Mechanical properties of carbon fibre-reinforced glasses

Carbon fibre-reinforced glasses exhibit very high values of flexural strength but usually a much less controlled fracture behaviour than SiC fibre-reinforced glasses. Some carbon fibre/glass composite combinations show a well controlled fracture, others a brittle fracture behaviour. The former combinations occasionally exhibit an increase in strength after an abrupt breakdown from the maximum strength. No correlation exists between the strength of the composites and the stresses in the glass matrix due to the thermal expansion mismatch between carbon fibres and glasses in contrast to the SiC fibre composites. The reason for that is seen in the structure of the surface and mainly in the anisotropic properties of the fibres, such as the large differences in the Young's moduli and thermal expansion coefficients parallel and perpendicular to the fibre axis. In particular, no radial compressive stress on the fibres can be built up at the fibre/glass interface because the thermal expansion coefficient of the fibres in the radial direction is much larger than that of the glass matrices used. Thus, the mechanism of load transfer from the matrix to the fibres is a complicated one, and cannot easily be predicted as in the case of the isotropic SiC fibres. A possible mechanism is described in order to interpret the experimental results.     

Analysis of brittle fracture of soda glass bottles under hydrostatic pressure

Imperfections in glass formed during manufacture or subsequent transportation can weaken bottles, creating a hazard by causing them to fail at lower pressure. When soda glass bottles are pressurized to fracture, the crack density in the broken glass and the fracture pressure are highly correlated. A higher fracture pressure yields a higher crack density as a result of the greater amount of stored energy released on fracture. Thus, after failure it is possible to estimate the pressure to which a bottle was subjected by analyzing the glass fragments. The crack patterns and density agree with analytical models for crack branching in brittle materials under stress. The crack patterns of pressurized bottles subjected to impact are also observed, and a minimum side impact velocity of 2.0 m/s for rupture of pressurized commercial soda glass bottles is determined.     

Cleavage in the K8 glass under submicrosecond impact loading

The dynamic strength of an optical glass of the K8 type was studied under submicrosecond impact loading conditions. A 80-ns-long pressure impact was generated by a laser radiation pulse acting upon an aluminum foil. The free sample surface velocity was measured by a laser differential interferometer. The onset of fracture at the free surface was detected using a He-Ne laser radiation reflected from a crack appearing as a result of the glass cleavage. The experimental data on the dynamic strength of a glass under submicrosecond impact loading conditions are obtained for the first time. For the K8 glass studied, the critical cleavage stress amounts to 0.45±0.03 GPa. Experimental investigations of the time characteristics of the fracture process, as well as the results of a fractographic analysis of the cleavage zone, do not unambiguously confirm the existence of the stage of damage accumulation during the fracture of inorganic glasses.     

玻璃纤维增强复合材料的Ⅰ型层间断裂韧性

介绍了玻璃纤维增强复合材料Ⅰ型层间断裂韧性“RoundRobinTest”的结果随着偶联剂浓度的改变，Ⅰ型裂纹的扩展方式从稳态向非稳态转变这类断裂韧性强烈地依赖界面性能关键词##4界面性能;;Ⅰ型断裂韧性;;裂纹扩展;;稳态;;非稳态     

Stable crack growth in a surface compression-strengthened hollow cylinder

In this paper the static fatigue problem for a circumferentially cracked hollow cylinder is examined. For this particular configuration, stable crack growth, in the absense of any external forces, is determined for cylinders with axial components of residual stress which are compressive on the inner and outer radial surfaces and tensile in the cylinder wall. An initial surface crack which is deep enough to penetrate the compression strengthened surface region and enters the tensile zone may propagate in a stable manner until either sudden spontaneous failure occurs or the crack arrests. Since a portion of the crack near the cylinder surface will be closed because of the compressive residual stress field, an additional unknown in the problem is the extent of the crack surface contact. This crack surface contact length is determined by iteration on the integral equation which arises in the mathematical derivation for an embedded circumferential crack in a hollow cylinder. As an illustration of stable crack growth for this geometry with a realistic residual stress distribution, numerical results are presented for a hollow, soda-lime glass cylinder, based on crack growth rates in soda-lime glass exposed to water at 25‡ C. Using the fracture toughness and slow crack growth characteristics for soda-lime glass, the conditions for no crack propagation, crack propagation leading to crack arrest, and catastrophic failure are established.     

Investigation of impact characteristics of tempered vehicle and vessel glasses

Glass is widely used at various engineering applications, especially in vehicle and vessel industry due to the reasons such as transparency, hardness at the room temperature and its strength against impact. One of the processes to be applied to glass is tempering. This process is applied to glass with the aim of providing 2–5 times more impact resistance. Additionally, if tempered glass is fractured it goes to pieces without sharp edges. These pieces are too small to injure people around them. Thus, nowadays side and rear glasses of vehicles and vessels are tempered glasses. In this study, tempered and untempered vehicle glasses were tested by using Instron Dynatup 9250 HV Impact Apparatus in the Mechanical Engineering Department of Pamukkale University, impact was applied to 145 samples with an average of 5.3 (771) times and their impact strength values were determined. In the first stage of this study, magnitudes of impact energies causing damages at tempered and untempered vehicle and vessel glasses with a thickness of 4 mm and 6 mm at +20 °C, were determined. In the second stage, impact experiments were performed at the environment temperatures of –20 °C and +40 °C apart from the room temperature, because the glasses to be produced will be used in different climate zones. In this way, a useful source of knowledge, especially for developing tempered vehicle and vessel glasses, will be constituted by determining the impact strength characteristics of these glasses.     

含半椭圆表面裂纹圆柱壳体的三维热弹性动态断裂

研究了含轴向半椭圆表面裂纹的圆柱壳体在热应力与冲击载荷作用下的动态断裂情况,并应用所研制的三维动态断裂有限元程序进行了大规模的数值计算,确定了圆柱壳体的三维温度分布及热-力耦合下的动态应力强度因子,所得结果在一定程度上揭示了热-力作用下圆柱壳体的边界表面、裂纹面、物质惯性和弹性波的相互作用在结构动态断裂中的重要性。     

The Fractography and Crack Patterns of Broken Glass

The topographical features which appear on the fracture surfaces of broken glass objects and the resulting crack patterns which develop are Nature’s documentation of the fracture event. They are considered after a brief discussion of glass strength. Strength is central to the fracture surface features for it determines the strain energy release rate and the dynamics of crack extension. The surface features known as the mirror, the mist, and the hackle are illustrated and addressed through the principles of fracture mechanics and associated energy criteria. Quantitative aspects of the fracture process such as the stress level at fracture for a glass object are directly related to the size of the fracture mirror. The concept of a fracture mirror constant is related to the strength. Formation of the mist and hackle surface regions are also fundamentally addressed, as is crack branching. Distinctive crack patterns that evolve during fracture, that is the traces of the cracks intersecting the glass free surfaces, are described. Dicing fragmentation of high-strength tempered glass and the long sword-like shards of low-strength annealed glass fracture are contrasted through their strain energies. Characteristic cracking patterns are reviewed for several common glass fractures including those for pressure breaks, both bottle explosions and flat glass window failures from wind pressure whose basic similarities are described. The patterns of crack branching or forking, the branching angles and the crack length prior to forking, are also discussed. Other glass crack patterns such as those from impact and thermal stress are also considered.     

Prediction of stable crack growth geometry in residually stressed glass

Processing procedures have been developed that produce stress distributions in glass with a maximum compressive stress below the surface. These glasses can exhibit rising apparent fracture toughness behavior and reduced strength variability associated with the stable growth of surface cracks under applied tensile stress. A weight function approach was used to determine stress intensity factors as a function of crack geometry for surface cracks under the effects of stress distributions similar to those found in these glasses. These calculations were then used to predict the growth behavior of surface cracks as a function of the applied and residual stress fields.     

Comparison of compressive deformation and fracture behaviors of Zr- and Ti-based metallic glasses with notches

Compressive tests on the Zr- and Ti-based metallic glasses with different notches were investigated to compare their shear fracture mechanism and plastic deformation abilities. It is found that the plasticity of the two metallic glasses can be improved by installing two semicircular symmetrical notches even for the Ti-based metallic glass which has nearly zero compressive plasticity. The enhanced plasticity may be ascribed to the easy initiation of shear bands (SBs) around the notches, and the consequent blocking effect of notches on the propagation of shear bands according to the large-scale stress gradient. Additionally, based on a theoretical model originated from the concept of critical steady shear displacement (CSSD), compared with the sizes of smooth regions on the fracture surface, the plasticity difference of the two different metallic glasses was analyzed quantitatively. The current findings might provide an approach to understand and estimate the difference in the plastic deformation abilities on diverse metallic glasses, as well as the ones with large-scale stress gradient.     

Strong and Tough Glass with Self‐Dispersed Nanoparticles via Solidification

Glassy materials can be broadly defined as any amorphous solid, which are important in nature and have significant societal value for their applications in daily life and industry. Although many methods have been applied, the fracture toughness of traditional glasses is still very low due to intrinsic brittleness, significantly limiting their use for structural applications. While nanoelements may be added into glasses and ceramics to form nanocomposites with enhanced properties, it is extremely difficult to distribute and disperse them inside the liquid glass/ceramic matrix with traditional processing methods. It is shown that a strong and tough glass can be fabricated through a direct‐solidification process using a nanoparticle self‐dispersion mechanism in a glass melt (2MgO·2Al₂O₃·5SiO₂) with the assistance of B₂O₃, delivering a 6.1% strain limit and strength up to E/14 (E is elastic modulus), which is close to the theoretical limit of E/10 and one of the highest among all materials reported so far. The fracture toughness of the glass with 30 vol% SiC nanoparticles is significantly higher than any other inorganic glass tested under similar conditions. This new method opens up remarkable opportunities for glass and ceramic research, manufacturing, and applications.     

Unidirectional Fracturing of Super Engineering Plastic Films

Polyamideimides and polyimides are prepared based on chemical imidization using aromatic diamine, diacid anhydride, and diacid chloride as monomers, with the precursor polyamic acid remaining in part, to produce mechanically unique films through convection drying. The resulting films are colorless and transparent and exhibit unidirectional fracture behavior. These films do not break when bent in the direction of the air contact surface but easily break when bent in the opposite direction. A cross-sectional electron microscope image of the broken film shows that the film consists of a double layer. After examining both sides of the film through various spectroscopic and gel permeation chromatography analyses, it is found that the residual polyamic acid undergoes both hydrolytic and thermal decomposition, exclusively on the air contact surface. Later, the polymer film is laminated with two sheets of glass through UV curing of commercial acryl resin. Because of the unidirectional fracture characteristics of the film, the laminated glass does not completely break when subjected to bending toward the air contact surface but easily breaks (without fragments) in the opposite direction, indicating its potential application in safety glasses suitable for emergency escapes.     

皮卡车钢板弹簧断裂分析

通过断口分析、化学成分分析、金相检验和硬度测试对皮卡车的钢板弹簧断裂的原因进行了分析。结果表明:钢板弹簧表面存在凹坑造成了应力集中,而且板材的非金属夹杂物超标,降低了疲劳强度,在交变应力载荷的作用下,最终造成钢板弹簧发生了早期疲劳断裂。     

Surfaces formed by subcritical crack growth in silicate glasses

The topography of surfaces formed in glass by subcritical crack growth was investigated by a method of mapping using atomic force microscopy. The objective of the study was to determine how well “upper” and “lower” surfaces matched after having been formed by a crack moving at slow velocity. The question arose, were features left in the fracture surfaces of silicate glasses that would indicate the formation of cavities during the fracture process? Studies were performed on silica glass and soda-lime-silicate glass. Fracture surfaces were formed either in water or in moist environments at velocities that ranged from 10^?2 m/s down to 10^?10 m/s. This procedure covered almost the entire range of velocities used for subcritical crack growth experiments in glass. Opposing fracture surfaces formed during our studies were found to “match” over the entire range of velocities and for all environments studied. For silica glass, the surfaces were found to match to an accuracy of better than 0.3 nm normal to the fracture surface and 5 nm within the fracture surface. For soda-lime-silicate glass, surfaces were found to match to an accuracy of 0.5 nm to 0.8 nm normal to the fracture surface and 5 nm within the fracture surface. Within these limits, no evidence for cavitation was found in either glass.     

变电站阻波器吊环断裂原因分析

变电站阻波器吊环在受力较小的情况下异常断裂。为查清断裂原因,运用宏观检验、扫描电镜及能谱分析、金相检验等方法进行了深入探讨。结果表明：吊环为疲劳断裂,断裂源位于吊环外表面,该部位同时存在机械损伤及应力集中;材料中较多的夹杂物及晶间析出物进一步降低了材料的疲劳强度,以上诸因素共同作用,最终导致了吊环的断裂失效。     

快卸卡箍螺栓断裂原因分析

通过断口形貌观察、X射线能谱分析、金相检验和硬度检测等试验方法,对某燃油供油导管快卸卡箍螺栓的断裂原因进行了分析,并与螺栓冲击断口和氢致疲劳断口进行了比较分析。结果表明:该快卸卡箍螺栓断口特征与冲击断口和氢致疲劳断口明显不同,其断裂性质为应力腐蚀断裂,裂纹起源于螺栓光杆段的侧表面;螺栓表面加工粗糙且没有防护对裂纹的萌生有一定的影响。对螺栓表面进行防腐处理可有效避免该类故障的再次发生。     

冰箱压缩机阀片断裂失效分析

压缩机是冰箱的心脏,压缩机阀片的断裂失效可引起制冷系统严重故障。本文利用表面应力分析、金相组织和显微硬度分析、成分分析等方法,以及三维视频光学显微镜、扫描电子显微镜等,研究了阀片断裂的特征和机制。断口和裂纹分析表明,阀片失效是疲劳断裂机制,断口具有明显的疲劳扩展区和多处裂纹源。阀片的材质和组织正常。阀片表面的局部损伤容易引起断裂。塑料垫片和阀片形状设计对断裂失效有重要影响。在上述分析的基础上,提出了质量改进措施并取得了良好效果。     

In situ observation of crack propagation in ESP (engineered stress profile) glass

Important features of the ESP (engineered stress profile) glasses are the crack arrest and multiple cracking phenomena that occur even in an unstable stress field. In this work a detailed “in situ” observation of crack observation and analysis was performed with the aim to examine crack propagation in detail and relate it to the residual stress field produced by ion exchange and to the final mechanical performances of the material. The results showed that the peculiar residual stress field with a maximum below the surface is responsible for the formation of a multitude of stable cracks on the tensile surface of the glass that evolved into through-thickness flaws. The propagation within the material is limited by the increasing compressive residual stress, which also leads to kinking of the cracks in a direction parallel to the surface. The observed fracture phenomena are also responsible for a shielding effect that makes the measured failure resistance of ESP glass larger than predicted by simplistic single crack models.     

Structure,thermal properties,dissolution behaviour and biomedical applications of phosphate glasses and fibres: a review

For the last few decades, there has been a growing interest in using glasses for biomedical applications. Bioactive glasses are a group of surface reactive glasses which can initiate a range of biological responses by releasing ions into the local environment. Silicate, borate and phosphate glasses are known to show good bioactive characteristics and could be potentially used as favourable templates for bone-tissue formation. Phosphate glasses are unique group of materials that offer great potential for hard and soft tissue engineering over other types of bioactive glasses due to their fully resorbable characteristics, with some formulations possessing chemical composition similar to the mineral phase of natural bone. Moreover, these phosphate glasses can be prepared as fibres which could be used for soft tissue engineering and as fibrous reinforcement for resorbable polymers such as poly-(lactic acid) for fracture fixation applications. This review details some of the properties of phosphate glasses, such as thermal, viscosity/temperature, dissolution and biocompatibility of and how different factors can effectively alter these properties. The effect of the addition of different modifier oxides on the structure in terms of chain length is included. This review also reports on the manufacturing process, mechanical properties and biomedical application of phosphate glass fibres. A brief comparison between three different types of bioactive glasses has also been presented in this review. The main aim of this review is to present the factors affecting the properties of phosphate glasses and glass fibres and how these may be exploited in the design of a biomaterial.     

X-ray Micro Computed Tomography investigation of accelerated thermal degradation of epoxy resin/glass microsphere syntactic foam

The heat resistance and the structural integrity of syntactic foam materials are vital for their high performance. Syntactic foam made of hollow glass microspheres and Diglycidyl Ether of Bisphenol A (DGEBA) based epoxy resin cured with Isophorone Diamine (IPD) hardener was subjected to oxidative thermal stress cycles. The degraded syntactic foam sample was examined using an X-ray Micro Computed Tomography (XμCT) to evaluate its internal damage between each state in a combined effect of cycling and increased temperature. Glass microsphere fracture, void enlargement and resin microcracks were observed as a result of the thermal stress using 3D XμCT images. The reconstructed slice representation showed the microcracks and microsphere damage distribution inside the sample. The damaged glass spheres percentage is shown to increase sharply with the progress of the thermal cycle. There was no change in the local density of the syntactic foam as a result of the thermal cycle. An XμCT system proves to be a successful non-destructive technique for examining syntactic foam for defects and structural damages in the micron scale.