave interacts with the crack and the field at the crack tip.
TL;DR: In this article , a compact stress measurement system for transparent objects was proposed based on the combination of photoelascity and DGS methods, where the interferometry fringe and speckle image of the deformed specimen were captured from perpendicular and slant directions, respectively.
TL;DR: In this article, the photoplastic and photoelastic effects of point defect ionization on semiconductor optical properties were investigated using nanoindentation, and it was shown that the optical properties of semiconductors can be tuned by materials processing, and that processing dependence can be understood within a framework of defect equilibrium.
Abstract: We show that the wide-band gap compound semiconductors ZnO, ZnS, and CdS feature large photoplastic and photoelastic effects that are mediated by point defects. We measure the mechanical properties of ceramics and single crystals using nanoindentation, and we find that elasticity and plasticity vary strongly with moderate illumination. For instance, the elastic stiffness of ZnO can increase by greater than 40% due to blue illumination of intensity 1.4 mW/cm^{2}. Above-band-gap illumination (e.g., uv light) has the strongest effect, and the relative effect of subband gap illumination varies between samples-a clear sign of defect-mediated processes. We show giant optomechanical effects can be tuned by materials processing, and that processing dependence can be understood within a framework of point defect equilibrium. The photoplastic effect can be understood by a long-established theory of charged dislocation motion. The photoelastic effect requires a new theoretical framework which we present using density functional theory to study the effect of point defect ionization on local lattice structure and elastic tensors. Our results update the longstanding but lesser-studied field of semiconductor optomechanics, and suggest interesting applications.
TL;DR: In this paper , the authors investigated the Hertzian contact of a rigid sphere and a highly deformable soft solid using integrated photoelasticity, and found that the maximum equivalent stress of each ray carries the cumulative effect of traversing the contact-induced axisymmetric stress field.
Abstract: Hertzian contact of a rigid sphere and a highly deformable soft solid is investigated using integrated photoelasticity. The experiments are performed by pressing a styrene sphere of 15 mm diameter against a 44 × 44 × 47 mm3 cuboid made of 5% wt. gelatin, inside a circular polariscope, and with a range of forces. The emerging light rays are processed by considering that the retardation of each ray carries the cumulative effect of traversing the contact-induced axisymmetric stress field. Then, assuming Hertz's theory is valid, the retardation is analytically calculated for each ray and compared to the experimental one. Furthermore, a finite element model of the process introduces the effect of finite displacements and strains. Beyond the qualitative comparison of the retardation fields, the experimental, theoretical, and numerical results are quantitatively compared in terms of the maximum equivalent stress, surface displacement, and contact radius dimensions. A favorable agreement is found at lower force levels, where the assumptions of Hertz theory hold, whereas deviations are observed at higher force levels. A major discovery of this work is that, at the maximum equivalent stress location, all three components of principal stress can be determined experimentally and show satisfactory agreement with theoretical and numerical ones in our measurement range. This provides valuable insight into Hertzian contact problems since the maximum equivalent stress controls the initiation of plastic deformation or failure. The measured displacement and contact radii also reasonably agree with the theoretical and numerical ones. Finally, the limitations that arise due to the linearization of this problem are explored.
TL;DR: In this article , a generic, viscoelastic finite strain framework for the simulation of the curing process of adhesives, which renders a thermodynamically consistent model regardless of the selected free energy density, is presented.
Abstract: Abstract The transition of polymer adhesives from an initially liquid to a fully cured viscoelastic state is accompanied by three phenomenological effects, namely an increase in stiffness and viscosity in conjunction with a decrease in volume (curing shrinkage). Under consideration of these phenomena, some of us (Hossain et al. in Computational Mechanics 46:363-375, 2010) have devised a generic, viscoelastic finite strain framework for the simulation of the curing process of adhesives, which renders a thermodynamically consistent model regardless of the selected free energy density. In the present work, this generic curing framework is modified by means of more precise integration schemes and is applied to a hyperelastic Mooney–Rivlin material based on an additive volumetric-isochoric split of the strain energy density. The benefit of this decomposition is directly related to the distinct material responses of various polymers to volumetric and isochoric deformations [4]. The resulting Mooney–Rivlin curing model provides the foundation for implementing a user-defined material subroutine ( UMAT ) in Abaqus requiring the Cauchy stress and a non-standard formulation of the tangent operator. To this end, the corresponding transformations are presented. Additionally, a first attempt to determine the evolution of the curing-dependent material parameters through optimization with respect to a photoelasticity measurement is presented. A subset of the material properties, which reflect the emergence of shrinkage stresses inside a ceramic-epoxy composite after its fabrication, is determined via inverse parameter identification. However, due to a lack of experimental data and some rather strong assumptions made on the physics involved, this demonstration can currently be considered only as a proof-of-concept.
TL;DR: In this article , a partially debonded rigid line inclusion is modeled experimentally using a linear over-deterministic least-squares approach involving the digital photoelasticity.
TL;DR: In this article , the orthodontic forces generated by aligners are estimated by measuring near infrared 2D birefringence, and the optical retardation distribution that occurred when stress was applied to the sample was mapped and visualized.
Abstract: Recently, the number of patients who request esthetically pleasing aligner-type orthodontic appliances (referred to as aligners) has been increasing. However, the orthodontic forces generated by these aligners are still unknown. This study aimed to verify whether the orthodontic force in aligners can be estimated by measuring near infrared 2D birefringence, and to visualize the orthodontic force. We measured the mechanical and photoelastic properties of transparent orthodontic thermoplastic specimens to correlate the optical retardation with the applied load. The results confirmed equivalence between the mechanical properties and the photoelasticity. In addition, the 2D retardation distribution that occurred when stress was applied to the sample was mapped and visualized. This indicates that it is possible to estimate and visualize the orthodontic force using the retardation obtained by near infrared 2D birefringence measurement.
TL;DR: In this article, the interaction between the oblique incident blast stress wave and the prefabricated crack is studied using the dynamic photoelastic method and numerical simulation method, and the experimental results show that incident angle has a great influence on the way the stress wave interacts with the crack and the field at the crack tip.
TL;DR: In this paper , an extension of photoelasticity for coupled fluid-granular systems was used to image particle stresses during fracture by air injection in an oil-saturated granular pack.
Abstract: Unraveling the complex behavior of wet granular media has been challenging, because the effective stresses transmitted through the particles have remained unobservable. The authors use their recently developed extension of photoelasticity for coupled fluid-granular systems to image particle stresses during fracture by air injection in an oil-saturated granular pack. They discover two states of the granular medium evolving with the fractures, plus an ``effective-stress shadow'' behind the propagating fracture tips. This study points out the power of photoporomechanics for studying coupled fluid-solid processes in granular media, including energy recovery, gas venting, and geohazards.
TL;DR: In this paper , the authors proposed error correction equations for the instantaneous phase-shifting method based on theoretical analysis and simulation of a diametrically stressed disc, where the error distributions of the stress direction angle and phase retardation are discussed, and correction equations of the isochromatic and isoclinic lines are deduced.
TL;DR: In this article , a photo-mechanical modeling approach is presented for soft actuators, where the necessary constitutive equations are used in combination with the respective balance laws into a finite element implementation, and the capabilities of the numerical solution approach are illustrated by a simple two-dimensional bench-mark example.
Abstract: When molecular photo‐switches, such as azobenzene or norbornadiene, are embedded into a sufficiently soft polymer matrix the resulting compound can undergo a mechanical deformation induced by light of a specific wavelength. These photo‐sensitive compounds have the potential to be applied as soft actuators without the need for hard wired electronics or a separate energy source. Such characteristics are especially attractive in the design of micro‐scale robots but also other applications such as high‐speed data transfer or the conversion of photonic energy into a mechanical response holds great promise. Despite these almost futuristic possibilities, photo‐sensitive polymers have not yet experienced a sufficient attention in industrial applications. One important factor to increase the acceptance of this group of soft smart materials is the formulation of a rigorous constitutive modeling approach in combination with numerical simulation methods. Thus, in this contribution we present a photo‐mechanical modeling approach, departing from the fundamentals published previously. We briefly introduce the necessary constitutive equations which are subsequently utilized in combination with the respective balance laws into a finite element implementation. Finally, the capabilities of the numerical solution approach are illustrated by a simple two‐dimensional bench‐mark example and subsequently extended to a more complex three‐dimensional problem.
TL;DR: In this article , the authors demonstrate the quantitative analysis of stress-induced birefringence in 3D direct laser written structures and present the measurement setup based on a rotating polarizer and an elliptical analyzer.
Abstract: 3D direct laser writing is a widely used technology to create different nano- and micro-optical devices for various purposes. However, one big issue is the shrinking of the structures during polymerization, which results in deviations from the design and in internal stress. While the deviations can be compensated by adapting the design, the internal stress remains and induces birefringence. In this Letter, we successfully demonstrate the quantitative analysis of stress-induced birefringence in 3D direct laser written structures. After presenting the measurement setup based on a rotating polarizer and an elliptical analyzer, we characterize the birefringence of different structures and writing modes. We further investigate different photoresists and the implications for 3D direct laser written optics.
TL;DR: In this paper , the authors investigated the cracks interaction process is accompanied by the deflection of the crack, and the cracks are mainly affected by the shear stress field at the crack tip.
Abstract: 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.
TL;DR: In this paper , the point-wise distribution of the dispersion data of birefringent materials is analyzed using the well-known digital photoelasticity technique, which can be applied to profile the data in three dimensions during static, online, real-time, and dynamic investigations.
Abstract: In this paper, we are presenting a new photoelastic pattern analysis technique to find the point-wise distribution of the dispersion data of birefringent materials. This technique can be applied to profile the dispersion data in three dimensions during static, online, real-time, and dynamic investigations using the well-known digital photoelasticity technique. This method is applied to characterize the dispersion parameters of monofilament isotactic polypropylene fibers. The photoelastic patterns are included for illustration.