表面处理对氮化硅陶瓷力学性能的影响

采用X射线衍射应力分析的sin2ψ法计算了Si3N4陶瓷试样的残余应力，并分别测量了表面处理前后Si3N4试样的力学性能。结果表明，经平面磨削后的Si3N4试样表面残余应力为拉应力，而抛光处理可适当降低残余应力。两种方法都使试样抗弯强度降低。     

磨削加工对陶瓷制品强度的影响

通过阐明陶瓷的磨削机理,探讨在陶瓷磨削过程中产生的表面／亚表面损伤及表面／亚表面裂纹、残余应力对陶瓷材料强度的影响,提出了减小表面／亚表面损伤,提高陶瓷制品强度的措施。     

陶瓷材料加工表面完整性及其对材料可靠性的影响

采用磨削-抛光加工、金刚石锯片切割加工、超声波加工和电火花线切割加工技术对Al2O3/TiC陶瓷材料进行加工.研究了各加工方法对陶瓷材料的加工表面完整性及其可靠性的影响.结果表明:加工方法对陶瓷材料加工表面完整性和可靠性有很大的影响.磨削-抛光加工的陶瓷试样表面粗糙度小,硬度高,抗弯强度及其可靠性最高.金刚石锯片切割加工和超声波加工次之;电火花加工陶瓷试样表面粗糙大,硬度低,抗弯强度及其可靠性最低.电火花加工陶瓷表面产生一硬度低且表面粗糙的约8μm厚的热影响层,加工表面含有大量的电火花腐蚀凹坑,随电流的增大,电火花加工陶瓷试样的抗弯强度及其可靠性降低.超声波加工陶瓷试样的表面完整性与磨料粒度有关,随磨料粒度的减小,陶瓷试样的抗弯强度及其可靠性增加.     

陶瓷结合剂含量对金刚石磨具性能影响研究

以47SiO_2-18Al_2O_3-9B_2O_3-9Li_2O-13Na_2O-4ZnO陶瓷结合剂为实验结合剂,制备了不同陶瓷结合剂含量金刚石试样,通过硬度(HRB)、抗弯强度及断口扫描电镜(SEM)测试,研究了不同陶瓷结合剂含量对金刚石试样力学性能的影响,通过金刚石试样与YG8试片的磨削实验研究了不同陶瓷结合剂含量对金刚石试样加工硬质合金的加工性能影响。实验结果表明,受结合剂含量对气孔形成的影响,随着结合剂含量的提升,试样洛氏硬度与抗弯强度增加,在结合剂含量超过35wt%时增幅趋于平缓。随结合剂含量的提升,磨耗比增加,磨削效率先增大后减小,在结合剂含量为35wt%时磨削效率达到最高值。综合考虑,37wt%结合剂含量金刚石试样对YG8具有最佳磨削寿命与磨削效率。     

X射线衍射分析微晶玻璃陶瓷复合砖表面残余应力

运用X射线衍射的方法测试了微晶陶瓷复合砖表面的残余应力，发现抛光微晶玻璃表面残余应力较小。通过分析微晶玻璃陶瓷复合砖表面残余应力产生的原因，指出X射线衍射测得的表面残余应力主要由瓷坯与微晶玻璃间的膨胀系数差别及冷却时温度梯度引起的热应力造成。X射线应力测试和微晶玻璃表面扫描电镜图像都显示，微晶玻璃中硅灰石晶相有取向性。     

金属材料应力释放工艺对陶瓷岩板内部应力释放影响的初步探讨

陶瓷岩板的大面积商业化应用大幅提高了建筑陶瓷材料在室内装饰领域的应用面积。但由于陶瓷岩板的面积尺寸较大,生产过程中残余应力在陶瓷岩板内部非均匀分布,严重影响了陶瓷岩板的可加工性能。本研究使用超声波探伤仪对陶瓷岩板进行扫描,探测陶瓷岩板的内部是否存在宏观裂纹;通过应力仪电阻应变仪监测陶瓷岩板的残余应力释放情况;通过调节全自动振动时效仪的激振器振动频率和振动时间消除陶瓷岩板在生产过程中产生的残余应力,提高陶瓷岩板的可加工性能。     

氧化锆基梯度功能材料的设计、制备与性能优化

以石墨为单相润滑剂,设计、制备了梯度层热膨胀系数呈连续变化的氧化锆基功能梯度材料,研究了结构参数与梯度材料力学性能的关系。结果表明:通过调节石墨在复合材料中的空间分布特征,可实现对材料内残余应力大小的调节,进而实现材料力学性能的优化。增大梯度层数和承载层厚度均有利于梯度材料力学性能的提高。梯度指数p为2.5时,材料具有最佳的抗弯强度,抗弯强度可达750 MPa。材料的梯度结构设计实现了陶瓷复合材料的结构/润滑功能一体化。     

压缩机主轴变形分析

通过对压缩机Cr17N i2主轴的热处理、试磨以及残余应力测定等试验,找出了主轴变形的主要影响因素。合理的热处理能够使主轴的残余应力值减至合格,而不适当的磨削也可使轴内产生应力。     

相变增韧陶瓷压痕开裂的力学分析

在相变增韧陶瓷中，压痕裂纹形成的原因除了因压痕导致塑性区体积变化产生的残余应力外，还与应力诱发相变导致塑性区体积膨胀而产生的附加应力或称相变应力有关。传统的压痕法和压痕－强度法忽略了相变应力对压痕开裂和试样断裂的贡献，所测得相变增韧陶瓷的断裂韧性数据往往偏低。     

新型梯度功能陶瓷刀具材料的设计模型

本文首次提出对陶瓷刀具材料的组成分布，微观结构进行设计以形成梯度模型，通过不同组成分布的刀具工作过程中的热应力，机械应力及材料制备过程中的残余热应力进行了模拟，以使刀具材料内部形成与外载应力部分抵消的机制，从而提高陶瓷刀具抗磨损破损的性能。     

The effect of testing conditions (hot and residual) on fracture toughness of fiber reinforced high-strength concrete subjected to high temperatures

This paper presents experimental work on the fracture toughness of fiber reinforced high-strength concrete subjected to high temperatures. Bending and fracture energy tests were conducted during and after cooling (i.e. hot and residual tests). It was observed that bending strength for the residual tests is higher than that for the hot tests because of the effect of tensile stresses arising in concrete which occurs in the hot tests but does not occur in the residual tests. Also it was observed that fracture toughness of steel fiber reinforced high-strength concrete in the hot tests is lower than that in the residual tests. However, steel fiber reinforcement is efficient in maintaining bending strength, and is more importantly effective in improving fracture toughness of high-strength concrete during and after cooling. Thus, the hot test should be conducted for evaluating mechanical properties of high-strength concrete due to its severity compared to the residual test.     

HDPE及增韧HDPE的力学性能与测试条件的关系

于23℃时,研究了拉伸、弯曲速度及试样缺口剩余宽度对高密度聚乙烯(HDPE)、HDPE/弹性体、HDPE/E型增韧母料(E-TMB)的拉伸、弯曲及冲击强度等力学性能的影响。结果表明,所研究的测试条件对这三种材料力学性能影响的程度不同:对于这三种材料,均是拉伸速度对拉伸屈服应力、弹性模量影响的程度较小,对断裂伸长率影响的程度较大,弯曲速度对弯曲弹性模量、弯曲强度影响的程度较大;三种材料中,拉伸速度对断裂伸长率影响程度最大的是HDPE/弹性体,最小的是HDPE/E-TMB,弯曲速度对弯曲弹性模量、弯曲强度影响程度最大的是HDPE/E-TMB,最小的是HDPE/弹性体;随外力作用速度增大性能并非匀速变化,对不同的材料、不同的性能有相应的敏感区;试样缺口剩余宽度对HDPE/E-TMB的悬臂梁缺口冲击强度影响程度较大,而且缺口剩余宽度由7.8mm增加到8.0mm是影响的敏感区,对HDPE、HDPE/弹性体的影响的程度很小。     

Strengthening of Vickers indented 3Y-TZP by hydrothermal ageing

The effect of hydrothermal ageing on indentation cracks has been determined in 3Y-TZP by measuring the flexure strength of indented specimens before and after ageing. A substantial increase in strength was observed after ageing, in contrast to the well known decrease in strength in smooth specimens with only natural flaws. The increase in strength with ageing also occurs if the indentation residual stresses are previously removed by annealing. Observations around the crack tip show the formation of a highly microcracked zone during vapour exposure. Fractographic and micro-Raman analysis observations show that the profile of the cracks is marked on the fracture surface by this zone which is intergranular with a crumbled appearance and in which transformation has taken place. The increase in strength is discussed in terms of crack tip blunting induced by the multiaxial stresses that develop in front of the crack under bending.     

Effect of impact damage on the curved beam interlaminar strength of carbon/epoxy laminates

The bending interlaminar strength and bending interlaminar strength after impact of carbon/epoxy-laminated curved beams were studied experimentally using four-point bending test and low velocity impact. First, the post- impact damage of the laminated curved beams with different radii was analyzed based on ultrasonic C-scan images. Then, the effect of impact damage on both the interlaminar strength and the maximum interlaminar radial stresses of the laminated curved beams were investigated. Finally, the full-field displacement distributions of the laminated curved beams were obtained using digital speckle correlation method. Four-point bending experimental results play a significant role for interlaminar strength in evaluating the laminated curved beams with and without impact damage.     

Uncovering the critical factor in determining the residual stresses level in Si3N4–GM filler alloy–42CrMo joints by FEM analysis and experiments

The influence of gradient materials (GM) filler alloy on the distribution of thermal stresses and on the bending strength of the brazed Si₃N₄–42CrMo steel joints was examined by using finite element modeling (FEM) computations in combination with experiments. In order to form a smooth thermal expansivity change across the whole joint, a novel GM filler alloy was fabricated by stacking each layer with different content of Mo particles (Ag–Cu–Ti+Mo) addition together. We examined the effect of GM compositions, layer numbers and thicknesses on the residual stresses in the brazed joint. In particular, the monolayer composite filler produced by incorporating 10 vol% Mo particles induced the minimum residual stresses in the joint, agreeing with the experimental results. The results indicated that the CTE mismatch between the joined materials and the ability of plastic deformation in the filler alloy were two factors that determine the residual stresses level in a brazed joint. The results reported here will provide us guidance to choose an appropriate filler alloy for improving the ceramic–metal joint performance.     

Development of warpage and residual stresses in film insert molded parts

Residual stresses, bending moments, and warpage of film insert molded (FIM) parts were investigated by experimental and numerical analyses. Thermally induced residual stresses in FIM parts were predicted by numerical simulations with both commercial and house codes. Bending moments and warpage of FIM tensile specimens were calculated numerically and compared with experimental results. Thermally induced residual stresses were predicted by utilizing a one‐dimensional thermoelastic model where constant material properties are assumed. The residual stress distribution depended remarkably on the Biot number and the heat was removed rapidly through the surface resulting in high residual stresses. Asymmetric residual stresses generated by nonuniform cooling of the part provoked nonuniform shrinkage and warpage of the molded tensile specimen. It was found that the numerically calculated bending moment is in good agreement with the experimental results. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Effects of coupling agent thickness on residual stress in polyimide/γ-APS/silicon wafer j oints

The adhesion strength of and the residual stress in pyromellitic dianhydride-4,4'-oxydianiline polyimide (PMDA-ODA PI)/y-APS/silicon wafer joints were investigated for various coating thicknesses of γ-aminopropyltriethoxysilane (γ-APS). The largest adhesion strength (780 N/m) was observed in the joint with 11 nm of γ-APS coating thickness. The residual stress was measured by a He-Ne laser thin film stress analyzer and calculated by a finite element analysis. The residual bending stresses obtained by finite element calculations agreed very well with the experimental results. Residual stress increased with increasing γ-APS coating thickness.     

Effect of thermo-mechanical and low-cycle preloading on the strength of carbon fiber-reinforced ceramic matrix composites

Fiber-reinforced ceramic matrix composites (CMCs) exhibit excellent thermo-mechanical properties including outstanding resistance against damage and fatigue. Some CMCs show occasionally even a strength enhancement after fatigue, often interpreted with relieve of internal stresses and interfacial degradation. This study reports the influence of low-cycle thermo-mechanical preloading on the bending and tensile strength of carbon fiber-reinforced silicon carbon (C/C-SiC). For this purpose two C/C-SiC materials with the same fiber architecture but different assumed internal stress states were subjected to single and cyclic mechanical preloads up to 90% of their ultimate strength level at room temperature and at 350 °C. Statistical evaluations of the experiments show that the ultimate strength values were surprisingly unchanged after preloading. The results are discussed regarding the thermal residual stresses (TRS).     

Strength Distributions of a Quench-Strengthened Aluminosilicate Ceramic

The quench strengthening of an aluminosilicate ceramic body was studied by measuring the strengths and determining the strength distributions, estimating the residual compressive stresses at the surface by measuring the bending moments, and directly observing the surface crack patterns of quench-strengthened specimens. When considered in combination, these related results enable the assessment of the individual contributions of the residual compressive surface stresses and the changes in the flaw populations to the quench strengthening phenomenon. The quench strengthening phenomenon is discussed as a combination of those features of the process and a general schematic diagram of the phenomenon is presented.