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Crack Propagation in Flexural Fatigue of Concrete 总被引:1,自引:0,他引:1
Subramaniam V. Kolluru Edward F. O'Neil John S. Popovics Surendra P. Shah 《Canadian Metallurgical Quarterly》2000,126(9):891-898
In this paper the behavior of concrete subjected to flexural fatigue loading is studied. Notched concrete beams were tested in a three-point bending configuration. Specimens were subjected to quasi-static cyclic and constant amplitude fatigue loading. The cyclic tests were performed by unloading the specimen at different points in the postpeak part of the quasi-static loading response. Low cycle, high amplitude fatigue tests were performed to failure using four different load ranges. The crack mouth opening displacement was continuously monitored throughout the loading process. Crack propagation caused by quasi-static and fatigue loads is described in terms of fracture mechanics. It is shown that the crack propagation in the postpeak part of the quasi-static load response is predicted using the critical value of the mode I stress intensity factor (KIC). The ultimate deformation of the specimen during the fatigue test is compared with that from the quasi-static test; it is demonstrated that the quasi-static deformation is insufficient as a fatigue failure criterion. It is observed that crack growth owing to constant-amplitude fatigue loading comprises two phases: a deceleration stage when there is a decrease in crack growth rate with increasing crack length, followed by an acceleration stage where the rate of crack growth increases at a steady rate. The crack length where the rate of crack growth changes from deceleration to acceleration is shown to be equal to the crack length at the peak load of the quasi-static response. Analytical expressions for crack growth in the deceleration and acceleration stages are developed, wherein the expressions for crack growth rate in the deceleration stage are developed using the R-curve concept, and the acceleration stage is shown to follow the Paris law. It is observed that the crack length at failure for constant amplitude fatigue loading is comparable to that of the corresponding load in the postpeak part of the quasi-static response. Finally, a fracture-based fatigue failure criterion is proposed. 相似文献
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Russian Journal of Non-Ferrous Metals - In this study, the micro-mechanisms involved in fatigue crack propagation are investigated qualitatively in a Al/Al2O3/SiC hybrid metal matrix composite... 相似文献
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D. V. Ramsamooj 《Canadian Metallurgical Quarterly》2003,129(6):672-682
An analytical model for fatigue crack propagation of long cracks in metals and metal alloys is presented. The key features of the model are an extension of Griffith’s theory of fracture to include fatigue, a dislocation model for the crack tip opening displacement, and cyclic plasticity-induced closure. The net cyclic stretch of the process zone at the crack tip plays a major role in the fatigue crack propagation under cyclic loading. Only constant amplitude loading is considered in this paper. The model predictions utilize only the readily available material properties, such as Young’s modulus, yield strength, threshold stress intensity factor, and the fracture toughness. There are no empirical fitting constants. The model predictions are validated by an extensive amount of published fatigue crack growth studies. The agreement between the model predictions and the experimental data is good. 相似文献
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《Canadian Metallurgical Quarterly》2013,52(3):157-167
AbstractAlloy 2219 has been evaluated under corrosion fatigue conditions. The effect of the microstructures present in the T851 and T6 conditions on crack propagation rates has been determined. Tests were performed on compact tension specimens in air and in NaCl solutions at 23 and 70°C. The corrosion fatigue behavior of the material under these conditions was evaluated by studying the crack propagation kinetics and also crack fractography.The results of this study show that 2219 aluminum is resistant to corrosion fatigue in aqueous solutions containing up to 10% NaCl. However, the material is more resistant in the T6 than in the T851 condition. In the absence of stress corrosion cracking, the initial stages of the crack growth were characterised by ductile fracture while a mixed fracture mode dominated the final stages of the growth. At low loading frequencies (0.1 Hz), crack branching and blunting were observed when tests were performed at 70°C. © 1997 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd Résumé On a évalué l'alliage 2219 sous des conditions de fatigue due à la corrosion. On a déterminé l'effet des microstructures présentes dans la condition T851 et la condition T6 sur le taux de propagation de crique. On a conduit des épreuves sur des échantillons de traction compacts, à l'air et dans des solutions de NaCl à 23 et à 70°C. On a évalué le comportement de fatigue due à la corrosion du matériau sous ces conditions en étudiant la cinétique de propagation de crique ainsi que la fractographie de criques.Les résultats de cette étude montrent que l'aluminium 2219 est résistant à la fatigue due à la corrosion, en solutions aqueuses contenant jusqu'à 10% de NaCl. Cependant, le matériau est plus résistant sous la condition T6 que sous la condition T851. En absence de fissuration par corrosion sous tension, les étapes initiales de la croissance. À basses fréquence de charge (0.1 Hz), on a observé une ramification et un émoussement des criques, lorsque les épreuves avaient lieu à 70°C. 相似文献
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An experimental procedure is presented to quantify damage in terms of microcrack density. This is accomplished by experimentally evaluating the components of a second-order damage tensor for a metal matrix composite material. The procedure involves the use of a scanning electron microscope and image analyzing software to quantify physical damage features found on a representative volume element. These features are quantified in terms of crack density, which is used in developing the second-order damage tensor. The procedure could be applied to voids in a similar fashion. This procedure is applied to the following two different balanced symmetric layups: (1) (0∕90)S; and (2) (±45)S. Uniaxial tensile loads are used to induce damage in test specimens for each of the layups. Damage evolution is obtained by loading specimens over a range of load intensities from rupture load down to 70% rupture load. A good comparison is obtained between experimentally evaluated and numerically calculated damage values. A companion paper by Voyiadjis and Deliktas used the experimental data presented here in order to verify their proposed formulation for a coupled anisotropic damage model for the inelastic response of composite materials. A physical interpretation of the second-order damage tensor, ;qf, is presented in their work. 相似文献
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颗粒增强铝基复合材料疲劳断裂研究 总被引:1,自引:0,他引:1
对粉末冶金法制备的碳化硅颗粒增强铝基复合材料进行了旋转弯曲疲劳试验研究。采用金相显微镜和扫描电镜分别观察了疲劳试验后复合材料纵向显微组织和疲劳断口。通过金相显微镜,观察了增强体颗粒在疲劳循环应力水平下可能的损伤形式。通过疲劳断口观察,分析了断面上不同区域的疲劳裂纹传播特征。结果表明,增强体的加入有效地提高了复合材料的屈服强度、弹性模量和疲劳性能,使复合材料高周疲劳极限提高到约250MPa(1×10^7循环周次)。复合材料的疲劳损伤随机分布于试样内。断口分析还表明复合材料疲劳同样遵循裂纹萌生,长大,失稳断裂规律,其裂纹起源于铝基体内。加入SiC颗粒减弱或遮盖了疲劳裂纹传播时的晶体学特征,使得复合材料高周疲劳断面没有发现常见的疲劳辉纹。 相似文献
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将复型技术应用于疲劳小裂纹扩展试验中的裂纹长度测量。在等载荷比R=0.1、不同平均载荷水平影响的疲劳条件下,板试样V型缺口小裂纹疲劳扩展速率做了试验测试;通过结果分析,提出了缺口小裂纹疲劳扩展速率表达式,并以εP为控制参数,求出45*钢的计算式。 相似文献
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The effect of hybrid fiber reinforcement on fracture energy and crack propagation in cement matrix composites is examined. The crack in cement matrix composites is allowed to fracture under mode-I loading with three-point bending beam specimens. The influence of fiber types and their combination is quantified by using the toughness index and fracture energy. A proper hybrid combination of steel fibers and polyvinyl alcohol microfibers enhances the resistance to both the nucleation and growth of the crack. The micromechanical model of hybrid composites by using a fiber bridging law is emphasized, and the numerical model prediction closely matches the behavior obtained from the experiment. The influencing role of the material parameters in the fracture tests (e.g., the fracture toughness index and fracture energy) becomes more apparent than ones used in some conventional strength-based or fiber pullout tests, and these fracture parameters could screen the effect of fiber/microfiber reinforcement in enhancing the crack growth resistance of cementitious composites. This study demonstrates that fundamental fracture tests are effective to characterize and develop high-performance hybrid fiber–reinforced cement matrix composites. 相似文献
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A theoretical framework along with an experimental comparison and numerical simulation is presented, for the modeling of the viscoplastic behavior of metal matrix composites (MMCs). MMCs are finding increasing applications in aerospace structures. MMCs have strong directional properties that directly influence the evolution of the internal variables, namely, the backstress and viscoplastic strain. The model is developed within a micromechanical framework for MMCs using the equilibrium surface approach. The directional properties of MMCs are incorporated by proposing a constrained equilibrium surface, which is based on the constrained stress terms proposed. The micromechanical framework combines the viscoplastic properties of the matrix with the elastic properties of the fiber. Model-generated experimental comparisons and simulations are also presented. 相似文献
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《粉末冶金学》2013,56(2):72-78
AbstractA new technique for producing metal matrix particulate composites, consisting of the spray deposition of the metal matrix and the particles, is described. The deposit is removed from the substrate and hot rolled to produce composite strip for examination and testing. It is shown that up to 36 vol.-% of SiC, Al203, chilled iron, graphite, and sand particles, and mixtures of these, 75–120 μm in size, can successfully be incorporated in aluminium and Al–5Si alloy matrixes. The friction properties of some of the composites were shown to be particularly promising. High coefficients of friction of ~0·6 were obtainable under dry contact conditions, and these were remarkably constant with time. The friction properties compared very favourably with conventional asbestos based and sintered friction materials which showed lower coefficients of friction that increased with time. PM/0310 相似文献
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SiC纤维增强钛基复合材料研究进展 总被引:2,自引:0,他引:2
概述了作者研究组近年来在SiC纤维增强钛基复合材料研究领域开展的工作及取得的进展.采用具有自主知识产权的SiC纤维,研究了PVD先驱丝制备方法和真空热压/热等静压复合材料成形工艺,获得700℃拉伸强度>1500MPa的SiCf/Ti-6A1-4V复合材料,分别制备出长度>400mm和直径>200mm的钛基复合材料棒材和环形件.此外,分别采用粉末布与粉浆涂挂先驱丝两种低成本方法制备出钛基复合材料,确定了新的胶粘剂并优化了相关工艺参数. 相似文献
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An aluminum metal matrix composite (MMC) brake drum was tested in fatigue at room temperature and extreme service temperatures. At room temperature, the hybrid composite did not fail and exceeded estimated vehicle service times. At higher temperatures (62 and 73 pct of the matrix eutectic), fatigue of a hybrid particle/fiber MMC exhibited failure consistent with matrix overloading. Overaging of the A356 matrix coupled with progressive fracture of the SiC particles combined to create the matrix overload condition. No evidence of macro-fatigue crack initiation or growth was observed, and the matrix–particle interface appeared strong with no debonding, visible matrix phases, or porosity. An effective medium model was constructed to test the hypothesis that matrix overloading was the probable failure mode. The measured particle fracture rate was fit using realistic values of the SiC Weibull strength and modulus, which in turn predicted cycles to failure within the range observed in fatigue testing. 相似文献