Crack Initiation by Indentation Fatigue in Lead Alkali and Soda–Lime Glass

An indentation technique using a conventional Vickers microhardness tester was used to evaluate fatigue properties of lead-alkali and soda-lime silica glasses. The specimens were indented repeatedly at the same point with subcritical loads until radial cracks were initiated. The number of cycles to initiate the cracks at different subcritical loads demonstrated typical fatigue curves for both glasses. The uniqueness of the experiment was that the diagonal lengths of the deformed cavity were observed to increase with the number of cycles. This increase of the deformed cavity for a certain number of cycles prior to the visibility of crack initiation was analyzed, correlating the elastic-plastic phenomenon and the accumulation of the residual stress in each cycle.     

Controlled Crack Shapes for Indentation Fracture of Soda–Lime Glass

Radial cracks for indented soda–lime glass aged in distilled water were highly elliptical because of truncation by lateral cracks. Indentation in silicone oil minimized radial/lateral crack interaction but still produced cracks having nominally constant ellipticity during bend testing. Analysis of applied stress/indentation crack length data using stress intensity factors based on half-penny crack shape resulted in apparent R -curve behavior and/or overestimation of the fracture toughness. Incorporation of elliptical shape factors eliminated the R -curve behavior and reduced measured toughness to near the accepted value for soda–lime glass.     

In Situ Cube-Corner Indentation of Soda–Lime Glass and Fused Silica

Indentation fracture with a cube-corner diamond pyramid on soda–lime silicate glass and fused silica is investigated during the entire indentation cycle in both silicone oil and ambient-air environments. Radial cracks form immediately on loading in all cases. The two-component, elastic-contact + elastic-plastic mismatch (residual) stress field model that has been used successfully to describe radial crack evolution at Vickers indentations fails to describe the fracture response with the cube-corner. The amplitudes of both elastic-contact and residual stress-intensity factors as deduced from these cube-corner experiments are up to a factor of 10 greater than have been previously observed.     

Indentation-Cycling Tests on Soda–Lime Glass

Repeated indentation loading produces lateral-crack-controlled chipping in brittle materials. This has been investigated in soda–lime glass for a load-cycling range P _min < P _max≤ P , where P is the indentation load. Extensive chipping damage occurs after a critical number of cycles for P _max= P and P _min= 0, whereas subcritical cycling with P _min > 0 suppresses the failures. This is consistent with an environmental interaction. Postcycling aging can produce delayed chipping, and the response depends upon the load-cycling history.     

Lead-Ion Stability in Soda–Lime Lead Silicate Glasses

Sodium-calcium-lead silicate glass compositions were prepared over a wide compositional range by conventional glass-melting methods. The acid chemical stability of the glass structure was studied by corroding samples of glass in 4% acetic acid solution at 22°C for periods up to 24 h. Lead corrosion stability was evaluated by measuring lead concentrations in the corrosion solution. At short times, parabolic time dependence was observed and the parabolic time coefficients were regressed against composition, yielding a simple additive relationship. A similar model was fitted to 24-h release data, which showed compositional effects similar to the 2-h data. Of the oxides studied, sodium was the most detrimental to durability, and the coefficients of the oxides decreased in the series: Na₂O, PbO, CaO, SiO₂. The effects of the oxides could be partially explained by the number of nonbridging oxygens expected in the glass structure, and the residual effect was attributed to cation characteristics. Small phosphate additions to the glass greatly increased the lead-ion stability under nearly all experimental conditions examined.     

Crack-Tip Structure in Soda–Lime–Silicate Glass

The topology of crack tips in soda–lime–silicate glass was investigated using atomic force microscopy (AFM). Studies were conducted on cracks that were first propagated in water and then subjected to stress intensity factors either at or below the crack growth threshold. Exposure to loads at the crack growth threshold resulted in long delays to restart crack growth after increasing the stress intensity factor to higher values. After breaking the fracture specimen in two, the "upper" and "lower" fracture surfaces were mapped and compared using AFM. Fracture surfaces matched to an accuracy of better than 0.5 nm normal to the fracture plane and 5 nm within the fracture plane. Displacements between the upper and lower fracture surfaces that developed after a critical holding time were independent of distance from the crack tip, and increased with holding time. Despite the surface displacement, crack tips appeared to be sharp. Results are discussed in terms of a hydronium ion–alkali ion exchange along the crack surfaces and corrosion of the glass surface near the crack tip by hydroxyl ions.     

Mechanism of Mechanical Strength Increase of Soda–Lime Glass by Aging

Two models have been proposed to explain the mechanical strength increase of abraded or indented soda–lime glasses upon aging, namely, crack tip blunting and the release of residual tensile stress near the crack tip. To clarify the mechanism, the time dependence of the strengthening of an abraded soda–lime glass was investigated. Effects of aging media, such as moist air, distilled water, 1 N HCI and 1 N NaOH solutions, as well as the abrasion flaw depth, were determined. The strength increase rate in water of abraded soda–lime glass was compared with those of borosilicate and high-silica glasses. The effect of stressing during aging was also investigated. It was found that the rate of strength increase was faster with decreasing abrasion flaw depth and with decreasing chemical durability. For a given flaw depth, an acidic solution produced the fastest strengthening. The strengthening rate was found to accelerate because of the "coaxing'effect of stressing during aging. From these observations, it was concluded that the strengthening rates relate to the diffusion process and chemical reactions, especially the alkali–hydrogen (or hydronium) ion-exchange reaction, near the crack tip. The role of the residual tensile stress appears to be similar to that of the applied tensile stress, helping the diffusion process near the crack tip. The observed strength increase of soda–lime glass by aging was thus attributed to the effective blunting of the crack tip geometry by the glass–water reaction.     

Subcritical Crack Growth in Soda–Lime Glass under Mixed-Mode Loading

Subcritical crack growth in glasses and ceramics has been studied extensively under Mode I loading. In this study, subcritical crack growth in soda–lime glass under mixed-mode loading has been determined, using the double cleavage drilled compression (DCDC) specimens with a hole offset from the center line. With this test configuration, cracks are nucleated at the pole of the hole and propagated parallel to the centerline of the specimen under mixed-mode loading. Under mixed-mode loading, subcritical-crack-growth rates are significantly less than those under Mode I loading at the same energy-release rates. Possible mechanisms for this increased resistance to subcritical crack growth under mixed-mode loading are discussed.     

Thermal Analysis of Reactions in Soda–Lime Silicate Glass Batches Containing Melting Accelerants: II, Multicomponent Systems

The glass melting reactions in a multicomponent system (sand–soda ash–calcite–dolomite–feldspar) were studied using data from DTA, TGA, and XRD interactively. The first-formed liquid phase occurred at 700°C from eutectic melting among CaCO₃, Na₂CO₃, and MgO. Further liquid phase formed at the CaCO₃–Na₂CO₃, eutectic at 785°C and a fusion reaction among SiO₂, CaO, and the molten phase at 812°C. Reactions between molten soda ash and silica grains to form a sodium disilicate coating also occurred in this temperature range. The effects of reaction accelerant additions (Na₂SO₄, NaNO₃, NaCI) on batch fusion were analyzed. Sodium chloride was found to be the most effective melting accelerant due to the formation of a NaCI–Na₂CO₃ eutectic liquid phase at ∼636°C, which effectively attacked the silica relic. CO₂ gas release terminated ∼80°C earlier with 1 wt% NaCI additions to the base glass.     

Thermal Analysis of Reactions in Soda–Lime Silicate Glass Batches Containing Melting Accelerants: I, One- and Two-Component Systems

To identify each glass melting reaction in a multicomponent system, one-component and two-component reaction processes were studied using DTA, TGA, and XRD. Two-component mixtures were prepared by choosing pairs in the same ratio as in a commercial container glass batch composition (sand-soda ash-calcite-dolomite-feldspar). The presence of silica in the silica-calcite system decreased the termination temperature of the decomposition of calcite, but did not alter the onset of decomposition. Similar behavior was found in the dolomite-silica system. A double carbonate (Na₂Ca(CO₃)₂) formed via solid-state reaction in the calcite-soda ash system, and metasilicate/disilicate phases were detected during the fusion process in the soda ash-silica system. The effects of reaction accelerant additions in the soda ash-silica system were investigated using 1 wt% additions of sodium sulfate, sodium nitrate, and sodium chloride. Sodium chloride was the most effective melting accelerant, lowering the termination temperature of CO₂ release by ∼80°C compared with the soda ash-silica system with no additives. NaCl additions caused complete reaction and/or fusion of Na₂CO₃ prior to its melting temperature. Sodium sulfate additions acted to suppress metasilicate/ disilicate formation by coating quartz grains and shifted consequent CO₂ release to higher temperature.     

Crack Growth in Soda–Lime–Silicate Glass near the Static Fatigue Limit

The atomic force microscope (AFM) was used to explore the nature of features formed on the surfaces of cracks in soda–lime–silicate glass that were held at stress intensity factors below the crack growth threshold. All studies were conducted in water. Cracks were first propagated at a stress intensity factor above the crack growth threshold and then arrested for 16 h at a stress intensity factor below the threshold. The stress intensity factor was then raised to reinitiate crack growth. The cycle was repeated multiple times, varying the hold stress intensity factor, the hold time, and the propagation stress intensity factor. Examination of the fracture surface by optical microscopy showed surface features that marked the points of crack arrest during the hold time. These features were identical to those reported earlier by Michalske in a similar study of crack arrest. A study with the AFM showed these features to be a consequence of a bifurcation of the crack surface. During the hold period, waviness developed along the crack front so that parts of the front propagated out of the original fracture plane, while other parts propagated into the plane. Crack growth changed from the original flat plane to a bifurcated surface with directions of as much as 3° to 5° to the original plane. This modification of crack growth behavior cannot be explained by a variation in the far-field stresses applied to the crack. Nor can the crack growth features be explained by chemical fluctuations within the glass. We speculate that changes in crack growth direction are a consequence of an enhancement in the corrosion rate on the flank of the crack at stresses below the apparent crack growth threshold in a manner described recently by Chuang and Fuller.     

Effects of Particle Size on the Fusion of Soda–Lime–Silicate Glass Containing NaCl

The coupled effects of particle size and 1 wt% NaCl additions on the sequence of melting reactions in a multicomponent system (sand–soda ash–calcite–dolomite–feldspar) were studied using data from DTA, DTGA, and XRD interactively. Glass batches varied in average particle size from 250 μm to finer than 45 μm. Milestone events in the fusion process of the coarse particle base glass were elucidated. The termination temperature of the last significant reaction associated with CO₂ release was 35°C lower in the fine particle size batch than with the coarsest batch. Liquid-phase formation at ∼523°C in the batch with 1 wt% NaCl occurred to an increasingly sizable extent with decreasing particle size. This contrasts with a similar effect at ∼630°C for a comparable batch without NaCl via eutectic melting between soda ash and dolomite. Sodium chloride additions significantly enhanced dissolution of CaO relic.     

Leaching Behavior of Sodium from Fine Particles of Soda–Lime–Silicate Glass in Acid Solution

The leaching behavior of Na from soda–lime–silicate glass was investigated by preparing glass powders with average particle diameters of 53 and 19 μm, and leaching in HNO₃ at 90°−140°C. A new theoretical equation for Na leaching from a spherical particle is proposed based on the assumption that a rate-determining process is the three-dimensional self-diffusion of Na in glass. The diffusion constant ( D ) of Na in glass was obtained by fitting the experimental data to a theoretical equation. The values of D and activation energy obtained are comparable to those obtained in other studies on larger particles.     

Creep Behavior of Soda-Lime Glass in the 100–500 K Temperature Range by Indentation Creep Test

The loading time and temperature dependences viscoelastic behavior of a soda-lime-silicate glass (SLS) were studied by indentation creep experiments. Experiments were conducted in air, water and silicone oil with 15–10 000 s loading times, and temperatures ranging between 100 and 500 K. The indentation size was found to depend much on the loading time and temperature. Hardness was found to decrease significantly with increasing loading time, even at 173 K, and to decrease rapidly with rising temperature, even well below the glass transition temperature ( T _g). Water on the surface of glasses appeared to reduce the hardness and indentation viscosity of the glass.     

Creep Parameters of Alumina Containing a Glass Phase Determined in Bending Creep Tests

An alumina ceramic containing a glass phase is investigated in bending creep tests. It is shown how the constitutive equation describing the material behavior can be derived from outer fiber strain measurements.     

IR Practical Extinction Coefficients of Water in Alkali Lime Silicate Glasses Determined by Nuclear Reaction Analysis

Infrared spectroscopy (IR) is widely used to determine the water concentration in glasses, whereas determination of the IR practical extinction coefficient is necessary to deduce the absolute water concentration of glasses on the basis of Beer–Lambert law. From the nuclear reaction analysis data, the IR practical extinction coefficients of water were successfully determined for the alkali lime silicate glasses with different levels of sodium/potassium cation (Na/K) ratio. The two‐band method is well‐known to be useful for the determination of the water concentration in some alkali lime silicate glasses. It is proved here that the two‐band method is not applicable to the variety of composition for alkali lime silicate and soda lime aluminosilicate glasses, whereas it is valid for the similar composition of soda lime silicate glasses [SLS: Composition (in mol%) 16Na₂O·10CaO·74SiO₂]. The single‐band procedure with the IR practical extinction coefficient is crucial for the determination of the precise water concentration in the wide variety of glass composition although the determination of the IR practical extinction coefficient is troublesome. It also appears that the ion radius of alkali affects the IR practical extinction coefficient and the chemical state of OH group in glasses.     

Mechanism for the Radiolytically Induced Decomposition of Soda–Silicate Glasses

A mechanism is proposed for the radiolysis which occurs in soda-silicate glasses when they are irradiated. The mechanism is consistent with the observations of the reaction products which are produced and the rates at which the decomposition proceeds.     

Surface-Energy Determinations of Tin Oxide-Coated Soda–Lime–Silica Glass

The dispersive and polar surface-energy components, as well as the total surface energy, of tin oxide coatings on soda–lime–silica glass were determined by the Owens–Wendt method. The total surface energy of tin oxide is greater than soda–lime–silica glass and, more importantly, exhibits significantly more-dispersive and less-polar character. These results indicate that tin oxide is significantly more covalent than soda–lime–silica glass. It is postulated that the more-covalent tin oxide coatings increase the bond strength of organic coatings to soda–lime–silica glass. These effects improve the friction-damage resistance of glass surfaces coated with metal oxides and organics, compared with glass surfaces coated with organics only.     

黏弹材料动态纳米压入过程的尺度效应

提出柔度因子分析法表征压入尺寸效应（ISE)通讨聚甲基丙烯酸甲酯(PMMA)及热塑性聚氨酯(TPU)的动态纳米压痕试验,探讨黏弹材料动态压入过程中的压入尺度效应及其影响因素。结果表明,Berkovich针尖对黏弹材料进行纳米压痕动态测试时,主载荷是压入尺度效应产生与否的决定因素,频率对此影响较小,谐振载荷控制方式影响甚微;测试材料存在一临界值,当压入深度大于其临界值时,动态纳米压痕测试获得的黏弹材料参数与传统的动态力学分析(DMA)试验结果基本一致。     

Carbon Dioxide Uptake by Hydrated Lime Aerosol Particles

The reaction of the greenhouse gas, CO₂, with Ca(OH)₂ was explored using single-particle Raman spectroscopy to track the chemical reaction. Single particles were levitated in an electrodynamic balance (EDB) to maintain the particle in a laser beam. The levitation voltage provided gravimetric data. The humidity in the EDB chamber was varied to determine the effects of humidity on the reaction. It is demonstrated that no appreciable reaction occurs at low relative humidities (RH < 70%). This is evidenced by no disappearance of the Raman peak associated with the [OH]^? vibrational bond, but at high humidities (RH > 70%) the Raman spectrum of CaCO₃ developed as the reaction proceeded. The results are consistent with results from packed-bed studies of the reaction and are in agreement with similar findings for the SO₂/Ca(OH)₂ reaction used for desulfurization, that is, the reaction does not proceed until multiple monolayers of water are adsorbed on the particle surface.