梯度功能材料的研究进展

梯度功能材料(FGM)自二十世纪八十年代作为一种新型功能材料出现以来,得到了迅速发展。本文介绍了FGM的概念及其开发背景;综述了近年来FGM在设计、制备以及性能评价方面的研究现状;最后对FGM的发展前景作了展望。     

梯度功能材料的研究进展

梯度功能材料(FGM)自二十世纪八十年代作为一种新型功能材料出现以来，得到了迅速发展。本文介绍了FGM的概念及其开发背景；综述了近年来FGM在设计、制备以及性能评价方面的研究现状；最后对FGM的发展前景作了展望。     

功能梯度材料的低温挤压成形过程建模与实验研究

使用低温挤压成形方法制造功能梯度材料（FGM）过程中,膏体材料存在气泡、结块和一定程度的液相迁移现象,导致挤压成形过程难以控制。使用系统辨识的方法建立了FGM成形过程的差分模型,运用残差的方差分析方法对系统模型的阶次进行估计,运用递推最小二乘法对参数进行辨识,得到FGM成形的控制模型。设计了自适应控制器,对FGM成形过程进行实时控制。实验验证了控制模型的准确性和控制方法的有效性。     

含自重载荷的功能梯度材料结构时域动力学拓扑优化设计

提出了一种含自重载荷的功能梯度材料(FGM)结构时域动力学拓扑优化设计方法。在固体各向同性材料惩罚(SIMP)框架下,提出了一种针对FGM-SIMP的结构自重载荷分布策略。以FGM结构动柔度最小为优化目标、以结构体积为约束,建立了动力学结构优化列式。基于伴随法,在时域内进行了灵敏度推导,并用移动渐近线方法进行求解。通过二维和三维典型数值算例系统研究了含自重载荷下FGM结构的拓扑优化设计问题,并深入探讨了自重载荷和材料梯度分布方向对结构优化结果的影响,发现自重载荷和材料梯度分布方向对FGM结构的优化构型和动刚度具有很大影响。最后,以均一材料(FGM的特例)为例,通过数值仿真和实验测试方法验证了所提方法的有效性,并证实了所提方法可有效提高结构的固有频率和结构动刚度。     

基于喷射成型的主动混合喷头制备功能梯度材料的研究

针对现有喷射成型的主动混合喷头制备功能梯度材料存在能力不足、无法充分混合基料以及所用扇叶部分推动基料能力缺失等问题,提出了一种新型制备方式,即内径变动螺杆搅拌器喷头制备FGM。这种创新的喷头可增大基料在喷头中的受力,使基料通过变内径螺杆搅拌得到充分混合,并增加机械推动方式。基料混合后喷射出功能梯度材料质量变得更加优异,故对内径变动螺杆搅拌器喷头制备FGM进行研究具有一定指导意义。     

计及不同剪切变形的功能梯度材料梁的弯曲分析

研究矩形截面功能梯度材料(Functionally graded materials,FGM)梁在不同剪切变形理论下的静力弯曲问题。假设FGM梁由金属和陶瓷两种材料构成,其等效物性参数沿厚度方向连续变化,且遵从简单幂率变化规律。基于最小势能原理,建立以轴向位移、横向位移及转角为未知函数的FGM梁的运动微分方程组。对简支FGM梁,采用Fourier级数法获得5种剪切变形理论下FGM梁的挠度、轴向位移及转角曲线,分析梁的长高比、梯度指标对弯曲变形的影响,分析不同剪切变形理论下FGM梁的切应力和正应力的分布特性,并与均质材料梁的静力弯曲特性进行比较。给出FGM梁的中性轴位置随梯度指标的变化曲线并进行分析。     

陶瓷/金属非保守FGM斜板的颤振分析

研究了陶瓷/金属非保守功能梯度材料（FGM）斜板的颤振问题。以薄板理论为基础,假定材料的等效物性参数为沿厚度方向体积分数的幂律变化,在斜坐标系下建立了非保守FGM斜板的运动微分方程。运用微分求积法,对四边固支边界条件下陶瓷/金属非保守FGM斜板的量纲一复频率进行了数值计算,分析了FGM斜板的梯度指标、夹角和长宽比的变化对非保守FGM斜板稳定性的影响。结果表明,非保守FGM斜板的临界颤振荷载随梯度指标和夹角的增大而减小,随长宽比的增大而增大。     

纤维增强FGM梁的自由振动和临界屈曲载荷分析

基于经典梁理论（CBT）研究轴向力作用下纤维增强功能梯度材料（FGM）梁的横向自由振动和临界屈曲载荷问题。首先考虑由混合律模型来表征纤维增强FGM梁的材料属性,其次利用Hamilton原理推导轴向力作用下纤维增强FGM梁横向自由振动和临界屈曲载荷的控制微分方程,并应用微分变换法（DTM）对控制微分方程及边界条件进行变换,计算了纤维增强FGM梁在固定-固定（C-C）、固定-简支（C-S）和简支-简支（S-S）3种边界条件下横向自由振动的无量纲固有频率和无量纲临界屈曲载荷。退化为各向同性梁和FGM梁,并与已有文献结果进行对比,验证了本文方法的有效性。最后讨论在不同边界条件下纤维增强FGM梁的刚度比、纤维体积分数和无量纲压载荷对无量纲固有频率的影响以及各参数对无量纲临界屈曲载荷的影响。     

汽车摩擦材料的研究现状与发展趋势

现代汽车的发展对汽车摩擦材料提出了更高的要求,摩擦材料性能的优劣将直接影响到汽车行驶安全性、稳定性、舒适性。从汽车无石棉摩擦材料种类、配方设计、制备工艺与设备、摩擦材料性能评价与测试方法等方面介绍了现代汽车摩擦材料的研究现状与发展趋势。     

等成分轮廓线的FGM零件直接成形路径规划方法

提出了一种新的基于层片数据的等成分轮廓线/面的FGM实体模型与成形路径规划方法.将材料信息与零件几何模型分层后得到的层片文件相关联,之后在层片内将连续材料分布离散成等成分轮廓线/面,以等成分轮廓线/面为单元进行路径规划,较现有方法简便、效率高,用于FGM火车车轮等离子熔积直接成形的路径规划.     

非对称梯度功能材料聚合物齿轮的瞬态弹流润滑分析

梯度功能材料是一种应用广泛的新型复合材料,其制成的齿轮有着独特的性能。为研究梯度功能材料对齿轮的润滑性能的影响,用多重网格法对非对称聚合物齿轮进行瞬态弹流润滑分析,比较均质复合材料齿轮与梯度功能材料齿轮的润滑性能,分析梯度功能材料齿轮分别作为主动轮与从动轮时的齿轮润滑规律,研究梯度功能材料的热性能对齿轮润滑的影响。结果表明:梯度功能材料能够减小齿轮润滑压力,增大润滑膜厚,从而有效改善齿轮润滑;梯度功能材料齿轮作为从动轮时对齿轮润滑较为有利。热弹流润滑分析表明,梯度功能材料齿轮作为从动轮时齿轮啮入的润滑温度较低,其作为主动轮则相对有利于其后的热弹流润滑。     

梯度功能材料的应用研究及发展趋势

介绍了梯度功能材料的特点与制造工艺,分析了目前梯度功能材料制备方法存在的问题以及应用领域。指出梯度功能材料的发展将朝着计算机专家系统辅助设计、低温制备、统一评价标准的方向发展。     

Effect of the volume of a functionally graded material layer on frictionally excited thermoelastic instability

A finite element model is used to identify the effect of the volume of a functionally graded material (FGM) on thermoelastic instability (TEI). An optimal FGM volume that exhibits the highest critical speed was found to exist. Beyond the optimal FGM volume, the critical speed is much lower than that of a homogeneous steel layer. For all FGM volumes, the performance against TEI is dominant for the same nonhomogeneous parameter, which determines the compositional shape of the material property grading in the FGM. In addition, the thermal conductivity of the frictional material and the modulus of elasticity of the FGM were found to have the most significant impact on an increase in the critical speed.     

功能梯度材料应用在齿轮上的可行性分析

为解决齿轮热处理过程中存在畸变、齿根处弯曲应力增加、齿轮的寿命降低等问题,将功能材料技术应用到齿轮工作接触面处(简称功能梯度齿轮)。首先,开展了单质齿轮性能与单质齿轮热处理后性能的对比分析;然后,建立了单质圆柱渐开线齿轮模型与功能梯度材料圆柱渐开线齿轮模型,对其进行了弯曲应力有限元计算,并对其性能进行了对比分析。将未经热处理的单质齿轮作为桥梁,建立了单质齿轮热处理后的性能与功能梯度材料齿轮性能之间的关系。功能梯度材料不仅在轮齿表面硬度与齿根弯曲应力方面比热处理后的齿轮有更好的性能,而且能避免齿轮热处理过程中产生的畸变、渗碳层不均匀等缺陷。分析结果表明:将功能梯度材料应用到齿轮上是可行的。     

面向复杂梯度材料模具等离子熔积制造的建模与轨迹规划

为满足复杂功能梯度材料（FGM）模具设计和制造的需求,提出了基于非均匀梯度源的体素建模和双数据模型驱动的轨迹规划新方法。双数据模型中的STL模型用于梯度源设计和几何轨迹生成,体素模型用于材料分布设计和FGM表征建立。通过几何轨迹离散和材料信息检索与融合,生成了熔积成形轨迹。新方法不仅具备多个局部复杂参考特征同时描述的能力,还使得成形轨迹兼具几何精确快速和材料分布复杂的特点。最后通过汽车翼子板模具实例验证了算法的有效性。     

三种工况下SiC/Al FGM紧凑拉伸试件的力学行为研究

SiC/Al梯度功能材料各梯度层由不同体积浓度的陶瓷和金属组成,由于材料组分梯度变化,克服了双材料界面的应力突变问题,从而获得优异的使用性能。文中应用Ansys软件和激光云纹干涉法,对具有四个梯度层的SiC/Al梯度功能材料紧凑拉伸试件在三种工况下的力学行为进行研究。通过Ansys分析得出试件裂纹扩展的规律以及裂前4mm处的应变分布,后续实验采集试件随各载荷变化的位移场云纹图,根据位移与条纹级数的关系以及小变形条件下应变与条纹级数关系式,得到梯度功能材料紧凑拉伸试件预制裂纹区的应变分布。通过两种方法相应结果对比分析,得出有关梯度功能材料的裂纹扩展准则的适用性方面的结论;同时,就实验获得的应变测量结果,讨论梯度功能材料的物性变化规律,以及材料组分和梯度层结构对材料整体物性参数的影响。     

The effect of scanning strategy on laser fusion of functionally graded H13/Cu materials

In recent years, research has been undertaken on manufacturing of functionally graded materials (FGM) using layered manufacturing technologies (LMT), also commonly known as rapid prototyping (RP), solid free-form fabrication (SFF) etc. The use of LMT to build complex FGM parts could meet optimum engineering design for various applications such as high performance die casting tools. In this context, H13 tool steel is considered a suitable material because of the high resistance to thermal fatigue and dimensional stability. Nevertheless, H13 with a low heat conduction coefficient is not thermally efficient for certain part geometries. With this in mind, the use of functionally graded techniques to disperse copper to specific regions/volumes of a H13 mould could lead to higher performance of the tool. The laser fusion of different proportions of Cu (0, 25 and 50% by weight) powder dispersed in H13 were analysed in this work. Additionally, different laser strategies were used to statistically analyse effects with respect to the composition of Cu. It was found that the refill strategy produces better results compared to all other scanning methods. The H13 with 25% Cu mix produced a homogeneous structure but cracks were observed along the cross section of the 25% Cu specimens. The pure H13 had a lower porosity with fine dendrite structures. The H13 with 50% Cu produced a non-homogeneous structure. This paper also discusses the microhardness tests results with respect to Cu composition and scanning strategy. Also, in order to identify the effect of powder composition layer on the subsequent layers and the cooling rate effect, samples were produced and analysed. One started with 100% H13 and ended with H13+50% Cu while the other started with H13+50% Cu and ended with 100% H13.     

Frictionally excited thermoelastic instability in a thin layer of functionally graded material sliding between two half-planes

Frictionally excited thermoelastic instability (TEI) is investigated in the system of a layer of finite thickness which is composed of functionally graded material (FGM), sliding against two homogeneous frictional materials of half-planes at speed V. Results show that ceramic-based FGM, which is composed of ceramic at the sliding interface and steel at the middle of the layer, reduces the susceptibility towards TEI. The effect of nonhomogeneous parameters of FGM on critical speed is investigated for the several combinations of FGM such as steel- or ceramic-based FGM with positive and negative nonhomogeneous parameters, respectively. The material sensitivity to the critical speed for the nonhomogeneous parameter of FGM shows that the nonhomogeneous parameters of the thermal expansion coefficient are strong influential factors in ceramic- or steel-based FGM. The transient evolution of temperature perturbation is also obtained to determine the susceptibility towards hot spotting, showing that the ceramic-based FGM with negative nonhomogeneous parameters has the lowest temperature perturbation amplitude during engagement.     

Performance evaluation of laser lithographic machine for computer-generated hologram

Computer-generated holograms (CGHs) are often used for testing of aspheric optical surfaces. The precision of CGH mainly depends on the errors of the fabrication machine. We have developed a cylindrical-type direct laser lithographic machine whose working area is up to 360?mm. In this paper, the performance evaluation results of the lithographic machine are given.     

Dynamic propagation of a weak-discontinuous interface crack between two dissimilar functionally graded layers under anti-plane shear

The dynamic propagation of an interface crack between two functionally graded material (FGM) layers under anti-plane shear is analyzed using the integral transform method. The properties of the FGM layers vary continuously along their thicknesses. The properties of the two FGM layers vary and the two layers are connected weak-discontinuously. A constant velocity Yoffe-type moving crack is considered. The Fourier transform is used to reduce the problem to a dual integral equation, which is then expressed to a Fredholm integral equation of the second kind. Numerical values on the dynamic energy release rate (DERR) are presented for the FGM to show the effect of the gradient of material properties, crack moving velocity, and thickness of FGM layers. The following are helpful to increase resistance to interface crack propagation in FGMs: a) increasing the gradient of material properties, b) an increase of shear modulus and density from the interface to the upper and lower free surface, and c) increasing the thickness of the FGM layer. The DERR increases or decreases with increase of the crack moving velocity.