Measurement of edge residual stresses in glass by the phase-shifting method

Control and measurement of residual stress in glass is of great importance in the industrial field. Since glass is a birefringent material, the residual stress analysis is based mainly on the photoelastic method. This paper considers two methods of automated analysis of membrane residual stress in glass sheets, based on the phase-shifting concept in monochromatic light. In particular these methods are the automated versions of goniometric compensation methods of Tardy and Sénarmont. The proposed methods can effectively replace manual methods of compensation (goniometric compensation of Tardy and Sénarmont, Babinet and Babinet-Soleil compensators) provided by current standards on the analysis of residual stresses in glasses.     

The measurement of residual stresses by sandwich holographic interferometry

Sandwich holographic interferometry was first proposed by Prof. N. Abramson in 1974. There are many advantages in using this method. One of its most important virtues is that it can compensate for rigid body displacements between the two exposures and is very convenient in practical operation. The authors have already made a detailed theoretical analysis of in-plane and out-of-plane displacements. This paper describes experimental measurements of the residual stresses in welds, by studying the curvature or the second-order derivative of the fringes of in-plane or out-of-plane displacements, using sandwich holographic interferometry. The stresses are obtained quantitatively, and are verified by an experiment involving measurements of the stresses of a flat plate.     

一种新型双间隙输出腔的理论和实验研究

 从双间隙分离腔的色散关系式出发,通过数值计算求出了分离腔中IM₀₁₀模对应的谐振频率,并给出了腔内轴向电场的分布图,证实了分离腔中存在着电场反相的π模场。因此,可以将其用作电场反相的双间隙输出腔,来实现双间障提取。并用2.5维粒子模拟程序——卡拉特（KARAT）程序对这种分离腔输出回路进行了粒子模拟和优化设计。通过详细的冷测和调试实验,研制出了中心频率为3.74GHz、Q_L值为7.8的低Q_L值双间隙输出腔。     

Photodegradation of melanin by an interferometric technique

Photodegradation of melanin thin films is investigated for a UVA wavelength of 355 nm and a UVC wavelength of 244 nm. The technique involves interferometric exposure of melanin with two coherent beams from a low-power UV laser. The periodic photodegradation-grating pattern is monitored by diffraction of a second low-power He-Ne laser. Dependence of the photodegradation rate on UV intensity as well as the effect of ambient humidity is investigated and explained with a simple model. The technique has promise for investigating photo-induced effects in other biomolecular substrates as well.     

Analysis of residual stresses in ternary electroconductive composites

Residual stresses in ceramic particle electroconductive composites were investigated by Raman microprobe spectroscopy and X-ray diffraction. The composites were ternary electroconductive ceramics in the system AlN+SiC+(ZrB₂,MoSi₂). Due to the poor definition of the reinforcing phase peaks, only the matrix residual stress could be evaluated by Raman spectroscopy, whilst the residual stress in the reinforcing phase was calculated by the equilibrium conditions. These calculated values were compared with those experimentally obtained by X-ray diffraction. The agreement between Raman and X-ray results was quite satisfactory. The values of residual stress calculated by the composite theory were in good agreement with those measured by Raman and X-ray diffraction for the MoSi₂-containing composite. For the ZrB₂-containing composite, the value calculated by the composite theory falls between the values measured by Raman and X-ray diffraction. PACS 81.05.Je; 87.64.Je; 87.64.Bx     

Estimate of the cosmic ray background in an interferometric antenna for gravitational wave detection

The effect of the cosmic ray interaction in the masses of an interferometric antenna for gravitational wave (GW) detection is evaluated. In a 3 km antenna this background, mainly due to muons gives a limit, for 1 ms GW pulses, of h∼8.5×10^-23 with a frequency of 2×10^-1 events/year and 8.5×10^-26 with 4.1×10^-6 events/year. For GW having frequency>10 Hz the sensitivity limit is h∼1.7×10^-31. This background seems to allow unshielded operation of the interferometer test masses.     

Evaluation of residual deformations generated by a pulsed ion implanter using interferometric phase measurement

A Fourier transform method of holographic fringe pattern analysis is applied to measure surface residual deformations generated by a pulsed ion implanter. The technique uses a fixture that makes it possible to remove the specimen and put it back into the same position after being implanted. The phase information from interferograms extracted by means of the Fourier transform method is unwrapped using an algorithm based on cellular automata. Results computed from the application of a numerical model are compared with those determined experimentally and a reasonable agreement is obtained.     

残余应力对光弹实验中超声图像的干扰分析

动态光弹成像技术是观测固体内部超声应力场的重要手段,然而样品在制作过程中会产生残余应力,给观测带来一定干扰,特别是缺陷附近的应力集中效应,使得缺陷散射声场的研究更为困难。本文利用线性应力理论分析了超声应力与残余应力的相互关系,并推导出该叠加应力场在光弹系统中的光强表达式,通过实验验证,证明了该理论的可行性。本文结果可为应力集中区域的散射声场分析提供借鉴。     

High level compressive residual stresses produced in aluminum alloys by laser shock processing

Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results for metal surface treatments in underwater laser irradiation at 1064 nm. A convergent lens is used to deliver 1.2 J/cm² in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG, two laser spot diameters were used: 0.8 and 1.5 mm.Results using pulse densities of 2500 pulses/cm² in 6061-T6 aluminum samples and 5000 pulses/cm² in 2024 aluminum samples are presented. High level of compressive residual stresses are produced −1600 MPa for 6061-T6 Al alloy, and −1400 MPa for 2024 Al alloy. It has been shown that surface residual stress level is higher than that achieved by conventional shot peening and with greater depths. This method can be applied to surface treatment of final metal products.     

Monitoring of residual stresses in injection-molded plastics with holographic interferometry

Residual stresses are often trapped in injection-molded plastic parts due to the rapid cooling of the material in this manufacturing process. These stresses are a common source of failure in plastic components in automobiles, appliances and computers and are difficult to measure with conventional residual-stress experimental methods. Real-time holographic interferometry appears to be a viable technique to identify and monitor these stresses in plastic parts. In this investigation, holographic interferometry was used to monitor the relaxation of residual stresses in the plastic-molded actuator arm of a computer hard drive. In the first phase of this study, the relaxation of these residual stresses as a function of temperature was observed. In the second phase, the time to completely relax the residual stresses in the plastic part at an elevated temperature, the annealing temperature, was determined. In the third phase of this investigation, the rate of relaxation of these residual stresses as a function of time at various operating temperatures, was studied. Based on the results of this study, holographic interferometry appears to be a powerful research tool in the study of residual stresses in plastic parts. It also has the potential to be a practical tool for the inspection of manufactured plastic parts for the presence of residual stress.     

Experimental study of three-dimensional residual stresses in rails by moiré interferometry and dissecting methods

Residual stresses in rails produced by rolling cycles are studied by a destructive testing procedure. Thin slices of rails are cut and small grid elements are made by cutting slots onto the surface of the slice. Residual stresses are believed to be released near the surface of the slice when those grid elements have right angles and are sufficiently small. The resulting deformation produced by the stress relief is measured by moiré interferometry. On assuming all strain components be constant along the longitudinal axis of the rail and this axis is one principal direction, three-dimensional strain and stress components are solved.     

Influence of ion bombardment on residual stresses in diamond-like carbon films

The dependence of internal residual stresses in thin diamond-like carbon films grown by the PECVD technique on the most important growth parameters such as the power of the exciting RF discharge and the substrate bias potential is considered. The results have shown that the mechanical stresses in films reach the uppermost value of 1.9 GPa at the smallest values of power and potential. The stress decreases with the growth of both parameters and has only a slight dependence on the film thickness in the range 0.1–1 μm. The bombardment of the obtained films by argon ions with energy of 300 keV and phosphorus ions with energy of 200 keV has resulted in the reduction of compressive stress with the ion dose growth down to its inversion. AFM study of the bombarded films has revealed significant changes in their surface morphology.     

Spatially resolved Raman spectroscopy evaluation of residual stresses in 3C-SiC layer deposited on Si substrates with different crystallographic orientations

Raman scattering studies were performed on hot-wall chemical vapor deposited (heteroepitaxial) silicon carbide (SiC) films grown on Si substrates with orientations of (1 0 0), (1 1 1), (1 1 0) and (2 1 1), respectively. Raman spectra suggested that good quality cubic SiC single crystals could be obtained on the Si substrate, independent of its crystallographic orientation. Average residual stresses in the epitaxially grown 3C-SiC films were measured with the laser waist focused on the epilayer surface. Tensile and compressive residual stresses were found to be stored within the SiC film and in the Si substrate, respectively. The residual stress exhibited a marked dependence on the orientation of the substrate. The measured stresses were comparable to the thermal stress deduced from elastic deformation theory, which demonstrates that the large lattice mismatch between cubic SiC and Si is effectively relieved by initial carbonization. The confocal configuration of the optical probe enabled a stress evaluation along the cross-section of the sample, which showed maximum tensile stress magnitude at the SiC/Si interface from the SiC side, decreasing away from the interface in varied rate for different crystallographic orientations. Defocusing experiments were used to precisely characterize the geometry of the laser probe in 3C-SiC single crystal. Based on this knowledge, a theoretical convolution of the in-depth stress distribution could be obtained, which showed a satisfactory agreement with stress values obtained by experiments performed on the 3C-SiC surface.     

Determination of mechanical stresses in solids by an acoustic method

Different versions of linearized problems of the elastic wave propagation in prestressed bodies are considered. The influence of the version of the linearized elasticity theory chosen for calculating the magnitude of the acoustoelastic effect on the result of calculation is analyzed for longitudinal and shear waves and for Rayleigh surface waves. The results of theoretical calculations are compared with the experiment. Experimental data on the effect of bending stresses on the propagation velocity of Rayleigh waves are presented. These results extend the range of problems that can be solved by using the acoustoelastic effect.     

"Negative" backaction noise in interferometric detection of a microlever

Interferometric detection of mirror displacements is intrinsically limited by laser shot noise. In practice, however, it is often limited by thermal noise. Here we report on an experiment performed at the liquid helium temperature to overcome the thermal noise limitation and investigate the effect of classical laser noise on a microlever that forms a Fabry-Perot cavity with an optical fiber. The spectral noise densities show a region of "negative" contribution of the backaction noise close to the resonance frequency. We interpret this noise reduction as a coherent coupling of the microlever to the laser intensity noise. This optomechanical effect could be used to improve the detection sensitivity as discussed in proposals going beyond the standard quantum limit.     

Optical anomalies and residual stresses in basal-plane-faceted ribbons of Stepanov-grown sapphire crystals

The effects of an anomalous biaxiality and a residual-stress field in basal-plane-faceted single-crystal sapphire ribbons were studied by an optical polarization method using a conoscopic light beam. Formulas that relate the difference between the principal stresses to the angle of optical-axis divergence are obtained. It is shown that the central regions of the ribbons undergo compressive stresses whereas their edges undergo tensile stresses. As compared to block-free ribbons, the stresses in block-containing ribbons increase more intensely with distance from the seed.     

On X-ray measurements of residual stresses in materials with lattice strain gradient

The non-linear distribution of lattice strain ³¹⁰vs sin² observed on the surface of a polished steel specimen can be interpreted by tri-axial stress state with surface components of stress tensor ₁₁(0)= ₂₂(0) and gradientsg ₁₁= ₁₁/T, g ₃₃= ₃₃/T. The distribution of experimental values is duscussed from the viewpoint of various ways of calculating ₁₁.The authors would like to thank Dr. J. Musil, D. Sc. of the Institute of Physics of Czechoslovak Academy of Sciences for kindly providing the samples which made possible this study.     

The minimization of residual stresses in magnetic systems with quasi-force-free current distribution

The feasibility of a magnet experiencing very low mechanical stresses is studied. Megagauss fields can be generated without failure of the solenoid winding and excessively increasing the winding dimensions if the current distribution is force-free in its inner part and the axial current closes in its outer part. The approximation of the quasi-force-free current distribution by discrete conductive layers is considered. Analysis and computations are performed for two force-free winding approximations. In the former case, the conductors are divided into N paired balanced layers where the azimuth and poloidal currents, respectively, pass. The equal and oppositely directed forces arising in the layers of a pair are transferred to insulating spacers between the layers. Stresses in the spacers can be reduced down to values N times as low as the magnetic field pressure B ₀ ² /(2μ₀) at the solenoid axis. If the current direction in each of the layers meets the balance condition, the residual stresses can be N ² times lower than B ₀ ² /(2μ₀), because the tensile and compressive forces in the layers partially cancel.     

Control of temperature field and residual stresses in growing basal-plane-faceted sapphire ribbons

The influence of different heat shielding constructions on the distribution of temperature and thermoelastic and residual stresses in growing basal-plane-faceted sapphire ribbons (Al₂O₃) is studied. It is shown that inclined shields decrease thermoelastic stresses owing to the redistribution of heat fluxes from a heater to a ribbon, which allows growing block-free basal-plane-faceted sapphire ribbons.