金属─陶瓷梯度材料的热弹塑性分析

本文对金属-陶瓷梯度材料的稳态热弹塑性行为进行了研究.文中首先采用平均场和自洽弹塑性微观力学方法预测了金属-陶瓷梯度材料的非弹性性能,然后用非线性有限元法计算了材料制备过程中的热弹塑性应力.结果表明,梯度材料的热弹塑性行为对梯度材料的热应力缓和性能有显著影响.     

高炉风口上超音速火焰喷涂金属-陶瓷梯度层的可行性

在高炉风口表面制备一层适宜的金属-陶瓷梯度热障涂层,是提高风口寿命的一种有效的方法.本文旨在验证在风口上制备金属-陶瓷梯度保护层,提高高炉风口寿命的可行性.通过大型的有限元仿真软件AN-SYS,模拟分析了在紫铜表面喷涂陶瓷热障层的隔热效果,并且探讨了HVOF涂层的性能.结果发现,仅仅0.4 mm厚的ZrO2涂层就可以使铜基体温降200℃左右,而且超音速火焰喷涂打底的金属-陶瓷涂层的抗氧化性、热震性优于其他喷涂方法,这表示能够从材料和工艺两方面解决风口喷涂陶瓷层易脱落的问题.证明了在风口上喷涂金属-陶瓷梯度热障涂层的可行性以及利用HVOF打底层制备金属-陶瓷热障层的优势.     

热流温度场下功能梯度板的热问题研究

功能梯度材料因其内部组分沿着空间位置连续变化,能有效缓解热应力集中等现象,在高超音速飞行器的热防护系统设计中具有良好的应用前景.以金属-陶瓷功能梯度板为研究对象,探讨在不同热环境下功能梯度板热传导、热变形和热应力的变化规律.首先,基于功能梯度材料的幂律分布模型,分析了线性温度场、正弦温度场、热流温度场和非线性温度场四种...     

等离子喷涂功能梯度涂层抗热震性研究

对等离子喷涂方法制备的金属-陶瓷功能梯度涂层的抗热震性能进行了研究,结果表明:2mm厚金属陶瓷功能梯度涂层整体热震35次后涂层从铝基体上整体剥落失效,主要原因为热震冷却时最大热应力位置在基体与涂层界面位置,位于试样边缘处靠近基体一侧,使铝基体产生周期塑性变形,最终导致基体与涂层的热疲劳失效,同时基体与涂层中金属组元的氧化行为促进了涂层的剥落.     

陶瓷／金属梯度热障涂层的制备及性能评价

为了评价陶瓷／金属梯度热障涂层的性能，设计了4种涂层方案和2种基体材料（1Cr18Ni9Ti和2Cr13）．利用单枪单送粉器成功地制备了线性梯度涂层．通过观察涂层的微观结构、测量涂层的抗热震性能和热残余应力来评价涂层的性能．利用扫描电镜对各种陶瓷涂层的微观结构进行了观察和分析，利用X射线能谱分析得到了陶瓷梯度涂层试样中的不同区域的衍射图．热震试验表明，梯度涂层比非梯度涂层具有更好的抗热震性能．采用钻孔法对不同涂层方案进行了残余应力的测量，结果表明，压应力出现在1Cr18Ni9Ti基体材料上，而拉应力出现在2Cr13基体材料上．     

燃烧合成TiC-A12O3/Fe梯度材料及其抗热震行为

采用自蔓延高温合成结合准热等静压(SHS/PHIP)制备出了具有对称结构的TiC-A12O3/Fe梯度材料,并对其抗热冲击及抗热疲劳行为进行了测试和分析。结果表明,SHS/PHIP制备的TiC-A12O3/Fe梯度材料具有预期的梯度式组成,在热冲击和热疲劳实验过程中均无梯度层间横向贯穿裂缝,克服了传统陶瓷/金属直接接合界面的热应力剥落。     

燃烧合成TiC-Al2O3/Fe梯度材料及其抗热震行为

采用自蔓延高温合成结合准热等静压（SHS／PHIP）制备出了具有对称结构的TiC-Al2O3/Fe梯度材料,并对其抗热冲击及抗热疲劳行为进行了测试和分析,结果表明,SHS／PHIP制备的TiC-Al2O3/Fe梯度材料具有预期的梯度式组成,在热冲击和热疲劳实验过程中均无梯度层间横向贯穿裂缝,克服了传统陶瓷／金属直接接合界面的热应力剥落。     

金属-陶瓷梯度功能材料的研究和发展

一、引言 金属—陶瓷梯度功能材料(FGM)是具有全新材料复合概念的新型复合材料。它以金属和陶瓷为基本原材料,通过控制材料的组成和微观结构的梯度分布,消除传统的金属和陶瓷复合材料的性能不匹配界面,充分发挥金属和陶瓷的优异性能。金属—陶瓷梯度功能材料实质上是为了解决金属和陶瓷的界面连接问题。金属—陶瓷梯度功能材料是一种高新复合材料,具有优异的性能和可设计性,引起了材料科学工作者们的高度重视。金属—陶瓷由于能够缓和热应力,是未来航天飞行的理想耐热、隔热材料,同时在核能、电子、化学和生物医学等领域有着广阔的应用前景。 二、金属—陶瓷FGM的开发研究背景 梯度功能材料是日本学者于1984年首先提出来的。这一新材料的设想,与高新的航天技术的发展密切相关。航天飞机是人类征服宇宙空间时必需的运载工具。众所周知,目前的航天飞机是由火箭助推,垂直地     

非均质梯度功能材料三维本构关系及宏细观结构分析

对非均质耐热梯度功能材料的结构与性能进行了研究。通过对陶瓷-金属梯度功能结构的分析,建立了宏、细观力学模型,并在此基础上导出了反映其宏观力学性能的三维本构关系。      

燃烧合成TiC-Al_2O_3/Fe梯度材料及其抗热震行为

采用自蔓延高温合成结合准热等静压（ＳＨＳ／ＰＨＩＰ）制备出了具有对称结构的 ＴｉＣ－Ａｌ２Ｏ３／Ｆｅ梯度材料,并对其抗热冲击及抗热疲劳行为进行了测试和分析·结果表明, ＳＨＳ／ＰＨＩＰ制备的 ＴｉＣ－Ａｌ２Ｏ３／Ｆｅ梯度材料具有预期的梯度式组成,在热冲击和热疲劳实验过程中均无梯度层间横向贯穿裂缝,克服了传统陶瓷／金属直接接合界面的热应力剥落．     

Micromechanical analysis of thermoelastoplastic behavior of metal matrix composites

A micromechanics model based on the variational asymptotic method for periodic composites was developed using an incremental formulation to capture the coupled thermo-elasto-plastic behavior of metal matrix composites. Taking advantage of the small size of the microstructure, a variational statement of the unit cell through an asymptotic expansion of an functional of energy change was formulated to calculate the effective instantaneous tangential elasto-plastic matrix and thermal stress matrix of the composite materials. An iterative homogenization and localization technique was proposed to simulate the nonlinear thermo-elasto-plastic behavior of metal matrix composites. This model was implemented using the finite element method. For validation, a numerical example was examined to demonstrate the application and accuracy of this theory and companion code.     

Determination of thermal stress intensity factors for an interface crack in a graded orthotropic coating-substrate structure

The thermal fracture problem of an interface crack between a graded orthotropic coating and the homogeneous substrate is investigated by two different approaches. For the case that most of the material properties in the graded orthotropic coating are assumed to vary as an exponential function, the integral transform and singular integral equation technique is used to obtain some analytical results. In order to analyze the case with more complex material distribution, an interaction integral is presented to evaluate the thermal stress intensity factors of cracked functionally graded materials (FGMs), and then the element-free Galerkin method (EFGM) is developed to obtain the final numerical results. The good agreement is obtained between the numerical results and the analytical ones. In addition, the influence of material gradient parameters and material distribution on the thermal fracture behavior is also presented.     

TiC-Ni梯度功能材料的优化设计

对ＴｉＣ－Ｎｉ梯度功能材料在制备过程中的残余热应力进行了计算机有限元模拟,考察了梯度组成分布指数对热应力大小,最大热应力发生的位置以及纯陶瓷ＴｉＣ侧热应力状态的影响,综合分析了热应力的大小和分布,得到了缓和制备热应力的梯度组成分布指数Ｐ＝１．０的优化设计结果。     

Transient thermo-mechanical analysis of dynamic curving cracks in functionally graded materials

Mixed-mode dynamic crack growth behavior along an arbitrarily smoothly varying path in functionally graded materials (FGMs) under transient thermo-mechanical loading is studied. An asymptotic analysis in conjunction with displacement potentials is used to develop transient thermo-mechanical stress fields around the propagating crack-tip. Asymptotic temperature field equations are derived for exponentially varying thermal properties, and later, these equations are used to derive transient thermo-mechanical stress fields for a curving crack in FGMs. The effect of the transient parameters (loading rate, crack-tip acceleration, and temperature change) and temperature gradient on the maximum principal stress and circumferential stress associated with the propagating crack-tip is discussed. Finally, using the minimum strain energy density criterion, the effect of temperature gradient, crack-tip speeds, and T-stress on crack growth directions is determined and discussed.     

Residual stress and thermal properties of zirconia/metal (nickel, stainless steel 304) functionally graded materials fabricated by hot pressing

To analyse the residual stress and the thermal properties of functionally graded materials (FGMs), disc-type tetragonal zirconia polycrystal (TZP)/Ni- and TZP/stainless steel 304 (SUS304)-FGM were hot pressed, and compared with directly jointed materials (DJMs). The continuous interface and the microstructure of FGMs were characterized by electron probe microanalysis, wavelength dispersive spectrometry, optical microscopy and scanning electron microscopy. It has been verified that the defect-like cracks in FGMs are induced by the preferential shear stress and shown to cause fracture. These facts have corresponded well with the residual stress distribution analysed by the finite element method. The thermal diffusivity and the thermal conductivity of FGMs and DJMs were also measured by the laser flash technique. As a consequence, this work has described the interfacial stability, the residual stress release mechanism and the thermal protection characteristics of FGMs via a compositional gradient. This revised version was published online in November 2006 with corrections to the Cover Date.     

A systematic AMF–FEM coupled method for the thermo-elasto-plastic contact analysis of the plasma sprayed HA-coated biocomposite

Hydroxyapatite (HA) coated Ti-6Al-4V alloy biocomposite has been accepted as one of the most promising implant materials for orthopaedic and dental applications because of its favorable biocompatibility and mechanical properties. After the plasma sprayed HA composite coating on titanium alloy substrate biocomposite was prepared, a novel meshless numerical analysis method of the coupled adaptive meshfree method and finite element method (AMF–FEM) is developed for the simulation of the thermo-elasto-plastic contact problems of the biocomposites in this paper. The adaptive meshfree method based on strain energy gradient is used in the concerned contact domain, and FEM is used in the non-contact domain to overcome the difficulties of the meshfree method and improve the calculation efficiency. The thermo-elasto-plastic contact model using the incremental-initial stiffness method, error estimation and the local adaptive refinement strategy for the AMF–FEM method are combined. The AMF–FEM thermo-elasto-plastic model takes into account the temperature variation, micro plastic flow, the thermo-elasto-plastic coupling behavior and the strain-hardening property of the materials. The examples of the elastic/thermal-elastic contact of real HA-coated rough surfaces using the AMF–FEM is studied for two biomaterial models, respectively. The results all show that the AMF–FEM solutions are accurate, efficient, and can be widely applied to different thermo-elasto-plastic contact multi-layer biomaterial models considering different geometric parameter, material parameter, thermal and friction properties.     

Nonlinear bending and postbuckling of FGM cylindrical panels subjected to combined loadings and resting on elastic foundations in thermal environments

A nonlinear analysis is presented for FGM cylindrical panels resting on elastic foundations subjected to the combined actions of uniform lateral pressure and compressive edge loads in thermal environments. The two cases of postbuckling of initially pressurized FGM cylindrical panels and of nonlinear bending of initially compressed cylindrical panels are considered. Heat conduction and temperature-dependent material properties are both taken into account. Material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction based on Mori-Tanaka micromechanics model. The formulations are based on a higher order shear deformation theory and von Kármán strain displacement relationships. The panel-foundation interaction and thermal effects are also included. The governing equations are solved by a singular perturbation technique along with a two-step perturbation approach. The numerical illustrations concern the postbuckling behavior and the nonlinear bending response of FGM cylindrical panels with two constituent materials resting on Pasternak elastic foundations. The effects of volume fraction index, temperature variation, foundation stiffness as well as initial stress on the postbuckling behavior and the nonlinear bending response of FGM cylindrical panels are discussed in detail.     

不同变形状态下变物性梯度功能材料板瞬态热应力

用非线性有限元法分析了由ZrO2和Ti-6Al-4V组成的变物性梯度功能材料板的对流换热瞬态热应力问题,与已有文献比较检验了方法的正确性,给出了该材料板在不同变形状态下的瞬态热应力分布,并与常物性时的结果进行了比较。结果表明:无限自由长板内的热应力最小;当无限长板只能伸长、不能弯曲时,板内瞬态拉应力最大;当无限长板伸长、弯曲受限时,板内的瞬态压应力最大;考虑变物性时的最大拉应力比常物性减小48.9%,最大压应力减小39.6%;此外,对流换热系数的变化对不同变形状态下该变物性材料板瞬态热应力场的影响显著。此结果为该材料的设计和应用提供了准确的理论计算依据。