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61.
试验用00Cr18Ni10N钢(/%:0.018C,0.41Si,1.68Mn,18.18Cr,10.38Ni,0.16N)经1t EAF-AOD-ESR冶炼,锻成Φ30 mm材和1 050℃固溶处理,进行了00Cr18Ni10N钢200~600℃光滑(Kt=1)、缺口(Kt=3)的轴向高周疲劳性能研究,绘制了疲劳S-N曲线、计算了疲劳极限,并对疲劳试样的典型断口进行了SEM观察。结果表明,光滑试样的疲劳极限随试验温度升高而降低,缺口试样的疲劳极限对试验温度变化不敏感。当应力集中系数由Kt=1提高到Kt=3时,00Cr18Ni10N钢的200、400、600℃下107周次条件疲劳极限分别从530、506、410 MPa,降低到323、370、392 MPa。表明在高温下00Cr18Ni10N钢存在疲劳极限对应力集中敏感,且应力集中敏感性随着试验温度的升高而降低。疲劳试样的断口形貌由疲劳源区、疲劳裂纹扩展区和瞬断区组成,疲劳起源于表面加工刀痕的不连续位置,呈韧性断裂特征。 相似文献
62.
Islam S. Humail F. Akhtar S.J. Askari M. Tufail Xuanhui Qu 《International Journal of Refractory Metals and Hard Materials》2007,25(5-6):380-385
Tungsten heavy alloys (WHAs) are metal–metal composites consisting of nearly pure spherical tungsten particles embedded in a Ni–Fe–W or Ni–Co–W or Ni–Cu–W ductile matrix. In this dual phase alloy, there are several complicated relations between the ductile matrix and hard tungsten particles. The aim of this research was to examine the effect of varying tungsten content on the microstructure and mechanical properties of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity and solid volume fraction) were measured and were found to have a significant effect on the mechanical properties of tungsten-based heavy alloys. The result shows that the binding strength between the W and the matrix phase has a major influence on the ductility of tungsten-based alloys. The larger this binding force is, the better the ductility is. 相似文献
63.
压痕法测定热压MoSi2基复合材料K1C值的研究 总被引:8,自引:1,他引:8
用不同的压痕方程计算了纳米ZrO2粒子韧化MoSi2基复合材料的室温断裂韧性K1c值,同时研究了压痕载荷对K1c值的影响。结果表明,试验材料在试验条件下的断裂韧性不遵从半月状裂纹系统方程,而遵从巴氏裂纹系统方程,其室温压痕断裂韧性保持与压痕载荷的独立性。 相似文献
64.
The application of a new approach, design for performance, for high-temperature alloy development, design analysis, and remaining
life assessment, based on short-time high-precision testing, is described in this paper. The material tested was a directionally
solidified nickel-base alloy, GTD111. It was found that the creep strength at 850 °C was indeed superior to that of a competitive
alloy, IN738, but was not necessarily enhanced by the preferred alignment of grain boundaries and crystal orientation. In
contrast, the fracture resistance at 800 °C was improved in the longitudinal direction compared with transverse and diagonal
orientations in terms of susceptibility to gas phase embrittlement (GPE) by oxygen. Specimens cut transversely and diagonally
to the growth direction were more sensitive to GPE than specimens taken from conventionally cast IN738. The new conceptual
framework allows account to be taken of GPE and other embrittling phenomena, which may develop in service, leading to rational
life management decisions for gas turbine users. Additionally, straightforward design analysis procedures can be developed
from the test data, which for the first time allow separate measurements of creep strength and fracture resistance to be used
for performance evaluation. 相似文献
65.
通过对40CrNiMo光滑与三种不同缺口状态的试样进行试验发现,氢对材料强度的影响与外加应变速率的大小有关。在空气中试验,缺口状态对材料断裂强度几乎无影响;而在氢气中试验,则发现缺口根部半径R的变化对材料断裂强度影响极大;当缺口根部半径一定,仅改变外径D或缺口处最小直径d所得两种缺口状态对缺口强度的影响不大。 相似文献
66.
采用不同类型的WC硬质合金颗粒及不同成分的金属基本组成的两种复合耐磨材料,研究了复合材料的韧性及其影响因素,观察分析了其断口形貌及断裂机理.结果表明,复合材料的韧性与断面上WC硬质合金颗粒及金属基体的面积分数有关,主要取决于金属基体的成分、组织状态、韧性和含量,基体的韧性越好,含量越多,则复合材料的韧性越高.在冲击载荷作用下,WC硬质合金的断裂为脆性解理断裂,而金属基体则为具有少量塑性变形的准解理断裂。 相似文献
67.
Processing-structure-multi-functional property relationship in carbon nanotube/epoxy composites 总被引:1,自引:0,他引:1
Erik T. Thostenson 《Carbon》2006,44(14):3022-3029
The novel properties of carbon nanotubes have generated scientific and technical interest in the development of nanotube-reinforced polymer composites. In order to utilize nanotubes in multi-functional material systems it is crucial to develop processing techniques that are amenable to scale-up for high volume, high rate production. In this research we investigate a scalable calendering approach for achieving dispersion of CVD-grown multi-walled carbon nanotubes through intense shear mixing. Electron microscopy was utilized to study the micro and nanoscale structure evolution during the manufacturing process and optimize the processing conditions for producing highly-dispersed nanocomposites. After processing protocols were established, nanotube/epoxy composites were processed with varying reinforcement fractions and the fracture toughness and electrical/thermal transport properties were evaluated. The as-processed nanocomposites exhibited significantly enhanced fracture toughness at low nanotube concentrations. The high aspect ratios of the carbon nanotubes in the as-processed composites enabled the formation of a conductive percolating network at concentrations below 0.1% by weight. The thermal conductivity increased linearly with nanotube concentration to a maximum increase of 60% at 5 wt.% carbon nanotubes. 相似文献
68.
Statistical prediction of fracture parameters of concrete and implications for choice of testing standard 总被引:2,自引:0,他引:2
This article shows how the fracture energy of concrete, as well as other fracture parameters such as the effective length of the fracture process zone, critical crack-tip opening displacement and the fracture toughness, can be approximately predicted from the standard compression strength, maximum aggregate size, water-cement ratio, and aggregate type (river or crushed). A database, consisting of 238 test data, is extracted from the literature and tabulated, and approximate mean prediction formulae calibrated by this very large data set are developed. A distinction is made between (a) the fracture energy, Gf, corresponding to the area under the initial tangent of the softening stress-separation curve of cohesive crack model, which governs the maximum loads of structures and is obtained by the size effect method (SEM) or related methods (Jenq-Shah two-parameter method and Karihaloo's effective crack model, ECM) and (b) the fracture energy, GF, corresponding to the area under the complete stress-separation curve, which governs large postpeak deflections of structures and is obtained by the work-of-fracture method (WFM) proposed for concrete by Hillerborg. The coefficients of variation of the errors in the prediction formulae compared to the test data are calculated; they are 17.8% for Gf and 29.9% for GF, the latter being 1.67 times higher than the former. Although the errors of the prediction formulae taking into account the differences among different concretes doubtless contribute significantly to the high values of these coefficients of variation, there is no reason for a bias of the statistics in favor of Gf or GF. Thus, the statistics indicate that the fracture energy based on the measurements in the maximum load region is much less uncertain than that based on the measurement of the tail of the postpeak load-deflection curve. While both Gf and GF are needed for accurate structural analysis, it follows that if the testing standard should measure, for the sake of simplicity, only one of these two fracture energies, then Gf is preferable. 相似文献
69.
This paper explores the use of acoustic emission (AE) and X-ray tomography to identify the mechanisms of damage and the fracture process during compressive loading on concrete specimens. Three-dimensional (3D) X-ray tomography image analysis was used to observe defects of virgin mortar specimen under different compressive loads. Cumulative AE events were used to evaluate damage process in real time according to the sand/cement ratio. This work shows that AE and X-ray tomography are complementary nondestructive methods to measure, characterise and locate damage sites in mortar. The effect of the sand proportion on damage and fracture behaviour is studied, in relation with the microstructure of the material. 相似文献
70.