Field strength effect on elastoplastic behavior of aluminoborosilicate glass: I. Elastic moduli and indentation size effect

The modifier field strength (FS) is believed to play an important role in determining the elastic–plastic responses of aluminoborosilicate (ABS) glasses, but its effect is not well understood. Three novel alkali and three alkaline earth (AE) ABS compositions were created for this study which is the first part of two studies that explored the elastoplastic responses of these glasses. Six compositions were designed using different network modifiers (NWMs) to cover a range of cation FS. The glasses were also designed such that the concentrations of NWM and Al₂O₃ were similar, which maximized the three-coordinated boron fraction in the network. It is well known that modifier FS can affect the coordination number (CN) of Al and B in an ABS glass structure, for example, a higher FS modifier can promote B³ → B⁴ and higher [Al^5,6], but the degree of this depends on network former (NWF) ratios. Previous work used solid-state NMR spectroscopic analysis on the current glasses to find that there was variation between [B⁴] and [Al⁴] between the two glass series (alkali vs. AE) but that was attributed to synthesis factors and no trend with FS was associated with the varying NWF CN. Further, ²⁹Si ssNMR showed no evidence of NBOs which made sense based on composition. The conclusion, therefore, was that there was a far greater correlation with modifier FS for the increased mechanical and physical properties rather than the CN of Al and B. Part I of the current work focused on the elastic moduli, Poisson's ratio, the indentation size effect (ISE), and the bow-in parameter. This part laid out the foundation to investigate the intersection of these elastoplastic properties with hardness and crack resistance as a function of NWM FS. Results showed that: (i) the Young's, bulk, and shear moduli increased with modifier FS, whereas Poisson's ratio did not trend with FS; (ii) the alkali glasses had a significantly higher magnitudes of ISE compared to the AE glasses; and (iii) the bow-in parameter was load dependent and decreased with modifier FS at the highest indentation load.     

Field strength effect on structure,hardness, and crack resistance in single modifier aluminoborosilicate glasses

Although the interactions among glass formers and modifiers, for example, connectivity and charge distribution, have been studied extensively in oxide glasses, the impact of a particular modifier species on the mechanical performance of aluminoborosilicate (ABS) glasses is not well understood. This work compares the indentation properties of six ABS glasses, each of which contains a different network modifier (NWM) with varying field strength (FS). Three alkali and three alkaline earth ABS glasses were designed with low NWM content and [NWM] ≈ [Al₂O₃], to test the modifier FS effect at low concentrations and to maximize three-coordinated boron. It has been found that both hardness and crack resistance increase with increasing FS in these ABS systems, which is surprising in the context of historical reports. Using ¹¹B, ²⁷Al, and ²⁹Si solid-state nuclear magnetic resonance, this work provides evidence of how charge distributions differ as a function of NWM species, and how this relates to the observed indentation behaviors.     

Ab initio molecular dynamics simulation of the structural and electronic properties of aluminoborosilicate glass

In this study, the structural and electronic properties of aluminoborosilicate glass, which has a wide range of applications in fields such as microelectronics and displays, were examined using ab initio molecular dynamic simulations. Computing models containing 220 atoms correctly described the local structure of the glass. The reliability of the computing models was verified by the consistency between the experimental results, obtained using high-energy X-ray diffraction and solid-state nuclear magnetic resonance, and the simulation results pertaining to structural factors, pair distribution functions, Qⁿ distribution, and elastic properties. The presence of B and Al increased the flexibility and asymmetry of the system, as shown by the bond angle and ring size distributions. Based on the electronic properties, we observed that the introduction of Al and B atoms into the network could also cause covalent interactions with the O atoms, similar to that with Si atoms. However, the Na and Mg atoms still interacted with all kinds of atoms in the network via charge transfer and exhibited highly non-localized effects on the charge of the network formers. These results extend our understanding of the structure of aluminoborosilicate glass and have guiding significance for improving and designing new types of this glass.     

Enhancement of emission intensity in Ce3+-activated aluminoborosilicate scintillating glass synthesized in air

A highly effective method of synthesizing transparent and colorless Ce³⁺-activated aluminoborosilicate glass in air by high temperature melt-quenching is reported. This is achieved by partial substitution of AlN for Al₂O₃ without using any reduction in atmosphere. The optimized Ce³⁺-activated aluminoborosilicate scintillating glass is featured with a density of ~4.5 g/cm³ and a lifetime of 41.74 ns. Compared to the glass synthesized without AlN substitution, both the photo and raidoluminescence intensity of the optimized Ce³⁺-activated aluminoborosilicate scintillating glass are enhanced by a factor of 24.4 and 6.76, respectively. The corresponding integrated raidoluminescence intensity is about 17.6% of that of BGO crystal under X-ray excitation at 30 kV and 3 mA, respectively.     

A comparative study on the effect of loading speed and surface scratches on the flexural strength of aluminosilicate glass: Annealed vs. chemically strengthened

Quasi-static and dynamic three-point-bending experiments were conducted on both annealed and chemically strengthened aluminosilicate glass scratched by different normal loads. Scratched areas were observed by optical microscope and atomic force microscope. Chemically strengthened glass shows better resistance to surface scratch. These dynamic experiments were carried out using a modified Split Hopkinson Pressure Bar (SHPB) device and a pulse-shaping technique was used to keep constant loading speed to the specimens. In tests, high-speed photography was also used to observe the failure process of the specimens. The test results showed that the flexural strength of aluminosilicate glass (AG) strongly depends on the applied loading speed. Compared with its annealed counterpart, the chemically strengthened glass (CSG) showed higher flexural strength to both static and dynamic loadings. Moreover, the three-point bending experiments were conducted on scratched AG and CSG specimens and decrease of 20–40% in flexural strength was observed. The fractography analysis showed that in dynamic loading conditions the fracture surface was not smooth and has more secondary cracks as compared to static loading.     

Statistical interference of material strength and surface prestress in heat‐treated glass

It is customary to assume that the characteristic design value for heat‐treated glass is represented by the sum of the characteristic values of the annealed glass strength and of the heat‐induced surface prestress, even though experiments have provided evidence that the resulting strength may be much higher. Here, we investigate the statistical interference between an assumed two‐parameter Weibull distribution for the annealed glass strength and a Gaussian distribution for the surface prestress. We show how the compound distribution confirms the experimental findings and, in particular, that the type of stress induced by the applied loads, ie, uniaxial vs biaxial, has an important role. This effect, which is more relevant for “weak” than for “strong” glasses, is the mechanical counterpart of the well‐known principle of diversification of investments in economy, and leads to a critical consideration of the design approach commonly suggested by structural standards.     

Adhesion behavior of PDMS-containing polyimide to glass

The effect of the incorporation of poly(dimethyl siloxane) (PDMS) segments into a poly[N,N'-(p,p'-oxydiphenylene) pyromellitimide] (PMDA-ODA) polyimide backbone on the adhesion between PMDA-ODA polyimide and glass was investigated using X-ray photoelectron spectroscopy (XPS), infrared (IR) spectroscopy, contact angle measurements, and the peel test. The peel energy of PMDA-ODA polyimide to glass was significantly improved when low molecular weight PDMS (248.5 g/mol) was incorporated, while little improvement was observed for the incorporation of high molecular weight PDMS (900 or 1680 g/mol). Exposure to air resulted in a considerable deterioration in the peel energy for the pure PMDA-ODA polyimide, while no deterioration was observed for the PDMS-containing polyimides. The improvement in peel strength was successfully achieved by the incorporation of very small quantities of PDMS such as 2 wt%. Based on XPS, IR spectroscopy, and contact angle measurements, it is suggested that the incorporated PDMS segments migrated from the bulk polyimide to the polyimide/glass interface and chemically bonded to the glass surface, which resulted in enhancement of the peel energy. However, a weak boundary layer was formed between the bulk polyimide and glass when a high molecular weight PDMS (900 or 1680 g/mol) was incorporated and thus the peel energy deteriorated.     

玻璃鳞片含量对环氧胶强度和吸水性的影响

通过测试环氧胶粘剂剪切强度、经冷热循环水浴浸泡的试块的吸水性和密度变化,研究了玻璃鳞片含量对环氧胶粘涂层界面粘接强度、吸水性能的影响。研究结果表明,玻璃鳞片增加时,胶层的密度增加;经长时间浸泡后试样的密度均明显提高,含量为30%的试样增幅最大,但其体积几乎保持不变。分析试验结果后可知,胶层经浸泡后的体积变化率也应是评定其耐水性能的重要因素。     

Preparation of laminated safety glass based on high strength polyurethane film by solution annealing

Compared with the traditional polyvinyl butyral (PVB) laminated glass, the polyurethane (PU) based laminated glass has the advantages of higher impact strength and longer service life. Thus, aromatic polyurethane films have attracted more attentions in recent years due to their high light transmittance, adhesion and functionality. In this paper, the tensile strength of polyurethane films based on bis(4-isocyanatocyclohexyl)-methane (HMDI) have been increased from 27 to 51 MPa and their elongation at break have been increased from 330% to 525% after solvent annealing in toluene. It is attributed to molecular segments with high crystallization and hydrogen bond formation of PU, which are confirmed by FT-IR and XRD characterization. Based on this, laminated glasses with higher impact strength based on the thermoplastic polyurethane films are constructed successfully.     

Contact residual stress relaxation in soda-lime glass: Part II. Aspects relating to strength recovery

Strength recovery of Vickers indented soda lime glass was measured and compared after annealing at two temperatures: one below and one above T_g. The atomic force microscope was used to study the cracks. At 540 °C, no changes were observed in crack morphology either below the surface or on the surface relative to the pre-anneal state. At 630 °C, both sub-surface and surface crack morphology changes were observed. The trends in strength recovery were compared with residual stress relaxation as measured by a new method of stress estimation based on nanoindentation elastic response. At short hold times at 630 °C, and regardless of the length of hold time at 540 °C, strength recovery of only ∼30% was measured while at moderately long hold times at 630 °C, strong recovery of fracture strength, ∼132% was measured. Trends in strength recovery above T_g are shown to match those of crack tip radius instead of trends in stress relaxation across the residual stress field.     

Vickers crack extension and residual fracture strength of annealed and thermally tempered glass in water

The effect of water contact on the propagation of microscale surface cracks is investigated in two types of glass: annealed and tempered glass. Initial flaw is artificially created on the glass surface using a Vickers indenter, and is covered with a water droplet for 20 min. Micrographs of the flaw taken before and after water contact confirms the increase in crack length from around 61–103 μm for thermally tempered glass. After water dipping, the maximum length to which the crack growth is approximately 57 % smaller in the thermally tempered glass than in the annealed glass. Despite the severe effect of water contact on crack propagation, it is found that the fracture strength is not substantially altered by water dipping; even though the crack length is enlarged, the fracture strength of glass is similar, and in the case of tempered glass, its fracture strength is slightly changed within 7% due to the blunting of the crack tip by water or others.     

Effects of enamel surface preparation on bonding strength of resin-modified glass ionomer cement: an in vitro study

The purpose of this study was to evaluate a more suitable and efficient preparation method of enamel surface and a safe duration of loading in orthodontics when bonding with resin-modified glass ionomer cement (RMGIC). 300 human premolars were divided into five groups: G0, etched–Transbond XT; G1, etched–moistened; G2, etched–dry; G3, unetched–moistened; and G4, unetched–dry. Using an universal testing machine, we measured shear bonding strength (SBS) and tensile bonding strength (TBS) at 30 min, 24 h, and 30 d post-bonding. The adhesive remnant index was evaluated using stereomicroscopy. The results showed that enamel surface etching significantly improved SBS and TBS of RMGIC. The moist environment could accelerate both of SBS and TBS, but not the final bonding strength. Etching with moistening was the best processing method with RMGIC. When using RMGIC on unetched enamel, the bonding surface should be moistened and loading time delayed. When evaluating mechanical properties of the adhesive materials, it seemed that the TBS was more reasonable and objective than the SBS.     

Glass foam of high compressive strength produced from photovoltaic module waste glass,eggshell, and clay

A glass foam (GF) of high specific compressive strength (12.17±1.91 MPa g⁻¹ cm⁻³) and low thermal conductivity (.121±.001 Wm⁻¹ K⁻¹) was produced from waste glass of photovoltaic module, eggshells, and bentonite clay. The influences of the amount of clay and heat-treatment temperature on the GFs final properties were assessed. X-ray diffraction results and the data of microscopic analyses demonstrated that addition of clay affected the structure and porosity of the GFs, and consequently their mechanical properties. On the basis of the mechanical property (density), the GF that composed of 80% waste glass, 10% clay, and 10% eggshell at the sintering temperature of 900°C was the best. The GFs reported in this study could serve as promising insulators in situations where high load support is required.     

Weibull statistical analysis of the mechanical strength of a glass eroded by sand blasting

In Saharian regions, the erosion of glass by sand particles during sandstorms is a regular phenomenon. The progressive loss of matter on surface affects both the optical transmission and mechanical strength. In this work, the influence of sand impacts on glass strength was simulated in laboratory. We used Weibull distribution function to characterize statistically the variation of the mechanical strength of a soda-lime glass in the as received state and eroded by sand blasting during 30 and 60 min. From the failure probabilities distributions, we notice an important drop in strength values (about 13%) after 30 min and a tendency to level out with a much reduced dispersion after 60 min. The Weibull plots for the as-received state and for the 30 min eroded state present curves with a knee. They were considered as bimodal forms (two straigth lines) denoting the presence of two kinds of defects that control strength. The Weibull plot for the 60 mins eroded state sample presents one straight line (unimodal form) that indicates the predominance of erosion defects. From micrographical observations on eroded specimen, we observed a tendency toward a damaging homogeneity of the surfaces exposed to sand blasting. This explains the uniformity of the strength values obtained after 1 h of sand blasting.     

Role of silanes in adhesion. Part II. Dynamic mechanical properties of silane-treated glass fiber/polyester composites

—Glass fiber/unsaturated polyester composites, prepared by impregnating glass braid with varying thickness coatings (from 200 Å up to 1600 Å thick) of polyester resin, were tested with a DuPont Dynamic Mechanical Analyzer. The effects of the polyester resin thickness and silane treatments on the dynamic mechanical properties of the composites were evaluated. The results are supported by Fourier transform infrared spectroscopy of the composite materials. It is shown that both the concentration and the organo-functional group of the silane coupling agent influence the damping, storage, and loss moduli as well as the glass transition temperature (T_g) of the matrix resin in the closest vicinity to the glass/resin bondline. In the absence of a silane inner layer, a low T_g, 'soft' boundary layer exists due to inhibition of the polyester resin cure by the glass surface. It is noted that a reactive silane, such as γ-methacryloxypropyltrimethoxysilane, promotes the formation of a 'soft' or 'rigid' (high T_g) boundary layer, depending on the concentration of the silane in the treating solution. On the other hand, a non-reactive silane, such as methyltrimethoxysilane, produces a 'rigid' interphase in the entire range of concentrations of the silane solution. An attempt was made to correlate the dynamic mechanical properties of the boundary layer with the fiber/polymer interfacial shear strength. Upon pretreatment of glass fibers with silane coupling agents, the relative magnitude of the loss modulus, E", and the nature of the boundary layer (T_g) seem to be better indicators of efficient stress transfer from the polymer to the glass fiber in the composite system than tan δ. Efficient stress transfer is characterized by a low value of E" and 'soft' boundary layers. The results suggest that the mere presence of glass/polyester chemical bonding is insufficient to ensure effective stress transfer. A strong bond results from the synergistic effect of glass/silane/polymer chemical bonding and a 'soft' boundary layer.     

Woven glass fabric/polyester composites: effect of interface tailoring on water absorption

An experimental investigation was carried out to study the effect of different surface treatments on the moisture absorption behavior of glass fabric/polyester composites. The materials under study included composites containing clean glass fabrics, fabrics treated with a silane coupling agent, and fabrics coated with a poly(dimethylsiloxane) elastomer. Weight gain data versus time of immersion were collected at three immersion temperatures and water uptake at equilibrium as well as apparent diffusion coefficients were calculated. The interlaminar shear strength was also measured at the initial dry state and at different stages of the absorption process to estimate the interfacial contribution to sorption behavior. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 843–851, 2005     

Impact of the cation field strength on physical properties and structures of alkali and alkaline-earth borosilicate glasses

The impact of the cation field strength (CFS) of the glass network-modifier cations on the structure and properties of borosilicate glasses (BS) were examined for a large ensemble of mixed-cation (R/2)M₍₂₎O–(R/2)Na₂O–B₂O₃–KSiO₂ glasses with M⁺ ={Li⁺, Na⁺, K⁺, Rb⁺} and M²⁺ ={Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺} from four series of {K, R} combinations of K = n(SiO₂)/n(B₂O₃) = {2.0, 4.0} and R =[n(M₍₂₎O) ?+ ?n(Na₂O)]/n(B₂O₃) = {0.75, 2.1}. Combined with results from La³⁺ bearing glasses enabled the probing of physical-property variations across a wide CFS range, encompassing the glass transition temperature (T_g), density, molar volume and compactness, as well as the hardness (H) and Young's modulus (E). We discuss the inferred composition–structure/CFS–property relationships. Each of T_g, H, and E revealed a non-linear dependence against the CFS and a strong T_g/H correlation, where each property is maximized for the largest alkaline-earth metal cations, i.e., Sr²⁺ and Ba²⁺, along with the high-CFS La³⁺ species. The ¹¹B MAS NMR-derived fractional BO₄ populations decreased linearly with the average M^z+/Na⁺ CFS within both K–0.75 glass branches, whereas the NBO-rich K–2.1 glasses manifested more complex trends. Comparisons with results from RM₂O–B₂O₃–KSiO₂ glasses suggested no significant “mixed alkali effect”.     

Compressive strength and biomineralisation improvement by water glass coating on porous calcium phosphate scaffolds

Calcium phosphate (Ca–P) based scaffolds were found to be a favourable alternative for orthopaedic applications because of their similar chemical composition to natural bone. In this study, porous triphasic Ca–P scaffolds containing macropores (∽200?μm) interconnected with micropores (∽20?μm) were fabricated using an extrusion method. The hydroxyapatite/tricalcium phosphate ratio of the porous scaffolds was varied using different ratios of starting materials while keeping the Ca/P ratio fixed (1.5). A water glass coating on the porous Ca–P scaffolds increased the compressive strength by 45% without significantly decreasing the porosity of the H100D50 scaffold. The maximum compressive strength, ～15?MPa, was achieved on the H100D50 scaffold. The ability for apatite formation in simulated body fluid was amplified by the water glass coating on the sintered Ca–P scaffolds. Therefore, a water glass coating can be used to enhance the mechanical properties as well as the biomineralisation of the porous ceramic scaffolds.     

Effect of normal scratch load and HF etching on the mechanical behavior of annealed and chemically strengthened aluminosilicate glass

Micro-cracks generated by hard body scratch are a major cause of strength decrease for silicate glass. The influence of normal scratch load on the cracking patterns and flexural strength of annealed glass (AG) and chemically strengthened glass (CSG) were studied. With the increase of the normal load, the load capacity of scratched AG specimens decreased to about 40 MPa at 20gf immediately. However, the residual strength of CSG decreased to a steady value of 145 MPa as the scratch load increased to 500gf. Then the effect of hydrofluoric acid (HF) etching on the surface morphology and mechanical properties of the 500gf scratched glass were investigated. After 8min (for CSG) and 16 min (for AG) acid treatment, the flexural strength of CSG and AG increased to a considerable value of 900 MPa, which is 3.6 and 5.5 times higher than the flexural strength of undamaged specimens. Microscopic observations show that the blunting and eliminating of median cracks as well as the formation of new surfaces are the main causes of strength enhancement.     

Speed effect on the material behavior in high-speed scratching of BK7 glass

Scratch tests are often performed at a speed that is significantly lower than the real application like machining and grinding. However, brittle materials like BK7 behave very differently under high-speed conditions due to the more promising temperature and stain rate effects Therefore, it is important to study its material behavior under high-speed condition. In this study, single scratch tests and consecutive scratch tests were performed on BK7 under scratch speeds of 1, 5 and 20 m/s, which were much higher than the traditional scratch tests. The surface morphology as well as the subsurface cracks of the scratch grooves was inspected under AFM and FIB-SEM. The thermal effect that caused the changes in ductile-brittle transition (DBT) and scratch morphology was simulated and explained by a thermal-stress coupled finite element analysis. Finally, the changes in material removal behavior as well as the crack initiation mechanism due to speed effect was revealed.