陶瓷基复合材料界面结合强影响断裂过程的有限元研究

提出了纤维增强复合材料断裂有限元模型,该模型既用弹簧单元考虑了基体与纤维之间的分离,又用接触单元考虑了基体与纤维之间的摩擦,较真实地模拟了纤维增强复合材料的断裂过程。通过有限元计算,预测了基体与纤维之间的界面结合强度对整个复合材料断裂模式的影响。还对强弱两种不同基体弹性模量的材料进行进一步的探讨。对比其他文献 , 本文中预测结果与真实情况较为吻合。结果表明,对于纤维增强复合材料,不论是强基体还是弱基体,适中的界面结合强度有助于提高其韧性及整体抗拉强度。       

The effect of plasma polymer coating using atmospheric-pressure glow discharge on the shear bond strength of composite resin to ceramic

If plasma technology can come out of the vacuum chamber and plasma can be extruded through a small pencil-type torch, it can be applied widely to dental practices. For this study, we designed a small pencil-type non-thermal atmospheric-pressure glow discharge plasma torch. The purpose of this study was to determine the effect of plasma polymer coating on the adhesion of composite resin to feldspathic porcelain. The effect of plasma polymer coating was evaluated using shear bond strength (SBS) test. Contact angle measurements and fracture mode analysis were also performed. Among the groups treated with plasma polymer coating, the SBS of the adhesive (Adper Scotchbond Multi-Purpose, 3M ESPE) to the ceramic surface pre-treated sequentially with water plasma and triethyleneglycol dimethacrylate (TEGDMA) plasma in helium gas was significantly higher than that of the adhesive to the untreated surface (p < 0.05). In this group, the predominant fracture mode was mixed fracture, where small cohesively fractured fragments of ceramic were dispersed on the adhesively fractured flat adhesive surface. However, the SBS values of all the plasma polymer-coated groups were lower than those obtained through a routine porcelain bonding procedure with HF acid and silane coupling agent (p < 0.05). The non-thermal atmospheric-pressure plasma polymer coating technique was found to have a potential promoting adhesion to dental materials.     

The effect of grinding on the flexural strength of a sialon ceramic

The effect of selected grinding parameters on the flexural strength of a sialon ceramic was studied. Support compliance was found to have no significant effect, while depth of incursion and grinding direction did. Weibull statistics and analysis of variance techniques were used to detect these effects which are explained through flaw magnitude and direction.     

Dissolution of quartz in vitrified ceramic materials

The dissolution of quartz in vitrified ceramic materials was investigated. A mathematical model was derived and compared with published data and experimental data using X-ray diffraction techniques. When compared with published experimental data, the model correlated better than other dissolution models. However, over longer periods of heat treatment, the model becomes less accurate. The model may be of practical use in describing various types of kinetic data used by manufacturers of vitrified ceramic materials. This revised version was published online in November 2006 with corrections to the Cover Date.     

R-curve effect on strength and reliability of toughened ceramic materials

An improved theoretical analysis is presented for the strength and mechanical reliability of ceramic materials with an R-curve characteristic. There is good agreement between the predicted flexural strength distribution of an Al₂O₃/ZrO₂ ceramic and experimental datA. Unlike the conventional two-parameter Weibull approach, this new analysis is able to predict the non-linearity observed in the lnln 1/(1–P _f) versus In _f strength distribution curve. Compared to the untoughened Griffith material, the R-curve material has higher strength and better strength reliability.     

Time gap effect on bond strength of 3D-printed concrete

An advancing technology that combines the concrete extrusion with a motion control to create structures with complex geometrical shapes without the need for formwork is known as 3D concrete printing. Since this technique prints layer by layer, the time taken to reach the same position in the subsequent layer is important as it will create an anisotropic property that has a weaker tensile strength at the bond interface of the two printed filaments. Through rheological measurement, which reveals the material deformation and flow behaviour, it is possible to examine the material structural build-up due to time-gap effect by measuring at different time delay. This paper focuses on investigating the time-gap effect on the printed filament with rheological and observation at macroscopic-scale to understand the material behaviour of the initial and subsequent printed layer during its fresh phase. Rheological experiment findings reveal that the tensile strength of the printed specimen is correlated to the material modulus at the initial layer.     

The effect of silane contents on fluidity and green strength for ceramic injection moulding

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Fibre-matrix bond strength studies of glass,ceramic, and metal matrix composites

An indentation test technique for compressively loading the ends of individual fibres to produce debonding has been applied to metal, glass, and glass-ceramic matrix composites; bond strength values at debond initiation are calculated using a finite-element model. Results are correlated with composite longitudinal and interlaminar shear behaviour for carbon and Nicalon fibre-reinforced glasses and glass-ceramics including the effects of matrix modifications, processing conditions, and high-temperature oxidation embrittlement. The data indicate that significant bonding to improve off-axis and shear properties can be tolerated before the longitudinal behaviour becomes brittle. Residual stress and other mechanical bonding effects are important, but improved analyses and multiaxial interfacial failure criteria are needed to adequately interpret bond strength data in terms of composite performance.     

Mechanical testing of plasma-sprayed ceramic coatings on metal substrates: Interfacial fracture toughness and tensile bond strength

Plasma-sprayed ceramic coatings applied to metal components have uses in many diverse fields, including aerospace, electronics and, more recently, biomaterials. In all such applications success of the component relies on adequate bonding between the ceramic coating and metal substrate. In this study, a convenient and reliable test method to assess the fracture toughness of this metal/ceramic interface was developed by modifying an existing homogeneous short-bar configuration. Additionally, conventional tensile adhesive bond strength testing was conducted. For the alumina-coated Ti-6Al-4V model system studied, an interface toughness value of 1.84±0.20 MPa m^1/2 was obtained. An interfacial tensile bond strength of 13.6±2.9 MPa was also measured for this system. Further refinement of this modified short bar technique taking into account experimental compliance behaviour and potential complex or mixed-mode stress intensities is needed to confirm these preliminary toughness values, which nevertheless offer a potentially more sensitive means of monitoring the mechanical integrity of this metal/ceramic interface.     

负偏压增强金刚石膜与衬底结合强度的理论研究

由于金刚石与Si有较大的晶格失配度和表面能差,利用化学气相沉积(CVD)制备金刚石膜时,金刚石在镜面光滑的Si表面上成核率非常低.而负衬底偏压能够提高金刚石在镜面光滑的Si表面上的成核率,表明金刚石核与Si表面的结合力也得到增强.利用负偏压增强CVD系统制备金刚石膜时,气体辉光放电产生的离子对Si表面轰击,使得Si衬底表面产生了微缺陷(凹坑),增大了金刚石膜与Si衬底的结合面积.本工作主要从理论上研究离子轰击对金刚石膜与Si衬底结合力的影响.     

铁族金属对金刚石磨具陶瓷结合剂性能的影响

采用粉末冶金技术制备了铁族金属(Ni、 Co、 Fe)掺杂的R₂O-B₂O₃-Al₂O₃-SiO₂系陶瓷结合剂。研究了添加不同铁族金属对R₂O-B₂O₃-Al₂O₃-SiO₂系陶瓷结合剂耐火度、 流动性、 微观结构、 氧化性能以及抗折强度的影响。结果表明: 结合剂耐火度随着金属Co粉添加量的增加而升高, 在Fe粉的添加量小于20%(质量分数, 下同)时结合剂耐火度有明显的降低趋势, Ni粉的加入对陶瓷结合剂耐火度影响不大; 在空气气氛下750℃烧结时, 所添加的金属粉均有部分发生氧化, 氧化程度为Fe>Co>Ni; 添加金属粉后结合剂抗折强度均有不同程度的提高, 其中添加25%Co的结合剂强度最高, 达到75.42 MPa, 所添加的金属颗粒与陶瓷结合剂结合紧密程度为Co>Ni>Fe。     

热处理对羟基磷灰石涂层相组成、表面形貌与结合强度的影响

羟基磷灰石(HA)涂层的喷涂及其后处理工艺对其组织结构和结合强度具有重要影响.比较了热处理对不同粒度HA涂层相组成、表面形貌与结合强度的影响,为该类涂层制备工艺的优化提供实验依据.采用等离子喷涂法在纯钛表面制备了不同粒度的HA涂层,对其进行650℃不同保温时间的后热处理.利用X射线衍射仪、扫描电子显微镜和电子拉伸机检测了涂层的相组成、表面与断口形貌及剪切结合强度等.结果表明,涂层经650℃保温0.5h热处理后,非晶相和分解相基本全部转变为结晶HA.经热处理晶化后,涂层表面生成300nm以下的微粒子,双重涂层BC表面更易形成.粗粉末涂层CC和BC热处理后的剪切强度提高,而细粉末涂层FC则相反;HA涂层的剪切断裂主要是发生在涂层与基体间的界面上.     

The strength of two-phase ceramic/glass materials

The strengths of various glasses, with a range of expansion coefficients, containing 10 vol % thoria spheres, of diameter 50 to 700m, have been measured. Stresses occur around the spheres, due to differences in the expansion coefficients of the glass and the spheres, on cooling from the fabrication temperature. Stress magnification occurs near the spheres, due to differences in elastic properties, in the presence of an applied stress. When the expansion coefficient of the sphere is greater than that of the glass, circumferential cracks form around the spheres but only when the sphere diameter is greater than a critical value. An approximate value for the critical diameter may be obtained by an energy balance criterion. Cracks may form around spheres smaller than the critical diameter under application of applied stress at stresses below the macroscopic fracture stress. In these cases the strength is governed by a Griffith relationship with the crack size equal to the sphere diameter. When the expansion coefficients of the spheres and glass are similar, the strength of the glass is reduced only when large spheres (300m diameter) are present. When the expansion coefficient of the spheres is less than that of the glass, linking radial cracks form between the spheres and the material has very low strength.     

The effect of composition on the bond structure and refractive index of silicon nitride deposited by HWCVD and PECVD

Silicon nitride (SiN_x) is a material with many applications and can be deposited with various deposition techniques. Series of SiN_x films were deposited with HWCVD, RF PECVD, MW PECVD and LF PECVD. The atomic densities are quantified using RBS and ERD. The influence of the atomic densities on the Si-N and Si-Si bond structure is studied. The density of N-N bonds is found to be negligible. New Si-N FTIR proportionality factors are determined which increase with increasing N/Si ratio from 1.2 · 10¹⁹ cm^− 1 for Si rich films (N/Si = 0.2) to 2.4 · 10¹⁹ cm^− 1 for N rich films (N/Si = 1.5). The peak position of the Si-H stretching mode in the FTIR spectrum is discussed using the chemical induction model. It is shown that especially for Si-rich films the hydrogen content affects the Si-H peak position. The influence of the composition on the refractive index of the films is discussed on the basis of the Lorentz-Lorenz equation and the Kramers-Kronig relation. The decreasing refractive index with increasing N/Si ratio is primarily caused by an increase of the band gap.     

Effect of hydrothermal ageing on bond strength

Changes in the fibre/resin interfacial zone due to hydrothermal ageing can be detected using the TRI microbond technique for measuring interfacial shear strength. The procedure involves exposing fibre/resin microdroplet assemblies to the specified environmental condition for a given time and comparing their interfacial shear strengths with those of unaged specimens. We have investigated the effect of hydrothermal exposure on Kevlar^® 49, AS4 carbon and E-glass fibres embedded in Epon 828 thermosetting resin and two thermoplastic resins (polyethylene and polycarbonate). For the fibres embedded in Epon 828 and polycarbonate resins, consistent and significant bond strength reductions (13–50%) were obtained after refluxing in water at 88°C. These reductions could be partially or completely reversed, depending on the fibre/resin system. In contrast, interfacial shear strengths for the same three fibres embedded in polyethylene resin were increased irreversibly by 36 to 46% upon exposure to water at 88°C for 24 h. Evaluation of these results suggests that the mechanisms of bond strength changes due to hydrothermal ageing may be different for various combinations of fibres and resins.     

Tensile strength of ceramic powders

The tensile strength of granular materials has been extensively studied and is of great technological importance. Several theoretical or experimental relationships between density and strength have been proposed. This paper compares these models with experimental data from zirconia powders. It is shown that the most important parameter determining the strength of a green compact is not density but compaction pressure. A micromechanical model, which gives a qualitative understanding of ceramic powder behaviour under tensile stress, is also presented.     

Effect of mullite particles on the mechanical strength and chemical durability of vitrified CBN composites

The effects of mullite particles on the mechanical strength and chemical durability of vitrified CBN composites were investigated. Incorporating mullite particles to vitrified CBN composites contributes to an obvious improvement of the mechanical strength and the chemical durability of vitrified bond. The enhancement of the mechanical strength may be ascribed to the observed mechanisms including crack deflection and crack pinning. The improvement of chemical durability may be ascribed to the resistance of mullite particles to the dissolution of binders.