玻璃及微晶玻璃的脆性表征

脆性是玻璃和陶瓷等材料的一个重要力学性能,但是目前对于脆性材料的脆性表征,没有统一的明确的表征方法.简述了玻璃及微晶玻璃的脆性断裂机理,对文献中可见的各种脆性表征手段进行了综述和比较,认为压痕法是一种方便、快捷、高效和低成本的实验方法.进一步,本文用压痕法对不同的微晶玻璃的脆性进行了测试,并和抗冲击法进行了对比,结果表明,压痕法对样品脆性的区分能力可以满足对微晶玻璃进行脆性评价的需求,可用于玻璃与微晶玻璃的脆性评判.     

玻璃的脆性(四)

综述了裂纹的容忍度与玻璃脆性的关系。对不同品种玻璃的裂纹扩展力也作了阐述。此外,还讨论了应力腐蚀下各种玻璃的裂纹扩展速度和影响裂纹扩展的因素。     

玻璃的脆性(五)

阐述了采用合适的玻璃成分,降低玻璃中的微观和宏观缺陷、减少玻璃表面裂纹和进行表面处理等措施,以降低玻璃的脆性。     

耐冲击无机合成材料

玻璃和陶瓷虽然具有足够高的耐压强度,但作为结构材料,均有共同的弱点:在张应力的作用下易于爆碎,这种情况特别是发生在制件表面有裂纹的时候。曾试图用石墨与金属丝强化玻璃和陶瓷材料,但均未改变其脆性。     

陶瓷及玻璃力学性能评价的一些非常规技术

介绍了陶瓷、玻璃等脆性材料力学性能评价的一些非常规技术,包括:脆性材料的损伤容限、层状材料和镀膜材料的力学性能和界面强度测试、材料表面局部强度的非破坏性测试,弹性模量和能量耗散能力的估评、残余痕迹预测材料性能等。这些方法可以对服役中的构件进行在线测试和可靠性预测,为陶瓷及玻璃等脆性材料的工程应用和安全检测提供了一些简易的评价手段。     

玻璃的脆性(三)

玻璃的缺陷可分为纳观缺陷、微观缺陷和宏观缺陷。纳观缺陷为纳米尺度的缺陷,指玻璃结构缺陷,包括微相、微不均、配位不全,空穴等。微观缺陷指微米尺度缺陷,主要为玻璃表面Griffith裂纹。宏观缺陷为玻璃制造中产生的缺陷,如气泡、结石、条纹,以及使用过程中的损伤。这些缺陷的存在增加玻璃的脆性。描述了玻璃表面Griffith裂纹的尺寸、分布以及形貌。     

在玻璃中加入金属颗粒以提高其韧性

本文叙述了在脆性材料中加代金属颗粒作为第二相以提高其韧性的研究结果.通过研究揭示了脆性材料的弹性、热弹性和层间性质对金属颗粒增强的复合材料的断裂韧性的影响.在研究中采用了两种复合材料,一种是玻璃与部分氧化的镍粒组成的复合材料,另一种是玻璃与部分氧化的铝颗粒组成的复合材料.     

玻璃的脆性(一)

评述了玻璃脆性的特征。维氏硬度和断裂韧性的比例可方便地确定玻璃脆性,并计算了不同成分玻璃的脆性。石英玻璃的脆性最大,氧化物玻璃次之,金属玻璃最小。而在氧化物玻璃中,微晶玻璃脆性最小,铝硅酸盐玻璃次之,钠钙玻璃又次之。     

玻璃黏度理论模型的研究进展

玻璃黏度对玻璃材料的研制、应用和发展起着重要的作用.本文介绍了与活化能、自由体积、构型熵及液相脆性相关的经典黏度理论基础.根据影响玻璃黏度的主要因素,介绍了国内外有关黏度-温度,黏度-结构和黏度-组成之间的计算模型及近年来的研究成果,并对玻璃黏度计算模型的发展进行了展望.     

玻璃的脆性(一)

评述了玻璃脆性的特征。维氏硬度和断裂韧性的比例可方便地确定玻璃脆性,并计算了不同成分玻璃的脆性。石英玻璃的脆性最大,氧化物玻璃次之,金属玻璃最小。而在氧化物玻璃中,微晶玻璃脆性最小,铝硅酸盐玻璃次之,钠钙玻璃又次之。     

A fractal analysis of crack branching in borosilicate glass

Many fractography techniques involve precise measurements of features on the fracture surface and can be difficult to perform in the field, or rapidly. Macroscopic crack branching observations offer a more robust and forgiving method of analysis, but often are not strongly correlated with standard fractography techniques. In this study, the crack branching patterns of annealed borosilicate glass disks previously fractured in biaxial tension were analyzed using fractal methods and compared with more typical fracture surface measurement techniques. The results confirm that the fractal dimension of macroscopic crack branching (called the Crack Branching Coefficient) increases with increasing failure stress, as has been shown with other brittle materials. In addition, the existence of a threshold stress previously reported was confirmed using new techniques. The findings herein can be used to further increase the fidelity of fractography-based failure analysis of brittle materials.     

Crack propagation in biaxially oriented polypropylene at low temperature

The crack growth behavior of polypropylene biaxially oriented by cross-rolling was studied at low temperature. Single edge notch testing produced a stable tearing type of crack growth in both 50% and 80% biaxially oriented polypropylene at ?40°C, in contrast to the brittle fracture of unoriented polypropylene. The crack growth in the two oriented materials began slowly and accelerated to a constant rate that was higher in the 80% oriented material than in the 50% oriented material. The main difference between the crack growth behavior of the two was the longer period of initial slow growth in the case of 80% orientation. This period of slow growth corresponded to crack growth through the notch tip damage zone. Residual strength diagrams were used to present the crack growth data obtained when the stress state was intermediate between plane stress and plane strain. Fractography revealed large differences among the fracture surfaces of the three materials with the unoriented polypropylene showing a grainy appearance from the brittle fracture. The two oriented materials showed considerable ductility. The 50% oriented material showed many voids in the fracture surface, indicating that voiding during the fracture process contributed significantly to the toughness improvement. The 80% oriented polypropylene showed delamination crazing on the fracture surface with layered material and fibrils bridging the crazes.     

玻璃在平面双向和单向应力状态下慢裂纹扩展特性

采用热弹性力学方法对含裂纹的玻璃薄片在双向和单向平面拉和下的亚临界裂纹扩展进行了观测和研究。该实验方法使得玻璃、陶瓷等危性材料的双向拉伸,直通裂纹预制和裂纹扩展过程记录这３个难度大的实验得以完成。对６０多个玻璃试件的断裂阻力随载荷速度的变化进行了观测和分析,从而较精确地了解了玻璃在平面和状态下的阻力曲线和断裂特性。     

双金属材料复合圆板Ⅲ型界面裂纹扩展的研究

采用分离变量的方法求解了双金属材料复合圆板Ⅲ型界面裂纹动态扩展问题,得到了裂纹尖端的应力、位移场的理论解表达式,并通过典型算例,研究了裂纹区应力、位移及应力强度因子等关系,为认识双金属材料复合圆板Ⅲ型界面裂纹扩展机理提供理论依据。     

Evaluation of crack-Growth resistance curve for a particulate ceramic–Metal composite

A technique is described to evaluate the crack growth resistance behaviour in brittle ceramic-base materials. In this method, the crack increment measurements during the stable crack propagation process are not required. The crack growth resistance curves are studied for a particulate ceramic–metal composite in the system lanthanium chromite–chromium. Experiments were performed with standard fracture mechanics single-edge notched beam specimens in a temperature range from room temperature up to 1100°C. Effect of temperature on crack growth resistance behaviour is discussed.     

A New Method for Precracking Beam for Fracture Toughness Experiments

A simple and versatile precracking method using a triangular notch as a crack starter in limited bending was developed, which is suitable for both brittle ceramics and quasi-plastic materials that are difficult to precrack by the conventional bridge-indentation technique. Slow growth of large crack in brittle or quasi-brittle ceramics was controlled and observed in situ in this way. The precracking tests performed on various ceramics exhibited high reliability and feasibility. The precracked specimens were subsequently used to measure the fracture toughness, and the resultant data showed that the fracture toughness determined by using the precracked specimens reflected the minimum value of the toughness measured in single edge-notched beam (SENB) tests.     

Finite-Element Simulations of Cracks Near Interfaces: Effects of Thermal, Elastic, and Plastic Mismatch

Cracks situated parallel to, and very near, the interface in layered, ductile-brittle composite specimens were investigated with finite-element analysis. Elastic, plastic and thermal properties previously obtained from experiments were utilized in the model. A routine was employed for automatic crack extension and remeshing, enabling simulation of incremental crack propagation. The elastic, thermal and plastic contributions to crack propagation behavior were investigated, along with the variation of these with crack length and crack-tip position. Thermal residual stresses are shown to have a large influence on crack path, although this is mitigated to some extent by plasticity. The implications on the inherent reliability of joints and layered materials containing brittle constituents are discussed.     

Crack Growth in Solid Oxide Fuel Cell Materials: From Discrete to Continuum Damage Modeling

This paper addresses the damage and fracture issues of glass and ceramic materials used in solid oxide fuel cells. Analyses of an internal crack and of an interface crack between dissimilar materials were conducted using a modified boundary layer modeling approach. In this approach, fracture is allowed to occur in a small process window situated at an initial crack tip. Elastic displacement crack-tip fields are prescribed as remote boundary conditions. Crack propagation was first modeled discretely. Next, a continuum damage mechanics (CDM) model for brittle materials was developed to capture damage and crack growth in the process window. In particular, the damage model was applied to a glass-ceramic material that had been developed in-house for sealing purposes. Discrete and continuum damage solutions were then compared. Finally, the CDM model was used to determine the crack propagation direction as a function of a mode mixity measure.     

Prediction of ring crack initiation in ceramics and glasses using a stress–energy fracture criterion

Crack initiation in brittle materials upon spherical indentation is associated with the tensile radial stresses during loading. However, location of crack onset often differs (offset) from the site of maximal stress. In addition, experiments reveal a strong dependency of crack initiation forces on geometrical parameters as well as the surface condition of the sample. In this work, a coupled stress–energy fracture criterion is introduced to describe the initiation of ring cracks in brittle materials, which takes into account the geometry of the contact and the inherent strength and fracture toughness of the material. Several experiments reported in literature are evaluated and compared. The criterion can explain the location offset of the ring crack upon loading, as observed in various ceramics and glasses. It also predicts the ring crack initiation force upon contact loading, provided that surface compressive stresses, introduced during grinding or polishing processes, are taken into account. Furthermore, the stress–energy criterion may be employed to estimate the surface residual stress of ceramic parts, based on simple contact damage experiments.     

Mechanical evaluation of propylene polymers under static and dynamic loading conditions

The present investigation is concerned with the evaluation of the impact toughness of commercial‐grade Propylene polymers. Conventional impact static stress–strain and static fracture experiments were carried out. Static stress–strain experiments revealed different pattern behaviors among the materials that were reflected in the fracture behavior. Under static conditions, all materials exhibited ductile behavior and crack grew under J‐controlled conditions displaying stress whitening through the whole fracture surface with the sole exception of the homopolymer, which displayed a ductile instability after some stable crack growth. Under dynamic conditions the homopolymer exhibited brittle behavior, the block copolymer exhibited some plastic deformation at the crack tip, and the random copolymer samples exhibited a whitening effect due to voiding and craze formation through the whole fracture surface, indicating that stable crack propagation was occurring. Fracture mechanics tests were analyzed by following different methods, depending on the mode of fracture presented by the polymer. The Normalization J‐method was used under static conditions. The elastic method, the corrected elastic method, and the essential work of fracture methodology were used to characterize brittle, semibrittle, and ductile behavior, respectively. Fracture mechanics parameters arisen from both static and dynamic conditions are compared. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2681–2693, 1999