Contact-Induced Static Fatigue of Annealed and Tempered Glass

The role of environmentally assisted crack growth in the contact-induced strength degradation of brittle surfaces was studied. Indentation fracture mechanics, incorporating a standard crack-velocity function, are used to predict remaining strength as a function of contact load and duration. Strength tests on annealed and tempered glass disks, indented with a diamond pyramid or tungsten carbide sphere in a water environment, are in accord with the predicted degradation characteristics. The results indicate that fatigue effects are likely to be of only secondary importance in designing for maximum resistance to in-service contact damage.     

Spherical Indentation and Fracture of Glass Plates

Spherical indentation of thick and thin glass plates was investigated numerically and experimentally. The energy release rate at the tip of a cone crack was calculated by using finite element techniques and used to investigate the applicability in thick plates of Roesler's law relating the cone crack radius to the indentation load. Indentations of thin glass specimens resting on different substrates were also studied numerically and experimentally. The stresses in the thin specimens were calculated and correlated with the observed failures. On the basis of these results, a crack initiation mechanism map was developed for glass specimens on different substrates.     

Strength Degradation of Thermally Tempered Glass Plates

An earlier theory of contact-induced strength degradation of brittle materials is extended to include plates in residual surface compression. The scale of the strength-controlling flaw is predicted by indentation fracture mechanics, with the modifying effect of the residual field incorporated into both indentation and strength equations. Experimental verification of the predictions is obtained from diamond-pyramid indentation tests on thermally tempered glass plates. As with untempered plates, the theory accounts for the load dependence of the strength loss; it also explains the insensitivity of the degradation characteristics to initial flaw distribution and identifies toughness as the controlling material parameter. Most significant, however, is the demonstration that surface strengthening can produce dramatic improvements in degradation resistance. The possibility of obtaining all parameters necessary for a complete degradation analysis of a given tempered inaterial entirely by routine indentation/strength testing is discussed.     

Conical-Indenter Penetration Viscometry on Thin Glass Plates

A method is proposed for calculating the viscosity of glasses from the rate of penetration of a conical indenter into thin samples with a thickness of 0.11–4.00 mm under conditions of continuous heating at a rate ranging from 1 to 10 K/min and an indenter loading in the range from 300 to 20 g. This method makes it possible to measure the viscosity of glasses in the range 10¹²–10⁷P for samples in the form of plates 0.13–0.18 mm thick with an error of no more than ±0.2log(, P). The described variant of the indentation method requires the preliminary calibration against a reference (standard) glass; i.e., it is a relative method. This method can be successfully used for determining the viscosity of easily crystallizing glasses.     

Acoustic Emission in the Fracture of Glass Plates

The ring-down counting method was used to measure acoustic emission (AE) during the subcritical cracking of float-glass plates. It was found that AE emanated primarily from surface flaws and that a flaw =4 μm deep was capable of producing one AE count. The dependence of AE count rate on experimental parameters such as system gain and specimen size was determined and the use of AE simulators for calibrating AE systems was examined. The results were used to show how data on different ceramic materials might be compared.     

Failure Waves in Glass

Failure waves have been recently observed in glass plates and rods struck by high-speed projectiles. These waves propagate into material that has been prestressed by a compressive shock. The wave propagation speed exceeds the maximum crack speed and is not constant. Behind the failure wave there is a total loss of tensile strength and a substantial drop in shear strength. The failure is explosive, leading to radial expansion in unconfined targets and presurization in confined targets.     

Nondestructive Heat-Treatment Regimes for Glass and Ceramic Plates

Unilateral heating of a glass or ceramic plate freely fixed along its contour by a surface source is considered in the context of a quasistatic non-coupled problem. An analytical relationship is obtained, which is a criterion of thermal strength of the plate and allows for identifying nondestructive treatment regimes. It is shown that for many materials there is a range of Fourier number variations in which the plate under treatment can be destroyed by thermoelastic stresses.     

Surface Sintering of Porous Glass Plates under Laser Radiation

The kinetics of surface sintering of flat plates of the 96SiO₂ · 3.8B₂O₃ · 0.2Na₂O (mol %) porous glass exposed to CO₂ laser radiation is investigated under conditions when either the irradiation time is varied at a constant radiation power density or the radiation power density is varied at a constant irradiation time. It is established that the irradiation time is the most appropriate controlled parameter in the process of sintering. A decrease in the thickness of the porous layer sintered on the plate surface is accompanied by an increase in the radii of curvature of the interfaces of this layer.     

Calculation of Temperature Distributions in Glass Plates Undergoing Heat-Treatment

A method is presented for calculating temperature distributions in diathermanous sheets that are being heated or cooled. It differs from previous calculations of this type in that it takes a more comprehensive account of radiative effects that play a part in these processes. Principally, these effects are the penetration of external radiation into the sheet, the emission and partial re-absorption of radiation within the sheet, and multiple internal reflection between the surfaces of the sheet. A high-speed digital computer has been programmed to perform these calculations. The results of a few representative examples are presented to illustrate the influence of diathermancy on the thermal history of glass plates undergoing various heat-treatments.     

Failure of Glass with Subthreshold Flaws

Conventional postthreshold crack analysis cannot be used to predict the strength and fatigue behavior of glass with subthreshold flaws. Therefore, a fracture mechanics model for failure of glass with subthreshold indentation flaws was developed. This model accounts for both the near- and farfield residual stresses associated with the indentation impression. It is shown that these stresses play a major role in the initiation and subsequent propagation of cracks that eventually cause failure. The model predicts "pop-in" of a well-developed crack and failure under continuous and discontinuous crack growth in both inert and fatigue conditions. The results of experiments with bare fused silica fibers with indentation subthreshold flaws in inert and fatigue (water) environments were in good agreement with the predictions by the model.     

Analysis of Localized Impact Damage in Biaxially Stressed Glass Plates

A fracture mechanics method was used to estimate the impact loads necessary to cause penetration of damage to various depths in glass plates stressed biaxially to several levels. Velocities of glass spheres necessary to obtain these impact loads were calculated using Hertzian theory. Penetrations estimated for given impact velocities were compared with experimental values; those resulting from impacts on compressively stressed surfaces were much smaller than those caused by impacts on tensile surfaces.     

Nondestructive Methods in Laser Treatment of Glass and Ceramic Plates

One-sided heating of a plate freely fixed along its contour by a volume source is considered in the context of a quasistatical disjoint thermoelasticity problem. An analytical relationship is obtained, which is the criterion of the thermal strength of the plate, making it possible to identify nondestructive laser treatment regimes, as well as the thermal strength of existing and newly developed materials. An experimental verification of the adequacy of the proposed model is performed.     

浅谈平板显示器用玻璃基板的生产

介绍了平板显示器用玻璃基板的特点（简称“FPD”玻璃),如液晶显示器玻璃,等离子显示器玻璃等。重点探讨了组分及生产工艺,同时阐述了其应用前景。     

用粉煤灰生产建筑装饰用微晶玻璃板材

对粉煤灰进行适当处理后按一定技术工艺过程 ,生产高附加值新材料产品—建筑装饰用微晶玻璃     

Stress Analysis of Large Deflection of Glass Plates by the Finite-Element Method

A computer program is used in analyzing stress and deflection characteristics of plates undergoing large deflection. Experimental data were obtained for glass plates with different area, aspect ratio, and thickness subjected to simulated windload. The theoretical predictions and test data are correlated herein and show excellent agreement.     

Measurement and Prediction of the Dynamic Temperature Distributions in Soda-Lime Glass Plates

Experimental measurement of the dynamic internal temperature distribution in soda-lime glass plates using thermocouples fused in the glass has been carried out. Experimentally measured temperatures are compared to predictions obtained from the solution of the transient energy equation where the internal radiative transfer has been accounted for using rigorous radiative transfer theory. A discussion of the experimental method, the process used to fuse the thermocouples in the test plates and the rigorous formulation of the energy equation, for semitransparent materials is given. Predicted and measured instantaneous surface temperatures are compared and very good agreement is obtained. It is also concluded that the empriical equation for the phonon conductivity used in the analysis underpredicts the conductivity. A 20% increase in phonon conductivity is shown to significantly improve the agreement between measured and predicted centerline to surface temperature differences.     

板式换热器不锈钢板片失效分析

利用光学显微镜、扫描电镜、电子能谱等测试手段,从材料成分、微观组织、断口形貌以及腐蚀产物成分等角度,分析了板式换热器不锈钢板片穿孔泄漏的原因。结果表明,不锈钢板片失效的主要原因是氯离子引起的点腐蚀和缝隙腐蚀所致。