Field strength effect on elastoplastic behavior of aluminoborosilicate glass: II. Volumetric recovery

The field strength (FS) effect of six different network modifiers on the elastoplastic properties of aluminoborosilicate glasses was explored using a volumetric recovery study. This work, in conjunction with Part I, explored the intersection of hardness, crack resistance, and other physical properties with glass elasticity. Results showed that (1) the elastic volume fraction decreased with FS for both the alkali and alkaline earth (AE) glasses; (2) the Poisson's ratio did not trend with pile-up or shear flow volume fraction; (3) the elastic-to-plastic deformation ratio increased with applied load and decreased with modifier FS for both the alkali and AE glasses; and (4) an increase in plasticity correlated with increased hardness, crack resistance, and elastic moduli.     

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.     

Temperature dependence of indentation size effect,dislocation pile‐ups,and lattice friction in (001) strontium titanate

Nanoindentations with a Berkovich type indenter were performed on (001) strontium titanate (STO) single crystal at 25°C and 350°C, analyzing the influence of temperature on the indentation size effect (ISE) and dislocation structure around the residual impression. It is found that the STO exhibits an ISE, which is strongly reduced at 350°C compared to 25°C. The dislocation structure around the residual impression has been resolved using an etch‐pit technique. At 25°C, the extension of the dislocation pile‐ups were found to be shorter as compared to 350°C. This also correlates with the smaller size effects at 350°C. Peach‐Koehler forces and the elastic‐plastic indentation stress field were used to model the influence of the lattice frictional stress on the dislocation pile‐ups. Based on an equilibrium position of the outermost dislocations, the average lattice frictional stresses were calculated to be 89 MPa and 46 MPa at 25°C and 350°C, 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.     

Contrast on tensile and flexural properties of glass powder reinforced epoxy composites: Pilot study

Epoxy resin was filled with glass powder to optimize the tensile and flexural strength of the composite for structural applications by a research center in the University of Southern Queensland (USQ). To reduce costs, the center wishes to fill as much glass microspheres as possible subject to maintaining sufficient strength of the composites in structural applications. This project varies the percentage by weight of the glass powder in the composites. After casting the composites to the molds, they were cured at ambient conditions for 24 h. They were then postcured in a conventional oven and subjected to tensile and flexural tests. The contribution of the study was that if tensile and flexural properties were the most important factors to be considered in the applications of the composites, the maximum amount of glass powder can be added to the resin will be five (5) percent. It was also found that the fractured surfaces examined under scanning electron microscope were correlated with the tensile and flexural strength It is also hoped that the discussion and results in this work would not only contribute toward the development of glass powder reinforced epoxy composites with better material properties, but also useful for the investigations of tensile and flexural properties in other composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

粉煤灰与矿渣再生骨料混凝土弹性模量的研究

研究了粉煤灰单掺、粉煤灰与矿渣双掺对再生骨料混凝土(RAC)弹性模量的影响,并初步探讨了其影响机理;建立了再生骨料混凝土弹性模量与立方体抗压强度的相关关系式。试验结果表明:粉煤灰单掺会降低再生骨料混凝土的弹性模量,粉煤灰与矿渣双掺对弹性模量的影响随两者组合比例不同而有显著差异。     

Fabrication of bioactive glass scaffolds by stereolithography: Influence of particle size and surfactant concentration

For decades, bioactive glass (BAG) has been utilized as a competent bone substitute owing to its intrinsic properties, such as outstanding biocompatibility and bioresorbability. Stereolithography (SL) is an additive manufacturing technology used to produce highly accurate three-dimensional BAG-based bone substitutes. However, the preparation of BAG-based SL resin is always a challenge, especially because of the inevitable sedimentation of BAG particles. In this study, BAG particles with different sizes were prepared by dry grinding (BAG_dry, greater particle size) and wet grinding (BAG_wet, finer particle size). Then, BAG_dry or BAG_wet SL resins with various amounts of surfactant were analyzed. The sedimentation rate for BAG powder increased with increasing particle size but decreased with increasing amounts of surfactant added to the resin. BAG_wet SL resins had a longer shelf life, so printing could still be finished after 14 days, whereas BAG_dry SL resins were no longer useable after 5 days. However, the BAG particle size did not affect the printing accuracy or scaffold strength. According to our results, BAG-based SL resin fabricated with BAG_wet (particle size <1.6 μm) and 5 wt% surfactant exhibited better resistance to sedimentation.     

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。     

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.     

Ionomer. I. The effect of woven glass mat reinforcement on tensile properties

An investigation was conducted on ionomer polymer. The ionomer pellets were molded into a thin sheet before fabrication into composites. The reinforcing agent used was woven glass mat. Before fabrication, the woven glass mat was treated with the following: 1. silane coupling agent for 5 min and dried at room temperature; 2. silane coupling agent for 5 min and dried in the oven at 110°C for 15 min; 3. Ultraviolet radiation for 5 min; and 4. silane (oven dried + ultraviolet). The composites were fabricated at various pressure, time, and temperature. An ideal processing condition was established, i.e., pressure = 5 MPa, temperature = 180°C, and the impregnation time = 30 min. The void contents of the composites were estimated using the ignition method and the tensile properties were measured. The results revealed that good impregnation of the matrix ionomer into the reinforcing agent can be achieved at 180°C. This was confirmed by low void content as compared with other test temperatures. Further clarification was through the tensile properties, which were higher than those at lower temperatures (120 and 150°C). The effect of fiber orientation was checked, and both 0 and 90° had identical strengths and moduli irrespective of the various fiber treatments. Apart from the void contents, the degree of impregnation was also checked based on the tensile strengths in 45, 25, and 60° fiber orientations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1395–1400, 2001     

Effect of potassium and silver ion-exchange on the strengthening effect and properties of aluminosilicate glass

In this work, the aluminosilicate glass was subjected to ion-exchange using the KNO₃-AgCl mixed molten salt in order to strengthen the glass while imparting antimicrobial properties. The concentration distribution of K⁺ ions and Ag⁺ ions of the ion-exchanged glasses was characterized by EDS, the effects of ion-exchange temperature (460-500 °C), ion-exchange time (0.5-3 h) and AgCl concentration (0–2.5 wt%) in the mixed molten salt on the strengthening effect and properties of the glass were investigated. The results showed that Ag⁺-Na⁺ ion-exchange, K⁺-Na⁺ ion-exchange existed simultaneously, and Ag⁺-Na⁺ ion-exchange occurred preferentially. Due to the presence of metallic silver, the appearance of the Ag⁺ ion-exchanged glass was light yellow and its transmittance showed a decrease. The surface compressive stress trended up and then down with increasing temperature and time because of the stress relaxation effect. The Vickers hardness of ion-exchanged glass increased by 15%, and the densities and chemical stability were also increased. Ions leaching experiments showed that the Ag⁺ ions release concentration of silver-loaded glass in aqueous environment can reach the bactericidal level. It has been shown that ion-exchange of glass in KNO₃-AgCl mixed molten salts allowed the glass to be strengthened and incorporated with antimicrobial active ions, its chemical stability was improved, too.     

Large size self-assembled quantum rings: quantum size effect and modulation on the surface diffusion

We demonstrate experimentally the submicron size self-assembled (SA) GaAs quantum rings (QRs) by quantum size effect (QSE). An ultrathin In_0.1 Ga_0.9As layer with different thickness is deposited on the GaAs to modulate the surface nucleus diffusion barrier, and then the SA QRs are grown. It is found that the density of QRs is affected significantly by the thickness of inserted In_0.1 Ga_0.9As, and the diffusion barrier modulation reflects mainly on the first five monolayer . The physical mechanism behind is discussed. The further analysis shows that about 160 meV decrease in diffusion barrier can be achieved, which allows the SA QRs with density of as low as one QR per 6 μm². Finally, the QRs with diameters of 438 nm and outer diameters of 736 nm are fabricated using QSE.     

弹性模量设定对胎圈钢丝破断伸长率和屈强比测试结果的影响

研究弹性模量设定值对胎圈钢丝断后伸长率和屈强比测试结果的影响。结果表明,胎圈钢丝断后伸长率和屈强比测试时,对于高强度胎圈钢丝,弹性模量设定值取其强度的40%～65%,以800～1400N.mm^-2为宜;对于普通强度胎圈钢丝,弹性模量设定值取其强度的50%～70%,以800～1200N.mm^-2为宜。     

基于结构胶种类及搭接长度变化的胶接接头剪切强度及应力测试分析

通过对3种类型(双组分丙烯酸酯结构胶、双组分环氧树脂结构胶、单组分环氧树脂结构胶)共9款结构胶的搭接长度–剪切强度曲线测试及回归方程拟合,获得搭接长度–剪切应力曲线并对比分析曲线差异,基于结构胶种类及参数提出匹配不同搭接长度的选胶建议。结果表明:对此3种类型的结构胶单搭接满黏结接头,随搭接长度延长,平均剪切强度减小;低模量胶的搭接长度–剪切强度曲线形态与高模量胶的相反,前者为由缓降转为陡降,后者为由陡降转为缓降最后稳定;单组分环氧树脂结构胶适用于承受静载结构;用于承受动载的接头,建议选用双组分结构胶,搭接长度30mm以下选用丙烯酸酯型,搭接长度30mm以上选用环氧树脂型。     

含粉煤灰微珠混凝土的强度和徐变特性研究

利用粉煤灰微珠按10%、20%和30%（质量分数）部分替代水泥制备了混凝土试样,并对混凝土试样的抗压强度、弹性模量和徐变进行了测试,同时通过压汞孔隙率实验对试样的微观结构进行了研究。结果表明,粉煤灰微珠会使混凝土的早期抗压强度和弹性模量下降,但是对混凝土长期强度增长和弹性模量增长有明显的促进作用,在90 d时粉煤灰微珠掺量为20%的试样强度和弹性模量最高。掺入20%的粉煤灰微珠可以降低混凝土的比徐变,但是过多的粉煤灰微珠反而会增加混凝土的徐变变形。孔隙分析结果表明,总孔隙体积较高时,混凝土的强度较低,徐变变形较大;而加入20%粉煤灰微珠会降低混凝土的中孔隙、大孔隙和总孔隙体积,从而改善混凝土的强度和徐变特性。     

Shape and size effects on the compressive strength of high-strength concrete

In this paper we investigate the influence of the shape and of the size of the specimens on the compressive strength of high-strength concrete. We use cylinders and cubes of different sizes for performing stable stress-strain tests. The tests were performed at a single axial strain rate, 10^{− 6} s^{− 1}. This value was kept constant throughout the experimental program. Our results show that the post-peak behavior of the cubes is milder than that of the cylinders, which results in a strong energy consumption after the peak. This is consistent with the observation of the crack pattern: The extent of cracking throughout the specimen is denser in the cubes than in the cylinders. Indeed, a main inclined fracture surface is nucleated in cylinders, whereas in cubes we find that lateral sides get spalled leading to the so-called hour-glass failure mode. The remaining cube core gets fragmented due to crushing, in some cases exhibiting a dense columnar cracking in the bulk of the specimen. Finally, we investigate the relationship between the compressive strength given by both types of specimen for several specimen sizes.     

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.     

Effect of particle size distribution of raw powders on pore size distribution and bending strength of Al2O3 microfiltration membrane supports

To lower the sintering temperature of Al₂O₃ microfiltration membrane support, Al₂O₃ powders with particle size distribution of tri-modal are chosen. The results show that the function of fine Al₂O₃ grains depends on their agglomeration state: if fine Al₂O₃ grains distribute discretely, the bending strength of the support increases along with a slight increase in porosity; however, the aggregated fine grains are harmful to both bending strength and pore size distribution of the support. The bridging of medium Al₂O₃ grains between coarse grains contributes to increase the bending strength, but has less effect on porosity. The addition of medium (and/or fine) Al₂O₃ powder has less effect on the pore size distribution of the support if only coarse Al₂O₃ grain forms the support's framework, which suggests a new way to prepare the support with both high bending strength and high porosity at low temperature.