Classification of ceramics and glass (edge chipping and fracture toughness)

The standard classification of advanced ceramics is based on their strength, although in many cases the performance of products made of such materials is controlled by their deformation behavior and fracture resistance. In this article, ceramics and glass are classified according to their edge chipping resistance (EF-method). Such a classification is based on the idea of a baseline (direct proportionality between edge chipping resistance and fracture toughness of ceramics that are similar to the model material of linear elastic fracture mechanics). Use was made of various elastic and inelastic, oxide and non-oxide ordinary ceramics, composite ceramics capable and incapable of retarding cracks and intended for engineering and biomedical applications. Attention is also given to silicate glass.     

Role of cement content on the properties of self-flowing Al2O3 refractory castables

In this work, Al₂O₃ self-flowing castables (SFCs) were produced based on various cement contents. The SFCs were sintered at 1273 K, 1573 K and 1773 K and the exhibited properties were experimentally determined. Among the properties determined in this work are bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS), modulus of rupture (MOR) and fracture toughness (K_IC). It is found that additions of 5% cement lead to SFCs with maximum MOR and K_IC values after firing at 1773 K. Firing at 1573 K leads to a reduction in both, MOR and K_IC. In SFC containing 3% cement, maximum K_IC values of 3.53 MPa m^1/2 were achieved after firing at 1573 K. In the low cement SFCs (1 wt%) after firing at 1773 K the exhibited K_IC values were below those obtained in either the SFC-3 or SFC-5, but they were significantly high (3.43 MPa m^1/2).     

In situ fabrication of highly-dense Al2O3/YAG nanoeutectic composite ceramics by a modified laser surface processing

Alumina-matrix eutectic in situ composite ceramics present excellent high-temperature mechanical properties, which have been considered as promising next-generation ultra-high temperature structural materials. A modified laser surface processing is developed to in situ fabricate highly-dense Al₂O₃/YAG bulk nanoeutectic ceramics with large size and homogeneous three-dimensional network of nanoeutectic microstructure by introducing two-side remelting and high-temperature preheating. The crack and porosity are avoided, and the eutectic structure achieves a good continuous growth between two solidified layers. The eutectic phases show sharp interface bonding with a defined orientation relationship. The dislocations and crack deflection at high-density phase interfaces importantly contribute to the enhanced fracture toughness.     

Fracture toughness of zirconia from a shallow notch produced by ultra-short pulsed laser ablation

Fracture toughness of submicron grain size tetragonal zirconia polycrystals doped with 3 mol% yttria (3Y-TZP) is measured by the single edge V-notch beam (SEVNB) method from a shallow sharp notch produced by ultra-short pulsed femtolaser ablation (UPLA) on the surface of a bending bar. It is shown that the radius of the notch tip achieved is in the submicron range and the damaged volume in front of the notch tip is characterized by using focus ion beam milling and scanning electron microscopy. It consists of a narrow fully microcracked region less than ∼4 μm wide and ∼15 μm deep in front of the notch. If the extension of this region and the length of the notch are used in the determination of the fracture toughness (K_Ic) in the four bending test, the values obtained for submicron grain size 3Y-TZP are in agreement those obtained by using very sharp cracks. It is concluded that the SEVNB testing method with a sharp notch induced by UPLA may be used for K_Ic testing of submicron grain size ceramics.     

高延性水泥基复合材料的断裂性能分析

实验测试了不同纤维掺量下的高延性水泥基复合材料的载荷—挠度曲线,并对试件加载过程中的声发射信号进行收集,分析了试件断裂后的裂纹分布及纤维在基材中的破坏形式。结果发现:(1)当纤维体积掺量2.0%时,水泥基材的极限挠度、极限抗弯承载力分别可达20.16mm、19.47MPa;(2)高延性水泥基复合材料破坏主要来自于微裂纹的萌生、扩展以及损伤积累过程,试件从加载至完全破坏的时间为素水泥基复合材料破坏持续时间的2~5倍;(3)高延性水泥基复合材料中纤维的破坏以纤维被拔出和纤维被拉断两种模式,试件表现出明显的多缝开裂特征。     

下寺湾油田柳洛峪区长8油层组裂缝特征与开发效果关联评价

利用构造应力场的研究结果,结合岩心薄片观测和测井解释资料,本文对下寺湾油田柳洛峪区长8油层组裂缝特征进行了综合研究。结果表明：研究区长8储层微裂缝以构造缝为主,占微裂缝总数的70%;大部分为全充填缝（即闭合缝）;充填物成分主要为泥质,少数为方解石和铁质及其它充填物;压裂施工过程中当油井不存在过井天然缝时,压裂过程中破压明显,产生新人工缝。当存在过井天然缝时,压裂过程中破压不明显,人工缝沿天然裂缝延伸。长8层的裂缝方位与构造最大主应力方向一致,均为为北偏东70°左右。     

砂泥岩裂缝性储层测井识别及评价技术

致密砂岩裂缝储层形成的复杂油气藏,已经成为国内外油气勘探开发的焦点,常规勘探理论和方法在裂缝型油气藏评价中面临许多挑战,本文从砂泥岩裂缝型油气藏储层评价出发,分析各种常规预测裂缝有利发育带方法的优势和局限性,针对砂泥岩裂缝性储层识别这一难点,提出利用测井方法综合预测裂缝发育带的方法,指出储层裂缝预测研究存在的问题及发展趋势。     

定向拉伸对有机玻璃性能的影响

介绍了定向拉伸的原理,从工艺角度阐述了定向拉伸对有机玻璃性能的影响。     

Effects of soft-segment prepolymer functionality on the thermal and mechanical properties of RIM copolymers

Segmented copolyureas (PUr) and copoly(urethane–urea)s (PUU) comprising 50% by weight of polyurea hard segments (HS) and polyether soft segment (SS) with different functionalities, have been formed by reaction injection moulding (RIM). The HS were formed from 4,4′-diphenylmethane diisocyanate reacted with mixed isomers of 3,5-diethyltoluene diamine. The nominal functionality of the SS prepolymers used (either amino- or hydroxyl-functionalised polyoxypropylenes with a constant molar mass per functional group of ∼ 2000 g mol⁻¹) was systematically increased from 2 to 4. RIM materials were characterised using dynamic mechanical thermal analysis, differential scanning calorimetry, tensile stress–strain and fracture mechanics studies. Generally, the PUr exhibited far superior thermal-mechanical properties than equivalent PUU materials but inferior fracture resistance, owing to morphological variations resulting from differences in copolymerisation behaviour. For both systems, tensile behaviour was shown to be dominated by the degree of phase separation, whereas fracture properties showed a degree of dependence on SS functionality.     

HYPERSINGULAR BEM FOR TRANSIENT ELASTODYNAMICS

The topic of hypersingular boundary integral equations is a rapidly developing one due to the advantages which this kind of formulation offers compared to the standard boundary integral one. In this paper the hypersingular formulation is developed for time-domain antiplane elastodynamic problems. Firstly, the gradient representation is found from the displacement one, removing the strong singularities (Dirac's delta functions) which arise due to the differentiation process. The gradient representation is carried to the boundary through a limiting process and the resulting equation is shown to be consistent with the static formulation. Next, the numerical treatment of the traction boundary integral equation and its application to crack problems are presented. For the boundary discretization, conforming quadratic elements are tested, which are introduced in this paper for the first time, and it is shown that the results are very good in spite of the lesser number of unknowns of this approach in comparison to the non-conforming element alternative. A procedure is devised to numerically perform the hypersingular integrals that is both accurate and versatile. Several crack problems are solved to show the possibilities of the method. To this end both straight and curved elements are employed as well as regular and distorted quarter point elements.