Fracture Surface Of Glass Research Articles

Low‐temperature bubble formation in silica glass

AbstractPhase separation was observed in silica glass following low‐temperature heat treatment in high water vapor pressure through the formation of bubbles. Although the 6 day diffusion treatment in saturated water vapor pressure at 250°C does not normally cause phase separation, the reactive fracture surface and subsurface damage caused by polishing with cerium oxide (CeO2) allowed for an increase in water absorption during treatment and heterogeneous nucleation of the bubbles at damaged sites. The sub‐surface damage, characteristic of blunt contact damage, was only revealed when the polished sample was etched. The formation of bubbles and polishing damage were observed in two silica glasses—one containing chlorine impurities and the other containing OH impurities. Raman spectra collected after fracture or polishing and water diffusion treatment demonstrated an increase in the abundance of –OH species including silanol (SiOH) groups and an evolution in the glass structure in the bubble regions compared with the bubble‐free regions. These results indicate an increase in the reactivity between water and glass fracture surfaces relative to the bulk.

REUSING MANUFACTURING WASTES AS CRACK RETARDANT

Global production uses millions of metric tons of metals. The waste of these metals can be recycled to increase the economic benefit and lessen the negative impact on the environment. In this work, a manufacturing waste is used as a reinforcement material for epoxy to improve the fracture toughness and the stress intensity factor, where the machining chip is used with different weight fractions 5, 10, 15 and 20 wt. % and each percentage is added with three chip lengths 0.6, 0.8 and 1.18 mm. Three-point bending test of notched sample is used to test crack behaviour in addition to using Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), Differential Scanning Calorimeter (DSC) and Scanning Electron Microscope (SEM) to show the effect of chip on structure, bonding, glass transition temperature (Tg), dispersion and fracture surface of the epoxy. Results show that adding the machining wastes in the form of chips can enhance crack behaviour, and it is greatly dependent on the amount and size of chip. On the contrary, these chips change the glass transition temperature and change the fracture surface from brittle to ductile, thereby reducing the velocity of crack growth.

Silicate glass fracture surface energy calculated from crystal structure and bond-energy data

We present a novel method to predict the fracture surface energy, γ, of isochemically crystallizing silicate glasses using readily available crystallographic structure data of their crystalline counterpart and tabled diatomic chemical bond energies, D0. The method assumes that γ equals the fracture surface energy of the most likely cleavage plane of the crystal. Calculated values were in excellent agreement with those calculated from glass density, network connectivity and D0 data in earlier work. This finding demonstrates a remarkable equivalence between crystal cleavage planes and glass fracture surfaces.

In situ observation of glass-like fragmentation of high-temperature silicate melts generating fine ashes

Volcanic ash originating from the fragmentation of magma damages infrastructure and the environment. Bubble expansion is crucial in magma fragmentation, but low-intensity eruptions frequently emit ashes with fewer bubbles. We here conducted tensional experiments on silicate melt at a high temperature, at which the melt elongates or fractures depending on the strain rate. A fracture occurs by appearing of a crack on the melted silicate rod, followed by a generation of small fragments. The fracture surface shows a smooth and rough region dichotomy, similar to those observed on glass fracture surfaces at room temperature. The rough surface region generates small fragments. Interestingly, the measured stress-strain curves indicate fragmentation occurs under viscous deformation. These results suggest that silicate melts under viscous deformation fragment, as glass does at room temperature. The ductility around the crack tip promotes void nucleation and coalescence, causing the crack to branch to generate dense, fine volcanic ashes.

Cup-cone statistical investigation assess the relationship between the micro-structure and spall strength of metallic glasses under planar impact loadings

Modern industries including the aircraft, rail transportation, and military equipment necessitate a thorough grasp of the dynamic fracture process of materials. Metallic glass, as a typical high-performance modern material, has a broad application prospect in these areas. However, its trans-scale damage evolution process is still shrouded in veil. In this work, we conducted systematic dynamic loading experiments to investigate a distinctive “cup-cone structure” phenomenon that emerges on fracture surface of metallic glass as the impact energy increases. We proposed a new approach of statistical analysis centred on the idea of neighbouring nucleation sites. On the basis of this defect statistical technique, the correlation between the initial nucleation density and spall strength was clarified. The result implies that the macro response does not provide a complete picture of the information regarding the evolution of microstructure. In addition, the meso statistical analysis can play a greater role in establishing the structural-performance correlation.

M1 - Fracture Toughness and Fractal Dimension of Two Dental Glass-Ceramics

Studies have reported the fractal dimensional increment of glass and glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two types of dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness. Fifteen bar-shaped specimens were prepared from lithium disilicate (LDS) by sectioning the blocks (IPS e.max CAD, Ivoclar Vivadent). Ten beams were prepared by mixing and layering the nanofluorapatite (NFA) glass-ceramic powder (IPS e.max Ceram, Ivoclar Vivadent). One face of each of the specimens was indented using a Knoop diamond at 25 N (LDS) or 10 N (NFA) followed by loading in deionized water in 4-point, or 3-point flexure, respectively, until failure. Fracture surfaces were analyzed using scanning electron microscope (SEM). Fracture toughness (Kc) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm. In addition, surface roughness was computed from the AFM scans using the Gwyddion software. The median (25%, 75% quartiles) fracture toughness of LDS and NFA bars were 1.62 (1.59, 1.69) MPam1/2 and 0.68 (0.66, 0.74) MPam1/2, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before and after noise filtering for LDS were 2.16 (2.15, 2.17) and 2.14 (2.14, 2.15), respectively, and for NFA were 2.29 (2.21, 2.38) and 2.17 (2.17, 2.18), respectively. The NFA follows the regression model (Y=1.99 X) between Kc and sqrt. D* for glasses as previous studies, but the LDS deviated from the model. The median (25%, 75% quartiles) surface roughness before and after noise filtering for LDS were 139 (119, 188) nm and 137 (118, 187) nm and for NFA were 7 (6, 15) nm and 7 (6, 15) nm, respectively. Noise filtering successfully eliminated noise from the AFM scans of the material with smooth fracture surfaces (NFA), resulting in a decrease in measured fractal dimension. The LDS data deviated from the model because of toughening due to crack bridging. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.

A Model for Triboluminescence from Fracture Surfaces of Silica Glass

A Model for Triboluminescence from Fracture Surfaces of Silica Glass

Quantitative Fractography of Mixed‐Mode Fracture in Soda Lime Silica Glass

Fracture surfaces of soda lime silica glass failed from controlled surface cracks in diametral compression, under mixed‐mode loading conditions were studied using fractography. Mode mixity was introduced by orienting indent precracks in different directions with respect to the loading axis. The mixed‐mode fracture surfaces were characterized by an absence of the mist region. The hackle markings on the mixed‐mode fracture surfaces appear as lances and differ from those observed on surfaces failed in pure mode I. Atomic force microscopy on the mixed‐mode fracture surfaces revealed that the features at different regions are similar and differ only by scale. Fracture surface measurements for mixed‐mode loading are compared to the measurements for mode I loading. The stress intensity at microbranching was determined to be a constant irrespective of the loading conditions. The practical implications of these observations are that forensic analyses can be used without a priori knowledge of the loading conditions.

Glass fracture patterns and the (G,R) vs ∆C diagram

The crack patterns of glass which form when a propagating crack intersects a free surface are considered in terms of the (G,R) vs ∆C universal energy diagram for crack growth after Broek (1974) [1]. After briefly reviewing its derivation, the diagram is applied to glass fracture and the bifurcation of cracks in glass. The concepts are then extended to address the formation of the mirror/mist boundary on glass fracture surfaces. Features of the (G,R) vs ∆C diagram and the KI−V diagram after Richter (2002) [2] are combined to estimate the kinetic energy associated with a crack in soda lime silica glass at its terminal velocity. The kinetic energy is ~70% of the total energy requirement for crack growth. Implications regarding other glass fractures, such as the absence of the mirror/mist boundary for nano-whiskers, are also discussed. The (G,R) vs ∆C approach appears to have far reaching applications in describing glass fractures.

Outer medium effects and fracture nucleation sites in model experiments to mimic fracture surface features of metallic glasses

Model experiments have been conducted in order to simulate the fracture morphology of metallic glasses at low temperatures or high strain rates. The effects of specimen geometry, stress state, and external pressure on the fracture surface features in model grease systems has been investigated. It is shown that the fracture surface feature size decreases with increasing viscosity of the viscous layer. Increasing the external pressure via testing samples submerged in media with different viscosities similarly produces decreases in the fracture surface feature sizes. Results on the model systems have been compared to metallic glass fracture surfaces.

Understanding the correlation of plastic zone size with characteristic dimple pattern length scale on the fracture surface of a bulk metallic glass

Fatigue pre-crack toughness measurements following standard procedures for a model Zr61Cu17.3Ni12.8Al7.9Sn1 glass in as-cast and annealed states were performed. Plastic zone size was found to be very sensitive to the internal states of this glass and be correlated with the characteristic dimple pattern length on fracture surfaces. Effect of plastic work energy dissipation on two characteristic length scales in the vicinity of a crack tip was discussed, in addition to the analyses of excess free volumes and Poisson's ratio. (C) 2011 Elsevier B.V. All rights reserved.

Application of atomic force microscopy in determining the fractal dimension of the mirror, mist, and hackle region of silica glass

Abstract Fractal analysis has been used as a method to study fracture surfaces of brittle materials. However, it has not been determined if the fractal characteristics of brittle materials is consistent throughout the fracture surface. Therefore, the fractal dimensional increment of the mirror, mist, and hackle regions of the fracture surface of silica glass was determined using atomic force microscopy. The fractal dimensional increment of the mirror region (0.17–0.26) was determined to be statistically greater than that for the mist (0.08–0.12) and hackle (0.08–0.13) regions. It is thought that the increase in the fractal dimensional increment is caused by a greater tortuosity in the mirror region due to, most likely, the slower crack velocity of the propagating crack in that region and that there is a point between the mirror and mist region at which the fractal dimension decreases and becomes constant.

Compressive fracture characteristics of Zr-based bulk metallic glass

The compressive fracture characteristics of Zr-based bulk metallic glass under uniaxial compression tests are studied. The zigzag rheological behavior is observed in the compression stress-strain curves of amorphous alloys. At room temperature the uniaxial compression fracture takes place along the plane which is at a 45-degree angle to the direction of the compressive stress. The microstructure of a typical fracture pattern is the vein network. A unique, finger-like vein pattern is found to exist at the fracture surface of Zr-based bulk metallic glass.

Effects of Finite Probe Size on Self-Affine Roughness Measurements

The roughness of fracture surfaces exhibits self-affinity for a wide variety of materials and loading conditions. The universality and the range of scales over which this regime extends are still debated. The topography of these surfaces is however often investigated with a finite contact probe. In this case, we show that the correlation function of the roughness can only be measured down to a length scale Deltax{c} which depends on the probe size R, the Hurst exponent zeta of the surface and its topothesy l, and exhibits spurious behavior at smaller scales. First, we derive the dependence of Deltax{c} on these parameters from a simple scaling argument. Then, we verify this dependence numerically. Finally, we establish the relevance of this analysis from AFM measurements on an experimental glass fracture surface and provide a metrological procedure for roughness measurements.

Cooperative shear and catastrophic fracture of bulk metallic glasses from a shear-band instability perspective

The morphology of the fracture surfaces of a bulk metallic glass (BMG) tested under compression was systematically studied. Experimental results showed that the fracture surface always comprises two kinds of zones, starting with a relatively smooth zone followed by the second zone with vein patterns. It implies strongly that the plastic deformation of BMGs always starts with a cooperative shear. The following catastrophic fracture characterized by the vein patterns may or may not occur, depending on the magnitude of this shear, which is controlled by the sample size and machine stiffness. This phenomenon was interpreted based on the temperature rise resulting from the work done during the cooperative shear. It revealed that for small samples, the shear is so small that the temperature increase is insignificant, accounting for the extensive serrated flow, while the temperature increase in samples beyond a critical size is sufficiently high so that the temperatures are higher than the glass transition temperature or even the melting temperature, leading to catastrophic fracture.

Nanoscale ripples on the compressive fracture surface of a bulk metallic glass with microscale crystals

Some periodic and straight strips with about 60 nm spacing were observed on the compressive fracture surface of Ni42Cu5Ti20Zr21.5Al8Si3.5 bulk metallic glass (BMG) rods containing minor microscale crystals. The characteristic difference between amorphous matrix and microscale crystals also reveal why periodic corrugations could not be observed on the fracture surface of metal crystals. The dynamic crack instability may be explained by the interaction of the propagating crack and the internal micro-cracks. This kind of periodic morphologies showed in-plane feature, which may be attributed to the non-intense interaction between dynamic crack and micro-crack.

Fractography and tensile strength of glass wool fibres

Mechanical reliability such as strength and brittleness is of great interest for application of brittle materials, i.e. glasses and glass fibres. In this paper we study the fracture behaviour and the tensile strength of glass wool fibres (GWFs) of both basalt and E-glass compositions, which play an important role in both transportation and application of GWFs (as insulation material). GWFs are tested in uniaxial tension. The surfaces of the fractured fibres are imaged using scanning electron microscopy. Three main types of fracture surfaces produced in tensile stress are observed, all of which include fracture mirror, mist and hackle features comparable to fracture surfaces of bulk glass and continuous fibres. The three types are: a) surface without visible origin; b) surface with visible origin; c) surfaces originated from internal pores. The relations between the fracture mirror size and the mechanical strength shown for bulk glass and continuous glass fibres are also valid for GWFs. Relation between the fractographic observations and the strength Weibull distributions are discussed in relation to chemical composition and homogeneity.

Cycles of sub-critical tensile and shear alternating fracturing in diminishing dimensions, under tensile loading

A microscopic study reveals that when the curvature of striae that mark the fracture surface of PMMA glass with a chevron pattern increase beyond the critical angle, μc = 3° ± 2°, a breakdown into alternating tensile dark zones, and bright, ragged shear zones occurs. This breakdown was repeated in primary, secondary and tertiary cycles in diminishing scales. The secondary and tertiary breakdowns occurred exclusively in the shear zones. Similar breakdowns were found in chevron patterns on the fractured surface of a silicate glass ceramics. Due however to their different properties, certain differences were identified between the two materials in their breakdown characteristics, e. g. in the glass ceramic μc = 20° ± 2°. A similar primary breakdown was also identified on tensile fractures cutting rocks in geological outcrops. In the glass ceramic the interface angle $${\phi}$$ , which the striae form with the fracture boundary, decreased from 32° ± 2°in the early stage of the striae growth at relatively low velocity, to 13° ± 2° during their advanced growth, at greater velocity, demonstrating that $${\phi}$$ is a good tool for monitoring the change in fracture velocity in a given material. It was found that four interconnected factors determine the geometries and breakdown styles of the chevron pattern: (1) the curvatures of the fracture front and that of the striae which intersect each other orthogonally, (2) the influence of the fracture boundaries, (3) the material properties, such as stiffness, and (4) the fracture velocity in the material.

Self-Affine Quasi-Static Fracture of Soda-Lime Glass

In the present work we discuss the self-affine properties of the fracture surfaces of sodalime glass obtained under quasi-static conditions. The fracture surfaces are generated using a threepoint bending system in normal room conditions and under high humidity conditions. The surfaces were recorded both by Scanning Electron Microscopy and Atomic Force Microscopy, and their selfaffine properties are characterized using the Variable Bandwidth method. For both conditions it is observed that the major part of the fracture surface is occupied by the mirror zone. On the other hand, the self-affine analysis reveals that for both conditions the roughness exponent has values centred at around 0.58 with moderate dispersion, in agreement with previous results. Our findings support the hypothesis of the existence of a characteristic roughness exponent for quasi-static fracture with a value that is significantly lower than the value of 0.8 reported for rapid fracture conditions.

Roughness of glass surfaces formed by sub-critical crack growth

This paper presents a study on the roughness of glass fracture surfaces formed as a consequence of sub-critical crack growth. Double-cantilever-beam specimens were used in these studies to form fracture surfaces with areas under well-defined crack velocities and stress intensity factors. Roughness depends on crack velocity: the slower the velocity, the rougher the surface. Ranging from approximately 1 × 10 −10 m/s to approximately 10 m/s, the velocities were typical of those responsible for the formation of fracture mirrors in glass. Roughness measurements were made using atomic force microscopy on two glass compositions: silica glass and soda lime silica glass. For silica glass, the RMS roughness, R q , decreased from about 0.5 nm at a velocity of 1 × 10 −10 m/s to about 0.35 nm at a velocity of 10 m/s. For soda lime silica glass, the roughness decreased from about 2 nm to about 0.7 nm in a highly non-linear fashion over the same velocity range. We attributed the roughness and the change in roughness to microscopic stresses associated with nanometer scale compositional and structural variations within the glass microstructure. A theory developed to explain these results is in agreement with the data collected in the current paper. The RMS roughness of glass also depends on the area used to measure the roughness. As noted in other studies, fracture surfaces in glass exhibit a self-affine behavior. Over the velocities studied, the roughness exponent, ζ, was approximately 0.3 for silica glass and varied from 0.18 to 0.28 for soda lime silica glass. The area used for these measurements ranged from (0.5 μm) 2 to (5.0 μm) 2. These values of the roughness exponent are consistent with values obtained when the scale of the measurement tool exceeds a critical size, as reported earlier in the literature.