共查询到19条相似文献,搜索用时 234 毫秒
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铸造一体化成形技术有助于制备大尺寸、复杂结构的陶瓷/金属复合构件,具有重要的理论意义和应用价值。本文基于有限元方法,针对SiC陶瓷/K4169合金复合铸件,探究铸造充型过程的流场,陶瓷-金属的热交互作用以及凝固过程中复合铸件热应力、残余应力的产生与分布特性。结果表明,金属液充型过程在内浇口处出现不稳定流动;陶瓷在接触金属液后,表面温度陡升,且在陶瓷内部形成20-30℃/mm的温度梯度;铸造热应力呈现出先降低后升高的趋势;残余应力集中在陶瓷和金属界面,且较大应力在陶瓷一侧,陶瓷端残余应力峰值在距离界面2-3mm处。 相似文献
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采用热弹塑性有限元方法,在考虑了材料性能参数随温度变化和界面反应层的情况下,计算了陶瓷/金属钎焊接头残余应力的大小和分布。通过计算发现:陶瓷/金属接头在冷却过程中产生的径向应力和剪应力对接头的影响较小。而在陶瓷表面的边缘接近焊缝的位置产生了最大的轴向拉应力,它影响接头的载荷承受能力,并且由于40Cr的屈服强度比45钢的高,计算出的Si3N4/40Cr接头的应力峰值比Si3N4/45钢的高。陶瓷/钎料和陶瓷/金属的界面反应层虽然薄,但它也是影响陶瓷/金属接头残余应力大小和分布的一个重要因素。另外,选择合适的钎料层、中问层和钎焊压力都可以有效地减小残余应力的峰值。 相似文献
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残余热应力对Si3N4/金属钎焊接头性能的影响 总被引:4,自引:1,他引:4
熊柏青 《中国有色金属学报》1998,8(2):210-213
利用X射线衍射微区应力测定及剪切断裂实验方法研究了Si3N4/金属钎焊接头中的残余热应力分布,分析和讨论了残余热应力对接头断裂形式及强度的影响。结果表明,在Si3N4/金属钎焊接头中由于残余热应力的作用,使断裂常常发生在Si3N4一侧。本实验通过选用热膨胀系数与Si3N4相近的金属进行钎焊,结果可以有效地降低接头中的残余热应力,提高接头强度。另外,钎焊界面上Cu应力缓解层的加入也有利于使接头中残余热应力进一步降低。 相似文献
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梯度功能材料研究的一些进展 总被引:6,自引:0,他引:6
综述了近年来梯度功能材料(FGM)在优化设计、制备、性能评价以及应用方面的最新研究进展,并对其中的热点问题作了系统阐述。对于热应力缓和型FGM,其优化设计的关键环节是准确分析残余热应力的大小和分布。液相法制备FGM以其低成本、操作简单的优势将会获得更大的发展。对FGM的性能测试要尽可能模拟实际使用环境下载荷的不均匀分布。梯度功能热障涂层是FGM的重要应用之一,它与传统的热障涂层相比可明显提高耐久性。此外,还介绍了FGM在面向等离子体护墙材料以及生物材料上的应用。 相似文献
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目的 研究W/ODS铁素体钢功能梯度材料(W/ODS FGM)服役条件下的热应力,期望获得较合理的W/ODS FGM材料设计,以达到热应力优化的效果。方法 采用有限元分析方法,结合偏滤器的服役条件,通过改变W/ODS FGM材料梯度层成分分布指数p、梯度层厚度HFGM以及金属W涂层厚度HW,探索各参量的变化对热应力大小及分布的影响。结果 梯度层成分分布指数p值增大,梯度层的应力值会随之增大,而W层的热应力先减小后增大。当p=0.5时,最大热应力出现在梯度层的中段;当p=1、2时,最大应力由FGM层中段转移至FGM/W层的交界处。梯度层厚度HFGM增大,涂层的热应力会大幅提高。梯度层厚度较厚或较薄都会导致热应力在FGM/W交界处集中。W涂层厚度HW增大,会导致W/FGM界面的热应力增大,增添了涂层自身的不稳定性。结论 梯度层成分分布指数和厚度的增大均会引起涂层热应力的增大,并导致最大热应力区的转移。W涂层的增厚会使结构的热应力增大,且最大应力值位于W/FGM界面,不利于涂层寿命的提高。HW=HODS=1 mm、HFGM=8 mm、p=0.5和HW=HODS=1 mm、HFGM=4 mm、p=1的最大热应力区位于梯度层中段,且后者的最大应力值小于前者,故HW=HODS=1 mm、HFGM=4 mm、p=1的结构较优。 相似文献
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A.M. Zenkour 《Journal of Materials Processing Technology》2009,209(7):3511-3517
In this article, two composite structures of functionally graded material (FGM) solid disks are considered. The composite structures are composed of three-layer sandwich solid disks with faces made of different isotropic materials and core made of FGM. For Structure 1, the inner layer is metal and the outer layer is ceramic while the core layer is a metal–ceramic FGM. Structure 2 is composed of the same constituent materials as in Structure 1 but interchanging the metal material with the ceramic one. An accurate elastic solution for the rotating structures is given according to the boundary condition at the outer surface of the disk. Numerical results for displacement and stresses at the interfaces of the composite structure disks are presented. Additional distributions of stresses and displacement through the radial direction of the rotating structures are plotted. The effect due to many parameters on the stresses and displacement is investigated. 相似文献
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《Acta Materialia》1999,47(9):2669-2684
The evolution of micro- and macrostresses in a duplex stainless steel during loading has been investigated in situ by X-ray diffraction. A 1.5 mm cold-rolled sheet of alloy SAF 2304 solution treated at 1050°C was studied. Owing to differences in the coefficient of thermal expansion between the two phases, compressive residual microstresses were found in the ferritic phase and balancing tensile microstresses in the austenitic phase. The initial microstresses were almost two times higher in the transverse direction compared to the rolling direction. During loading the microstresses increase in the macroscopic elastic regime but start to decrease slightly with increasing load in the macroscopic plastic regime. For instance, the microstresses along the rolling direction in the austenite increase from 60 MPa, at zero applied load, to 110 MPa, at an applied load of 530 MPa. At the applied load of 620 MPa a decrease of the microstress to 90 MPa was observed. During unloading from the plastic regime the microstresses increase by approximately 35 MPa in the direction of applied load but remain constant in the other directions. The initial stress state influences the stress evolution and even after 2.5% plastic strain the main contribution to the microstresses originates from the initial thermal stresses. Finite element simulations show stress variations within one phase and a strong influence of both the elastic and plastic anisotropy of the individual phases on the simulated stress state. 相似文献
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Neutron diffraction measurements of the strain profile in a quenched plate of an aluminium-dash;silicon carbide particle-reinforced metal matrix composite are reported. The results have been used to evaluate the efficacy of an analysis technique which allows distinction of the stiffness mismatch and shape misfit stresses between the matrix and reinforcement, as well as between these and any macrostress present. The analysis is presented for measurements made on a metal matrix composite plate which, as a consequence of quenching from elevated temperature, shows large variations in residual stress as a function of position through the plate thickness. The measurements illustrate the additional insight which can be obtained through the separation of the elastic mismatch and thermal misfit stresses. The stress components thus obtained show good agreement with calculated long-range residual and mismatch stresses. 相似文献
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《Acta Materialia》2003,51(4):1143-1156
The thermal residual stresses in two types of co-continuous composites copper/aluminum oxide (Cu/Al2O3) and aluminum/aluminum oxide (Al/Al2O3) were measured by neutron diffraction experiments. These stresses were generated during the cooling after high processing temperature. The coefficient of thermal expansion (CTE) mismatch of metal and ceramic phases led to significant amount of thermal stresses. In both the composites, the metallic phase was found to be under tension and aluminum-oxide phase under compression. Even though the magnitude of compressive stress in both the composites was similar; the two metal-phases had very different magnitude of tensile stresses. The difference in volume fraction, CTE, elastic stiffness and plastic flow properties led to this difference. The hydrostatic stresses were found to be predominant in both the phases. Finite element simulations were used to predict the stress distributions inside each phase and at the interfaces. A representative unit cell approach was considered to represent the composite. Concept of effective ΔT was utilized to simulate the thermal stress distribution inside the two phases in the unit cell. This model utilized the neutron diffraction measurements to predict the stress distribution inside each phase and at the interface. The simulations showed that significant amount of tensile stresses develop at the metal–ceramic interfaces. 相似文献
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Shang-Nan Chou Horng-Hwa Lu Ding-Fwu Lii Jow-Lay Huang 《Journal of Alloys and Compounds》2009,470(1-2):117-122
This study aims at investigating the thermal expansion behavior and internal residual strains in metal reinforced ceramic matrix composites (CMCs). A variety of Al2O3/A356 CMCs composites with an interpenetrating network structure and varying metal content, ranging from 10 to 40 vol.%, were produced using the pressure infiltration technique of Squeeze casting. Values of coefficients of thermal expansion (CTEs) were found to vary significantly with temperature, indicating an influence of the flow characteristics of the metal. Comparisons are made with well known methods for predicting CTEs values of metal/ceramic composites. The overall strain was found to increase with temperature and scaled proportionally with the metal content of the composite. Comparisons were also made with non-infiltrated porous ceramic preforms and a pure metallic sample. The uniform heating and cooling curves for the composite samples were found to exhibit hysterisis. Residual stress analysis and failure simulation were performed based on thermomechanics and the finite element method (FEM). This analysis is often utilized for the analysis of stress distribution or deformation of a structure. High angle X-ray and CTEs mismatch equation analysis were utilized to analyze the residual stresses at the ceramic/metal interface of the Al2O3/A356 composites. The relationship of residual stresses and the contact area of the ceramic/metal interface are also discussed. 相似文献
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C. Eichenseer I. Wittmann C. Hartig G. A. Schneider N. Schell W. Hintze 《Production Engineering》2013,7(2-3):283-289
To completely understand wear mechanisms of mixed ceramic cutting tools (Al2O3–TiC), residual stress states and the superposition of external loads during hard turning should be investigated. This can be done via X-ray diffraction using high-energy synchrotron radiation to determine lattice strains in the material. For this reason, in first model tests, strain states in mixed ceramics were determined during the application of external loads. An experimental setup was developed to measure lattice strains in the different phases of the ceramic material in situ during thermal, mechanical and thermo-mechanical loading for first reference. The accuracy of the setup was sufficient to clearly determine shifts in lattice parameters in the different phases due to external loads. By applying a thermal load on the mixed ceramic material the two main phases showed different elastic lattice strains. Thus, a slightly lower coefficient of thermal expansion in the Al2O3-phase than in the Ti(O,C)-phase could be determined. This indicated the development of compressive stresses in the Al2O3-phase and tensile stresses in the Ti(O,C)-phase at room temperature. By applying external bending stresses to the mixed ceramic material, for both phases equal lattice strains could be determined. From these strains stresses could be calculated for both phases which were in the same order of magnitude as external stresses. With further in situ investigations of strain and stress states in the different phases of mixed ceramics during friction and turning experiments a more comprehensive characterization of wear mechanisms is possible. 相似文献
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《Acta Materialia》2007,55(2):409-421
A procedure to predict the fracture toughness of a ceramic multilayer composite made of different phases is presented. The procedure requires experiments to measure the intrinsic fracture toughness of the phases and to determine the required material data. The numerical modeling includes a conventional finite element stress analysis and the calculation of the crack driving force based on the concept of configurational (material) forces. The procedure yields the fracture toughness of the composite as a function of the crack length. A bending bar consisting of layers made of alumina and an alumina–zirconia composite is investigated. The bar has a crack perpendicular to the interfaces. The spatial variations of both the thermal residual stresses and the elastic modulus induce shielding and anti-shielding effects on the crack, which are quantified. The numerically predicted fracture toughness is compared with the experimental values. 相似文献
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Plasma-sprayed thermal barrier coatings (TBCs) have been used to extend the life of combustors. Electron beam physical vapor deposited (EB-PVD) ceramic coating has been developed for more demanding rotating as well as stationary turbine components. Here 3 kW RF magnetron sputtering equipment was used to gain zirconia ceramic coatings on hollow turbine blades and vanes, which had been deposited NiCrAIY by cathodic arc deposition. NiCrAlY coating surface was treated by shot peening; the effects of shot peening on the residual stress are presented. The results show that RF sputtered TBCs are columnar ceramics, strongly bonded to metal substrates. NiCrAlY bond coat is made of β, γ‘ and Cr phases, ZrO2 ceramic layer consists of t‘ and c phases. No degradation occurs to RF ceramic coatings after 100 h high temperature oxidation at 1150℃ and 500 thermal cycles at 1150℃ for 2 min, air-cooling. 相似文献