具有中等组分不同网状结构功能梯度构件的三维动力特性分析

功能梯度材料具有复杂的细部结构,其内部构造远比匀质材料复杂,因此其构件动力分析很难求得其解析解。该文建议一种新颖的功能梯度构件动力分析的细观元法。细观力学研究的目的在于建立材料的宏观性能同其组分材料性能及细观结构之间的定量关系,它可揭示不同的材料组合具有不同的宏观性能的内在机制。此法可实现材料细观结构到构件宏观响应的直接过渡分析,而计算单元与自由度又等同一般常规有限元,却使得组成功能梯度材料构件的各种材料细观构造得到反映。通过细观元技术,对具有中等组分不同网状结构功能梯度构件进行三维动力特性分析,并给出其三维固有频率及振型的三维分布,特别是给出了不同网格结构功能梯度板件应力振型的平面等值线图差异。结果表明:不同细观网格结构对功能梯度材料结构三维动力响应有较明显影响。     

沿板平面变异功能梯度板件的三维动力特性

功能梯度材料具有复杂的细部结构,其内部构造远比匀质材料复杂,因此其构件动力分析很难求得其解析解。文中建议一种新颖的功能梯度构件动力分析的细观元法。细观力学研究的目的在于建立材料的宏观性能同其组分材料性能及细观结构之间的定量关系,它可揭示不同的材料组合具有不同的宏观性能的内在机制。目前功能梯度板件分析只能处理材料特性沿厚度方向梯度变化,而细观元法则直接从制备时给定的材料组分分布出发计算构件宏观三维动力特性,并给出了沿板平面方向材料特性梯度变化的功能梯度板件三维固有频率及振型的三维分布。     

复杂边界条件功能梯度板三维分析的细观元法

发展一种细观分析和宏观计算相结合的计算方法—细观元法。细观元法是使功能梯度构件宏观响应和材料组分的几何、物理、构造参数直接发生关联的分析方法,实现材料细观结构到构件宏观响应的直接过度分析,为解决功能梯度构件宏、细观跨尺度分析提供了一种有力工具。细观元方法不增加结点自由度,却使得功能梯度板件的任意功能梯度变化、各种复杂边界条件得到反映。用细观元法得到了几种具有不同复杂边界条件的功能梯度板件的力学量三维分布形态。     

功能梯度材料与构件的静动力识别

功能梯度材料具有复杂的细部结构,其内部构造远比匀质材料复杂.因此,以目前的实验条件,测量功能梯度材料的参数分布是十分困难的.建议一种新颖的功能梯度构件分析的细观元法.细观力学研究的目的在于建立材料的宏观性能同其组分材料性能及细观构造之间的定量关系,它可揭示不同的材料组合及其变异所具有不同的宏观性能的内在机制.利用细观元法探讨功能梯度材料与结构的识别问题,即在已知实验测量的位移或固有频率的情况下,对功能梯度材料的组分分布及组成材料名称进行识别.     

由材料组分直接计算功能梯度复合材料开孔板宏观响应的跨尺度分析

建议一种新颖的功能梯度构件分析的细观元法, 给出了方法模型、基本算式及特点与功能。细观元法对构件的常规有限单元内部设置密集细观单元以反映材料组分梯度变化, 又通过协调条件将各细观元结点自由度转换为同一常规有限元自由度, 再上机计算。此法可实现材料细观结构到构件宏观响应的直接过渡分析, 而计算单元与自由度又等同于常规有限元, 为解决功能梯度构件宏观、细观跨尺度分析提供了一种有效工具。本文中直接从制备时给定材料组分分布出发计算构件宏观响应, 给出了不同开孔形状与数量功能梯度板的力学量三维分布形态。      

复杂形状功能梯度板件的三维动力特性分析

从细观力学角度出发根据材料细观组分分布对具有不同复杂形状功能梯度材料构件进行三维动力特性分析,并相应给出其三维固有频率及其基频对应的位移振型和应力振型沿厚度方向的三维分布。结果发现对同样材料细观组分分布的不同功能梯度结构,其固有频率和相应的振型分布均有很大差异。此结果为建立专门的功能梯度板壳理论提供定量的资料依据。     

含椭球夹杂耐热梯度功能材料细观结构优化应力方程

梯度功能材料具有复杂的细观结构组合方式,对其进行细观力学的研究是当前的主要发展方向。本文作者对非均质、耐热、含椭球夹杂梯度功能材料的细观结构与性能进行了分析,研究其细观力学建模和在机械/热载荷下的损伤演化和破坏。结果可应用于多相夹杂梯度功能材料的细观应力分析和细观性能预测,并均以显式给出,以便于工程应用。     

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。      

复杂构造系统破坏与抑制分析

本文将超级元法思想应用于具有复杂细观构造的复合材料层合板的破坏过程分析与破坏抑制计算。形成一种细观元法，具有简易，实用和大规模节省计算工作量显著特点，并根据很地反映了复合材料构件的破坏特征。     

复杂边界条件功能梯度板三维分析的半解析方法

推导出适应功能梯度材料构件分析的半解析方法基本算式,并针对功能梯度构件的材料参数随空间坐标变化的特点,将材料参数纳入到力学方程中进行整体积分计算,从而编制统一程序计算不同边界条件下的板件问题.该法适应性强而又简洁高效,且不同于一般的半解析法,可采用一维离散,给出三维分析结果,是一种解决功能梯度构件力学性能分析的有效数值方法.文中用半解析法分析几种具有不同复杂边界条件的功能梯度板,给出了板件的力学量三维分布形态.     

The statistical second‐order two‐scale method for mechanical properties of statistically inhomogeneous materials

A class of random composite materials with statistically inhomogeneous microstructure, for example, functionally graded materials is considered in this paper. The microstructures inside a component are gradually varying in the statistical sense. In view of this particularity, a novel statistical second‐order two‐scale (SSOTS) method is presented to predict the mechanical properties, including stiffness, and elastic limit. To develop this method, the microstructures of statistically homogeneous, and inhomogeneous materials are represented. In addition the SSOTS formulas are derived based on normalized cell depending on the position variables by a constructing way, and the algorithm procedure is described. The mechanical properties of the different inhomogeneous materials are evaluated. The numerical results are compared with the experimental findings. It shows that the SSTOS method is effective. Copyright © 2010 John Wiley & Sons, Ltd.     

Rapid additive manufacturing of functionally graded structures using simultaneous wire and powder laser deposition

Laser additive fabrication allows the manufacturing of functionally graded structures that are not possible using conventional subtractive manufacturing. Laser deposition of injected powders with varying compositions, layer-by-layer, is often used for the building up of functionally graded fully dense structures or materials. This approach, however, has some drawbacks: the un-used powders (normally 60–80%) cannot be recycled as they will be contaminated by the powder mixture. In addition, multiple passes are needed to develop functionally graded structures. This paper reports the feasibility and characteristics of using simultaneous powder and wire feeding laser deposition to produce functionally graded structures in a single step. This approach has been shown to eliminate the above problems associated with powder feed laser deposition. In this work, copper powder and nickel wire have been used to deposit functionally grated copper/nickel/iron structures on H13 tool steel. A 1.5-kW diode laser is used for the build-up process. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and optical microscopy are used to analyse the deposited materials in terms of morphology, composition distributions, microstructures and phases formed. Successful deposition of functionally graded Cu–Ni–Fe structures has been demonstrated. Comparisons are made with the dual powder feed deposition process, which shows the inclusion of un-melted Ni powders in the Cu layer as a result of melting temperature difference of the two materials.     

Rapid additive manufacturing of functionally graded structures using simultaneous wire and powder laser deposition

Laser additive fabrication allows the manufacturing of functionally graded structures that are not possible using conventional subtractive manufacturing. Laser deposition of injected powders with varying compositions, layer-by-layer, is often used for the building up of functionally graded fully dense structures or materials. This approach, however, has some drawbacks: the un-used powders (normally 60-80%) cannot be recycled as they will be contaminated by the powder mixture. In addition, multiple passes are needed to develop functionally graded structures. This paper reports the feasibility and characteristics of using simultaneous powder and wire feeding laser deposition to produce functionally graded structures in a single step. This approach has been shown to eliminate the above problems associated with powder feed laser deposition. In this work, copper powder and nickel wire have been used to deposit functionally grated copper/nickel/iron structures on H13 tool steel. A 1.5-kW diode laser is used for the build-up process. Electron probe microanalysis (EPMA), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and optical microscopy are used to analyse the deposited materials in terms of morphology, composition distributions, microstructures and phases formed. Successful deposition of functionally graded Cu-Ni-Fe structures has been demonstrated. Comparisons are made with the dual powder feed deposition process, which shows the inclusion of un-melted Ni powders in the Cu layer as a result of melting temperature difference of the two materials.     

Three-dimensional static and dynamic analysis of functionally graded elliptical plates, employing graded finite elements

On the basis of the three-dimensional theory of elasticity, a graded finite element method capable of modeling static and dynamic behaviors of elliptical plates made of functionally graded materials (FGMs) subjected to uniform pressure is developed. In the present paper, two different material properties distributions are considered. For the dynamic analysis, the effective through-the-thickness continuous material properties distribution of the FGM (which is assumed to be composed of ceramic and metallic constituents) is determined based on Mori–Tanaka homogenization technique. The three-dimensional graded finite element formulation is derived based on the principle of minimum potential energy and Rayleigh Ritz method. To solve the time-dependent equations, Newmark’s direct integration method is employed. To present the efficiency of the present work, several numerical examples are included. Since similar results are not available in the literature, results of the present formulations are verified by comparing them with available ones of a homogenous elliptical plate.     

用Timoshenko梁修正理论研究功能梯度材料梁的动力响应

采用Timoshenko梁修正理论研究了功能梯度材料梁的动力响应问题,利用静力方程确定了功能梯度材料梁的中性轴位置,在此基础上应用Timoshenko梁修正理论建立了功能梯度材料梁的振动方程,求得其自振频率表达式及其在简谐荷载作用下强迫振动的解析解。讨论分析了中性面位置、梯度指数等因素对功能梯度材料梁的动力响应的影响,并用有限元法验证了Timoshenko梁修正理论。通过实例计算,得到了中性轴位置对功能梯度材料梁动力响应有较大影响的结论。     

Property gradation for modification of response of rotating MMC discs

Abstract

Aerospace and industrial gas turbine engine components such as discs, blades, and propeller shafts for which long fibre reinforced metal matrix composites are being made, operate under complex mechanical and thermal loading conditions. A major aim of functionally graded materials application is to optimise component response through appropriately tailored microstructures. This paper explores the influences of property gradation, centrifugal body force loading, and thermal loading on stresses in rotating discs. The discs were modelled as non-homogeneous orthotropic materials such as those obtained through non-uniform reinforcement of a metal matrix by long fibres. The results show how different temperature change distribution patterns and property gradation types correlate with hoop stresses developed in the disc.