Photoelastic Constants Research Articles

Determination of Stress Values Based on Calculation of Photoelastic Constants on the Example of the Sub-Frame Connection with the Hull in a Small Training Aircraft

Abstract The above paper presents the example of sub-frame connections with the hull in a small training aircraft and the results of the analysis of a selected connection using the method of reflected light. The connection model was subjected to the loads similar to those existing in a structure using various materials of the connection. Thus, photoelastic deformation image, showing the load applied on the joint was obtained. Then, for the materials used in the model, photoelastic constants were determined, which were used to estimate the stress values in the model. The analysis allowed us to determine the effect of kind and features ( mainly hardness) of the used material pads, on mechanical behavior of the elements of joint.

Temperature Dependence of Photoelastic Effect in KTa1-xNbxO3 Crystals and Investigation of Its Origin

The temperature dependence of the photoelastic effect in KTa1-xNbxO3 crystals was evaluated by measuring the elastic stiffness coefficient c11 and the change in the refractive index with stress. The elastic stiffness coefficient c11 was measured by using an ultrasonic thickness gauge and the change in the refractive index with the stress was measured by using a Mach–Zehnder interferometer. By considering the effect of the increased departure from the Curie–Weiss law with stress, we succeeded in obtaining a theoretical fit with the measured temperature dependence of the photoelastic effect. The temperature dependence of the photoelastic constant was described by combining the effects of the thermal fluctuation of the ionic and electronic polarizations and the effect of the local polarization.

Ab-initio calculations of the photoelastic constants of the cubic SiC polytype

Residual defects after growth of semiconductors crystals is a hot issue to be solved for manufacturing new efficient electronic or optic devices. These defects can be conveniently observed using birefringence optical microscopy for extended defects that will create a local strain field which in turn can cause a nominally isotropic optical material to become anisotropic and induce birefringence. In order to perform a quantitative analysis, the knowledge of the photoelastic constants (Pij) of the material that measure the strength of the change of the refractive index under application of strains or stresses is necessary. As an experimental determination of the whole set of constants is not always possible, a theoretical evaluation can be of valuable interest. In this work, we propose ab-initio calculations by the WIEN2k program of the optical properties of the zinc blende silicon carbide polytype with a self-consistent scheme by solving the Kohn-Sham equations using a full potential linearized augmented plane waves (FPLAPW) method in the framework of the density functional theory (DFT) along with the generalized gradient approximation (GGA) pseudo-potentials. A combination of specific compressive and tensile strains is applied to the two atoms unit cell and the tensor containing each specific combination of the Pij constants is extracted.

A simple approach to photoelastic calibration of glass using digital photoelasticity

Quantification of residual stresses in glass articles necessitates the knowledge of photoelastic constant of the glass material. The recent developments in digital photoelasticity have increased its applicability in residual stress analysis of glass. In this paper, photoelastic calibration of the glass material has been performed using the carrier fringe method (CFM) and phase shifting technique (PST) in digital photoelasticity. The retardations measured by both of these techniques are used for the calculation of photoelastic constant of the glass material and they were found to be in good agreement with each other. Calibration of glass by CFM is recommended for industrial applications since it requires only a few images as compared to PST.

The Brillouin gain coefficient of Yb-doped aluminosilicate glass optical fibers

Provided herein is a detailed analysis of the Brillouin spectroscopy of the ytterbia (Yb2O3) dopant in aluminosilicate glass optical fibers. Yb-doped fiber lasers have become ubiquitous, and the results presented here may be used to design lasers and amplifiers for narrow linewidth systems and applications. It is found, with a high degree of certainty, that Yb2O3 has an acoustic velocity that is lower than that of silica, a Brillouin spectral width (or material acoustic damping coefficient) that is about 80 times greater than that of silica, and photoelastic constants (Pockels’ coefficients) that are negative. It is found that the primary influence of ytterbia in concentrations typical of active fibers is to broaden the Brillouin gain spectrum, thereby reducing the peak Brillouin gain. A set of design curves is provided outlining the Brillouin gain coefficient as a function of alumina concentration for several ytterbia concentrations, which can be utilized to design fiber structures with reduced Brillouin gain. The Yb-doped aluminosilicate fiber system is compared to the Yb-doped phosphosilicate system, and a high degree of similarity is found between them at low Al2O3 or P2O5 doping levels. However, for fiber produced utilizing conventional techniques, the phosphosilicates are found to have the potential for lower Brillouin gain since more P2O5 can be reliably incorporated into the glassy matrix.

Pockels’ coefficients of alumina in aluminosilicate optical fiber

The photoelastic constants of the alumina component in aluminosilicate optical fibers are evaluated and determined to be p11=−0.237±0.020 and p12=−0.027±0.012, thus confirming that the low and negative pij characteristics of bulk alumina are conserved as part of a binary aluminosilicate glass system in optical fiber form. In order to enumerate these values, the strain- and stress-optic coefficients of two fibers (one with an aluminosilicate core and one with a pure silica core) were measured by applying mechanical tension or twist, respectively, to the fibers and measuring changes to an optical system as a function of the mechanical deformation. In the former, the strain-optic coefficient (eOC) is measured directly by recording changes to the free spectral range of a ring fiber laser. In the latter, the stress-optic coefficient (σOC) is found by measuring the change in polarization angle after linearly polarized light propagates through a segment of twisted test fiber. To the best of our knowledge, this is the first such measurement of its type, i.e., the retrieval of the component photoelastic constants, with their signs, of a multicomponent glass. Binary glass compositions wherein the constituents have opposite signs of the photoelastic constant (such as the aluminosilicates) have the potential to give rise to extremely low values of the Brillouin gain coefficient.

G031033 液晶ディスプレイを利用した光弾性実験([G031-03]材料力学部門,一般セッション : 画像,計測)

This paper aims to analyze stress by a simple photoelastic experiment with liquid crystal display (LCD). First, we investigated angle of the Principal surface of polarization plate in LCD. Second, fringe of acrylic rod which was subjected to static four-point bending loading was observed by the simple photoelastic experiment with LCD and linear polarization plate only. The photoelastic constant was then measured. As the results, isochromatic lines were only seen at area acting maximum stress. The photoleastic constant value measured from the isochromatic lines was good agreement with that of acrylic.

Four-wave mixing spectroscopy of the photo-elastic scattering resonance in Nd:YVO4 crystal

A new method of non-linear laser spectroscopy based on four-wave scattering of pump laser radiation into the probe laser cavity is suggested and realized. As a result of intracavity amplification there is an opportunity to investigate weak narrow resonances of different types including the resonances of photo-elastic scattering in optical materials and laser crystals. A theory describing this phenomenon is suggested and experiments with narrowband (1 MHz linewidth) tunable continuous-wave diode laser were carried out. It is shown that the four-wave scattering of pump laser radiation into the cavity of the probe laser can be used for measurement of dispersion of photo-elastic constants in solid and liquid dielectrics.

Zero photoelastic zinc tin phosphate glass without lead oxide

The photoelastic constant (PEC) is evaluated for 15 zinc tin phosphate glasses in a series of xZnO-(67-x)SnO-33P(2)O(5) where x is 0-30 mol. % at 0.5-7 mol. % intervals. The phase retardation of polarized light, passing through a disk sample with applying various uniaxial loads, was measured for PEC determinations by using a frequency stabilized transverse Zeeman He-Ne laser as a polarized light source. The substitution of ZnO for SnO results in the increase of PEC from negative to positive values in the range of -1.43 and +1.45×10(-12) Pa(-1). The minimum PEC value of 0.04±0.02×10(-12) Pa(-1) was experimentally obtained in the 18.5 mol. % ZnO-48.5 mol. % SnO-33 mol. % P(2)O(5) glass.

Photoelastic lensing effect in Ti:sapphire crystal pumped by high-energy pulses

We have built a setup with high temporal resolution to measure the very fast photoelastic lensing effect, which is on the scale of microseconds in a Ti:sapphire crystal pumped by very strong laser pulses (up to 5 J/cm2). The experimental results measured by this method and the real multimode beam profile taken by a CCD camera are applied to a three-dimensional crystal model to calculate one of the photoelastic constants of Ti:sapphire crystal, which is found to be p31=-0.03±0.01. This value is helpful to evaluate the photoelastic lensing effect in Ti:sapphire crystal for a laser beam polarized along the c axis, commonly used for laser amplification.

Theory of coherent generation and detection of THz acoustic phonons using optical microcavities

The coherent generation and detection of acoustic phonons in a superlattice embedded in an optical microcavity is theoretically analyzed. In this optical resonator, femtosecond light pulses can be spatially confined and amplified. We show that the acoustic phonon generation is enhanced as the intensity of the incident electromagnetic field is amplified in resonance with the optical microcavity. The detection process is also enhanced by the optical resonator. In the case of real photoelastic constants the maximum sensitivity occurs when the probe wavelength is tuned to where the derivative of the reflectivity has its maxima, at the optical cavity mode edges. We also analyze the role of the imaginary part of the photoelastic constants of the structure in the generation and detection processes. Finally, we study the enhancement efficiency of the microcavities when the coherent generation and detection are optimized simultaneously; we estimate phonon signals up to six orders of magnitude higher than the ones obtained with the superlattice without optical confinement.

Photo-elastic properties of the wing imaginal disc of Drosophila

In the study of developmental biology, the physical properties and constraints of the developing tissues are of great importance. In spite of this, not much is known about the elastic properties of biologically relevant tissues that are studied in biology labs. Here, we characterize properties of the wing imaginal disc of Drosophila, which is a precursor organ intensely studied in the framework of growth control and cell polarity. In order to determine the possibility of measuring mechanical stresses inside the tissue during development, we quantify the photo-elastic properties of the tissue by direct mechanical manipulation. We obtain a photo-elastic constant of 2 x 10(-10) Pa(-1).

Brillouin spectroscopy of YAG-derived optical fibers

We present Brillouin spectroscopy of YAG-derived optical fibers. It is found that the addition of yttria and alumina both tend to raise the acoustic velocity when added to silica, with the change due to yttria being much weaker. The temperature-dependence of the Stokes's shift in the YAG-derived fibers is also measured, disclosing a lesser temperature dependence than conventional Ge-doped fibers. These fibers are found experimentally to have a substantially larger acoustic attenuation coefficient relative to that of bulk silica, and assuming a photoelastic constant of amorphous YAG similar to that of pure crystalline YAG, a much-reduced Brillouin gain coefficient as a result. A 40 weight percent yttria and alumina fiber has a Brillouin gain coefficient estimated to be roughly one sixth of pure silica. We also show that the addition of Er to the YAG-derived system decreases the acoustic velocity and broadens the Brillouin spectrum.

Characterization of the Residual Stress State in Commercially Fully Toughened Glass

Toughened glass is often used in load carrying elements due to the relatively high tensile strength compared with float glass. The apparent tensile strength of toughened glass is a combination of the pure material strength and the residual stresses imposed by the toughening process. This paper is concerned with an experimental characterization of the residual stress state for toughened glass. Results for the variation of residual stresses within 32 square specimens with a side length of 300 mm are investigated. The specimens varied in thickness and one group was glass with low iron content. The photoelastic constant was estimated from a four-point bending test. The experimental results revealed large variations in the residual stress state within each specimen and between groups of different thicknesses. The results are compared with a nonstandard fragmentation test, showing that the fragment size does not seem to be dependent on the local variations of the residual stress state in a specimen.

Photo-elastic Constant of Silica Fibers at Visible Wavelengths

In this paper, we measured the photo-elastic constant of silica-fibers as a basic constant of silica fibers for a wavelength range of λ =0.4 μm ∼ 0.65 μm (visible wavelengths). Previously, we measured stress-induced time of flight variations for λ =0.7 μm ∼ 1.7 μm and we evaluated the photo-elastic constant for these wavelengths. Recently, photonic crystal fibers (PCFs) have been devel- oped and they have an endlessly single mode property. With these fibers, wide wavelength ranges may be used in future. For this purpose, it is very important to evaluate the photo-elastic constant at visible wavelengths. For measurements, the phase method was used to detect phase changes of intensity-modulated wave propagating in a graded-index fiber with and without stress. Combined with the previously measured data for λ =0.7 μm ∼ 1.7 μm, we evaluate the photo-elastic constant of silica- fibers for wavelength ranges of λ =0.4 μm ∼ 1.7 μm.

Automatic evaluation of photoelastic fringe constant by the nonlinear least-squares method

A nonlinear least-squares method was applied to determine the photoelastic fringe constant from isochromatic phase field obtained by digital phase-shifting photoelasticity. To perform automatic evaluation, not only the photoelastic fringe constant but the center coordinates of a disk under diametral compression are also determined simultaneously using the nonlinear least-squares method. A set of over-determined nonlinear equations is obtained to estimate the unknown parameters by an iterative procedure based on Newton–Raphson method. Simulation and experimental results show that the parameters are evaluated accurately from the isochromatic phase field obtained from the phase-shifting photoelasticity. The photoelastic fringe constant and the disk center coordinates can be evaluated easily, simply and automatically by the technique.

Investigation of Thermal Properties of Heavily Doped 4H-SiC Crystals by a Picosecond Transient Grating Technique

We applied a picosecond dynamic grating technique for investigation of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped 4H-SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier absorption at excitation by an IR picosecond laser pulse (1064 nm) and subsequent carrier thermalisation. Decay of dynamic grating at its various periods and sample temperatures was monitored at 532 nm wavelength. The thermal diffusivity DT = 0.94 cm2/s, thermo-optic coefficient dn/dT = 3.610–5 K-1 and effective photoelastic constant = – 0.10 were determined at 300 K. DT value increased at lower temperatures and saturated below 100 K. Temperature dependences of thermo-optic coefficient and thermal expansion were found in good correlation with heat capacity peculiarities.

Application of a time-resolved four-wave mixing technique for the determination of thermal properties of 4H–SiC crystals

We applied a time-resolved four-wave mixing technique for the determination of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped n-type and p-type 4H–SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier excitation using a light-interference pattern at 1064 nm and subsequent carrier thermalization. Decay of the light-induced thermal grating at its various periods and sample temperatures was monitored by diffraction of a delayed probe pulse at 532 nm wavelength. The grating decay kinetics provided the thermal diffusivity DT = 0.94 cm2 s−1, thermo-optic coefficient dn/dT = 3.6 × 10−5 K−1 and effective photoelastic constant at 300 K. Temperature dependences of dn/dT and thermal expansion almost matched that of the heat capacity, Cp(T), and correlated well with the Eg(T) dependence.

Investigation of a mercurous chloride acousto-optic cell based on longitudinal acoustic mode

A number of spectral imagers using acousto-optic tunable filters (AOTFs) operating from the UV to the longwave infrared (LWIR) using KDP, MgF(2), TeO(2), and Tl(3)AsSe(3) crystals to cover different spectral regions have been developed. In the LWIR there is a lack of high quality acousto-optic (AO) materials. Mercurous halide (Hg(2)Cl(2) and Hg(2)Br(2)) crystals are highly anisotropic with a high AO figure of merit due to slow acoustic velocities and high photoelastic constants and are transparent over a wide spectral region from 0.35 to 20 mum for Hg(2)Cl(2) and from 0.4 to 30 mum for Hg(2)Br(2). AO modulators, deflectors, and AOTFs based on these crystals can operate over a wide spectral range. Single crystals of these materials are being grown and some prototype devices have been fabricated. Results are presented from device characterization for an AO cell fabricated in Hg(2)Cl(2) based on longitudinal acoustic mode propagation. This device was very useful in demonstrating the AO interaction as well as soundness of the transducer bonding technique. Acoustic phase velocity is calculated and measured, diffraction efficiency is obtained from experiments, and the AO figure of merit of the sample is evaluated.

The existence of five-wave non-collinear acousto-optical weakly coupled states

Five-wave Bragg solitary waves in the form of weakly coupled states, occurring within a four-order non-collinear scattering of light by acoustic waves in an optically anisotropic crystal, are identified and investigated. Generally, we study this phenomenon in an arbitrary regime with the phase, i.e. frequency-angular, mismatches, while, for simplicity's sake, the exact conditions appearing of localization for multi-pulse coupled states is illustrated in a regime of the phase synchronism. The spatial-frequency distributions of the optical components inherent in these solitary waves are investigated theoretically, simulated numerically and observed experimentally in a tellurium dioxide crystal. Much attention is given to the analysis of contributions conditioned by the effect of optical activity in a tellurium dioxide crystal of chosen orientation. The performed analysis makes it possible to estimate the effective photo-elastic constants for both normal and anomalous processes of light scattering rather accurately and, in so doing, to match theoretical estimations for the efficiency of multi-order acousto-optical interaction with the experimental results obtained.