红外硫系光学玻璃条纹度测量及表征方法研究

红外硫系光学玻璃属于不透可见光的玻璃材料,采用GB/T 7962不能进行条纹度测试。本文针对上述材料中条纹度难以检测与表征的问题,提出了基于平行光投影法的测试方法,开发了相应测试设备,并对制备的硫系玻璃样品进行了条纹度、灰度及调制传递函数(MTF)测试,研究了灰度和调制传递函数(MTF)的对应关系,提出了用灰度表征条纹严重程度的方法。结果表明:平行光投影法在近红外波段成像能清晰地检测到样品内部条纹缺陷和分布;中红外调制传递函数(MTF)可定性表征样品中条纹对成像质量的影响;条纹度可定量表征样品内部条纹状况,反映对成像质量的影响。为后续该材料的内部质量判定奠定了技术基础。

浮法超薄玻璃的光学性能指标改善

作为电子显示屏的盖板玻璃,光学性能是一项较为关键的品质指标。玻璃的铁含量是影响颜色及透光率的主要因素,需从原料成分粒度控制、配合料均匀性要求、熔窑火焰气氛、熔化及澄清温度场严格要求。玻筋条纹及波纹度都有规范的监测方法和量化指标,现阶段超薄线国内还达不到国际同行业水平;化学成分上的不均和熔窑锡槽横向温度上的不均会对光学均匀性产生影响;熔窑从结构上加强横向对流减少纵向对流,以及采用鼓泡、搅拌利于均化;卡脖水包及流道深度对层流有控制,液面下200 mm是质量较好的玻璃液;浮法成型通过锡槽锡液深度、拉边机、挡旗及电加热分布等控制温差,对光学均匀性有利。

Cracking process of rock mass models under uniaxial compression

Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.

Determination of dynamic modeⅠfracture toughness of rock at ambient high temperatures using notched semi-circular bend method

To investigate the influence of loading rate and high temperature on the dynamic fracture toughness of rock,dynamic fracture tests were carried out on notched semi-circular bend specimens under four temperature conditions based on the split Hopkinson pressure bar system.Experimental and analytical methods were applied to investigating the effect of temperature gradient on the stress waves.A high-speed camera was used to check the fracture characteristics of the specimens.The results demonstrate that the temperature gradient on the bars will not significantly distort the shape of the stress wave.The dynamic force balance is achieved even when the specimens are at a temperature of 400°C.The dynamic fracture toughness linearly develops with the increase of loading rate within the temperature range of 25-400°C,and high temperature has a strengthening effect on the dynamic fracture toughness.

Effect of surface roughness element on near wall turbulence with zero-pressure gradient

In the present paper,we present an investigation on the effect of roughness elements onto near-wall kinematics of a zeropressure-gradient turbulent boundary layer.An array of spanwisely-aligned cylindrical roughness elements was attached to the wall surface to regulate the near-wall low-speed streaky structures.With both qualitative visualization and quantitative measurement,we found that the regularization only occurs in the region below the height of the roughness elements.Statistical analysis on the probability distribution of the streak spanwise spacing showed that the mean spanwise streak spacing is dominated by the roughness elements;however,the latter's effect is in competition with the intrinsic streak generation mechanisms of smooth wall turbulence.Below the top of the roughness elements,local streamwise turbulent fluctuation intensity can be reduced by about 10%.We used POD analysis to depict such regularization effect in terms of near-wall structure modulation.We further found that if the spanwise spacing of roughness elements increased to be larger than the mean streak spacing in the smooth wall turbulence,there is no streak-regularization effect in the buffer region,so that the near-wall streamwise turbulent fluctuation intensity doesn't reduce.

A correction method of color projection fringes in 3D contour measurement

In the three-dimensional(3D) contour measurement,the phase shift profilometry(PSP) method is the most widely used one.However,the measurement speed of PSP is very low because of the multiple projections.In order to improve the measurement speed,color grating stripes are used for measurement in this paper.During the measurement,only one color sinusoidal fringe is projected on the measured object.Therefore,the measurement speed is greatly improved.Since there is coupling or interference phenomenon between the adjacent color grating stripes,a color correction method is used to improve the measurement results.A method for correcting nonlinear error of measurement system is proposed in this paper,and the sinusoidal property of acquired image after correction is better than that before correction.Experimental results show that with these correction methods,the measurement errors can be reduced.Therefore,it can support a good foundation for the high-precision 3D reconstruction.

Analysis of solid particle clusters in coherent structures of turbulent channel flow

A particle-laden turbulent channel flow is investigated to study particle clusters in large-scale turbulent coherent structures. The fluid phase is calculated by large eddy simulation and particles are tracked using Lagrangian trajectory method. The flow Reynolds number is 180 based on the friction velocity and half-width of the channel. The particle is lycopodium with St=0.93 which may well follow the fluid phase. The mean and fluctuating velocities of both two phases are obtained, which are in good agreement with previous data. The strongest accumulations of particles in low-speed streak structures are observed at y~=l 1.3. Moreover, once particles are captured in low-speed streaks, most of them will reside there for a long period. Particles clustered in low-speed streaks obtain smaller instantaneous wall-normal and spanwise velocities than those out of there, which induce a larger particle flux into low-speed streaks than that out of there. The study is important for understanding particle dispersion mechanisms in gas-particle turbulent channel flows.

Simultaneous Force and Temperature Measurement Using Optical Microfiber Asymmetrical Interferometer

A novel optical microfiber asymmetric Fabry-Perot interferometric （MAFPI） sensor is developed for simultaneous measurement of force and temperature. The MAFPI structure is formed by a weak fiber Bragg grating （FBG）, a section of the microfiber, and a cleaved fiber end surface. The narrowband beam reflected from the low-reflectivity FBG and the broadband beam from the Fresnel reflection interfere lead to its unique sensing performance. The force sensing is performed by detecting the bending-loss induced fringe contrast changes, while the Bragg wavelength shift is employed for temperature measurement. Sensitivities of 9.8pm/℃ and 0.025dB/μN were obtained experimentally for temperature and force measurements, respectively.

Nonlinear vibration of edged cracked FGM beams using differential quadrature method

This paper investigated the nonlinear vibration of functionally graded beams containing an open edge crack based on Timoshenko beam theory.The cracked section is modeled by a massless elastic rotational spring.It is assumed that material properties follow exponential distributions through the beam thickness.The differential quadrature(DQ) method is employed to discretize the nonlinear governing equations which are then solved by a direct iterative method to obtain the nonlinear vibration frequencies of beams with different boundary conditions.The effects of the material gradient,crack depth and boundary conditions on nonlinear free vibration characteristics of the cracked FGM beams are studied in detail.

Transport of Cu-H2O nanofluid through a channel with wavy walls under velocity slip and connective boundary conditions

Present study examines the mixed convective peristaltic transport of Cu-H2O nanofluid with velocity slip and convective boundary conditions. Analysis is performed using the two-phase model of the nanofluid. Viscous dissipation and heat generation/absorption effects are also taken into account. Problem is formulated using the long wavelength and low Reynolds number approach. Numerical solutions for the pressure rise per wavelength, pressure gradient, axial velocity, temperature and heat transfer rate at the boundaxy are obtained and studied through graphs. Results show that the area of peristaltic pumping decreases with an increase in the nanoparticles volume fraction. Increase in the velocity slip parameter shows an increase of the pressure gradient in the occluded part of the channel. Further, addition of copper nanoparticles reduces both the axial velocity and temperature of the base fluid. Temperature of the nanofluid also decreases sufficiently for an increase in the value of Blot number.