球壳与柱壳之功能梯度压电涂层的热效应分析

针对以球壳和圆柱壳为基体的功能梯度压电涂层,由多场耦合控制方程和层间连续条件导出递推关系,建立了显式的力-电-热多场耦合解。对于多层功能梯度压电涂层,此解为精确解;对于连续功能梯度压电涂层,可将涂层分为若干层,只要层数取得足够大,所得的近似解将收敛于精确解。研究表明：压电效应对基体的应力影响可以忽略,但对涂层的应力影响非常显著;增加层数并不能有效降低最大应力,但增加层数可显著减小相邻层层间周向应力的突变幅度,减小层间应力集中;然而涂层与基体之间的界面径向应力却随层数的增大而使界面强度弱化。     

3500m^3天然气球罐应力测试

3500m^3天然气球罐是上海1998年重点实事工程。球罐设计压力P=1．53MPa，球壳板材料为WEL-TEN610CF，板厚38mm。由于焊后不进行消除应力热处理，因此在气压试验前后对球壳板Y形焊缝、T形焊缝等部位进行了焊缝残余应力测试，在气压试验过程中对球壳板Y形焊缝、T形焊缝、赤道板支柱部位进行了应力应变测试。测试结果表明，经气压试验后焊缝残余应力有一定下降，应力应变测试表明球罐焊缝及热影响区没有出现明显的应力集中现象。球罐壳体的工作应力叠加残余应力的总和仍小于材料的屈服限，球罐在正常状态下运行是安全的。     

3500m~3天然气球罐应力测试

35 0 0m3天然气球罐是上海 1998年重点实事工程。球罐设计压力P =1 5 3MPa ,球壳板材料为WEL -TEN6 10CF ,板厚 38mm。由于焊后不进行消除应力热处理 ,因此在气压试验前后对球壳板Y形焊缝、T形焊缝等部位进行了焊缝残余应力测试 ,在气压试验过程中对球壳板Y形焊缝、T形焊缝、赤道板支柱部位进行了应力应变测试。测试结果表明 ,经气压试验后焊缝残余应力有一定下降 ,应力应变测试表明球罐焊缝及热影响区没有出现明显的应力集中现象。球罐壳体的工作应力叠加残余应力的总和仍小于材料的屈服限 ,球罐在正常状态下运行是安全的     

功能梯度Al2O3涂层残余热应力分析

Al2O3/316L功能梯度材料是一种聚变反应堆第一壁的候选材料。为避免制备过程中因材料之间热物理性能差别产生的热应力过大造成材料的失效,须对梯度材料进行合理的热应力缓和设计。运用有限元软件,分析成分分布指数、梯度涂层厚度和梯度层数目等参数对Al2O3/316L功能梯度材料残余热应力的影响。分析结果表明：体积分布指数p=1.0时所受热应力最小,涂层承受压应力作用;梯度层数为9时热应力缓和效果最好;梯度层厚度不宜过大;将非功能梯度材料与优化后的功能梯度材料的残余热应力进行比,结果显示：功能梯度材料缓和热应力效果十分显著。最后利用等离子喷涂方法制备了梯度涂层测试涂层残余应力,并与有限元结果进行对比,以验证模拟的准确性。     

热障涂层在多次热循环作用下残余应力的模拟

采用热弹塑性有限元方法,对热障涂层多次热循环降温过程中由于热梯度和材料参数不匹配而产生的残余应力进行了数值模拟,分析了平面和曲面的界面形貌对界面残余应力的影响.结果表明,在相同材料参数情况下,陶瓷层与粘接层的界面形状对残余应力及结构稳定状态有显著的影响,凹凸不平的界面将会使界面残余应力发生突变,不利于增强界面结合强度和涂层结构的热稳定性.该结果对分析涂层寿命及失效机制有指导意义.     

基于数值计算的切割焊接连续加工残余应力演变过程

热切割与焊接在船舶制造中以先后顺序连续作用于构件,形成复杂的工艺耦合残余应力场,给掌握船体结构残余应力分布带来困难.为此,以典型的平板结构切割成形后对接焊工艺过程为对象,基于热弹塑性有限元法,建立该过程的数值计算模型,分析切、焊耦合残余应力的分布规律与演变过程.结果表明,在切焊连续加工中,沿焊缝边缘存在超过材料屈服点的拉应力区,其宽度大于单独进行切割或焊接工艺时的情况;距焊缝较远位置的应力不仅受其温度升降影响,还要平衡热源周围的压应力,因此率先呈现出渐增的拉应力;初始切割残余应力对最终耦合残余应力的影响取决于温度变化梯度的大小.     

功能梯度涂层热残余应力

涂层中的残余应力严重影响着涂层零件的机械完整性与操作可靠性。对于功能梯度涂层,由于各界面位移协调条件的限制,很难得到涂层内部残余应力的闭合解。基于传统的悬臂梁理论,获得了功能梯度涂层热残余应力的闭合解;这一分析模型的优点是残余应力的闭合解与涂层层数无关。讨论了采用传统的近似解所带来的误差, 针对含不同层数的ZrO2/NiCoCrAlY功能梯度涂层内部的残余应力进行了计算。另外,对应力诱导的涂层失效模型也进行了分析。     

拉压强度不同材料厚壁球壳的安定性分析

对拉压强度不同材料厚壁球壳进行了安定分析，得出了球壳加载应力场、残余应力场及安定极限的解析解，所得的解能反映材料拉压强度差效应。最后，利用所得的解研究了材料拉压强度差效应对球壳安定极限的影响，结果表明，考虑材料拉压强度差效应时球壳安定极限将明显提高。     

功能梯度涂层滚压强化的有限元分析

在功能梯度涂层模型的基础上引入了刚性轧辊,建立了功能梯度涂层滚压强化的力学分析模型,并研究功能梯度涂层的非均匀材料参数、滚压速度对其涂层的等效应力和残余应力的影响,通过计算表明,非均匀材料参数对涂层前部和后部的等效应力有明显的影响,而对涂层中部基本没有影响;在整个涂层表面的残余应力是不相等的,最大等效残余应力为400MPa,最小等效残余应力为30MPa,两者相差近10倍,而滚压速度对于涂层的等效应力没有影响。这为滚压强化功能梯度涂层材料的设计提供了理论支持。     

功能梯度涂层滚压强化的有限元分析

在功能梯度涂层模型的基础上引入了刚性轧辊,建立了功能梯度涂层滚压强化的力学分析模型,并研究功能梯度涂层的非均匀材料参数、滚压速度对其涂层的等效应力和残余应力的影响,通过计算表明,非均匀材料参数对涂层前部和后部的等效应力有明显的影响,而对涂层中部基本没有影响;在整个涂层表面的残余应力是不相等的,最大等效残余应力为400MPa,最小等效残余应力为30MPa,两者相差近10倍,而滚压速度对于涂层的等效应力没有影响。这为滚压强化功能梯度涂层材料的设计提供了理论支持。     

Stochastic hybrid numerical method for transient analysis of stress field in functionally graded thick hollow cylinders subjected to shock loading

This investigation aims to study the random stresses in a functionally graded (FG) thick hollow cylinder with uncertain material properties subjected to mechanical shock loading using a hybrid numerical method. The mechanical properties are considered to vary across thickness of FG cylinder as a nonlinear power function of radius. The stresses are obtained by solving Navier equation and using Galerkin finite element and Newmark finite difference methods. The Monte Carlo simulation is used to generate the random mechanical properties for the problem. The failure probabilities and time history analysis of stresses are determined for various coefficient of variation considering various grading patterns of mechanical properties. The presented hybrid numerical method is effective, with high capability for stochastic analysis of dynamic and transient analysis of FG structures with various boundary conditions.     

SiC_f/Ti-6Al-4V复合材料的界面反应及其影响

采用扫描电镜和透射电镜研究了SiCf/Ti-6Al-4V复合材料的界面反应,并借助纤维顶出试验和有限元方法,分析了界面反应层厚度对界面剪切强度和残余热应力的影响.结果表明:SiCf/Ti-6Al-4V复合材料界面反应产物主要为TiC,其又分为二层,晶粒较粗大的TiC层靠近基体钛合金,晶粒细小的TiC层靠近SiC表面的碳涂层;随着反应层厚度的增加,界面抗剪强度提高,纤维和反应层内的径向残余热应力有所增大,反应层内的环向残余热应力分布有所改变.     

Analytical investigation on axisymmetric free vibrations of moderately thick circular functionally graded plate integrated with piezoelectric layers

In this paper, a free vibration analysis of moderately thick circular functionally graded (FG) plate integrated with two thin piezoelectric (PZT4) layers is presented based on Mindlin plate theory. The material properties of the FG core plate are assumed to be graded in the thickness direction, while the distribution of electric potential field along the thickness of piezoelectric layers is simulated by sinusoidal function. The differential equations of motion are solved analytically for two boundary conditions of the plate: clamped edge and simply supported edge. The analytical solution is validated by comparing the obtained resonant frequencies with those of an isotropic host plate. The emphasis is placed on investigating the effect of varying the gradient index of FG plate on the free vibration characteristics of the structure. Good agreement between the results of this paper and those of the finite element analyses validated the presented approach.     

Vibration analysis of piezoelectric FGM sensors using an accurate method

In this study, free vibration analysis of moderately thick smart FG annular/circular plates with different boundary conditions is presented on the basis of the Mindlin plate theory. This structure comprised a host FG plate and two bonded piezoelectric layers. Piezoelectric layers are open circuit therefore this plate can be used as a sensor. According to power-law distribution of the volume fraction of the constituents, material properties vary continuously through the thickness of host plate while Poisson's ratio is set to be constant. Using Hamilton's principle and Maxwell electrostatic equation yields six complex coupled equations which are solved via an exact closed-form method. The accuracy of the frequencies is verified by the available literature, finite element method (FEM) and the Kirchhoff theory. The effects of plate parameters like boundary condition and gradient index are investigated and significance of coupling between in-plane and transverse displacements on the resonant frequency is proved.     

Exact solution of a compositionally graded piezoelectric layer under uniform stretch, bending and twisting

Electromechanical responses of compositionally graded piezoelectric layers are analysed. The layers consist of polycrystalline piezoelectric ceramics poled along the thickness direction, and thus exhibit material symmetry of a hexagonal crystal in class 6mm. Two cases for layers (i) covered by surface electrodes and (ii) without surface electrodes are considered. Analytical solutions are exact in Saint Venant's sense for both cases. However, solutions are obtained for layers subjected to uniform mechanical loads, including stretch, bending and twisting. Numerical results to show the effects of different compositional gradients are presented.     

Semi-analytical solution of magneto-thermo-elastic stresses for functionally graded variable thickness rotating disks

In this paper, a semi-analytical solution for magneto-thermo-elastic problem in functionally graded (FG) hollow rotating disks with variable thickness placed in uniform magnetic and thermal fields is presented. Stresses and perturbation of magnetic field vector in FG rotating disks are determined using infinitesimal theory of magneto-thermo-elasticity under plane stress conditions. The material properties except Poisson’s ratio are modeled as power-law distribution of volume fraction. The profile of disk thickness is assumed to be a parabolic function of radius. The non-dimensional distribution of temperature, displacement, stresses and perturbation of magnetic field vector throughout radius are shown. Effects of material grading index, geometry of the disk and magnetic field on the stress and displacement fields are investigated. The results of stresses and radial displacements for two different boundary conditions with and without the effect of magnetic field are compared for a FG rotating disk with concave thickness profile. It has been found that imposing a magnetic field significantly decreases tensile circumferential stresses. Therefore the fatigue life of the disk will be significantly improved by applying the magnetic field. Results of this investigation could be applied for optimum design of FG hollow rotating disks with variable thickness.     

钎料对金属/陶瓷钎焊接头残余应力的影响

采用热弹塑性有限元方法,在考虑材料性能参数随温度变化的情况下,分析了采用Ag-Cu-Ti钎料钎焊Al2O3陶瓷与镍丝钎焊接头在钎焊过程中产生的应力大小和分布情况.结果表明：钎焊过程中,在钎料与陶瓷界面的陶瓷侧会产生较大的残余拉应力,影响了钎焊接头的连接强度.在此类连接结构中,钎料对接头残余应力的影响是主要的,而钎料性能参数及厚度是决定接头残余应力大小的重要因素.在选择金属/陶瓷钎焊用钎料时,为降低接头残余应力,除考虑钎料与陶瓷的润湿性和界面反应程度外,钎料的性能参数和厚度同样重要.     

Asymptotic homogenization modeling and analysis of effective properties of smart composite reinforced and sandwich shells

General micromechanical models for smart composite shells with periodically arranged actuators and varying thickness are developed using the asymptotic homogenization techniques. The models make it possible to determine both local fields, i.e., stresses, strains and displacements, and effective elastic and piezoelectric coefficients of the smart composite shells. It is shown that the original boundary value problem decouples into a set of simpler problems, known as unit cell problems. In particular, it is the solution of these unit cell problems that yields the aforesaid effective coefficients. These coefficients are universal in nature and may be used to study a wide variety of boundary value problems associated with a given smart composite structure. The derived models and the expressions for the effective coefficients are illustrated by means of four examples pertaining to hexagonal honeycomb sandwich structures and rectangular-reinforced, diagonally restrained and triangular-reinforced smart wafer shells. These structures are endowed with piezoelectric carrier layers made of orthotropic material and isotropic core or wafer. It is shown that the derived models can be used to tailor the effective properties of such smart composite structures to meet the requirements of particular applications of interest.     

功能梯度压电驱动器的结构设计、制备与功能验证

本文作者在以前的研究中,提出了一种新型的功能梯度驱动器。在此基础上,本文设计并制备了该驱动器,建立了理论模型,并对驱动器的性能进行了测试。这种新型功能梯度驱动器由4种基于Pb(Ni1/3Nb2/3)O3－PbZrO3－PbTiO3系列的材料复合而成,且四层材料的压电常数和介电常数在厚度方向上的梯度变化相反,这种梯度结构能够使得驱动器结构内部的应力分布优于传统弯曲驱动器。为了对驱动器进行优化设计,作者利用经典复合材料力学和压电方程建立了功能梯度压电驱动器的理论模型,并计算了不同厚度配比的驱动器受电压和自由端集中力单独作用时的准静态变形和应力分布。通过分析驱动器的内部应力确定了最优厚度配比。根据优化结果成功制备了功能梯度压电驱动器,并测量了驱动器自由端输出位移与输出力的关系。测量结果表明：功能梯度压电弯曲驱动器的输出位移和输出力呈线性关系,并且频率越低,输出位移和力就越大。